[TenTec] 221 CW filter insertion loss

[Chuck Guenther]

I recently acquired the coveted 221 filter from a nice ham who had one unused still in the box from Ten Tec.  I installed it in my Omni VI, Opt. 1 with CW roofing filter mod from INRAD.  

It was a big disappointment.  The insertion loss made it unusable on most bands.  I promptly reinstalled my INRAD 753 in the 9 MHz position.  According to the specs, the difference should not have been as great as I observed.  The INRAD 753 has a nominal insertion loss of about 9 dB, while the 221 is specified at 14.0 dB.  I estimated a theoretical loss of an additional 2-3 dB due to the mismatch in center frequencies of the 221 and the roofing filter.  So, there's a difference of 7-8 dB.  Yet, the 221 was unusable on 160m, 30m and 40m-- signals were down at least 3 s-units. The receiver seemed starved for gain.  Only on 80m was it useable.  
In fact, the difference was so great that I went outside and worked on my antenna for several hours before concluding it was my filter.  

I suppose this particular unit has excessive loss.  I'm planning to try it out again when I receive the new roofing filter from INRAD (the special order one with 500 Hz offset to match the 221).  I expect, though, that the INRAD 753 (400 Hz BW CW filter with 600 Hz offset) will prevail.

This is the second 250 Hz filter I've tried in the 9 MHz position.  I should have listened to Stan at Ten Tec Sales, who (at the time I ordered the Omni VI) told me I wouldn't like a 250 Hz filter up front.  

73 de Chuck  NI0C