EME Calc v11.11 reconciliation issues

A correspondent wrote about trying to reconcile by G/T worksheet with EME Calc.

Many times I have tried to validate it and run into problems. At one time I reported them to the author, but they were never acknowledged, much less fixed.

The specific problem on this occasion relates to the receiver performance tab.

Above is a screenshot (with my annotations) where I have basically stripped the configuration down to a receiver attached to a noiseless antenna with lossless line.

The receiver is specified in the box at (1), the up down arrows used to adjust the value. In this case, the Noise Figure is 2dB and the untitled quantity to the right is the equivalent noise temperature in kelvins (correctly calculated).

Note that the equivalent noise temperature at the receiver input (169.62K) is the ONLY noise source in the whole model, everything else is noiseless.

If we look at (2) we see two boxes entitled Rx Noise Temp °K (the ° symbol is an error) with value 329.4K. Despite the apparently similar title, this is clearly a different quantity to that at (1)… it is almost double (1).

But then the Rx Noise Figure box at (2) shows the Rx Noise Figure to be 2.00dB. But this does not reconcile with the Rx Noise Temp °K value at (2).

Now look at (3) to find System Noise Temp to have yet another value of  335.4K. Since there is no other noise in the system, no loss or gain elements other than the receiver at (1), one might have expected the value to be the same as (1) (169.62K).

Also at (3) is Sys Noise, presumably the system noise figure corresponding the System Noise Temp, and it is exactly that.

So whilst the values at (3) are consistent with each other, they don’t seem to relate to anything else detailed in the model on this tab. The term receiver or abbreviation rx seems to be used rather loosely to refer to at least two different entities (though in the simplified lossless model two should be equivalent).

This is only the start of difficulties I had reconciling / understanding the calculated values on this tab. The problems here were exposed by trying to simplify the model to explain issues with more complex scenarios.

This is not the first time I have had difficulty understanding or reconciling what are fairly basic calculations and I have come to the conclusion that I cannot depend on the tool and am not surprised that it does not reconcile with other tools.

Mind you EME Calc is apparently widely used by hams, but possibly by people who have not validated its results.