[time-nuts] Sun Outage
bob at evoria.net
Thu Oct 9 19:37:07 UTC 2014
I have more information and you may have explained it. The outages occurred at about 3:10PM, and with an azimuth here of about 180 degrees (which I just looked up), that makes no sense. Also, the cartoons I was recording for my granddaughter were unaffected, but the station I was watching had the outage. That doesn't all fit together unless it was the uplink that had the problem. I guess I should have checked all that before posting.
From: Henry Hallam <henry at pericynthion.org>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Cc: Bob Stewart <bob at evoria.net>; hmurray at megapathdsl.net
Sent: Thursday, October 9, 2014 2:27 PM
Subject: Re: [time-nuts] Sun Outage
On Thu, Oct 9, 2014 at 11:18 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
> What's the beam width of the DirectTV antennas? Does it agree with the "3 or
> 4" minutes at the back-of-envelope level?
DirecTV is a Ku/Ka-band system operating with a 460mm dish antenna.
At Ka-band, the 3dB full-width of the beam is 2.4 degrees. The earth
rotates at 0.25 degrees per minute, giving approx 10 minutes for the
sun to cross the beam assuming it crosses directly through the center
of the beam.
However, a little googling suggests that in fact the DirecTV
satellite signal usually has enough margin to overcome the sun noise,
but that the C-band feed that DirecTV uses at their uplink station
to receive programs from their providers may itself suffer from solar
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