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
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