VK2JDS wrote:Back again with some research findings.
Hi Dave,
Some good experiments in progress from your description.
A few points:
PCs can be noisy... the switched mode power supply is often the worst component, and optional... ie you can switch the AC power off during each measurement interval. I NEVER make measurements with the power supply running. The noise problem has to be solved no matter what software you use.
Elimination of hum/noise loops by use of an isolation box such as
Passive DI box or
Passive Direct Injection Box is often useful. I NEVER make measurements without such a device.
The interface unit that you need for sucessful WSJT operations is equally good... just make sure that it is working effectively.
I cannot really interpret your graphs. You mention Spectran, but show WSJT graphs.
In my limited exploration / validation of WSJT and related tools I have not developed confidence that it they are a good tool for measurement.
I have also used Spectran, Spectrum Lab, and Spectrogram, spent considerable effort validating them, and have much more confidence in those tools. I have also validated my own tools, FSM and NFM.
Spectrogram v16 is now freeware.
My article
Noise Figure inferences of spectrum analysis of weak signals shows examples of use of Spectran and Spectrogram on a weak beacon signal, and how to calculate S/N ratio. The article might give you some ideas, and demonstrates how a conventional spectrum plot is much more useful than a waterfall display for these purposes.
Measuring the S/N ratios achievable from the beacon with the different preamp configurations indicates which is better for that application, but the magnitude of the difference doesn't imply the same magnitude on EME because the noise environment is quite different. For example if you have two receiver systems with Teq say 100K and 500K, and you consider them in two ambient noise environments of a terrestrial shot (~290K) and EME (~60K), on the terrestrial shot the noise ratios (N2/N1) will be (500+290)/(100+290)=2, and on the EME shot (500+60)/(100+60)=3.5. The better receiver makes less difference on the terrestrial shot where its performance is masked somewhat by the high ambient noise.
The consequence of that is the 0.4dB difference with the 2 stage unit that you might expect to see on the moon, will be much less on a terrestrial shot (~0.1dB by my calcs).
Hope this helps.
Owen