[evlatests] Using S-band is Tough!

[Vivek Dhawan]

What are the specs on matching the phase and group delay from different
units, and their change with temperature.

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?
> 
>    
> 
> Jim Jackson wrote:
>> Rick,
>>
>> Rob has quotes coming in this week for filters to block out XM/Sirius 
>> radio. As soon as we get them all in, we'll choose a vendor and place 
>> an order for some filters to test.  I imagine there is a typical 8-12 
>> week delivery time which is typical of custom RF filters.  Just to 
>> make sure were getting the right amount, how many antennas do we need 
>> to equip with these filters as a valid test?
>>
>> Cheers,
>> Jim
>>
>>
>>
>>
>>
>>
>> At 02:03 PM 7/1/2011, Rick Perley wrote:
>>>     I've finally gotten around to trying to properly calibrate the
>>> S-band data from the Hercules A 'demo' run, from C-configuration --
>>> taken last December.
>>>
>>>     It ain't easy ...
>>>
>>>     The major problem is RFI, the majority of which is from
>>> geostationary satellites.  Because Herc A is near zero declination, it
>>> essentially travels right along the equatorial belt, passing by these
>>> satellites in turn.  Six of the 16 subbands are essentially unusable due
>>> to this -- subbands 2 through 5, and 13 through 16.   The first three
>>> are taken out by XM radio, plus the emitter at 2190 MHz (whose origin I
>>> forget -- but it most clearly is a geostationary satellite), the latter
>>> three are taken out by TV downlinks.
>>>
>>>     The emission is so strong in subbands 2 through 5 that it causes the
>>> accumulators to overflow, which then completely trashes the entire
>>> subband.  It would be useful, when we can find the time, to utilize the
>>> flag which is aware of accumulator overflow, so these ruined spectra
>>> never make it to the user.
>>>
>>>     An interesting question is whether we should be changing the
>>> requantizer gains to accommodate the extra power in these subbands.  I
>>> think the answer is 'no', but we should probably discuss the issue at
>>> some point.
>>>
>>>     On the brighter side, the calibrator observations on 3C286 and 3C48
>>> were not seriously affected by any of these emissions -- the antenna's
>>> forward gain is sufficient to suppress these transmission.  So observing
>>> in the north will generally work.  The specific frequencies allocated to
>>> the emission in subbands 2 through 4 may be unuseable, but the adjacent
>>> channels will be fine.  What we don't know is how close to the satellite
>>> we can point, and still get useable data.
>>>
>>>
>>>
>>>
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