I think I have found a supplier for a 32.800 Mhz crystal, which would
put the softrock at around 8200 and make it a more reasonable 15000hz
offset. I hope that this will still be far enough away from the 8215 IF
to not cause any problems, while making the bandpass a little more
symmetric.
Be _very_ careful to put a high reverse-isolation buffer between the K3
I.F. output and any sort of mixer like the Softrock that leaks a lot of
L.O. energy onto its input lines. The buffer in the K3 is an impedance
transformation device, not a reverse-isolation stage. It assumes the
attached device does not inject any appreciable energy back into the
I.F. output tap, and certainly not any energy at the 8.215 MHz I.F.
A better approach when using a quadrature sampling detector (QSD, or
Tayloe mixer) may be to mix the 8.215 MHz I.F. to a very different
frequency, then use the Softrock at that I.F.
For example, use a high reverse-isolatin amplfier at 8.215 MHz to feed
an H-mode mixer driven with an oscillator at 19.44 MHz. This will
result in an IF of 11.225 MHz where the Softrock can operate. 4x 11.225
is 44.900 MHz. 19.44 MHz and 44.90 MHz are standard (currently in stock
at Digikey) frequencies, and with careful construction and a reasonable
reverse-isolation input amplifier, there is little danger of interfering
with the K3. I have not tried this, so use this information entirely at
your own risk, YMMV, etc.
But, in any event, a high reverse-isolation amplifier is an absolute
must if the device you are attaching to the K3 I.F. output has _any_
chance of leaking energy into the K3 anywhere near its I.F. Use good
quality coax, keep RF out of the IF connector (the end of your 40 meter
dipole 15 feet away from your radio, that sort of thing...).
The SDR-14 and SDR-IQ appear to be safe in this regard as the input goes
to a buffer amp and then directly to an A/D converter clocked at about
65 MHz.
73,
Lyle KK7P
_______________________________________________
Elecraft mailing list
Post to: [email protected]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
