Changing the bandwidth on TenTec crystal filters (and other "open" crystal
filters) quite often can be easily accomplished by just changing the values
of the capacitors in the filter, and re-peaking the IF circuits on either
side of the filter. Short of exact formulas, noting the existing cap values
and experimenting with other "approximate formula" value ranges by carefully
desoldering old and replacing with new caps can yield great results.
Please note that if LARGE bandwidth changes occur (CW to wide SSB etc) the
filter input and output impedences will change, but if you simple want to
change from a SSB 2.2 kHz +/- .4 kHz or similar CW freq., the changes should
be close enough not to realistically cause problems when peaked.
I have done this in the past (very successfully) but it's been 15 years or
so, and I don't have my notes anymore. If anyone chooses to "computer model"
the various bandwidth cap values for these 9 MHz xtal filters and place the
findings on the www - I'm sure a huge audience would be grateful.
Thanks
Bill K5BDZ
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