[evlatests] Using S-band is Tough!

[Jim Jackson]

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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