Hello Chuck,
I'd like to see you expand the scope of #4 to include splatter from any
source.
Sure, if someone would be kind enough to send a recording:-)
For those of us that mostly DX the AM broadcasters, splatter is the
huge enemy.
Really? Are there bad AM transmitters out there or do you want
to listen near a strong local AM station?
A solution that I'd like to see is a sort of Costas loop where:
(1) the signal is split into two paths where one is demodulated with an
in-phase carrier and the second with a 90 degree shifted carrier,
Linrad already has this feature:
http://www.sm5bsz.com/linuxdsp/run/am.htm
(2) the Q output is shifted an additional 90 degrees, and (3) the two
demodulated
outputs are selectably added or substracted.
This will be equivalent to receiving one sideband or the other,
Linrad sends both I and Q to stereo head-phones to allow
your brains to do the processing. I think that will often
be a better solution. If one wants one sideband only, I think
it will be a better idea to just set the appropriate filter and
use the BFO to receive the SSB signal that remains.
BUT, if the problem is splatter, much better solutions are possible.
The splatter is a distortion on the modulation. It should be possible
to detect the modulation in the offending channel and to compute
the expected splatter which could then be removed. In principle
Linrad could learn exactly what non-linearities the offending
station suffers from and then build exactly the emitted signal
with an accuracy detemined by the S/N of the main components of
the offending station.
To try to implement something like this, I need a wideband recording.
Wide enough to include all of the desired station as well as the full
spectrum of the offending station (splatter on both sides included.)
73
Leif / SM5BSZ
Chuck
WD4ELO
-Original Message-
From: Linrad mailinglist [mailto:[EMAIL PROTECTED] On Behalf Of
Leif Asbrink
Sent: Sunday, October 28, 2007 10:31 AM
To: Linrad mailinglist
Subject: [linrad] Challenges!!
Hi All,
Any interference that is not random can in principle be
modelled and subtracted. In real life it might be too
difficult, but I guess there are man-made interferences
that could be significantly reduced. Improvements are
also possible with random interference in some cases.
I think the interference fighting in Linrad can be
significantly improved, but I do not want to work on
artificial signals where I try to simulate various forms
of QRM - mistakes are easily done so I look for real life
recordings of signals that are at the detection limit or
slightly below.
Is there really nobody reading this who has problems in
copying the other station occasionally? I have asked
before, but still I have no recordings to work with.
Currently I am only interested in the traditional modes
CW, SSB, AM or NBFM. Here are a few examples:
1) SSB in white noise but with inadequate S/N. Rather than using
a rectangular filter Linrad could use a filter that is shaped
as the power spectrum of the signal.
2) Interference from TV transmitters on 50 MHz.
3) Lightening crashes on (low?) HF bands.
4) Splatter from local amateurs.
On Nov 05 I will leave for one month spending my time in
a more pleasent climate than what Sweden can offer this time
of the year. I will have plenty of time to work on any
challenges you might give me.
The Tx side of Linrad is now producing 10mW on 144 MHz, but
I can not work on it when away from home because the next step
will be to arrange for the Rx/Tx switching for QSK in CW and
SSB. It is possible to listen while talking, one can cut holes
in the transmitted signal occasionally to generate perhaps 1% of
silence without affecting intelligibility. Will allow monitoring
of what happens in a pileup etc.
The next version, Linrad-02.40 will work under Windows Vista,
but only with 16 bit audio. Please report all bugs you have
noted in 02-39, I will upload 02-40 before leaving.
73
Leif / SM5BSZ
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