[time-nuts] Satellite TV messed up, how is GPS time
David I. Emery
die at dieconsulting.com
Fri Nov 4 19:25:03 EDT 2016
On Fri, Nov 04, 2016 at 06:19:13PM -0400, David I. Emery wrote:
> Solar outages are not greatly worse on C band.
> It WAS true that EIRPs at C band were kept lower at one time (to
> protect the now mostly completely abandoned terrestrial C band microwave
> telephone network which shares 3.7-4.2 Ghz with C band satellite) than
> at Ku band, but that is less true today...
Since folks have brought this up, a couple of more observations
C band has MUCH less weather absorption by normal storms...
Ku band satellite signal fades from rain in passing
thunderstorms often can and do exceed 10-12 db...
This means in practice that C band link budgets can get by with
significantly lower margin to handle rain fades...
So many Ku signals are run with big margins of excess signal so
as to reduce the number of seconds of reception lost to passing
thunderstorms .... something not needed as much for C band.
Thus a C band dish sized to just work reliably will have less
margin for the noise floor to rise as the sun goes past the satellite.
But it DOES rise for Ku dishes as well, just they may be sized to have
more margin and/or the satellite power is higher.
Some home DTH dishes don't leave much margin, others are better.
But it is not true that the sky noise temp doesn't go up a lot
at Ku band during sun outage season or that for some dishes and some signals
this will not eat the margin up and "ku does not have sun outages".
Dave Emery N1PRE/AE, die at dieconsulting.com DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."
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