Re: System Gain

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

Hi Fletch,

I don't use the IQ. I use the SDR-14 and haven't done any calibration 
myself. I'm afraid I am not much help there. Maybe someone else can get 
you started.

HNY

Dave, K4TO

Fletch wrote:
> 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?
> 
> 73
> Fletch
> K3JYD-FM18
> 
> 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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