diff --git a/explanations.json b/explanations.json index b6b8d70..db68f16 100644 --- a/explanations.json +++ b/explanations.json @@ -2447,6 +2447,1854 @@ "source": "https://50ohm.de/A_transverter_2.html", "confidence": 7 }, + "AF601": { + "revision": 1, + "explanation": "A continuous analog waveform is uninterrupted in time and amplitude, so it is both time-continuous and value-continuous.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF602": { + "revision": 1, + "explanation": "Time stays continuous when the curve is drawn without sample instants, but quantized amplitude levels make the value axis discrete.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF603": { + "revision": 1, + "explanation": "Sampling selects separate instants in time; if the samples can still take arbitrary amplitudes, only the time axis is discrete.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF604": { + "revision": 1, + "explanation": "A digital sample stream is discrete twice: samples occur at fixed instants and each sample is rounded to one of the available amplitude codes.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF605": { + "revision": 1, + "explanation": "Quantization maps a continuous amplitude range onto a finite set of amplitude levels.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF606": { + "revision": 1, + "explanation": "Sampling is the time operation: a continuous signal is observed at discrete time instants.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF607": { + "revision": 1, + "explanation": "An A/D converter has only finitely many output codes, so most input voltages must be rounded to the nearest code and a quantization error remains.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF608": { + "revision": 1, + "explanation": "An 8-bit converter has $2^8 = 256$ possible codes, so it can separate at most 256 input ranges.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF609": { + "revision": 1, + "explanation": "Ten digital bits give $2^{10} = 1024$ different output codes or voltage steps.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF610": { + "revision": 1, + "explanation": "Eight bits give 256 steps across 1 V; $1 V / 256$ is about 3.9 mV.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF611": { + "revision": 1, + "explanation": "Ten bits give 1024 steps across 1 V; $1 V / 1024$ is about 0.98 mV.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF612": { + "revision": 1, + "explanation": "With only 4 bits the sine stays within range but is represented by coarse voltage steps, so the output is visibly stair-stepped.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF613": { + "revision": 1, + "explanation": "A 12-bit converter over +/-2 V has enough range for a 1.5 V peak sine and fine quantization, so the reconstructed output closely follows the input.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF614": { + "revision": 1, + "explanation": "The converter range is only +/-1 V, so a 1.5 V peak sine clips at the limits even though the 12-bit resolution is fine.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF615": { + "revision": 1, + "explanation": "Sampling rate is a rate: number of samples taken per unit time, usually samples per second.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF616": { + "revision": 1, + "explanation": "The sampling theorem gives the theoretical minimum sampling rate needed to reconstruct a band-limited signal without aliasing.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF617": { + "revision": 1, + "explanation": "Frequency components above half the sampling frequency fold back into the sampled spectrum; that foldback is aliasing.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF618": { + "revision": 1, + "explanation": "Nyquist requires a sampling rate greater than twice the highest signal frequency, so the smallest safe rate is just above $2 f_{max}$.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF619": { + "revision": 1, + "explanation": "A 4 kHz speech bandwidth needs just over 8 ksample/s by Nyquist; 9600 samples/s is the smallest listed rate above that limit.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF620": { + "revision": 1, + "explanation": "A direct-sampling receiver first band-limits the analog input, then the sampling clock controls when the A/D converter takes samples.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF621": { + "revision": 1, + "explanation": "Clock jitter moves the sampling instant; with a changing input voltage that timing error becomes amplitude error and appears as added noise.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF622": { + "revision": 1, + "explanation": "An anti-alias filter must remove too-high analog frequencies before the A/D converter samples them, so it is a low-pass ahead of the converter.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF623": { + "revision": 1, + "explanation": "For an 8 ksample/s speech ADC, the useful passband must end below the 4 kHz Nyquist limit and then attenuate sharply.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF624": { + "revision": 1, + "explanation": "After D/A conversion, a reconstruction low-pass removes sampling images and smooths the stepped output waveform.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF625": { + "revision": 1, + "explanation": "The reconstruction filter should pass the wanted speech band but reject images above the 4 kHz Nyquist frequency for an 8 ksample/s stream.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF626": { + "revision": 1, + "explanation": "Digital voice transmission encodes speech into bits before modulation; the RF chain then converts the digital waveform to the transmitted signal.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF627": { + "revision": 1, + "explanation": "DATV transmission must encode/compress the video program into a digital transport stream before RF modulation.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF628": { + "revision": 1, + "explanation": "A digital voice receiver reverses the transmit chain: demodulate bits, decode the voice data, then convert it back to audio.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF629": { + "revision": 1, + "explanation": "A DATV receiver first recovers the digital transport stream from RF and then decodes the video and audio content.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF630": { + "revision": 1, + "explanation": "The FFT is an efficient discrete Fourier transform, used to convert sampled time-domain data into frequency-domain bins.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF631": { + "revision": 1, + "explanation": "Digital filters are implemented as algorithms or logic, and the two standard response classes are FIR and IIR.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF632": { + "revision": 1, + "explanation": "Quadrature modulation needs two carriers in quadrature; quadrature means a 90 degree phase difference.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF633": { + "revision": 1, + "explanation": "I is the in-phase component relative to the reference oscillator, while Q is the component shifted by 90 degrees.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF634": { + "revision": 1, + "explanation": "Complex I/Q sampling represents positive and negative baseband frequencies around the carrier, so 48 ksample/s covers -24 kHz to +24 kHz.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF635": { + "revision": 1, + "explanation": "For complex I/Q data, the displayed baseband span equals the sample rate, split symmetrically around zero: 96 ksample/s gives +/-48 kHz.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF636": { + "revision": 1, + "explanation": "With I and Q each sampled at 10 Msample/s, the complex baseband span is 10 MHz total, i.e. -5 MHz to +5 MHz.