[Elecraft] [K3] Best Filter for the K3 when operating PSK31

[Richard Ferch]

G4ILO wrote:
> Brandon673 wrote:
>> 
>> I would like to hear opinions and reasons for the best filter to use for
>> operating PSK31 with the K3.
>> 
> 
> You don't need anything more than the SSB filter. 

I agree with Julian. Remember, it is the DSP that is responsible for 
signal filtering. You do not need narrow roofing filters to enable 
narrow DSP filtering - you can narrow the DSP filter down to 50 Hz even 
if the only roofing filter you have is 2.7 kHz wide. The job of the 
roofing filters is just to keep unwanted strong signals out of the IF 
bandpass to prevent gain pumping (desense) and IMD (splatter generated 
in the receiver) caused by those unwanted signals.

Regarding DSP filter settings: Wide filter settings are useful to scan 
the band, for S&Ping, and for multiple signal decoding. Once you have 
picked a signal to work, or if you are calling CQ, narrow DSP filter 
settings can be helpful. You can put your DSP filter controls in 
SHIFT-WIDTH mode and use the two controls to focus on the desired 
frequency, or you can use an Align or Optimize feature in your software 
to center the desired signal at a chosen frequency so you only need to 
adjust the WIDTH control.

As for gain pumping and inter-signal IMD: the likelihood that you are 
actually going to encounter a situation that requires a narrow roofing 
filter for PSK seems quite remote. Extremely strong PSK signals are not 
that common, PSK signals turn on and off only on time scales of several 
seconds, and PSK detection is not highly amplitude-sensitive, so both 
the likelihood and the effects of gain pumping and inter-signal IMD 
would appear to be much reduced compared to other modes.

Bottom line: I'd suggest you base your decisions re roofing filters on 
your needs for other modes, not on PSK31.

73,
Rich VE3KI