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Re: Question about TV on Ham satellite - Correction



Howard et. al.

I made a big mistake with the link budget calculations; I thought I'd better
put it right.

An ATV receiver needs at least -80dBm for a reasonable picture :- noise
floor is -174 dBm/Hz, so with 18MHz bandwidth, the noise floor is -101dBm;
add to this 1dB for system noise figure and 20dB for a decent signal/noise
ratio, and you have -80dBm.

Therefore, if the satellite was transmitting 20W EIRP, the power at the Rx
antenna would be

(+43) -157 = -114dBm, so the antenna would need a whopping 34dBi gain.

OOPS.

If the satellite has a noise figure of 0dB, and an uplink antenna gain of
6dBi, then the groundstation would need to transmit

-80 -6 +151 dBm = +65dBm = 3.2kW EIRP, or 25dB antenna gain if using a 10W
Tx.

This does not take into account the noise figures of the receivers and other
losses.

So in summary, due to the very high bandwidth of FM ATV, you would need an
antenna about the size of a small house, which would need to be tracked very
accurately and quickly in real time.  Maybe this is why ATV is not the most
popular mode for amateur satellite use?

FWIW, the G1MFG modules are very sensitive, especially the Gold Receivers -
I have some other data to back up the claims made for their sensitivity.

Grant
G8UBN@amsat.org
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