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Re: S-band pre-amp kits ?




Yup, can verify that-- if you look at the data for any low noise device, 
there is a current range (bias) that will give you (nearly) optimum NF-- and 
in the case of the stripline microwave LNA's, the input match is already 
done on the board for best NF input match with microstripline.

So it's possible to get close to the minimum NF just with a DC meter.
Note:  In almost all cases maximum gain DOES NOT correspond with lowest NF.

We also measured an "old" DEMI preamp (LUA design from early 90's), a Drake 
that had only the IF mods, and the microstrip filter "extensions" done to it 
(blindly-- no optimizations).  I also had measured (correctly measured, 
thank you-- I'll write up later why) a new "purchased-from-the-flea" 
TransSystems ADC3033 converter with a "N" adapter (no stub cut-- sotck) at 
the Weak Signal Banquet with a 2401 MHZ input, 123 MHZ output, on one of the 
New Aglient Noise Figure Analyzers.

I'll write-up the results of this with some probably very opinioniated 
comments in the next week or so.  I'd do it now, but the numbers are at 
home, and I'm at work.

Fred W0FMS

>From: W1BFN@aol.com
>To: ns1z@arrl.net
>CC: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] S-band pre-amp kits ?
>Date: Mon, 21 May 2001 11:25:42 EDT
>
>In a message dated 5/21/01 1:36:27 AM Eastern Daylight Time, ns1z@arrl.net
>writes:
>
><< DEM says you can get good results with just a VOM but I would imagine it
>  hard to obtain best noise figure that way. I don't know of anyone else
>  kitting these. >>
>John, that's what I thought when I took the DEM PHEMT which I built from 
>his
>kit to the Weak Signal banquet at Dayton, and was pleasantly surprised to
>find noise figure measured at .58 dB and gain = ~18 dB.
>
>Doubtless the noise figure might be tweaked a tad lower, but the voltmeter
>method appears to work Just Fine.
>
>Mike, W1BFN
>----
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