[Elecraft] Filter Recommendations

[Don Wilhelm]

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.