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Re: [SPAM][Linrad] Re: system gain

Just now I think I determined that the width of the audio filter in the 
at baseband in my setup is more than 1 Khz. I believe this is at least 
part of the cause of my poor s/n ratio in the decoded output. I now have 
to figure out how to change that filter width.  I believe that there are 
other filters in other places in LINRAD that also may have to be changed 
by using the setup parameters. I am reading everything again, trying to 
get smarter.  Then maybe things will sound better.


Dave Sublette wrote:
> Good morning Chris,
> I have tried setting the scale on the left side of the spectrum display, 
> using the various little up and down arrows. It is currently set to a 
> maximum of 40 and a minimum of -10 dB. My system noise floor is at 0 to 
> +2 dB. Changing this range affects the usefulness of the display but 
> doesn't affect the sensitivity of the system, as far as I can tell.
> I should have stated my concern more clearly. I am talking about the 
> waterfall display and the audio demod features. I have adjusted the 
> various contrast settings, using the two boxes in the lower right hand 
> corner of the waterfall display to be able to see weak signals. I have 
> also compared the signal to noise ratio of the demodulated CW from the 
> LINRAD system to that of the IF radio,. 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.
> 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. I have read 
> W3SR, VK2DU and Leif's instructions until I am cross-eyed. I just don't 
> seem to "get it". Sorry to be such a lame brain  :-)
> All of these comments apply only to the "weak CW" or "A" mode. I don't 
> try anything else.
> I hope I have been able to clarify my concerns as presented earlier.
> Thanks very much for your response.
> 73,
> Dave
> Chris wrote:
>> Just for clarification...what are your Hi and Low markers set to on
>> the left side of the spectrum display?
>> Is it possible that you are just set to 0db high and -140db low or
>> something too wide like that?  That will flatten out all but the very
>> strongest signals, where if you set for -55 high and -100 low or
>> something similar to suit the signals, you would see a lot more
>> response on the pan.
>> How to adjust those in linrad, I don't know, but you definitely should
>> be able to and if you can hear the signals the same, that's all you
>> need to adjust to 'see' them better.
>> On Wed, Apr 8, 2009 at 10:57 AM, Dave Sublette <k4to@xxxxxxxx> wrote:
>>> The IF radio hears signals better than the LINRAD system displays them.
>>> My whole point is to bring the LINRAD system up to or better than the
>>> sensitivity of the IF radio. Of course this is a better problem to have
>>> than the other way around--I think :-).
> > 

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