[Elecraft] Re: K3 Noise Blanker ahead or behind roofing filter?

[Bruce McLaughlin]

Wayne:

Your mention of some reconstructive algorithms was very interesting to
me.  For some time, I've wondered if it would be possible to have a
circuit which would regenerate a CW signal and play it back in a noise
free environment.  I'm not an engineer, but I seem to remember that work
was done a number of years back with UARTs and the like to regenerate
fading or noisy TTY signals and they seemed to work reasonably well.  At
the very least, such a system might provide considerably improved copy
under heavy noise conditions.  I don't know of any other radio currently
using audio reconstruction.  Perhaps it's because it doesn't work or
hasn't been high on the priority list.  In any case, I think it's a very
interesting idea.

Bruce -- W8FU

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of wayne burdick
Sent: Tuesday, June 12, 2007 11:58 AM
To: Kenneth A. Christiansen
Cc: elecraft at mailman.qth.net
Subject: [Elecraft] Re: K3 Noise Blanker ahead or behind roofing filter?

Hi Ken,

The short answer is "both".

The 1st I.F. noise blanker module is ahead of the roofing filters, so 
it can blank wideband pulse noise. It has a wide AGC range and various 
threshold and blanking width settings.

There's also a DSP noise blanker *after* the roofing filters. This 
blanker has the advantage of not being modulated by signals outside the 
roofing filter bandwidth. Of course you can't use it in all cases, 
because the roofing filter stretches the pulses and thus requires 
longer blanking times. But I have some noise on 160 m that the DSP 
blanker suppresses by some 40 dB, making otherwise completely inaudible 
signals stand out clearly. We're also experimenting with reconstructive 
blanking algorithms to make the DSP blanker even more effective.

The noise blanker LEVEL switch displays the parameters for both the 
hardware blanker and the DSP blanker on the VFO A and VFO B displays. 
You can then adjust either or both to see which is most effective on 
noise. The settings are stored on a per-band basis.

73,
Wayne
N6KR


On Jun 12, 2007, at 4:50 AM, Kenneth A. Christiansen wrote:

> Is the noise blanker on the K3 ahead of the roofing filter or behind 
> the roofing filter....?


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