[evlatests] Using S-band is Tough!

[Todd R. Hunter]

On Fri, 1 Jul 2011, Frazer Owen wrote:

> Rick Perley wrote:
>>     Jim:
>>
>>     We'll need filters in two IFs (like, A and C), for at least a couple
>> of antennas.  I don't think we need as many as four (we're not checking
>> closure here).
>>
>>     Anybody else with an opinion?
>>
>>
>   If I understand correctly XM/Sirius affects all declinations, so it
> makes sense to block it out.

The Sirius satellites do have a very interesting elliptical orbit that 
allows them to maintain significantly higher elevations than the 
geostationary band as viewed from North America for over 8 hours. This 
probably helps reception in inner cities.  There are 3 of them equally 
spaced to provide 24 hour coverage (there may be more today, this was 3 
years ago). I could post plots if people are interested.

> However, the downlinks only affect 0 dec so

I cannot resist offering a small correction here.  Although geostationary 
satellites orbit above the equator, they do not appear at 0.0 dec unless 
you observe them from the equator. From the EVLA latitude, they appear at 
about -5.5 deg dec. This shift is due to their relatively small distance 
in units of Earth radii. I remember calculating this effect back in high 
school when our earth science class was donated a dish antenna so that we 
could receive GOES images in addition to the polar orbiters we tracked 
with crossed yagis.

Of course, older satellites whose orbits are no longer well-controlled can 
still be geosynchronous (not stationary) but can have significant diural 
variations in declination.

Todd