Hi Michael,

you may well be right, though there weren't any followup complaints or
correction IIRC on the article. With 73 magazine in bankruptcy court now,
it is too late for you to publish a correction ;-)

I don't think the idea was to replace or supplant the crystal filter skirt
selectivity with IF shift, or to change or shift the crystal passband.

Since some radio receivers only have one IF stage and one IF transformer,
as an example, shifting its frequency would be shifting the entire IF ;-)

Then again, some of the 455 Khz IFs use murata style resonators which are
at least as good and selective as some quartz crystal filters (so I'm
told, anyway ;-) In such a case, it would seem possible that detuning the
first IF transformer so an interfering signal is above or below the main
IF passband and out on those many dB down skirts, while leaving the
desired signal within the IF passband, with resonator skirts or subsequent
crystal filtering etc. providing the selectivity, as usual, could work?

Again, I can't reject the idea out of hand, for all radios or setups. When
an LPE (licensed professional engineer) tells me he has reviewed many
example cases and studied how IF shifting works, it carries more weight
than some of the stuff I see on and off-line ;-) ;-) At least the cost of
the experiment is low (~$5?), so it may be worth testing for some
experimenters?

regards bobm


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* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
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