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF637": { + "revision": 1, + "explanation": "Latency is elapsed delay through a link or processing chain, so it is a time quantity measured in seconds or fractions of a second.", + "source": "https://50ohm.de/future/NEA_slide_nea_digitale_signalverarbeitung.html", + "confidence": 8 + }, + "AF701": { + "revision": 1, + "explanation": "Block 1 is on the operator side, so it is the local computer or control head used to create audio and control data.", + "source": "https://50ohm.de/EA_remote_station.html", + "confidence": 8 + }, + "AF702": { + "revision": 1, + "explanation": "Block 2 is at the remote site and bridges the network to radio control/audio, which is the job of a computer or remote interface.", + "source": "https://50ohm.de/EA_remote_station.html", + "confidence": 8 + }, + "AF703": { + "revision": 1, + "explanation": "The operator-side block packetizes local audio and control commands before sending them through the network.", + "source": "https://50ohm.de/EA_remote_station.html", + "confidence": 8 + }, + "AF704": { + "revision": 1, + "explanation": "At the remote site, block 2 converts incoming network packets back into audio and control signals for the radio equipment.", + "source": "https://50ohm.de/EA_remote_station.html", + "confidence": 8 + }, + "AF705": { + "revision": 1, + "explanation": "The RF carrier is generated by the actual transceiver in block 3, not by the network or control interface.", + "source": "https://50ohm.de/EA_remote_station.html", + "confidence": 8 + }, + "AF706": { + "revision": 1, + "explanation": "Self-interference occurs at the remote site, so it can disturb the transceiver and remote-control electronics located there.", + "source": "https://50ohm.de/EA_remote_station.html", + "confidence": 8 + }, + "AF707": { + "revision": 1, + "explanation": "If the transceiver stops accepting control commands, removing its supply power remotely is the direct way to stop transmission.", + "source": "https://50ohm.de/EA_remote_station.html", + "confidence": 8 + }, + "AF708": { + "revision": 1, + "explanation": "A watchdog detects missing keep-alive communication and forces a safe state, preventing stuck transmission after link failure.", + "source": "https://50ohm.de/EA_remote_station.html", + "confidence": 8 + }, + "AF709": { + "revision": 1, + "explanation": "Remote operation adds network, buffering, codec and control delays, so received and transmitted signals arrive later.", + "source": "https://50ohm.de/EA_remote_station.html", + "confidence": 8 + }, + "AF710": { + "revision": 1, + "explanation": "In remote operation, latency is the time delay between user action or audio and the corresponding event at the remote station.", + "source": "https://50ohm.de/EA_remote_station.html", + "confidence": 8 + }, + "AG101": { + "revision": 1, + "explanation": "A half-wave dipole has total length $0.95 c/(2f)$; at 14.2 MHz that is about 10.04 m total, or 5.02 m per side.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG102": { + "revision": 1, + "explanation": "Using $0.95 c/(2f)$ at 7.1 MHz gives about 20.08 m total dipole length, so each half is about 10.04 m.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG103": { + "revision": 1, + "explanation": "For a shortened half-wave dipole, $f = 0.95 c/(2l)$; with 20 m total length this is about 7.125 MHz.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG104": { + "revision": 1, + "explanation": "A quarter-wave groundplane uses quarter-wave radiator and radials; $0.95 c/(4 \\cdot 7.1 MHz)$ is about 10.04 m.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG105": { + "revision": 1, + "explanation": "A 5/8-wave vertical length is $0.97 \\cdot 5/8 \\cdot c/f$; at 14.2 MHz this is about 12.8 m.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG106": { + "revision": 1, + "explanation": "A loading coil adds inductive reactance, making a physically short radiator behave electrically longer.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG107": { + "revision": 1, + "explanation": "Series or top capacitance can offset excess inductive electrical length, so the radiator behaves electrically shorter.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG108": { + "revision": 1, + "explanation": "A twice-15 m dipole is physically short for 3.6 MHz; loading coils in both arms add inductance and bring it to resonance.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG109": { + "revision": 1, + "explanation": "The inserted parallel resonant traps isolate or load parts of the dipole by band, which is the defining feature of a trap dipole.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG110": { + "revision": 1, + "explanation": "A trap presents high impedance near its resonance and different reactance away from it, allowing one dipole to work on multiple bands.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG111": { + "revision": 1, + "explanation": "Below the trap resonance the LC trap behaves mainly inductively, adding electrical length for the lower-frequency band.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG112": { + "revision": 1, + "explanation": "At its resonant frequency a parallel LC trap has high impedance, so it blocks the rest of the wire and acts as a band stop.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG113": { + "revision": 1, + "explanation": "Above the trap resonance the trap's equivalent reactance is capacitive, reducing the effective electrical length for the higher band.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG114": { + "revision": 1, + "explanation": "In a 20/15/10 m trap dipole, the inner trap pair must stop the 15 m current, so it is tuned near 21.2 MHz.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG115": { + "revision": 1, + "explanation": "The outer trap pair separates the 10 m section, so it is tuned near the 10 m operating frequency around 29 MHz.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG116": { + "revision": 1, + "explanation": "For 80 m a half-wave section is roughly 40 m, and traps for a 160/80 m antenna are tuned near the 80 m band around 3.65 MHz.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG117": { + "revision": 1, + "explanation": "A triangular full-wave wire loop is conventionally called a delta loop.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG118": { + "revision": 1, + "explanation": "A full-wave loop length is approximately $1.02 c/f$; at 7.1 MHz this gives about 43.1 m of wire.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG119": { + "revision": 1, + "explanation": "A quad loop is a full-wave loop divided into four equal sides, so each side is one quarter wavelength electrically.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG120": { + "revision": 1, + "explanation": "A Zeppelin antenna is the classic end-fed wire fed through a parallel-wire feeder at one end.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG121": { + "revision": 1, + "explanation": "The G5RV is recognized by its specified dipole length and matching section of open-wire feedline before the coax transition.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG122": { + "revision": 1, + "explanation": "A Windom antenna is an off-center-fed wire dipole, so the unequal wire lengths identify it.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG123": { + "revision": 1, + "explanation": "An end-fed multiband wire uses an end feed and matching/choking at the feed point; the sketch labels that end-fed multiband layout.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG124": { + "revision": 1, + "explanation": "An end-fed half-wave style multiband antenna is resonant on its intended bands and uses the matching unit plus choke at the end feed.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG125": { + "revision": 1, + "explanation": "NVIS needs high-angle radiation, which low horizontal wires produce when kept around a quarter wavelength or less above ground.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG126": { + "revision": 1, + "explanation": "Circular polarization requires two perpendicular linear fields with equal amplitude and 90 degree phase difference, so one Yagi must be delayed by a quarter wavelength.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG127": { + "revision": 1, + "explanation": "An offset dish moves the feed out of the aperture, avoiding feed blockage and improving illumination compared with a centered feed.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG201": { + "revision": 1, + "explanation": "On HF, both horizontal and vertical antennas are common; the ionosphere may change polarization anyway, so neither is exclusive.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG202": { + "revision": 1, + "explanation": "Real conductors have diameter and environmental capacitance, which increase electrical length, so the physical wire must be shortened from the ideal free-space value.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG203": { + "revision": 1, + "explanation": "The 28 MHz case is the highest listed harmonic, so it shows the largest number of current half-waves on the same dipole.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG204": { + "revision": 1, + "explanation": "At 14 MHz the 20 m dipole is excited at the next lower shown harmonic pattern, with fewer current lobes than at 28 MHz.