Fuchs MRV-1 VHF transceiver

Fuchs Electronics
MRV-1 VHF Transceiver
Frequency 118-149.950MHz
Channel Spacing 50kHz
Power Output 25Watts
Serial No 640

640 is a rather high serial number for a local radio, they made quite a few of these.

The top lid comes off, showing six removable boxes, a heatsink and some wiring. There's a tool clipped to the lid that's used to remove the modules.

Module #1, serial 099. The foam they used is not as acid free as one would like. It's disintegrating and harming the electronics. Some cleanup required.

This is obviously the IF, at 3.5 MHz which is rather low for a VHF rig. There's also a Torotel audio band-pass filter.

Module #2, serial 001 (!).

Module #3, serial 583.

Module #4, serial 449.

Module #5, serial 895. engraved "osc"

Module #6, serial 088.

The hour meter reads 1666, for what it's worth.

Google says that ZS-NTE, a 1943 Shackleton, was the first aircraft to be fitted with this type of radio (1984).

There are subtleties here. At first glance it looks as if more than one crystal will be selected at a time, but it's all about biasing.

One of the 10MHz lines need to be high and the other low. The high one is the active one and provides bias for the diodes. Of the five lines, the first low line pre-biases the diodes and the second line then provides more bias current via the inductors (which turn the diodes on but block the RF to keep the crystal out of the loop). Assuming all the diodes are matched, only the one with the most current through it will be on.