Grid Dip Oscillator (GDO) Instrument

This is a grid dip oscillator (GDO) circuit developed by Luigi Falcone. This circuit uses seven plug in coils covering 3.0 to 30Mhz. This circuit can be connected to the a frequency meter by using The coaxial socket J2.  The figure below shows the schematic diagram of the circuit and the coil information:

DC amplifier is formed by TR2 that permit the use of a 1mA FSD meter. R7 is used to control the sensitivity of 1mA FSD meter. a field strength meter/RF sniffer is formed by the instrument with TR1 switched off (via S2). The coils are wound on Teflon formers with two “female” sockets which plug-in to two “male” sockets on the instrument. [Source:]