[evlatests] Using S-band is Tough!

[Rick Perley]

    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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