Field Strength Meter - Balanced circuit with FET's
The field strength meter (FSM) is a very useful addition to any HAM toolbox.
If you are messing around with antennas, or building PA's, or trying to
repair some TX gear, the FSM will come to your rescue when there's
doubt about the output level.
This simple, but extremely useful circuit is very easy to build.
dont waste your hard earned cash, buying something this simple.
....BUILD IT YOURSELF.... :-)
The small diagram below shows the simple circuit in my FSM.
i used the balanced approach to get a stable wideband circuit.
Here i have mocked it up on veo-board, this is prior to assembly.
Here the internals are all wired up and the box ready to be clicked together.
i have used the meter from an old SWR meter, but hey, it was free and is perfect.
I have added a small DC socket in the side, to allow for stationary use and
DC feed from local power supply. you can feed it with anything from 9-12 Vdc
The top of the FSM with the ON/OFF and sensitivity button, and the arial socket
The final product. you might be better at the mechanics than i am, but it
works like a charm and will give a good indication of the output level from
the device being tested.
I have tested the FSM from 3.5 - 440Mhz with success.
This is @ 440Mhz with 1 watt radiated power from a hand held radio 1 meter away.