I've observed a curious effect on Eb/No measurements of a DVB-S signal. The Eb/No has periodical oscilations each day, getting the max value at 12:00 GMT and the minimum value at 00:00 GMT, as a sinusoid signal.
I've supposed that it is possible because the room temperature of the LNB used to recieve the signal, that I think it works better in not-extreme temperatures.
Hello,
you might think also that antennas are "looking" to the south!
As you said at noon you have a noise rise maximum...
it suggests that the sun is passing through your radiation pattern
that implies that your system is receiving the "radio sun".
If look on the internet you'll find a lot of interesting projects about
solar radioastronomy.
Hope that could help you in better understanding of the problem.
Regards
Added after 1 minutes:
Forgot to mention:
you may find a very interesting paper called:
"antenna patterns from the sun"