Emcom FC-4001

Emcom FC-4001 Mk II Courier

Rear view of FC-4001

Serial Number 01028. Rated for 10W output. This one is a low band VHF transceiver but I'm sure they would have been available in high band VHF versions as well.

Top view

The radio was used as a data link, since it came with a data cable and a plug in the back to disable the speaker.

View of solder side of PCB

PCB under the speaker

The actual design seems fairly mundane. A 10.7 MHz first IF stage, a 10.245 MHz crystal, a 455 kHz second IF stage. It looks as if the main PCB has provision for a low-power RF output stage, or alternatively this daughterboard can be used:

RF amplifier

The output transistor is a 2N5591 which is good for 30 Watts.

68.900R xtal 75.750T xtal

Here it gets interesting. The label on top of the radio says "6M Rig connections" but the crystals are marked as "68.900R" and "75.750T". The true crystal frequencies of 39.800 MHz and 6.3125 MHz are also indicated -- which implies the following crystal-to-frequency equations:

Rx frequency = Rx crystal * 2 - 10.7 : 39.800 * 2 - 10.700 = 68.900 MHz
Tx frequency = Tx crystal * 12       : 6.3125 * 12         = 75.750 MHz
Neither of these frequencies are in the 6m Amateur band. They also differ by 6.85 MHz which is not a standard repeater offset.

However, poking values into a pocket calculator shows that the following makes a lot more sense:

Rx frequency = Rx crystal + 10.7 : 39.800 + 10.700 = 50.500 MHz
Tx frequency = Tx crystal * 8    : 6.3125 * 8      = 50.500 MHz
50.500 MHz isn't really allocated to digital modes in the current band plan, but it's conceivable that it could have been used as such in the past.


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