On Fri, 24 Aug 2012, kt4hx wrote:

Can someone tell me if the crystals for an SPR-4 are compatible with the
SW-4A? I thought maybe the same crystals were used in the 4-line, SPR-4
and SW-4A, but of course I could be wrong.

Maybe, but I don't know. Drake used various schemes among their
equipment. Some, the receivers, relied on low frequency filters to
provide ultimate selectivity, while the transmitters obviously just used
filters in the 5MHz range. I thought sometimes there was some variation
on the HF filter frequency, and if so that would impact on the crystal
frequency. Counter to that, if they did that, then you couldn't
transceive with a T4 and an SPR-4.

Look for specs, see if you can find a page that has their IF frequencies.
Or maybe the manuals are online.

Wait, a simple search on "receiver IF frequencies" gets this page very
early on:
http://www.agder.net/la8ak/e13.htm
and it says the R4 and the SPR-4 has a 5645kHz IF. No mention of the SW-4,
but the 2a/b/c uses a tuneable first if, then 455KHz and 50KHz.

It's the Drake transceivers that use 9MHz IF, the TR4 going to 2 filters,
one for USB and one for LSB.

The manual for the SW-4 is certainly online, I didn't bother downloading.
Some more searching doesn't find the IF frequency, though I didn't try
that much harder. One article does say it was a "modification" of the R4,
so chances are good it used the same 5645kHz IF, but I wouldn't try
without verification.

If the IF is consistent, then the crystal frequencies are likely the same.
I can't imagine them using different crystal oscillators that would
require different stock in crystals if the IFs were the same.

The manuals would certainly tell you how to have crystals ground for the
receivers, since they tended to have

Michael VE2BVW