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG205": { + "revision": 1, + "explanation": "At 7 MHz the same 20 m wire is near one full wavelength overall, matching the intermediate current distribution.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG206": { + "revision": 1, + "explanation": "At 3.5 MHz the 20 m dipole is near its half-wave fundamental, so it has the simplest current distribution with the central maximum.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG207": { + "revision": 1, + "explanation": "A center-fed half-wave dipole and its odd harmonics have current maximum at the feed point, giving series resonance and low feed impedance.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG208": { + "revision": 1, + "explanation": "At even harmonics the center feed lies at a voltage maximum/current minimum, so the dipole is voltage-fed and high impedance.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG209": { + "revision": 1, + "explanation": "At resonance the reactive parts cancel, leaving the feedpoint impedance mainly resistive.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG210": { + "revision": 1, + "explanation": "Below resonance a dipole is electrically too short and capacitive; above resonance it is electrically too long and inductive.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG211": { + "revision": 1, + "explanation": "A half-wave dipole high enough above ground has a feed resistance close to the textbook free-space value, roughly 65 to 75 ohms.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG212": { + "revision": 1, + "explanation": "Yagi feed impedance depends strongly on mutual coupling, which is set by spacing between driven element, reflector and directors.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG213": { + "revision": 1, + "explanation": "Antenna gain over a dipole compares the power needed by the reference dipole with the power needed by the directional antenna for the same field strength.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG214": { + "revision": 1, + "explanation": "Front-to-back ratio compares radiation in the main direction with radiation in the opposite rear direction.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG215": { + "revision": 1, + "explanation": "The rear ERP is transmit power times forward gain divided by front-to-back ratio: 100 W x 10 / 100 = 10 W.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG216": { + "revision": 1, + "explanation": "15 dBd is a factor 31.6 and 25 dB front-to-back is a factor 316; $6 W \\cdot 31.6 / 316$ is about 0.6 W rear ERP.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG217": { + "revision": 1, + "explanation": "Front-to-back ratio is a power ratio: $10 log10(15/0.6)$ is about 14 dB.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG218": { + "revision": 1, + "explanation": "For field strengths, use 20 log10 of the voltage ratio: 300/128 gives 7.4 dBd, and 300/20 gives 23.5 dB front-to-back.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG219": { + "revision": 1, + "explanation": "Half-power is 3 dB down; field strength is proportional to the square root of power, so the boundary is $1/sqrt(2) = 0.707$ of maximum field.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG220": { + "revision": 1, + "explanation": "The half-power beamwidth is read at the 0.707 relative-field circle, which is the point marked c in the diagram.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG221": { + "revision": 1, + "explanation": "Beamwidth is the angular separation between the two intersections of the main lobe with the 0.707 field-strength circle; the sketch gives about 55 degrees.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG222": { + "revision": 1, + "explanation": "Adding Yagi elements increases directivity, which narrows the main lobe and therefore reduces the opening angle.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG223": { + "revision": 1, + "explanation": "A 5/8-wave vertical over ground has a low elevation-angle maximum, useful for flat long-distance HF radiation.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG224": { + "revision": 1, + "explanation": "A low horizontal NVIS antenna sends most energy upward, so the returned sky wave fills the normal skip zone near the transmitter.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG225": { + "revision": 1, + "explanation": "Dish feeds need to illuminate the reflector efficiently at microwave frequencies; dipoles, helices and horn antennas are standard feed types.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG226": { + "revision": 1, + "explanation": "Parabolic gain rises with aperture diameter over wavelength: with 30 cm at 5.7 GHz and ideal efficiency, $G=(pi D/lambda)^2$ gives about 25 dBi.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG227": { + "revision": 1, + "explanation": "At the same frequency, increasing dish diameter to 80 cm increases aperture area strongly; the ideal-gain formula gives about 33.6 dBi.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG228": { + "revision": 1, + "explanation": "For a fixed 80 cm dish, the shorter 10.4 GHz wavelength increases aperture gain to about 38.8 dBi.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG229": { + "revision": 1, + "explanation": "A 1.2 m dish at 10.4 GHz has a large diameter-to-wavelength ratio, so the ideal parabolic-gain formula gives about 42.3 dBi.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG301": { + "revision": 1, + "explanation": "A shielded feed line keeps high RF fields inside the cable and reduces coupling into building wiring and equipment.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG302": { + "revision": 1, + "explanation": "Common coax dielectrics are low-loss RF plastics: PTFE, solid polyethylene and foamed polyethylene.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG303": { + "revision": 1, + "explanation": "The important RF cable properties are characteristic impedance, attenuation and velocity factor, because they determine matching, loss and electrical length.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG304": { + "revision": 1, + "explanation": "A line is matched when the load equals its characteristic impedance; then no reflected wave is produced.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG305": { + "revision": 1, + "explanation": "For open wire line, $Z_0$ rises with conductor spacing and falls with conductor diameter; the given 20 cm spacing and 2 mm wire give about 635 ohms.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG306": { + "revision": 1, + "explanation": "For air coax, $Z_0 = 60 ln(D/d)$; with 5 mm over 1 mm this is about 97 ohms.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG307": { + "revision": 1, + "explanation": "Polyethylene lowers coax impedance by the dielectric factor; the given dimensions correspond to a common 75 ohm cable geometry.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG308": { + "revision": 1, + "explanation": "Over 60 m at 29 MHz, the cable must stay below 2 dB total loss; the 10.3 mm PE-foam cable is the thinnest listed type meeting that limit.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG309": { + "revision": 1, + "explanation": "At 2.35 GHz coax loss is high, so a 20 m run needs the low-loss 12.7 mm PE-foam cable to stay within 4 dB.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG310": { + "revision": 1, + "explanation": "At 5.7 GHz even short coax is lossy; among the listed cables, only the 12.7 mm PE-foam type keeps 8 m below 3 dB.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG311": { + "revision": 1, + "explanation": "Wide-spaced open-wire line has little dielectric loss and lower RF resistance for the same conductor size, so it has the lowest HF loss.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG312": { + "revision": 1, + "explanation": "A balanced two-wire line carries equal and opposite currents and voltages; without common-mode current the external fields mostly cancel.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG313": { + "revision": 1, + "explanation": "Air has nearly the same wave speed as free space, so an air-insulated parallel line has velocity factor close to 1.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG314": { + "revision": 1, + "explanation": "The dielectric in coax slows wave propagation compared with free space, so its physical wavelength is shorter.