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Re: AO-40 Beacon and Transponder noise calculations



Charles Suckling posted some insteresting tables of Beacon/Sky and Transponder/Sky signal-to-noise ratios with different size dishes and different RX noise figures (based on measurements of 5 and 10 ft dishes and extrapolations/interpolations to other sizes of dishes).

I think I understand the basic meaning of the two measurements "Beacon/Sky" and "Transponder/Sky", but I don't really know what is the subjective significance of the full range of "Transponder/Sky" numbers.  Obviously, a large "Transponder/Sky" ratio means that the transponder noise is clearly audible above the sky noise.  But I have two questions:

1. Would I be correct to assume that "Transponder/Sky" ratio refers only to the transponder noise floor, and does not include a signal on the transponder?

2. What minimum "Transponder/Sky" ratio corresponds to the point where the transponder noise floor becomes "audible"?
Would I be correct to assume that transponder noise floor becomes subjectively "audible" when the "Transponder/Sky" ratio is in the 1 to 2 dB range?

Wayne Estes W9AE
Mundelein, IL, USA


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