How do I know if a transmitter is working? Just bring close this circuit to its coil or antenna and check if there is any movement of the indicating instrument needle. This field strength meter operates transmitter of 100 kHz to more than 100 MHz, without the need for circuit tuning or changes.
The antenna may be a piece of stretched wire or even of the telescopic type 40-90 cm in length. The instrument is a 50 uA to 200 uA galvanometer which can be obtained from antique stereos. The diode can be any germanium such as 1N34, 1N60, etc.
To achieve needle deflection the signal must be at least about 10 mW of power. In Figure 1, we have the diagram and aspect of the assembly.
We recommend installing the unit in a small metal box which works as a ground.
Material list
M1 - 0-50 to 0-200 uA - microammeter
D1 - 1N34 - germanium diode
Miscellaneous: antenna, mounting box, wires, welding, etc.