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG315": { + "revision": 1, + "explanation": "Solid polyethylene has a relative permittivity that gives a typical coax velocity factor near 0.66.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG316": { + "revision": 1, + "explanation": "Free-space wavelength at 145 MHz is about 2.07 m; multiplying by velocity factor 0.66 gives about 1.37 m.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG317": { + "revision": 1, + "explanation": "A quarter wave at 145 MHz is about 0.517 m in free space; with velocity factor 0.66 it is about 0.342 m.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG318": { + "revision": 1, + "explanation": "At high frequency, current crowds toward the conductor surface; this is the skin effect.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG319": { + "revision": 1, + "explanation": "Skin effect reduces the effective conducting cross-section, so RF resistance and cable loss increase with frequency.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG320": { + "revision": 1, + "explanation": "A Lecher line resonates when its physical/electrical length fits a standing-wave condition, so length is the key parameter.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG401": { + "revision": 1, + "explanation": "Maximum power transfer occurs when load impedance equals the source impedance; a 50 ohm source therefore wants a 50 ohm load.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG402": { + "revision": 1, + "explanation": "A 3 dB line loss halves the power on the way to the far end; with open or short circuit, that 50 W reaching the end is reflected.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG403": { + "revision": 1, + "explanation": "The line looks matched with a dummy load but not with the antenna, so the fault is at the antenna or its termination, not in the line.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG404": { + "revision": 1, + "explanation": "With the end open, reflection travels down and back through 5 dB each way; the 10 dB round-trip loss makes the input SWR look only about 1.9.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG405": { + "revision": 1, + "explanation": "A folded dipole is roughly 240 to 300 ohms, so feeding it with 75 ohm coax gives an impedance ratio around 3.2 to 4.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG406": { + "revision": 1, + "explanation": "A pi network can transform impedance while its capacitors and inductor also form a low-pass path that suppresses harmonics.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG407": { + "revision": 1, + "explanation": "A quarter wavelength is one quarter of a full 360 degree RF cycle, so the phase shift is 90 degrees.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG408": { + "revision": 1, + "explanation": "One full wavelength produces a 360 degree phase shift, which is equivalent to 0 degrees at the input reference.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG409": { + "revision": 1, + "explanation": "A quarter-wave line inverts impedance: a short circuit at one end appears as very high impedance at the other.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG410": { + "revision": 1, + "explanation": "The quarter-wave section transforms the far-end condition so point X is at a current maximum and nearly zero impedance.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG411": { + "revision": 1, + "explanation": "A lossless quarter-wave line transforms an open circuit into a short-circuit-like low impedance at the other end.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG412": { + "revision": 1, + "explanation": "A half-wave line repeats its load impedance at the input, so 50 ohms remains 50 ohms.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG413": { + "revision": 1, + "explanation": "A half-wave dipole is low impedance at its feed, and a half-wave feed line repeats that low impedance at its input.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG414": { + "revision": 1, + "explanation": "A full-wave dipole is voltage-fed and high impedance at the feed point, and a half-wave line repeats that high impedance.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG415": { + "revision": 1, + "explanation": "A quarter-wave line transforms impedance, so a high-impedance full-wave dipole becomes low impedance at the line input.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG416": { + "revision": 1, + "explanation": "A half-wave transmission line repeats the load impedance independent of its own characteristic impedance, so the input remains 70 ohms.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG417": { + "revision": 1, + "explanation": "For a quarter-wave transformer, $Z_t = sqrt(Z_1 Z_2)$; $sqrt(60 \\cdot 240)$ is 120 ohms.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG418": { + "revision": 1, + "explanation": "The quarter-wave transformer impedance is $sqrt(240 \\cdot 600)$, which is about 380 ohms.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG419": { + "revision": 1, + "explanation": "An end-fed resonant wire has a high feed impedance when its length is a half wavelength or an integer multiple of that.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG420": { + "revision": 1, + "explanation": "A coax feed is unbalanced while a dipole is balanced, so a balun or equivalent phasing line provides the symmetry transition.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG421": { + "revision": 1, + "explanation": "A 2:1 turns ratio gives a 4:1 impedance ratio; transforming 50 ohms by 4 gives 200 ohms.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG422": { + "revision": 1, + "explanation": "The balun uses the winding ratio to transform the 200 ohm balanced load down by 4:1, so the coax-side impedance is 50 ohms.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG423": { + "revision": 1, + "explanation": "The half-wave bypass line provides both impedance transformation and phase reversal, matching the folded dipole's high balanced impedance to lower unbalanced coax.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG424": { + "revision": 1, + "explanation": "Each folded-dipole terminal is about 120 ohms to ground; the half-wave detour preserves magnitude but reverses phase, so the two 120 ohm paths combine to 60 ohms.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG425": { + "revision": 1, + "explanation": "Common-mode current on the outside of the coax shield is the mantle-wave condition; differential current inside the coax is normal feed current.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG426": { + "revision": 1, + "explanation": "A current-compensated choke cancels differential fields but presents high impedance to common-mode current on the outside of the feed line.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG427": { + "revision": 1, + "explanation": "Common-mode current arises when the antenna/feed system is unbalanced or nearby objects couple RF onto the outside of the coax shield.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG428": { + "revision": 1, + "explanation": "A common-mode choke or suitable balun raises the impedance for the unwanted shield current while leaving the wanted differential feed current mostly unaffected.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG429": { + "revision": 1, + "explanation": "A voltage balun enforces terminal voltage symmetry but cannot remove every environmental imbalance; asymmetric surroundings can still drive shield current.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG501": { + "revision": 1, + "explanation": "ERP is radiated power referenced to a half-wave dipole, so it is antenna input power times gain relative to a dipole in the specified direction.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG502": { + "revision": 1, + "explanation": "First subtract feed-line loss from transmitter power to get antenna input power; multiplying by antenna gain relative to a dipole gives ERP.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AG503": { + "revision": 1, + "explanation": "A 20 dB loss is a factor of 100; 50 W divided by 100 gives 0.5 W ERP.", + "source": "https://50ohm.de/future/NEA_slide_nea_antennen_uebertragungsleitungen.html", + "confidence": 8 + }, + "AH101": { + "revision": 1, + "explanation": "Solar UV radiation ionizes molecules in the ionosphere; the resulting free electrons refract radio waves back toward Earth.