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?


As information, the latest (and greatest?) iteration of the NTIA Red
Book reinforces the spectral purity requirements for the 2-30 MHz band.
The purity specification is currently 40db+10logPo. So, a 100 watt rig
would need to have all spurious emissions down by a nominal 60Db. Most
ham and a lot of commercial gear can't meet that spec. The 20HZ spec
has been on the books for some time, now, and is not hard to meet given
the current crop of equipment utilizing good quality TCXO's. It remains
to be seen what CAP and MARS will do in the short term, and ultimately,
with the spectral purity spec.

Finally, the VFOs in Drake and Collins equipment can't come close to
making any of the above specs or even coming close. Frequency tolerance
is the one factor that can be easily and accurately measured, at a
distance.