Re: [amsat-bb] AO-40 Beacon and Transponder noise calculations

[Charles Suckling <charles.suckling@xxxxxxxxxxxx>]

Estes

snip>>

>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?

Yes, the "Transponder/Sky" ratio refers to the transponder noise floor with 
no signals, just the noise.  It depends on your ears, but 1-2dB is probably 
a reasonable minimum amount to be audible.  You should be able to see that 
on an S-meter as well.  The figures refer to the dB increase you should 
actually see on the meter, assuming you have enough system gain to have a 
non-zero reading on the S-meter with the dish pointed off the satellite 
towards "cold sky".   I always try to arrange things to have a 
small  reading on the S-meter to make sure that the converter noise is 
dominant.

The transponder noise is highest near the beacon, and falls off towards the 
edges of the passband.

73

Charlie




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