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

[Dave Sublette <arrl.net; k4to@xxxxxxxxxxxxxxxx>]

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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