[TenTec] INRAD audio mod helps Omni 6 Low Pitch CW!

[Chuck Guenther]

About a year ago on this reflector, Bill Tippett, W4ZV, gave away one of his secrets for copying weak-signal CW, namely using very low pitch (below about 450 Hz).  Since then, I've installed the Ten Tec 221 filter and the INRAD 765 roofing filter ( both optimized for 500 Hz pitch) in my Omni 6/Opt. 1 radio, and have cranked the pitch control down as far as it would go (400Hz). 

However, I've also complained on this reflector about excessive insertion loss, which I tended to  blame on the narrow 221 filter. I was recently reminded that the 9 MHz IF in the Omni 6 always goes through the standard Ten Tec 2.4 KHz SSB filter, even in CW, and that the low frequency cutoff of this filter might be marginal for listening at a 400 Hz pitch.  In an effort to improve the low frequency response of the radio, I replaced the Ten Tec SSB filter with the INRAD 754 (2.8 KHz BW), and performed the low frequency part of the INRAD audio mod.  I had previously overlooked these mods, because I'm not interested in SSB.  

These two mods gave me at least 6 dB improvement at 400 Hz.  Now I am able to routinely use the attenuator on my radio, which always improves the s/n ratio for me.  I'm hearing better!  Before the latest mods, I didn't have enough signal to attenuate, so my ATTN button went unused.  By the way, reducing RF gain on this radio just doesn't seem to help s/n ratio like the ATTN does.

I looked extensively at the archives of this reflector concerning the INRAD 754 filter and saw lots of discussion; however I couldn't find any mention of its effects on CW performance.  Thought I'd pass along this experience.  

I should also mention that, after a year of listening to CW at 400-500 Hz pitches, the (once standard) 750 Hz pitch sounds downright shrill to me. (okay for ragchewing with strong signals, but not for copying your callsign from that weak DX on 160m).

73,
Chuck  NI0C