Dave Oldridge wrote in
9:

Near as I could measure it, the NF of the receiver after my mod was
1.2db. I had to resort to boiling and freezing water and a tiny dummy
load to measure it at all.

I haven't tried hot/cold tests using ice and boiling water, I didn't
think it was practical.

You finally measured a receiver noise temperature of 50K with hot and
cold loads of 270 and 370.

That means a Y factor of 1.059dB.

If Y were just 0.1dB greater, NF would be 0.78dB, 0.1dB lower and, NF
would be 1.66dB.

With this configuration the sensitivity of NF to changes in Y are
extreme, 0.4dB change in NF per 0.1dB change in Y around that point.

If you made the Y measurements using the audio output of a narrow band
receiver, it is very hard to make high resolution measurements (eg to
0.01dB resolution) with say, a multimeter.

I have done these tests with a liquid nitrogen cooled load and room
temperature load, and that gives more practical Y ratios, 3.7dB for a
1.2dBNF, and the sensitivity in NF is 0.08dB per 0.1dB change in Y. This
still demands high resolution measurement of noise power.

Owen