TF2603 RF Electronic Millivoltmeter
The TF2603 is a sensitive electronic millivoltmeter that covers the frequency range 50 kHz to 1500 MHz. Voltages between 300 μV and 3 V can be accommodated.
This is one of the later versions that uses an electronic, rather than electro-mechanical chopper, to convert the DC output from the detectors to an AC signal for ease of amplification.
The black meter surround (as opposed to the usual MI grey) indicates a "special" that was built for the military.
The instrument is in good order and agrees well with the output levels indicated on my 2018 signal generator.
The TF2603 probe uses a pair of germanium diodes that provide full-wave rectification of the input signal. The DC output from the detectors is "chopped" at a rate of 100 Hz, amplified and converted back to DC again to drive the meter. This is accomplished by a synchronous detector thereby minimising noise levels.