Bulletins from the Pacific Packet Radio Society - page 042


12 to 14.8 VDC

DIMENSIONS: 7" Wide X 2 3/411High X 911 Deep
WEIGHT: 5 lbs. including microphone & mobile mount

Note: Factory tune up sheet specs RX sensitivity at 0.35 uv for 12 db SINAD. TX spurs speced at -33 db. - Beware! - W2FPY

Applicability for wider band use or direct FSK, etc. RX IF frequency is 41 MHz (1st IF) and 10.7 MHz (2nd IF). RX uses monolithic crystal filter, and will be VERY broadband if filter removed or replace with wide-band unit. TX looks like it can run much wider-band deviation with little adjustment. The FM discriminator is a CA3075. It seems serviceable for higher bit rates. The PC board is large, with very "open" construction. This should make all "mods" simple.

The local RTTY group, here in NJ, says that there was a standard modification for using these rigs for AFSK. Basically, it involves injection of high-level audio to pin 1 of IC4 (MC3301). This leaves the mike-line available at all times. Similarly, you can tap audio off the speaker line, and leave the speaker on (your option!) at will.

Folklore here also says that the FM-21 is a poor mobile rig, due to temperature/stability problems. Therefore, it would not make a good RF deck for a digipeater (unless kept at home).

I hope this satisfies your curiosity I can supply more details about this rig as needed. Ed Clegg (W3LOY) is anxious to sell out his entire stock of parts for the FM-21, and this might include many spares, etc. He suggests that, if we don't need the box, he could simply supply completed and partially completed boards (one PC board for RX and TX). Incidentally, T/R switching is solid-state, too.

PLEASE BE AWAREIII I don't know how many of these rigs are complete. Ed says he will be able to supply anything needed to finish them, but he still hasn't filled me in on how-much-of -what is in his warehouse. It is likely that some parts will have to be stuffed onto the PC board to make it operate. You will definitely have to do the tune-up.

Happy reading & 73,
Steve, W2FPY

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