Micro-Spy 2

o BSY18 can be replaced with ECG123AP. BA121 can be replaced with ECG/NTE611 (10pF@4v). USW means 'Ultra-Short-Wave'.
o L1 = 7 turns of 0.8mm Silverwire(round) on a 5mm round adjustable Ferrit-core. Position 'X' = 0.5 ... 1 turn.
o This very stable oscillator has a frequency of approximately 100 Megaherz.
o Frequency determend by the Variac BA121 and 20pF capacitor. Feedback is thru 4.7pF capacitor.
o USW coil prevents HF signals (feedback) flow to ground.
o DC biased with the 12K resistor.
o Distance is from 100 to about 200 meters. Not bad for a little circuit like this!

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