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Re: System Gain

Dave, I am seeing about 10 dB drop disconnecting my XV-144 from the
SDR-14.  The SDR is not calibrated, so this is just a data point.
Setup is xv-144 to either K2 or SDR-IQ as I have not yet installed the
3dB splitter so it looks like we are headed the same direction.  I
have used Linrad to complete off the moon several weeks ago, and it
was a real help finding randoms, although I still have a lot to learn
about it's receive capabilities - right now it is a toss up whether
the K2 or Linrad is better, but as I say, I have not had a chance to
really become comfortable with it yet.

On a slightly different subject, can you point me to any notes on
calibrating the Linrad with the IQ?  I have arrives at a fairly
comfortable set of operating parameters for use with the IQ thanks to
a note from Leif regarding RCF parameters so now I need to cal
things.  Any suggestions?


On Dec 21, 1:54 pm, Dave Sublette <k...@xxxxxxxx> wrote:
> Good morning all,
> My education concerning the art of microwave systems is continuing. In
> reading through some reference material I ran across a statement that
> said when the voltage is removed from the first amplifier stage of a
> transverter, the system noise should drop 15 dB.
> My microwave transverters for 2,3,5,and 10 ghz are mounted remotely. I
> cannot turn off the power to just the preamps. So I am trying to devise
> an equivalent technique for measuring the system gain.
> My first approach is to just unplug the IF cable coming from the box. I
> am using an SDR-14 with the Linrad program. The 144mhz IF comes from the
> transverters and is divided in a 3dB hybrid. One output goes to a 1.2 dB
> nf, 20dB gain LNA, then through a 144 mhz bandpass filter, then to the
> SDR-14 input. The other output of the hybrid goes to the 144mhz input of
> my K2 IF radio.
> I am using the SDR-14 with the Linrad program to measure signal levels
> and background noise.
> When I unplug the IF cable, I see little or no drop in system noise on
> the Linrad screen. I think I should be seeing 15 dB drop if I read and
> understood my statement in paragraph one.
> So....the question is...is my test technique valid? If so, it would seem
> that I need an IF post amp in the output of all of my microwave
> transverters. Fortunately the DEMI design will accommodate this feature.
> Your comments are invited.
> Thanks, 73, and Merry Christmas everyone.
> Dave, K4TO
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