DERG
The basic detector is nothing more than a full wave or half wave vhf/uhf pin diode rectifier with an antenna on one side and high impedance meter to measure the output voltage on the otherside. No rocket science, the detection method is looking for a noise source within a meter or two and not miles away. Commonly known as Field Strength Meter.
Simplicity, is an existing VHF airband portable with some means of measuring the signal strength of the input noise on any vacant frequency. Access to the AGC voltage is a means of doing so.
There will be heaps of details on
RF rectifier devices on the www.