Touch up some explanations

explanations.json

@@ -258,8 +258,8 @@
     "confidence": 8
   },
   "AB402": {
-    "revision": 2,
-    "explanation": "The first overtone is the second harmonic, so the third overtone is one step higher again: the fourth harmonic.",
+    "revision": 3,
+    "explanation": "Overtones count only the harmonics above the fundamental: 1st overtone = 2nd harmonic, 2nd overtone = 3rd harmonic, 3rd overtone = 4th harmonic.",
     "source": "https://50ohm.de/A_slide_a_sender.html",
     "confidence": 8
   },
@@ -690,8 +690,8 @@
     "confidence": 8
   },
   "AC524": {
-    "revision": 1,
-    "explanation": "A flyback diode is placed antiparallel across the coil, reverse-biased during normal operation and forward-biased for the coil's turn-off current.",
+    "revision": 2,
+    "explanation": "When the switch opens, the inductor tries to maintain its current and reverses the voltage across itself. The flyback diode is wired antiparallel so it forward-conducts at that moment, providing a safe current path and clamping the back-EMF that would otherwise destroy the switching transistor.",
     "source": "https://50ohm.de/A_transistor_2.html",
     "confidence": 7
   },
@@ -1056,8 +1056,8 @@
     "confidence": 7
   },
   "AD313": {
-    "revision": 1,
-    "explanation": "Regularly spaced unwanted signals around 120 kHz are typical of switch-mode supply switching frequency and its related emissions.",
+    "revision": 2,
+    "explanation": "Spurs spaced 120 kHz apart across the spectrum point to a switch-mode supply: its switching frequency and harmonics radiate at multiples of that fundamental rate.",
     "source": "https://50ohm.de/A_schaltnetzteil_2.html",
     "confidence": 8
   },
@@ -3678,8 +3678,8 @@
     "confidence": 8
   },
   "EB205": {
-    "revision": 1,
-    "explanation": "A conductive copper or aluminium core supports induced RF currents that oppose field penetration, so the effective magnetic-field cross-section of the coil is reduced. The 50ohm page notes that the catalog wording is simplified, so this is partly a memorize-the-official-answer item.",
+    "revision": 3,
+    "explanation": "Eddy currents induced in the conductive copper or aluminium core oppose the changing RF flux, partially cancelling the field inside the core and shrinking the effective magnetic cross-section, so inductance drops. The catalog phrases this as the field 'not penetrating' the core — a simplification of what physically happens, but the wording to memorize.",
     "source": "https://50ohm.de/NEA_spule_1.html",
     "confidence": 7
   },
@@ -4332,8 +4332,8 @@
     "confidence": 7
   },
   "EC610": {
-    "revision": 2,
-    "explanation": "The base-emitter junction of a conducting silicon bipolar transistor is forward biased at about 0.6 V in the class-E model.",
+    "revision": 3,
+    "explanation": "A silicon BJT conducts when its forward-biased base-emitter junction reaches its threshold; for silicon that is about 0.6 to 0.7 V.",
     "source": "https://50ohm.de/NEA_slide_nea_bauelemente.html",
     "confidence": 8
   },
@@ -5274,8 +5274,8 @@
     "confidence": 8
   },
   "EG211": {
-    "revision": 1,
-    "explanation": "A ground-plane is roughly half a dipole against ground, and sloping radials bring its feed impedance into the 30 to 50 Ohm range.",
+    "revision": 2,
+    "explanation": "A quarter-wave vertical against a counterpoise has a feed impedance near 35 Ohm with horizontal radials; sloping the radials downward raises it toward 50 Ohm, so the practical range is about 30 to 50 Ohm.",
     "source": "https://50ohm.de/E_fusspunktimpedanz_1.html",
     "confidence": 8
   },
@@ -6018,8 +6018,8 @@
     "confidence": 8
   },
   "EJ123": {
-    "revision": 1,
-    "explanation": "A room antenna gives poor shielding and selectivity against strong local RF; an outdoor TV antenna improves wanted signal and allows better filtering.",
+    "revision": 2,
+    "explanation": "An indoor antenna sits inside the noisy local RF environment and gets little wanted signal; an outdoor antenna can be placed away from the interferer and offers more gain and directivity, improving the wanted-to-interferer ratio.",
     "source": "https://50ohm.de/E_slide_e_sender.html?print-pdf=&showNotes=true",
     "confidence": 8
   },
@@ -6240,8 +6240,8 @@
     "confidence": 8
   },
   "EK209": {
-    "revision": 1,
-    "explanation": "The current Class E material states that an existing building earthing system may be used for antenna earthing, so no separate electrode or BNetzA approval is required for this answer.",
+    "revision": 2,
+    "explanation": "An existing building earthing system per VDE 0855-300 may be used for antenna earthing; no separate electrode or special approval is required.",
     "source": "https://50ohm.de/NE_blitzerdung.html",
     "confidence": 8
   },