I pulled out the QST issues referred to in a recent post here and
found the one about adding a cw filter to the 540/544 very interesting.
(for reference, QST Sept 1081, p. 16). I also checked out the audio
filter (TT 245) and, with an assist from "Solid State Design for the
Radio Amateur", figured out how to lower the bandpass center frequency
a bit. By my figuring, one only needs to add a paralleled capacitor
of a value of 240pF to 330pF to the 8 caps in the filter
freq-determining circuitry. Now the only thing left is to figure out
a non-invasive way to switch in the 4 sections of the audio filter
one at a time. It might mean an outboard box (as in the Sep '81 QST
article on adding a crystal filter).
73 K7GT / AE6TT
--
Allan G Taylor
agtaylor@llnl.gov
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