Upconverter Weirdness
 

See if you can figure this one out.

I recently bought a used Palomar VLF-A converter and am experiencing a
strange frequency offset problem. WWVB 60 KHz appears about 5 KHz low
on the upconvert receiver, in this case a TS-130 transceiver.

This converter was evaluated in the January 2000 pg 59 issue of _QST_
and the author had the same problem, only in his case the receiver was
an ICOM IC-706.

When operating the converter into a direct conversion receiver WWVB
comes out on the correct frequency. Suspecting a problem with the
VLF converter's LO (3.5 MHz in this case), a peek at this LO signal
with a high-end spectrum analyzer shows a clean output with very
little phase noise, no spurs and exactly on 3.5 MHz.

BTW, I tried replacing the MC1496 active balanced modulator with a
Minicircuits SRA-6 passive DBM, same result. I don't suspect any
problems with the upconverter receiver's LO either.

So - what's going on?

73 Don K6LTS