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   Properties.
This broad band system gives an indication of the magnetic near field strength of a short wave  "Magnetic loop" antenna.
The little sensor unit of it is installed outside, near a loop antenna. Its input is protected against over voltage.
The relative field strength is read at the transmitter site with a meter unit, connected to the sensor through a twisted 3-wire cable. The sensitivity of the system is switch able between LOW  and 20dB more sensitivity, enabling testing with 100W, and less annoying low power.
Power source is a 4.5V from a three AA alkaline battery pack. Total supply current is 2 - 8 mA. Very long battery life can be expected.

    Testing the finished indicator, using a dip meter as RF source.
Connect the sensor unit to the indicator unit. Switch the indicator unit to sensitive. Hold the coil of a dip meter in line with the sensor ferrite rod, close to the grounded end of the ferrite coil. Set the dip meter signal strength to maximum. Change the dip meter frequency over the whole short wave range and observe the indicator meterdeflection. Using a Heathkit HD-1250 dip meter, a good meterdeflection was observed between 1.5MHz and 70MHz .

   Testing your magnetic loopantenna.
See the drawing at the right for a possible orientation of the ferrite sensor coil, in respect to the orientation of the loop antenna. In order to minimize RF induction onto the signal cable and obtaining best indications, the 3-wire twisted connecting cable  cable should run at 90 degr. angles away from both  :
a. the ferrite rod in the sensor unit
        and
b. the lowest part of the Magnetic loop antenna.

- Start with the sensor unit near the center of the lowest conductor of the loop,
- and change the distance in respect to this conductor.
- Keep the sensors ferrite rod at 90 degr. in respect to the loop surface.

You have to experiment with the location of the sensor unit (closer / further / higher / lower). 
With S2 on the indicator unit  in its UNsensitive position, and with 100W transmitter power applied to a correctly tuned loop antenna, you should then get nearly full meter scale deflection.
With S2 on the indicator unit  in its MOST sensitive position, you can test with low transmitter power, causing as little as possible interference on the communication channal.