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August 21st 04, 04:04 PM

(Bob Monaghan) wrote in message ...
yes, I found the brief article and the cite is 73 Amateur Radio Magazine,
August 1989, p.53, "IF Shift, Cheap - Easy IF Shift Add-on to your Older
Rig" by Terry F. Staudt, LPE, W0WUZ (LPE is licensed professional
engineer, IIRC?). He reviewed a number of 1970s upgraded receivers (A, S,
or Mk II versions ;-), and discovered how they did IF shift or passband
tuning in those updated models. The modification uses a varicap Motorola
MV 1872 and a pot and trimmer capacitor to vary the first IF transformer
frequency. He added it to a Galaxy V mk II transceiver, noting "the
circuit works wonders". You do have to make two adjustments to the
modified IF transformer to preserve selectivity etc., which he describes
briefly ;-)

If you can't find the article locally, let me know, email me directly with
your address to and I'll mail you a photocopy.

Drake IF tuning, IIRC, the R4C had an odd "feature" (aka bug ;-) in
that it didn't provide IF or passband tuning in all modes, as the earlier
Drake R4B did, although you could modify the R4C to do so (and other
mods too).

I probably shouldn't note that I found another 73 article in my search
that discusses how crystal filters could be built to provide any desired
CW or SSB bandwidth (though you might have to grind a crystal or two to
get precisely the bandwidth you want ;-) ;-)

grins ;-) bobm

Thanks for digging that up, it saves me looking for the issue that's
somewhere in a box.

Then, as I remembered and had intended to write the magazine at the time,
it's not IF shift. At the very most it's a tuneable peak within the
passband of the receiver.

He's tuning a single tuned circuit. That IF transformer will not provide
much selectivity, more important won't provide good skirt selectivity.
One tuned circuit won't do that, even if the IF frequency was low enough,
he'd need to be tuning all the tuned circuits in the IF strip. And given
that there is a crystal filter, and in the example in the HF range, the
IF transformers cannot supply anything narrower than the crystal filter.

He's not adjusting the crystal filter so the unwanted signal falls out
of the passband. The crystal filter supplies the ultimate selectivity.
So the good shape factor of the filter is not part of the "IF shift";
he is only shifting a far inferior selective element through the
passband of that crystal filter.

The article can provide no solution to "easy" IF shift.

Michael

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