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH102": { + "revision": 1, + "explanation": "Solar flux is the Sun's radio emission around the GHz range; higher values indicate stronger solar activity and more ionization for upper-HF propagation.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH103": { + "revision": 1, + "explanation": "The D region is the lowest ionospheric region relevant to HF propagation, typically around 50 to 90 km altitude.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH104": { + "revision": 1, + "explanation": "The E region sits above the D region and below the F region, roughly 90 to 130 km altitude.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH105": { + "revision": 1, + "explanation": "In daytime the F1 region forms below F2, typically around 130 to 200 km altitude.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH106": { + "revision": 1, + "explanation": "The F2 region is the highest regular HF-refraction region and can reach roughly 250 to 450 km on a summer day.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH107": { + "revision": 1, + "explanation": "For DX, F2 refraction is usually wanted; an intervening F1 region can absorb or bend the wave before it reaches F2 effectively.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH108": { + "revision": 1, + "explanation": "Solar heating is strongest around summer midday, so the F2 region expands upward then.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH201": { + "revision": 1, + "explanation": "Hamburg to Munich is a relatively short HF path; around midday, 40 m commonly supports such regional ionospheric links.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH202": { + "revision": 1, + "explanation": "In a sunspot minimum the higher HF bands open less reliably, while 20 m often remains the best daily long-distance band.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH203": { + "revision": 1, + "explanation": "At night the lower HF bands suffer less D-region absorption, making 160, 80 and 40 m the best choices among the options.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH204": { + "revision": 1, + "explanation": "The F2 critical frequency is defined for vertical incidence: it is the highest frequency still returned by F2 when sent straight upward.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH205": { + "revision": 1, + "explanation": "At 90 degree incidence the path is vertical, so the maximum returned frequency equals the critical frequency, here 12 MHz.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH206": { + "revision": 1, + "explanation": "MUF literally means maximum usable frequency: the highest frequency that can still support the specified ionospheric path.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH207": { + "revision": 1, + "explanation": "For a given path, MUF is the top of the usable range; above it the wave penetrates the ionosphere instead of returning.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH208": { + "revision": 1, + "explanation": "Oblique incidence effectively lengthens the path through the ionized region, so the usable frequency rises above the vertical critical frequency as the angle becomes flatter.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH209": { + "revision": 1, + "explanation": "Using $MUF = f_k/sin(45°)$ gives about 4.2 MHz; the optimum working frequency is about 85% of MUF, or 3.6 MHz.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH210": { + "revision": 1, + "explanation": "LUF is the lower edge of the usable range: below it, absorption and noise make the sky-wave path unusable.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH211": { + "revision": 1, + "explanation": "If the LUF is 6 MHz, frequencies below 6 MHz are not considered usable for that sky-wave path under those conditions.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH212": { + "revision": 1, + "explanation": "Skip distance is set by geometry, ionospheric height/refraction and radiation angle; changing transmitter power affects strength, not where the ray returns.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH213": { + "revision": 1, + "explanation": "A single F2-hop can span several thousand kilometres because F2 is high; the usual rule of thumb is about 4000 km maximum.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH214": { + "revision": 1, + "explanation": "The E region is lower than F2, so a single hop returns sooner and covers only about 2200 km at most.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH215": { + "revision": 1, + "explanation": "The nearby station lies beyond the ground wave but before the first sky-wave return point, so it is in the skip zone.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH216": { + "revision": 1, + "explanation": "The long path is the great-circle direction opposite the short path, so the beam heading differs by 180 degrees.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH217": { + "revision": 1, + "explanation": "Long path is short-path azimuth plus 180 degrees modulo 360; 38 degrees becomes 218 degrees.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH218": { + "revision": 1, + "explanation": "Long path is the reciprocal heading: 231 degrees plus 180 degrees wraps to 51 degrees.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH219": { + "revision": 1, + "explanation": "Ionospheric refraction occurs in a magnetized, non-uniform plasma, so wave polarization is rotated and changed during sky-wave propagation.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH220": { + "revision": 1, + "explanation": "Sporadic-E creates intense E-region patches that return higher HF signals closer to the transmitter, shrinking or removing the skip zone.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH221": { + "revision": 1, + "explanation": "Solar flares increase UV and X-ray ionization especially in the D region, and D-region absorption can wipe out HF sky-wave propagation.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH222": { + "revision": 1, + "explanation": "Two paths arrive with different phases and delays; their superposition produces constructive and destructive interference.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH223": { + "revision": 1, + "explanation": "Backscatter signals return from irregular ionospheric regions, so their field strength fluctuates rapidly and irregularly.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH301": { + "revision": 1, + "explanation": "Sporadic-E propagation comes from small, strongly ionized E-region patches that can refract VHF signals.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH302": { + "revision": 1, + "explanation": "Auroral ionization occurs at high geomagnetic latitudes, mainly in the E-region height range near the poles.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH303": { + "revision": 1, + "explanation": "Aurora is driven by charged solar particles guided into the polar atmosphere by Earth's magnetic field.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH304": { + "revision": 1, + "explanation": "The auroral zone becomes strongly ionized, and those irregular ionized regions can reflect or scatter VHF and UHF signals.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH305": { + "revision": 1, + "explanation": "An aurora contact on 2 m means the VHF signal was scattered or reflected by ionized auroral regions near the polar zone.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH306": { + "revision": 1, + "explanation": "From Europe the auroral oval is generally to the north, so the VHF antenna is pointed north for aurora operation.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH307": { + "revision": 1, + "explanation": "Aurora heavily distorts wide voice modes; CW remains readable because it is narrow and robust against the fluttery tone.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH308": { + "revision": 1, + "explanation": "Auroral scattering causes rapid Doppler and multipath changes, giving CW a rough, fluttering, buzzy tone.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH309": { + "revision": 1, + "explanation": "Tropospheric inversion layers can form ducts that guide VHF/UHF signals beyond the normal radio horizon.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH310": { + "revision": 1, + "explanation": "Aircraft scatter uses aircraft bodies as temporary reflectors for VHF, UHF or SHF signals beyond line of sight.