[HQRP] Changing BW on TenTec filters

[K5BDZ@aol.com]

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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