Many hams equate no signal band noise to receiver sensitivity. Nothing
could be further from the truth. Bob has pointed out some very good
guidelines.
For those who do not want to play with the RF Gain to simplify things,
the attenuation and preamp settings will still do a great deal to help.
Listen to a no-signal spot on the band. Listening to the noise level,
try attenuation first - if you can still hear the band noise, leave it
there.
On bands where the receiver seems silent, first turn off attenuation,
and if you do not hear band noise at a low level, turn on some
preamplification.
When you can just barely hear the no-signal band noise, signals will
tend to pop out of the noise.
Just a note - the KX2 and KX3 design point is to always have the preamp
on for the best front end "out of passband" protection. SDR receivers
are different animals and may change our habits with using the receiver
controls in the future. Attenuation is still effective.
73,
Don W3FPR
On 8/27/2018 1:01 PM, Bob McGraw K4TAX wrote:
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.
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
