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[Linrad] Re: system gain
- Subject: [Linrad] Re: system gain
- From: attglobal.net; radio1@xxxxxxxxxxxxxxxx>
- Date: Wed, 08 Apr 2009 14:40:46 +0000
In the old days, when every thing was analog, we would say that the
system noise figure was set by the first amplifier's noise figure. Assuming
you have enough gain. From the first amplifier noise is just added. I can't
visulize your system do you have any gain near the antenna? The losses
introduced by coax also adds to the system noise if the amplifier is after
the line loss.
Maybe this will help.
---- Original Message ----
From: Dave Sublette <k4to@xxxxxxxx>
Subject: [Linrad] system gain
Date: Wed, April 08, 2009, 10:11:00
I have been watching the email thread on setting optimum gain and other
settings for the LINRAD program. I have used the program, rather
casually, for two years or so to look at weak signals on the 144 mhz IF
outputs from my microwave transverters. I put a gain stage ahead of my
SDR-14's direct input and that stage measures at 0.9 dB nf and 18 dB
gain or so at 144 mhz.
When I remove this amplifier from the system, the noise floor on the
main spectrum display on LINRAD drops 8 dB. I read in the emails that it
should drop 15 dB, if I understand things correctly. I am looking at
about a 160-170 Khz slice of the spectrum around 144.1 Mhz,
I do note that the visual display on Linrad is not as sensitive as my
receiver on a splitter from the same IF.
My question is, "Where should I look next to either find the problem or
adjust the LINRAD parameters to bring the LINRAD system sensitivity up
I continue to read the web page and previous emails from VK2DU on
Nothing I have tried seems to be working. I would list all my settings
here, but perhaps that would be premature.
Any advice to be had out there?
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