[evlatests] High-Speed RFI!

[Dan Mertely]

I realize this is off-topic, but ...
Yes, I see you are right.  I was familiar with the passive
radiometer because it generated a great deal of interest
in the spectrum control community some years ago (lots of
chatter).  It found a number of commercial and military
terrestrial transmitters illegally operating in the 1400-
1427 MHz passive-only band (Illegal 2-way radio systems in
Chilean mines, paging systems in Disney/Europe, and malfunctioning
old military Dew-Line radar systems in Canada and Greenland.)

As regards the active radar, the technical document says:
"The SMAP radar operates in a “shared” band between 1215 and
1300 MHz...".  TNX.
-Mert

On 10/4/2016 10:39 AM, Bryan Butler wrote:
>
> there's an active and passive component...
>
>
> Dan Mertely wrote on 10/4/16 10:29 :
>> (BTW: The SMAP L-band sensor is passive.)  -Mert
>>
>> On 10/3/2016 4:41 PM, Bryan Butler wrote:
>>>
>>> if he was talking about SMAP, that's L-band.  i don't know of an
>>> orbiting NASA satellite doing radar at C-band.  not that i know
>>> everything that's up there!  there are two ESA C-band SARs - Sentinel-1
>>> and Sentinel-2 that might fit the bill, but they don't go over every
>>> day...
>>>
>>>      -bryan
>>>
>>>
>>> Barry Clark wrote on 10/3/16 16:22 :
>>>> One of the tour participants at the openhouse Saturday said NASA
>>>> has a downlooking radar satellite that probably passes, rather
>>>> rapidly, over the VLA about noon or a little later every day.
>>>>
>>>> On 10/03/2016 03:38 PM, Rick Perley wrote:
>>>>>      In calibrating astronomical data, mostly taken last year, a
>>>>> remarkable type of RFI has been seen.
>>>>>
>>>>>      Observations were made in all four configurations at C-band. Over
>>>>> one year elapsed between the first and last of these observations.
>>>>>
>>>>>      The effect was noted in the gains, starting with the
>>>>> D-configuration data.  In this configuration, it was noted that all 16
>>>>> spectral windows had a reduced amplitude, for all antennas, both
>>>>> polarizations, by about a factor of two.  The effect lasted 30
>>>>> seconds,
>>>>> after which all gains were again normal.   Only one event was seen.
>>>>>
>>>>>      Investigation (via 'SPFLG') showed that the cause was a strong
>>>>> RFI
>>>>> signal, located within SPW3 (spanning 4232 -- 4360 MHz).  The data in
>>>>> this SPW had very large and random values, presumably due to
>>>>> overflow in
>>>>> the accumulators.   All other SPWs retained their coherency, but the
>>>>> amplitudes were reduced.  Phases were unaffected.
>>>>> The signal was strong enough that the entire 2 GHz bandpass was
>>>>> compressed enough to lower the gains by a factor of up to two.
>>>>>      There were two C-band IF tunings in this experiment -- the other
>>>>> one (6 -- 8 GHz) showed no effect, indicating the the compression
>>>>> is in
>>>>> the IFs, not in the receiver.
>>>>>
>>>>>      But much more interesting (to me, at least) is that the data from
>>>>> the C, B, and A configurations also showed similar compression.  But
>>>>> the
>>>>> much larger spatial scale of these configurations clearly show that
>>>>> the
>>>>> range of the RFI effect is localized, and moving at high speed.
>>>>>
>>>>>      The evidence is clearest for the A configuration.  There were
>>>>> four
>>>>> 'events' during this run (which was taken in July 2015).  For all
>>>>> four,
>>>>> the effect was localized to a a subset of the array.  For all four,
>>>>> only
>>>>> the antennas on one or two arms were affected.  In all cases, the
>>>>> strength of the compression varied along the antennas of the arm
>>>>> affected -- usually with the end-most antenna the most strongly
>>>>> affected.
>>>>>      The timing of the 'events' gives us a pretty good estimate of the
>>>>> velocity.  The peak saturation for one of these four events showed
>>>>> a 30
>>>>> second lag between the end antenna of the east arm and a middle
>>>>> antenna
>>>>> of the north arm (and with the peak progressively later for antennas
>>>>> along the east arm).  That translates to ~ 2000 mph!
>>>>>
>>>>>      Might this be some sort of satellite imaging radar?   It's
>>>>> clearly
>>>>> highly focused, and moving quite quickly.
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> evlatests mailing list
>>>>> evlatests at listmgr.nrao.edu
>>>>> https://listmgr.nrao.edu/mailman/listinfo/evlatests
>>>>
>>>> _______________________________________________
>>>> evlatests mailing list
>>>> evlatests at listmgr.nrao.edu
>>>> https://listmgr.nrao.edu/mailman/listinfo/evlatests
>>>
>>> _______________________________________________
>>> evlatests mailing list
>>> evlatests at listmgr.nrao.edu
>>> https://listmgr.nrao.edu/mailman/listinfo/evlatests
>>
>> _______________________________________________
>> evlatests mailing list
>> evlatests at listmgr.nrao.edu
>> https://listmgr.nrao.edu/mailman/listinfo/evlatests