TEN-TEC called the receiver in the C-22 "Double Direct Conversion." I
think it was one of the best little rigs I ever owned. I did publish a
simple mod for it in THE FIVE WATTER. The Michigan QRP club news letter
to improve selectivity. This mod reduced the ultimate audio bandwidth by
a factor of two.
I don't have the radio any longer but I can describe the mod very
simply. At the output of the product detector is a double pie network
audio filter. By doubling the values of the three capacitors and two
inductors the cutoff frequency is cut in half but the input and output
impedances are kept the same. The 1 mh chokes are replaced by 2.2 mh. (
a standard value.) I saved the little shields on the original chokes and
installed them on the new ones. The three capacitors are also doubled.
I think the input and outputs became 2 micro farad and the center became
a 4 micro farad. This mod will eliminate the high pitched signals that
got by the audio filter but still allow SSB copy.
73,
Jerry K8JRO
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