Micr-Spy with FETs
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o T1 & T2 are BF245 N-channel FET's and can be replaced with a NTE133. The ECG312 could likely be used also. The varactor diode BA121 can be replaced with a ECG/NTE611. USW stands for 'Ultra-Short-Wave'.
o L1 = 7 turns of 0.8mm Silverwire on a 5mm round Ferrit-core (adjustable).
o This very stable oscillator has a frequency of approximately 100 Megaherz.
o Feedback via 16pF capacitor. No interference from antenna on resonance-loop.
o Distance is at *least* 300 meters!