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AH311": { + "revision": 1, + "explanation": "Rainscatter is microwave scattering from rain and storm cells, most useful at short wavelengths such as the 3 cm band.", + "source": "https://50ohm.de/future/NEA_slide_nea_wellenausbreitung.html", + "confidence": 8 + }, + "AI101": { + "revision": 1, + "explanation": "Voltage is measured in parallel with the PA input, while current is measured in series with the supply path, so the voltmeter and ammeter go at those positions.", + "source": "https://50ohm.de/EA_slide_ea_strom_spannung_widerstand_leistung_energie.html", + "confidence": 8 + }, + "AI102": { + "revision": 1, + "explanation": "An ammeter must be inserted in series; the instruments located in series paths are the current meters in the drawing.", + "source": "https://50ohm.de/EA_slide_ea_strom_spannung_widerstand_leistung_energie.html", + "confidence": 8 + }, + "AI103": { + "revision": 1, + "explanation": "Power is $U \\cdot I$; if both readings are 95% of true value, measured power is $0.95 \\cdot 0.95 = 0.9025$, or 9.75% low.", + "source": "https://50ohm.de/EA_slide_ea_strom_spannung_widerstand_leistung_energie.html", + "confidence": 8 + }, + "AI104": { + "revision": 1, + "explanation": "The meter input current is $I = U/R = 0.5 V / 10 MOhm = 50 nA$.", + "source": "https://50ohm.de/EA_slide_ea_strom_spannung_widerstand_leistung_energie.html", + "confidence": 8 + }, + "AI105": { + "revision": 1, + "explanation": "A thermal power sensor converts RF heating into a measurement, so it reads true effective power over a wide frequency range into the GHz region.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI201": { + "revision": 1, + "explanation": "A VNA sweeps a known RF signal into the device under test and measures amplitude and phase of the response, deriving impedance, phase and SWR curves.", + "source": "https://50ohm.de/A_vna_2.html", + "confidence": 8 + }, + "AI202": { + "revision": 1, + "explanation": "A trap is a resonant circuit; a VNA can sweep it and show the resonance directly from impedance or reflection behaviour.", + "source": "https://50ohm.de/A_vna_2.html", + "confidence": 8 + }, + "AI203": { + "revision": 1, + "explanation": "A VNA is suited to HF resonant circuits because it measures the frequency-dependent impedance or transmission response across a sweep.", + "source": "https://50ohm.de/A_vna_2.html", + "confidence": 8 + }, + "AI204": { + "revision": 1, + "explanation": "In complex impedance, negative $jX$ is capacitive reactance; the real part remains the 54 ohm resistance.", + "source": "https://50ohm.de/A_vna_2.html", + "confidence": 8 + }, + "AI205": { + "revision": 1, + "explanation": "R = 50 ohm and jX = 0 means a purely resistive 50 ohm antenna impedance, matching a normal 50 ohm VHF transmitter output.", + "source": "https://50ohm.de/A_vna_2.html", + "confidence": 8 + }, + "AI206": { + "revision": 1, + "explanation": "Positive $jX$ denotes inductive reactance, while R is the ohmic part of the impedance.", + "source": "https://50ohm.de/A_vna_2.html", + "confidence": 8 + }, + "AI207": { + "revision": 1, + "explanation": "The shown resonance is below the target band; shortening a dipole raises its resonant frequency toward 80 m.", + "source": "https://50ohm.de/A_vna_2.html", + "confidence": 8 + }, + "AI208": { + "revision": 1, + "explanation": "The shown resonance is above the target band; lengthening both dipole ends lowers the resonant frequency into 80 m.", + "source": "https://50ohm.de/A_vna_2.html", + "confidence": 8 + }, + "AI301": { + "revision": 1, + "explanation": "An oscilloscope displays voltage versus time, so it is the instrument for checking waveform shape.", + "source": "https://50ohm.de/EA_oszilloskop_2.html", + "confidence": 8 + }, + "AI302": { + "revision": 1, + "explanation": "A trigger starts each sweep at the same signal condition, making a repetitive waveform stand still on the display.", + "source": "https://50ohm.de/EA_oszilloskop_2.html", + "confidence": 8 + }, + "AI303": { + "revision": 1, + "explanation": "Pulse width is conventionally measured between the points where the waveform crosses 50% of its peak amplitude.", + "source": "https://50ohm.de/EA_oszilloskop_2.html", + "confidence": 8 + }, + "AI304": { + "revision": 1, + "explanation": "The RF envelope is a time-varying waveform; a sufficiently broadband oscilloscope can display that envelope directly.", + "source": "https://50ohm.de/EA_oszilloskop_2.html", + "confidence": 8 + }, + "AI305": { + "revision": 1, + "explanation": "From the trace the peak voltage is 100 V; $P_{PEP} = (100/sqrt(2))^2 / 50$ gives 100 W.", + "source": "https://50ohm.de/EA_oszilloskop_2.html", + "confidence": 8 + }, + "AI306": { + "revision": 1, + "explanation": "A 10:1 probe means the real peak voltage is ten times the displayed value; $P_{PEP} = (60/sqrt(2))^2 / 50$ gives 36 W.", + "source": "https://50ohm.de/EA_oszilloskop_2.html", + "confidence": 8 + }, + "AI401": { + "revision": 1, + "explanation": "An SWR meter uses directional couplers to sample forward and reflected line voltages and compares them.", + "source": "https://50ohm.de/A_swr_meter_2.html", + "confidence": 8 + }, + "AI402": { + "revision": 1, + "explanation": "The two directional detector branches for forward and reverse power identify the circuit as an SWR meter.", + "source": "https://50ohm.de/A_swr_meter_2.html", + "confidence": 8 + }, + "AI403": { + "revision": 1, + "explanation": "For a purely resistive mismatch, SWR is the impedance ratio; $150/50 = 3$.", + "source": "https://50ohm.de/A_swr_meter_2.html", + "confidence": 8 + }, + "AI501": { + "revision": 1, + "explanation": "A modulated carrier moves or varies around the carrier frequency, so an unmodulated carrier gives the cleanest frequency-counter reading.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI502": { + "revision": 1, + "explanation": "A CW transmitter emits a steady RF carrier, and with suitable attenuation that carrier can be measured safely by a frequency counter.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI503": { + "revision": 1, + "explanation": "A frequency counter is the direct instrument for carrier frequency, and FM modulation should be absent to avoid measurement variation.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI504": { + "revision": 1, + "explanation": "The counter accuracy ultimately follows its timebase; stabilizing the main oscillator improves the frequency measurement.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI505": { + "revision": 1, + "explanation": "A longer gate time counts more cycles, so the least significant count represents a smaller frequency increment and resolution improves.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI506": { + "revision": 1, + "explanation": "0.01% is $10^{-4}$; $29 MHz \\cdot 10^{-4} = 2900 Hz$.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI507": { + "revision": 1, + "explanation": "0.00001% is $10^{-7}$; $14100 kHz \\cdot 10^{-7}$ gives a maximum error of 1.410 Hz.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI508": { + "revision": 1, + "explanation": "One ppm is one part in a million; at 100 MHz that is 100 Hz.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI509": { + "revision": 1, + "explanation": "10 ppm of 145 MHz is 1450 Hz, so the counter may read 145 MHz plus or minus 0.00145 MHz.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI510": { + "revision": 1, + "explanation": "Protecting the 144.400 MHz beacon edge needs room for 2.7 kHz USB audio plus 1 ppm frequency error of 144 Hz, totaling 2.844 kHz below the edge.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI511": { + "revision": 1, + "explanation": "A GPS-disciplined generator or OCXO provides a much more accurate reference than an ordinary LC or RC oscillator.", + "source": "https://50ohm.de/A_slide_a_empfaenger.html", + "confidence": 8 + }, + "AI601": { + "revision": 1, + "explanation": "The resistor network uses 48 one-watt resistors to obtain about 50 ohms while sharing dissipation, so the continuous rating is 48 W.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI602": { + "revision": 1, + "explanation": "A peak rectifier on a dummy load samples RF voltage; with the load resistance known, that voltage gives RF power indirectly.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI603": { + "revision": 1, + "explanation": "A 5 ohm tap provides a reduced RF voltage sample, which can be read with a DMM through an HF probe to estimate output power.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI604": { + "revision": 1, + "explanation": "The diode-capacitor probe rectifies RF into a DC indication, useful as a simple measuring head while aligning RF circuits.