[VHFcontesting] [VHF] Re: Quick To the Mystery Machine! [The Case of the Phantom Pre-Amp]

[Zack Widup]

I have had pretty good luck designing amps using the gamma(optimum) 
[noise match] figure when it is provided by the manufacturer along with 
the s-parameters. I'm usually pretty close when doing it this way.  And 
yes, you are right; if you play with the designs using both the 
s-parameters and gamma(opt) you find the maximum gain is not at 
the same point for tuning.

Transistors like the MRF966 often don't have the noise matching parameters 
in the data sheets, in which case you have to do it with a noise figure 
meter.

Most of the newer HJFET's and PHEMT's have the noise match numbers along 
with the s-parameters.

73, Zack W9SZ

On Fri, 22 Aug 2008, Jim N7TCF wrote:

> I once had access to a 3GHz Network Analyzer after the engineering staff
> went home. With the help of an RF engineer, we set it up to measure my
> homebrew MRF966 preamps for 2m and 432.
>
> We found that max gain and low noise are different points while tuning.
> I would never have found best noise figure without the instrument. I had
> attempted to bench tune it using on-air signals, the results were only a
> S-Meter amp of course.
>
> Such instruments are far less costly today and some well-heeled VHFer
> have them. I hope to avoid blowing these devices up until I know someone
>  with another analyzer.
>
> Jim N7TCF
>
>
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