RE: [linrad] SSB Parameters

[Leif Åsbrink <leif.asbrink@xxxxxxxxxxxxxxxx>]

Hi Stan and Roger,

> I made NO attempt to optimize the parameters for SSB,as it wasn't  
> necessary.  It works fine with an almost random set of parameters 
> [meaning  
> I took the defaults, or my defaults made up and saved in a separate  
> directory long ago, which I copy to each new Linrad directory so 
> that each  
> new version of Linrad won't ask me for parameters].
You may want to choose a smaller bandwidth reduction compared to CW
to allow enough bandwidth for SSB.

More importantly, make sure you do not use too many points (on the 
yellow curve) for the SSB filter. The time delay through the filter
depends on the bin width. Use the arrow boxes on the upper left and right
corners to make the yellow points separated by 100Hz or so.
It may be a good idea to make the width of the baseband window small.

> The key issues to me are [1] setting the mouse-adjustable filter to the  
> appropriate bandwidth, which is [a] visual, matching the signal width  
> observed to the space between the yellow lines and [b] auditory, 
> for what  
> sounds good in terms of the backround noise creeping in around the ssb  
> signal and of course [2] adjusting the red bfo bars so that the signal  
> sounds natural when it is visually centered properly within the filter  
> bandpass limits.
> 
> The automatic polarization angle algorithm seems to work fine on ssb  
> signals here.
This is all ok.

> The noise blanker works well except when there are very  
> strong signals.  Then I have to turn it off to prevent distortion, and  
> suppression of desired signals.
The smart blanker will not work on very strong signals, those that
remain red even when selected by a mouse click. The dumb blanker should
still be doing a good job but it might be necessary to set the levels
more accurately. At these high levels a blanker is not usually very useful. 
I have tried it though, and it does work. On the test bench I have access to
some really strong pulses and signals:-)

> As noted above, I will send the parameters when I get to the 
> hilltop.  But  
> I wouldn't recommend waiting for them if you want to play with things on  
> ssb.  You can probably do better with minimal thought, as I gave 
> them none  
> or next to none since they worked so well right off.  That's how I've  
> tended to do things here.  If the defaults work just as I want, I don't  
> change things.  If they don't, then I start thinking.  Not very 
> academic,  
> but it gives me more time to do other things.  ;)
If you have a computer with overkill capacity everything becomes uncritical.
You may ask for filters with much better resolution than you need and that
would cause processing delay. Filtering is done by FFT and reverse FFT and 
one has to collect all the data points before starting FFT computation so
if you ask for a 524288 FFT the delay is 5.46 seconds. That is fine if you
really want 0.18 Hz/bin, but you should be aware of the consequences. In
SSB mode I would think 50Hz/bin is fully appropriate.


The defaults were set very long ago. Do not trust they are any good.


73

Leif  /  SM5BSZ

  




> 
> Have a great week, and
> 
> 73,
> 
> Roger
> W3SZ
> 
> On Sun, 26 Sep 2004 13:26:18 EDT, <Stanka1ze@xxxxxxx> wrote:
> 
> >  Hello Roger,
> >
> > Would you be so kind as to post all of the set up paramaters you use in
> > recieving SSB? My new contest QTH has very strong interferance comming  
> > from a gas
> > compressor plant 1 mile away. I am hoping the Linrad noise 
> blanker will  
> > be of
> > some help.
> >
> > Thanks, Stan, KA1ZE
> 
> 
> -- 
> Roger Rehr
> W3SZ
> http://www.qsl.net/w3sz
> 


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