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI605": { + "revision": 1, + "explanation": "The diode, capacitor and high-impedance DC output are the standard structure of an RF probe.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI606": { + "revision": 1, + "explanation": "Correcting the 15.3 V reading for the Schottky drop gives the sampled RF peak; scaling from the 5 ohm tap to the 50 ohm load yields about 60 W.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI607": { + "revision": 1, + "explanation": "The detector voltage plus Schottky drop gives the RF peak at the measurement point; applying $P = U_{rms}^2/R$ gives roughly 600 mW.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI608": { + "revision": 1, + "explanation": "The circuit terminates the RF path and rectifies a known sample voltage, so it is a measuring head for RF power.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI609": { + "revision": 1, + "explanation": "The measuring head is not rated for the full expected 15 W directly; a 20 dB, 20 W attenuator reduces both level and risk.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI610": { + "revision": 1, + "explanation": "For 1 W into 50 ohms, $U_{rms}=sqrt(50)$ and peak voltage is about 10 V; the divider and diode drop leave about 4.8 V DC at the output.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI611": { + "revision": 1, + "explanation": "Add the silicon diode drop to the DC reading to recover peak RF voltage, convert to RMS, then use $P=U^2/R$ with 54.1 ohms to get about 9.7 W.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI612": { + "revision": 1, + "explanation": "Detector diodes, resistors and layout introduce systematic errors, so accurate RF power readings require calibration correction values.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI613": { + "revision": 1, + "explanation": "The simple detector and meter respond to induced RF voltage without a direct connection, which is the function of a field-strength indicator.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI614": { + "revision": 1, + "explanation": "A spectrum analyzer displays signal amplitude versus frequency, so it can measure the amplitudes of individual harmonics.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AI615": { + "revision": 1, + "explanation": "Harmonics appear as separate frequency components above the fundamental, which a spectrum analyzer is designed to reveal.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ101": { + "revision": 1, + "explanation": "Using only the power needed for reliable communication reduces unnecessary field strength at other receivers and therefore lowers interference risk.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ102": { + "revision": 1, + "explanation": "An RF ground is useful only if it gives RF current a low-impedance return path at the operating frequency.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ103": { + "revision": 1, + "explanation": "A grounded metal enclosure shields the receiver circuitry from external RF fields and reduces direct pickup by the board.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ104": { + "revision": 1, + "explanation": "A tuner improves the match and filters suppress unwanted RF paths, both reducing unintended radiation from the antenna system.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ105": { + "revision": 1, + "explanation": "Direct radiation into an IF stage bypasses the intended front-end selectivity; this direct pickup is called Direkteinstrahlung.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ106": { + "revision": 1, + "explanation": "A transistor base-emitter junction behaves like a diode, so strong RF can be rectified there into audible interference.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ107": { + "revision": 1, + "explanation": "SSB and CW have strong amplitude changes; weakly immune audio amplifiers can demodulate those changes into audible signals.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ108": { + "revision": 1, + "explanation": "A broadband, unselective TV preamplifier has little rejection of nearby strong RF, so overload from a close transmitter is likely.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ109": { + "revision": 1, + "explanation": "A very strong 432 MHz signal aimed at the TV antenna can overload the receiver front end even if it is not on the wanted TV channel.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ110": { + "revision": 1, + "explanation": "A nearby VHF transmitter can drive the DAB receiver input beyond its linear range, causing overload rather than a true harmonic problem.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ111": { + "revision": 1, + "explanation": "Digital receivers often conceal errors until correction fails; then the audio becomes noisy or mutes instead of fading smoothly.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ112": { + "revision": 1, + "explanation": "A high-pass at the antenna blocks HF signals below the broadcast bands, while ferrite chokes suppress common-mode RF on every attached lead.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ113": { + "revision": 1, + "explanation": "DVB-T2 starts far above 144 MHz, so a high-pass around 460 MHz rejects the 2 m transmitter while passing TV signals.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ114": { + "revision": 1, + "explanation": "A TV high-pass should reject the interference but add little loss in the wanted band; more than a few dB would noticeably weaken reception.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ115": { + "revision": 1, + "explanation": "An RF isolation transformer can interrupt common-mode currents in a receive antenna lead while passing the wanted differential signal.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ116": { + "revision": 1, + "explanation": "If the TV is still disturbed with the antenna unplugged, the likely coupling path is mains or cabling, so a mains filter near the device is the first remedy.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ117": { + "revision": 1, + "explanation": "Once the mains lead is identified as the coupling path, a mains filter is the targeted way to block RF entering through that path.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ118": { + "revision": 1, + "explanation": "A mains RF filter combines series choking and capacitors to shunt common- and differential-mode RF before it enters the equipment.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ119": { + "revision": 1, + "explanation": "Ceramic capacitors have low inductance at RF, so they bypass high-frequency voltages better than wound film or electrolytic capacitors.", + "source": "https://50ohm.de/A_stoerungen_elektronischer_geraete_2.html", + "confidence": 8 + }, + "AJ201": { + "revision": 1, + "explanation": "The second harmonic is twice the fundamental: $2 \\cdot 3.730 MHz = 7.460 MHz$.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ202": { + "revision": 1, + "explanation": "The third harmonic is three times the fundamental: $3 \\cdot 7.050 MHz = 21.150 MHz$.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ203": { + "revision": 1, + "explanation": "The third overtone is the fourth harmonic, so $4 \\cdot 7.20 MHz = 28.80 MHz$.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ204": { + "revision": 1, + "explanation": "The third harmonic is $3 \\cdot 29.5 MHz = 88.5 MHz$, which lies in the FM broadcast band.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ205": { + "revision": 1, + "explanation": "Odd harmonics are 1st, 3rd, 5th, ...; the second odd harmonic is the 3rd, so $3 \\cdot 144.690 MHz = 434.070 MHz$.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ206": { + "revision": 2, + "explanation": "Of the harmonics of 144.300 MHz, the 3rd at 432.900 MHz lands in the 70 cm amateur band and the 9th at 1298.700 MHz lands in the 23 cm band; other harmonics fall outside amateur allocations and don't disturb amateur operation.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ207": { + "revision": 1, + "explanation": "Flattened or clipped waveform peaks indicate overdrive; clipping adds harmonic content to the transmitter output.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ208": { + "revision": 1, + "explanation": "A single-band transmitter needs a low-pass-style output curve that passes the wanted band and attenuates higher harmonics.