[Linrad] Re: system gain

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi Dave,

In an old posting you wrote:
> > In all cases, the IF radio hears 
> > better and can hear signals that cannot be seen on the waterfall. 
> > That's good, but with the poorer performance at the waterfall, I feel 
> > that I am missing off frequency signals that might be calling me.
Now, knowing that the S/N difference is a bit less than 5 dB I must
comment to this statement. In case you were able to copy signals that
were invisible in Linrad you have not selected parameters that give
optimum visibility for weak signals. You should be able to see CW
signals that are 5 dB below what you have any chance to copy.
To do that you need a bin bandwidth in the order of 5 Hz and
a waterfall averaging of 20 (or more)

> > It occurs to me that the band width of the filter in LINRAD's 
> > demodulation window (sorry I know I am probably not using correct 
> > terminology here) is affecting the signal to noise of the audio output. 
> > I have fiddled with the little green ellipses, but can't get them to go 
> > any narrower and really don't understand how this all works.
Little green ellipses?

> > I have read 
> > W3SR, VK2DU and Leif's instructions until I am cross-eyed. I just don't 
> > seem to "get it".

Just go ahead and do what seems reasonable to you. Then write to this
list and tell what you did and in what respect the result is not
what you expected. That kind of feedback would help me to understand
where the obstacles are:-)

73

Leif / SM5BSZ




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