Posted by
Dave Van Wallaghen on
Feb 21, 2008; 1:58am
URL: http://elecraft.85.s1.nabble.com/Roofing-Filters-tp461501p461509.html
Thanks again Lyle, I believe I now have the proper prospective (looking at
the block diagram of the K3 helped out too). So far in my limited operation
of K3 #338, anytime I've tried to dig out a weaker CW signal next to a
stronger one, the DSP filter has worked just fine. And I found when it was a
little too close I was able to shift the filter away from the offending
signal enough to hear the desired one very comfortably. Of course, these
were in non contest and non-aggressive situations.
I saw a post the other day about the notch filter. I have used it a couple
of times in the old novice portion of 40m (where I hang out with the QRS
crowd). When some of the BC stations start up, I was able to notch out that
carrier just fine and turn an irritating listening situation into something
very comfortable.
Very nice work. Thanks again Lyle (hope I didn't bore too many on the list).
73,
Dave
W8FGU
>
> Hello Dave!
>
> > So if I read this right (bear with me, I'm learning), in keeping strong
> > signals out of its passband, it will keep the hardware AGC from
> activating
> > to eliminate "pumping"...
>
> Correct.
>
> > But, in the same scenario, if I had a 2.7khz filter and a 200hz filter
> with
> > no strong signals, just band noise (or maybe static crash type QRN), the
> DSP
> > filter would act the same and my desired signal would come through the
> same
> > way regardless of which roofing filter I used...
>
> Also correct. The key is if signals stronger than the desired signal
> are in the roofing filter passband, and are also strong enough to
> activate the hardware AGC.
>
> > And if you would permit me one more scenario. In the case of strong
> static
> > crash type QRN, in my case, either the noise blanker or noise reduction
> > would be able to handle the really heavy stuff. I know the hardware
> noise
> > blanker is set in front of the roofing filters and well ahead of the
> DSP,
> > therefore protecting it. I guess that statement is more of a question
> than a
> > statement.
>
> We have pulse-suppressing AGC in addition to DSP and IF blankers. Won't
> kill all the noise types, but makes a very effective arsenal against
> noise. Narrow roofing filters can help in some cases here, too.
>
> In the end, you may not often need narrow roofing filters in your
> particular station's interference environment, but when you need 'em,
> you need 'em :-)
>
> 73,
>
> Lyle KK7P
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