This is a simple VHF dip meter circuit.The DIP meter is the frequency meter by use the LC resonance circuit that adjustable until the frequency show peak amplitude. The circuit include variable frequency generator circuit, rectifier and a moving coil meter.
In the oscillator include two transistors T1 and T2. The tuning circuit include C1 and coil Lx this coil will is outside the metal box.
When apply the power to circuit, the voltage from the oscillator will be rectifier by diodes D1 and capacitor C2. Then, send signal to P1 that use to adjust meter.
If bring the coil Lx near the others LC circuits, that resonance same the frequency is generated. This LC circuit will pull power from Lx, cause the lower voltage drop across the meter. The adjusting frequency by C1 if the frequency resonance can read frequency by the meter.
The coil made of copper wire No. 19 SWG or 1mm. Wrapped 2 times on the core diameter 15 mm. The frequency range 50-150 MHz.
This transistors No. BF494 can operate at frequencies up to 150MHz. If needed, use the higher frequencies to change the number BRF91. Which operate at frequencies up to 250 MHz. The capacitor C1 is 50 pF may be made of the mica capacitor value 100 pF 2 pcs in series.
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