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[Linrad] Re: success
- Subject: [Linrad] Re: success
- From: Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>
- Date: Thu, 13 Aug 2009 23:13:52 +0200
> After years of trying, I finally got my LINRAD setup to see and decode
> signals that are much weaker than I can hear on my receiver. I wish I
> could tell you what I did that made the difference, but I cannot. I just
> kept putting in different values for the various parameters.
This makes me confused.
I am afraid I have written too much at too many places and I am reluctant
to spend time in writing more text because it might as well create more
I need feedback in the form of specific questions. Maybe I can add info
at appropriate places in the F1 help or perhaps write an Internet page
on some specific question that I can formulate an answer to.
What is needed to see weak signals is:
1) Narrow FFT bandwidth in the waterfall.
2) Slow waterfall speed.
3) Adequate gain for the colour scale.
That is all and you can achieve it in many ways. Exactly what parameters
to set depends on what other aspects you consider.
> Now that I have it working, I would like to make some fine adjustments
> in the parameters to see if I can improve it.
"improve" does not tell me anything about what you might want.
You can always make the waterfall slower to see weaker signals
(if they last long enough.) You can also increase the FFT size - but
only to the limit given by the bandwidth of the signal itself. On
144 MHz CW EME one can go to 0.5 Hz or so - but there is normally
no reason to look for signals so far below what can be copied.
Having one waterfall line every 15 second or so would require 2 minute
> I do have one problem. The
> decoded audio has a periodic clicking sound in it. I would like to
> eliminate that, if possible.
There should be no such thing. Maybe something is overloaded,
there are several ways to overload the CPU(s)
If you have a single core CPU, just check that the CPU load is less
than 90%. If you have two or more cores it is a bit more complicated
because it is possible to make one thread require more than 100%
CPU in which case it will not deliver output in time. Other cores
might be idle in the meantime so the total load would look good.
If you select a large fft3 or the floating point implementation
of backwards fft1 or fft2 there is a risk that you saturate
The next version of Linrad has a time evaluation for each thread
so one can see if something might be using excessive CPU time.
Another problem could be due to soundcard drivers. You might try
a different sampling speed for the output.
> However, the problem is when I bring up the screen to set the
> parameters, it doesn't show what values are presently installed. It does
> indicate default values.
When you press 'X', then 'P' you should see the current parameters,
not the default ones. By pressing enter on each screen, then 'B'
to go back to the processing screen you should still have the
same parameters. (It may be different if you are using data
from the hard disk in which case you should specify a parameter file
> Other than writing down every value I install, how may I find a records
> of what these values are? As it stands now, I am afraid to do anything
> for fear that I will mess things up again and can't get it to work!
Linrad is an old-fashioned computer program. When you are happy
with it, just make copy *.* to another directory and do whatever
experiments there. In that way you will have the original absolutely
You can have any number of Linrad versions in any number of directories.
Each time I upload a new one you can copy your old working setup
to a new place and copy the new Linrad on top of it. Only when I
made changes to parameter files you will have to go through some
part of the setup.
You can also copy the par*.* files to another directory or pack
them in a suitably named zip file. Then you can go back to those
parameters by putting all the par*.* back.
> So, in summary: 1) how can I fine the present value of the parameters
'X', then 'P'.
If you see the default parameters and not the ones that you used
last time something is wrong. If so, please write a bit more about
> and 2) how to fix the clicking sound in the demodulated audio.
See above. If it does not help, please send some more information.
Hardware, CPU load etc.
Leif / SM5BSZ
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