Best Filter for the K3 when operating PSK31

[Brandon673]

I would like to hear opinions and reasons for the best filter to use for operating PSK31 with the K3.

[Don Wilhelm-4]

Brandon,

It all depends - if you are operating in the midst of normal strength
signals, then you can use the full 2.7 (2.8) kHz bandwidth and select
the station that you want anywhere on the waterfall display.
However, if there is a lot of QRM and/or a strong signal that is taking
over the AGC in the receiver, it is wise to narrow the bandwidth to
select only the desired signal and perhaps turn off the AGC and reduce
the RF Gain.  That takes a bit more effort than the easy Click and QSO
type operation, but if you really want the contact in the midst of QRM,
that is the way to accomplish it.  A 200 Hz roofing filter would be nice
for those particular situations.

73,
Don W3FPR

Brandon673 wrote:

> I would like to hear opinions and reasons for the best filter to use for
> operating PSK31 with the K3.
>  
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[Julian, G4ILO]

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 Don that to provide the best chance of copying a signal it's best to use narrow filtering around it but I would not go to the expense of buying a 200Hz filter just for PSK31 operation even though that is probably the mode I use most often. I have a 500Hz filter which I got for CW use which obviously comes into play when I reduce the bandwidth to 500Hz or less in DATA too. But its effect is hardly noticeable in digital modes (unlike CW where you have key clicks to contend with). I really feel that the DSP filtering does a good enough job for this application.

If you use a program that allows decoding of a wide swath of passband (PSK Browser or whatever) then it would be useful to have the AM filter which would allow you to open the receiver passband up to 4KHz.

[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
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[Joe Subich, W4TV-4]

> 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.

That's easy to say in theory.  However, when your neighbor fires
up with his amplifier in a pile-up and activates the HACG you
need the 200 Hz filter "bandpass" decoding simply is not going
to do the job.

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Richard Ferch
> Sent: Wednesday, December 30, 2009 9:19 AM
> To: [hidden email]
> Subject: Re: [Elecraft] [K3] Best Filter for the K3 when
> operating PSK31
>
>
> 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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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[Julian, G4ILO]

Joe Subich, W4TV-4 wrote

That's easy to say in theory.  However, when your neighbor fires
up with his amplifier in a pile-up and activates the HACG you
need the 200 Hz filter "bandpass" decoding simply is not going
to do the job.

I think that would be a rare situation for most people. I also think that, even without a narrow roofing filter, the K3 would cope with a very strong close-in signal better than most other radios. So I would hold off buying the 200Hz filter until I found that I actually needed it.