Micro-Spy with FETS

Micro Spy with FETS

o T1 & T2 are BF245 N-channel High-frequency FET’s and can be replaced with a NTE133/ECG133.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/L2 = 7 turns of 0.5mm Silverwire on a 5mm adjustable Ferrit-core.
o This very stable oscillator has a frequency of 400MHz and could preferred be a lot higher.At 5V the frequency is around 137MHz.
o Voltage supply is not critical. The oscillator starts working at 3V, the upper limit is given by threshold of the BF245 and is 30V.At 12V sinks at about 5mA.
o Feedback via 16pF capacitor.No interference from (dipole) antenna on resonance-loop.
o Distance is a minimum of 300 meters (900feet)!

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