RE: [linrad] Linrad use on 160 meters

["Leif Åsbrink" <SMTP:LEIF.ASBRINK@xxxxxxxxxxxxxxxx>]

Hi Bill and all,

> 	I am wondering if anyone has tried using Linrad on
> the low bands, especially 160 meters?  As you probably
> know, signals there are very weak just as you have in EME.
> My concern is whether the very narrow filters, which work
> quite well for galactic noise, would also work on 160.  The
> problem I'm wondering about has to do with the type of
> impulse  noise we have there.  Would noise like thunderstorm
> static crashes, keyclicks, etc. cause ringing problems with
> very narrow CW filters?
> 
> 	Would appreciate any comments if anyone has tried
> Linrad on 80 or especially 160 meters.

Linrad is extremely efficient for wideband impulse noise but
that is only one of the different kinds of interference that
one has on 160 meters. This means that local impulse noise:
powerline noise, farmers electrical fences and other things
are removed virtually completely. There are also relatively
long noise bursts, I guess that is what you call crashes, and
they are not affected at all by the noise removal algorithm.

Linrad will contain a second noise blanker designed to remove
this kind of interference, it should be very efficient for
keying clicks as well. In the meantime you should be able
to get a good performance by using a very low threshold for
the dumb blanker. It should work fine when you listen for weak 
signals but when you listen to signals well above the noise 
floor the dumb blanker will cause distortion if the level is 
set very low.

Linrad01-04 will have AGC so it can be used in full for normal
CW and for SSB. The automatic carrier adjust for SSB is not in 
place, it is low on the priority list. Next is a mode for QRSS.
Just a second waterfall graph using the baseband spectra that 
may be set for really narrow bin widths. I have some recordings
from 137kHz. The VLF noise floor has several different types of
QRN in these recordings and I think they will be fine for
implementing the baseband waterfall and the baseband noise blanker.

All the above is when using Linrad at 90 kHz bandwidth. If you
use Linrad to process 2.4 kHz bandwidth, the dumb blanker should 
take care of the crashes pretty well but the smart blanker will not
allow close spaced pulses so some kinds of powerline noise
might not be compatible with the noise removal (smart blanker).


73


Leif


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