[TenTec] Experience using the Omni 6 with INRAD 765 CW filter(s)

[Chuck Guenther]

Several people have asked me about this topic, so I thought I should share my experience on the reflectors.  Keep in mind I operate CW almost exclusively.  

I now have the "low pitch" CW roofing filter installed in the Omni 6/Opt. 1.  This is the INRAD mod kit that uses the INRAD 765 filter (4-poles, 600 Hz bandwidth, centered for a 500 Hz pitch.  Readers of the reflectors may recall that this product was developed for CW operators with Omni 6/6+ who prefer to have a CW roofing filter matched to a lower pitch, compatible with the discontinued Ten Tec 221 9 MHz IF filter (six poles, 250 Hz, 500 Hz center).   

In summary, the 765 and 221 combo works great and I use both filters nearly 100 percent of the time, followed by either a 400Hz or a 250 Hz BW INRAD filter in the 6.3 MHz IF.  If I need to use the noise blanker, I turn off the roofing filter.  My previous unsatisfactory experience (excessive attenuation) using the 221 filter with the 763 roofing filter can be explained by the mismatch in center frequencies of the 221 and 763.  With the new 765 filter, the insertion loss of the 221 is no longer excessive.  There is now enough gain to hear anything discernable in the background noise.

As an alternative arrangement to using the 221, I also tried a second 765 filter in the 9 MHz IF slot.  Although this resulted in a few dB less insertion loss, the selectivity was not dramatic.  In fact, there was little discernable difference with either of the 765's switched out.  One filter switched in provided virtually the same selectivity (to my ear, at least) as both.  So I opted for the 221 in the 9 MHz IF slot.  If I had an Omni 6+ with two 9 MHz slots, I would use a 765 in one and the 221 in the other.

I realize that "works great" sounds pretty general, but I'm a very picky operator, and went through a lot of filters in order to arrive at an optimum configuration.   

73,
Chuck  NI0C