I agree with Peter in that many hams use too much RX RF Gain and too
little attenuation. Per one authority on receiver performance, the
optimum receiver performance occurs when the no signal band noise is
about 10 dB above the receiver noise floor. Since we can't adjust the
receiver noise floor, we can adjust the overall signal coming into the
receiver by using attenuation and RF gain reduction. Typically, 160M -
40M one should expect to run 15 dB to 10 dB attenuation unless you are
in a super low noise receiving environment. For higher frequency bands,
less attenuation and more RF gain is found to be desired. Still
maintaining the 10 dB practice regardless of band and antenna and band
noise.
As example; if your no signal band noise is S-5 or -97 dBm and the
receiver noise floor is -130 dBm, thus a difference of 33 dB, then the
optimum performance will occur with about 15 dB attenuation and 6 to 8
dB of RF gain reduction. Or use 10 dB of attenuation and 12 to 13 dB
of RF gain reduction. It will vary from band to band and antenna to
antenna but will generally be stable across the band for a short period
of time, i.e. several hours considering atmospheric activity. Once
applied, you will find signals will pop out of the noise. Many hams
believe attenuation is used solely to prevent receiver overload.
Attenuation can be utilized for a more effective means as well.
73
Bob, K4TAX
On 8/27/2018 9:55 AM, Peter W2IRT wrote:
I find the best thing for phone contesting is a ton of attenuation and
judicious use of RF Gain, combined with narrow bandwidth. No way to get rid of
the low-frequency rumble from within the passband, but the combination of the
roofing filter, DSP high cut and shift/width will get rid of the high-pitched
adjacent noise enough to be reasonably efficient. I still don't like SSB
contests, but they're far more survivable with a loaded K3s than they were with
previous radios!
---------------------------------------------
GO FRC!
Peter, W2IRT
www.facebook.com/W2IRT
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