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ209": { + "revision": 1, + "explanation": "For VHF, unwanted components can be both below and above the wanted channel, so a band-pass after the transmitter is appropriate.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ210": { + "revision": 1, + "explanation": "A trap or notch circuit has high attenuation at one selected frequency, making it suitable for suppressing one specific harmonic.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ211": { + "revision": 1, + "explanation": "A mixer produces sum, difference and other products; a band-pass passes only the wanted mixer product to the following stages.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ212": { + "revision": 1, + "explanation": "Parasitic oscillations are self-oscillations of the circuit, not harmonics, so their frequencies need not have a fixed relation to the operating frequency.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ213": { + "revision": 1, + "explanation": "Small jumps in output while tuning are a classic symptom of a parasitic oscillation starting or stopping in the amplifier.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ214": { + "revision": 1, + "explanation": "RF chokes have stray capacitance, so their inductance and capacitance can form unintended self-resonances.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ215": { + "revision": 1, + "explanation": "Unwanted feedback from output to input can sustain oscillation; good input-output isolation reduces that loop gain.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ216": { + "revision": 1, + "explanation": "Shielding each RF stage reduces unintended capacitive and inductive coupling between stages, lowering the chance of self-oscillation.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ217": { + "revision": 1, + "explanation": "A ferrite bead adds lossy RF impedance in the transistor lead, damping VHF parasitic oscillation without affecting DC much.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ218": { + "revision": 1, + "explanation": "SSB has an amplitude-varying envelope and needs linear amplification; class C is nonlinear and would distort it badly.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ219": { + "revision": 1, + "explanation": "Excess microphone gain overdrives the SSB chain, broadening the signal and creating nearby intermodulation products known as splatter.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ220": { + "revision": 1, + "explanation": "Abrupt CW keying has sharp envelope edges; sharp transitions contain wide sidebands heard as key clicks.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ221": { + "revision": 1, + "explanation": "The least disturbing CW waveform has rounded rise and fall times, limiting high-frequency sidebands from keying transients.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ222": { + "revision": 1, + "explanation": "A varying supply voltage changes the RF stage gain or amplitude, so it unintentionally amplitude-modulates the carrier.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ223": { + "revision": 1, + "explanation": "NF ripple on the final-stage supply varies output amplitude at audio rate, which is unwanted AM on the transmitted signal.", + "source": "https://50ohm.de/future/NEA_slide_nea_sender.html", + "confidence": 8 + }, + "AJ224": { + "revision": 1, + "explanation": "For 1.7 to 35 MHz, the cited unwanted-emission rule uses the 0.25 µW threshold and at least 40 dB attenuation relative to maximum PEP.", + "source": "https://50ohm.de/NEA_unerwuenschte_aussendungen_3.html", + "confidence": 8 + }, + "AJ225": { + "revision": 1, + "explanation": "For 50 to 1000 MHz, the stricter cited limit is at least 60 dB attenuation for unwanted emissions above 0.25 µW.", + "source": "https://50ohm.de/NEA_unerwuenschte_aussendungen_3.html", + "confidence": 8 + }, + "AK101": { + "revision": 1, + "explanation": "In the near field, electric and magnetic fields are not locked to the fixed far-field phase and impedance relationship, so E and H cannot be simply converted.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK102": { + "revision": 1, + "explanation": "In the far field, E and H are tied by the wave impedance of the medium, about 377 ohms in free space.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK103": { + "revision": 1, + "explanation": "The simple distance formula assumes far-field behaviour; below roughly $lambda/(2 pi)$ or for electrically small antennas, measurement or near-field modelling is needed.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK104": { + "revision": 1, + "explanation": "Feed-line loss reduces transmitter power before it reaches the antenna, so antenna input power is transmitter power multiplied by the loss factor.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK105": { + "revision": 2, + "explanation": "Safety distance scales as $d \\propto \\sqrt{P_{EIRP}}/E$. A 6 dB pattern attenuation cuts EIRP in that direction by a factor of 4, so the distance shrinks by $\\sqrt{4}=2$: 20 m becomes 10 m.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK106": { + "revision": 1, + "explanation": "Use the person-protection distance formula with dipole gain and 100 W; solving against the 28 V/m limit gives about 2.50 m.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK107": { + "revision": 1, + "explanation": "Rearranging the field-strength formula for power with 5 m distance, 28 V/m limit and 6 dBd gain gives roughly 100 W transmitter output.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK108": { + "revision": 1, + "explanation": "After 0.5 dB cable loss, the dipole ERP/EIRP term in the safety-distance formula gives about 4.10 m for the 28 V/m limit.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK109": { + "revision": 1, + "explanation": "The same distance formula scales with the square root of power; raising input power from 300 W to 700 W increases the distance to about 6.26 m.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK110": { + "revision": 1, + "explanation": "Convert 11.5 dBd gain and 1.5 dB cable loss to linear factors, then apply $d = sqrt(30 P_{EIRP})/E$ to get about 6.86 m.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK111": { + "revision": 1, + "explanation": "With 100 W, 10.5 dBd gain and 1.5 dB cable loss, the far-field safety-distance formula against 28 V/m gives about 7.1 m.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK112": { + "revision": 1, + "explanation": "The 18 dBd dish gain minus 2 dB feed loss gives the EIRP term; using the 61 V/m limit yields about 4.6 m in the main beam.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK113": { + "revision": 1, + "explanation": "12.15 dBi is a linear gain of about 16.4; $sqrt(30 \\cdot 250 W \\cdot 16.4)/30 m$ is about 11.7 V/m.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK114": { + "revision": 1, + "explanation": "A vertical dipole has about 2.15 dBi gain; applying the free-space field formula at 10 W and 10 m gives roughly 2.2 V/m.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK115": { + "revision": 1, + "explanation": "Convert 100 W ERP to about 164 W EIRP, then $sqrt(30 \\cdot 164 W)/100 m$ gives about 0.7 V/m.", + "source": "https://50ohm.de/future/NEA_slide_nea_personenschutzabstand.html", + "confidence": 8 + }, + "AK201": { + "revision": 1, + "explanation": "Charged power-supply capacitors can remain dangerous after unplugging; a suitably rated high-value resistor discharges them without a violent short-circuit current.", + "source": "https://50ohm.de/future/NEA_slide_nea_sicherheit.html", + "confidence": 8 + }, + "AK202": { + "revision": 1, + "explanation": "Low-resistance bonding keeps exposed conductive parts at nearly the same potential, reducing touch-voltage risk to people.", + "source": "https://50ohm.de/future/NEA_slide_nea_sicherheit.html", + "confidence": 8 + }, + "AK203": { + "revision": 1, + "explanation": "A separate earth lead near a quarter wavelength can resonate as an RF conductor, creating a voltage maximum at the equipment end.", + "source": "https://50ohm.de/future/NEA_slide_nea_sicherheit.html", + "confidence": 8 + }, + "AK204": { + "revision": 1, + "explanation": "A transmitting antenna can have high RF voltage at current nodes or voltage maxima even with only a few watts, so touching it is unsafe.", + "source": "https://50ohm.de/future/NEA_slide_nea_sicherheit.html", + "confidence": 8 + }, "BA101": { "revision": 2, "explanation": "DD4UQ spells D as Delta, U as Uniform and Q as Quebec; the traps are country-style words such as Denmark, Uruguay and Queen, which are not the ITU code words.",