[Elecraft] Roofing Filters

[Lyle Johnson]

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