[Test-Equipment] Fwd: Re: [Mw] Fwd: Re: Mega-mode Sr.?

[Mike Manes]

Further from the uW guys re the noise gen ..

-------- Original Message --------
Subject: Re: [Mw] Fwd: Re: [Test-Equipment] Mega-mode Sr.?
Date: Fri, 05 Nov 2010 14:38:02 -0400
From: Doug <dmcgarrett at optonline.net>
To: microwave at lists.valinet.com

On 11/5/2010 10:27 AM, Mike Manes wrote:
> This came over the test equipment reflector.  Might be useful for
> some UHF+ NF testing, although it's HUGE - I'll pass.
> 73 de Mike W5VSI
>
> -------- Original Message --------
> Subject: Re: [Test-Equipment] Mega-mode Sr.?
> Date: Fri, 5 Nov 2010 08:28:48 -0500
> From: Barry Sherwood <ars.kf5gc at gmail.com>
> Reply-To: Discussion of Electronic Test Equipment
> <test-equipment at mailman.qth.net>
> To: Discussion of Electronic Test Equipment
> <test-equipment at mailman.qth.net>
>
> Nice case and panel, I see great potential for another project of sorts.
> Good find even if you don't need a noise generator for your testing
> purposes.
>
> On Fri, Nov 5, 2010 at 8:13 AM, Mike Sloane <mikesloane at verizon.net> wrote:
>
>> I rescued this from the dumpster - the woman told me that it was in her
>> grandmother's house when they were cleaning it out. I have no idea what
>> it is, aside from being a "noise generator". As noted in the image
>> referenced below, it was made by Kay Electronics in Pine Brook NJ (not
>> far from Boonton NJ, home of Boonton Electronics and Aircraft Radio,
>> etc.). I am not likely to even turn it on, as I don't know the condition
>> of the internals. BAMA came up empty, and I certainly am not going to
>> pay $25 for a manual for a boat anchor like this unless it is useful for
>> something.

This device is certainly useful for something: you can measure noise
figure of amplifiers up to (probably) 1GHz.  the trick is that above
about 150 MHz, you need a correction chart, which you could get from
the manual, or perhaps someone who has one would email you a copy.

The way you use it:  Connect your amplifier to the type N connector.
Connect the output of the amp to a receiver, or some device with
enough gain to make a measurement with, and a reasonably low noise
figure itself.  (You can measure the NF of the second stage, and then
run the usual calculation to get the first stage NF.)  Anyway: With
the noise pots on the front panel set to zero, get a reference noise
level on your receiver.  (The AGC should be off.)  Now increase the
noise pots until the reference level you measured out of the receiver
increases by 3dB.  Read the (composite) noise figure off the meter.

The theory of this is that the noise is proportional to the emission
of a thermionic diode--i.e., a carefully made vacuum tube. The filament
voltage is controlled by those coarse and fine pots on the front panel,
and the meter reads the plate current of the tube.  There is a direct
proportionality from the plate current to the amount of excess noise
the tube generates, and which is coupled to your UUT. The switch in
the upper left hand corner is probably a meter-scaler, so you can read
higher noise figure by increasing the current in the tube beyond
what the meter normally reads.

If you got this for nothing, you have a fairly decent piece of obsolete
test equipment which is still usable, providing that the meter reads
when you adjust the noise pots.  If it doesn't, you can look inside to
see if the tube filament is getting brighter.  If it isn't, the tube may
be burned out.  Pull it out and measure the filament with an ohm-meter.
If it's ng, then salvage the front-panel meter and
maybe the transformers, and throw it out.  (You'll probably never
find a replacement noise tube.) If the tube is OK, it should be fairly
easy to troubleshoot and fix the device--maybe one of the pots is bad.

--doug, wa2say

-- 
Blessed are the peacemakers...for they shall be shot at from both sides.
  --A.M. Greeley
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