"Ginu" wrote in message
...
On Dec 5, 6:10 am, Bob Bob wrote:
So at 5AM I may not be too sharp...

The formula you used doesnt seem to allow for the required demod s/n.
QAM64 for example (from memory) is around 30dB so this has to be "added"
to the path loss. Differing mod/demod/FEC have differing margin
requirmeents. Somewhere in there too you have to stipulate the bit loss
rate "allowed".

Can you explain this further please?

http://www.satsig.net/lnb/ebno-calculator.htm is one of many sites dealing
with considerations of Energy Per Bit to Noise Density Ratio, which may help
you.

The Eb/No -- or to some, Eb/N0 -- influences the bit error rate (BER). Let
the Eb/No go too low and the link is not error-free. Generally, a BER of
better than one error in ten-to-the-eighth bits is considered to be an
error-free link.

Navy satellite data links of my acquaintance usually ran at 256 kbps and, if
memory serves, needed an Eb/No around 8. The modem reported the Eb/No and
that value was the first thing we looked at if the mux started taking hits.