[Test-Equipment] Need info on Noise figure meter

[jeremy-ca]

Why not calibrate a good home brew against one of the HP or NoiseCom sources 
Steve?
You mignt not get the full frequency utilization but 2304 would be a good 
place to shoot for.

Carl
KM1H


----- Original Message ----- 
From: "Steve Harrison" <k0xp at dandy.net>
To: "Discussion of Electronic Test Equipment" 
<test-equipment at mailman.qth.net>; <test-equipment at mailman.qth.net>
Sent: Friday, December 28, 2007 1:38 AM
Subject: Re: [Test-Equipment] Need info on Noise figure meter


> At 05:31 AM 12/28/2007 GMT, k4pf at juno.com wrote:
>>
>>Hi,
>>
>>The ARRL 1965 Handbook, page 526, featured a home constructed
>>noise generator head with a 5722 tube.
>>Perhaps that's what the home-brewer based his design on.
>>
>>Someone said gas tube noise generators are problematic when testing
>>modern devices, but the 5722 is not gas-filled.  It is a vacuum tube diode
> with a cathode probably of uncoated tungsten,
>>shades of 1920's technology.
>
> That's entirely true; 5722 noise sources do NOT generate the killing 
> spikes
> that the higher frequency gas-filled tubes do. They're perfectly safe to
> use with solid-state LNAs. The main problem is they only generate a little
> more than 5 dB ENR of noise, and still present the impedance match problem
> when they're turned off. This is reduced considerably by the series 50-ohm
> resistor from the plate to the output blocking cap but then, you can
> encounter stray resonances.
>
> W6GGV and I built half a dozen 5722 sources and attempted to characterize
> each of them,. We gave up when we determined we could not repeatably
> measure to better than +/- 0.1 dB accuracy between each.
>
> A 5722 is a great noise source whose noise contribution, at 220 or lower,
> you can easily calculate presuming you've really built it using great
> UHF-construction techniques. It's also very useful at 432 in a relative
> application. But even N6CA gave up on a 5722 as any sort of calibratable
> noise source. And as far as I'm concerned, if N6CA says it can't be done,
> then even a pronoucement from God (otherwise known as W6XJ) would be 
> suspect.
>
> But a eally-well-built W1GHz solid-state homebrew noise source will easily
> be flatter up through at least 2304, we found. The problem was we could
> never actually charactize the actual ENR of the solid state sources 
> without
> referencing them to the calculatable 5722, at lower frequencies, and thus
> assuming our construction technique held through the lower microwave 
> bands.
>
> Steve, K0XP
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