The older equipment referenced, T4/R4, Collins KWM, Collins S-line do not
require any 'modification' to reach the CAP/MARS frequencies. I used the Drake
T4XC/R4C for years, 1970 through 1985, at AFF1C/AFB1JX/AFW1MCE and I used the
KWM-2A at AGA5HI in the 70s. All that is required is the proper mixing crystal.

This class of equipment, however, does not meet the frequency accuracy
requirements so external frequency measuring equipment or a FYMON station was
required to assure accuracy. The output tuned L/C circuits have a minor impact
on the efficiency of the final amplifier. Finally, this class of equipment will
NOT OPERATE in selected frequency ranges around the radio's i.f. frequencies.

More modern equipment can be modified to operate on CAP/MARS. Check the various
use groups for specifics. I have 'opened-up' my IC-746 and IC-706MKIIg without
any problems.

/s/ W1MCE

Rick (W-A-one-R-K-T) wrote:

Typically, can ham-bands-only receivers such as the Drake R4 and Collins
75A or 75S series, transmitters such as the Collins 32S and Drake T4
series, and transceivers such as Drake TR-4 and Collins KWM-2, be modified
to work on CAP and MARS frequencies?

I know that some radios have provisions for installing crystals so that
they'll work on off-band frequencies.

How can I determine which radios are modifiable that way, and also where
is a good place to get crystals these days?