[Test-Equipment] LF Ailtech 7514 and noise sorce

[J Forster]

Brooke Clarke wrote:

> Hi Ed:
>
> [snip]
> The other way of measuring noise is called the Y factor method.  I think it was
> an AIL box (brown color about 1 foot on a side) that has two 50 Ohm
> terminations, one in a LN dewar and the other in a heater.  You just measure
> the RMS voltage or power at the IF for each one and calculate the Noise Factor
> (different from Noise Figure).

It's called a 7009 Hot-Cold Noise source. If you ever take one apart for repairs,
it uses Silly Putty in the LN2 seals !!

> A variation on that is called a Dicke Radiometer.  You point an antenna at
> outer space and switch the input to your LNA from the antenna to a termination
> that's at a known temperature.  When you switch you also switch the video
> output polarity.  If both signals are at the same power the video out will be
> zero, but if they are different then you get some DC out in a polarity that
> tells you which is larger.

A Dicke Radiometer (or Switch) essentially uses a Lock-In amplifier.
-John

> Instead of using something pedestrian, like a square wave (which works fine),
> you can use a long PN code.  The later was built into one of our products.  On
> that one you could just hold the reference termination between your thumb and
> forefinger and after a while you knew your body temperature.
>
> Have Fun,
>
> Brooke Clarke, N6GCE