From: <John.Reynolds_at_email.protected>
Date: Wed, 23 Jun 2010 12:13:52 +1000 (EST)

Chris,

Of course not knowing a priori the location or speed of these sources will
render the correlation essentially phaseless. But I've long harboured a
secret desire to emulate Hanbury Brown & Twiss and operate an Intensity
Interferometer at radio wavelengths. So let's do it!

Cheers,
john R

On Wed, 23 Jun 2010, John Reynolds wrote:

>Chris,
>
>This might be worth a try. The ATCA phases during an event seen last week
>were useless - no obvious structure. This might be due to multipath
>scattering path through sidelobes, rapid motion of source, or possibly
>presence of multiple simultaneous sources (satellites). However on a
>longer baseline one might hope to get a usable delays/rates for each
>satellite. These peaks in delay might be quite broad though (~1/3MHz
>inverse linewidth). If you're offering to correlate, let's give it a go at
>the next opportunity! Last week it was seen on Tuesday and Thursday. This
>week seen yesterday, but not so far today. So tomorrow is on the cards.
>
>This RFI drives the Lunaska system crazy - too much information to be
>useful I suspect, and on-site baselines too short.
>
>
>Cheers,
>john R
>
>
>On Wed, 23 Jun 2010, Phillips, Chris (CASS, Marsfield) wrote:
>
>>Hi John
>>
>>Is it worth trying to do either VLBI or Lunaska style high time resolution sampling of the data to try and more
>>accurately determine the position of the emission?
>>
>>Cheers
>>Chris
>>
>>------------------------------------------------------------
>>Chris Phillips
>>CSIRO ATNF eVLBI project scientist
>>Office: (+61) (0)2 93724608 Mobile: (+61) (0)439487601
>>
>>
>>
>>On 23/06/2010, at 11:30 AM, John Reynolds wrote:
>>
>>>Hi all,
>>>
>>>Since March we've been seeing some particularly pernicious RFI in the
>>>1260-1340MHz band, which looks to have a satellite origin given that
>>>we've seen it simultaneously at Parkes and Narrabri. I'm wondering if
>>>anyone has seen or heard reports of anything similar at other
>>>observatories.
>>>
>>>So far this RFI has been seen only a few days each week, and usually in
>>>daylight hours, Typically it consists of a pair of very strong signals
>>>spaced apart by about 50MHz, e.g. 1260MHz and 1310MHz, and each about 3MHz
>>>wide. In other manifestations there've been up to six signals (three
>>>pairs), coming and going on timescales of hours. These signals are clearly
>>>related and have a complex time and frequency modulation. They can be
>>>incredibly strong - attachment #1 shows a measurement yesterday taken with
>>>a spectrum analyser and a 6dBi horn antenna. With the trace on max hold we
>>>recorded bursts in excess of -20dBm in a 1MHz resolution bandwidth, with
>>>three peaks of emission at 1276MHz, 1290MHz and 1335MHz. Observing in this
>>>band is impossible during such events. This is almost unbelievably strong
>>>- one wonders about the safety of our receivers should this chance through
>>>the 64m beam!
>>>
>>>Attachments #2 and #3 were taken with our filterbank DFB3 in 'search'
>>>(non-folding) mode and show something of the complexity of the modulation
>>>and how the DFBs are being driven hard into compression, splattering power
>>>across the whole band.
>>>
>>>In addition to the frequency pair there is often emission at around
>>>1247MHz and a number of lower frequencies that looks to be related, though
>>>these don't seem to have the strongly impulsive character so inimical to
>>>observing.
>>>
>>>I also suspect that there is emission in the protected 20cm band.
>>>Attachment #5 shows emission at 1415MHz which is clearly related to the
>>>stronger peaks at (1275MHz and 1325MHz: not shown) but establishing that
>>>this is a real signal and not an higher order product within our receiver
>>>system (in this instance the Patriot 12m + DFB2) will take some doing.
>>>
>>>The source of these emissions must surely be satellites (to be seen
>>>simultaneously at Parkes and Narrabri on 17 June). One suspect is the
>>>COMPASS system, the Chinese version of GPS believed to be in the process
>>>of being deployed. There are 5 GSOs in this system and 20-30 MEOs with
>>>12-hr orbits. However the advertised frequencies of this system don't
>>>match those observed here. One of the Compass GSOs is clearly visible from
>>>Parkes at about Az=351f, El=51d and its spectrum is consistent with
>>>published information, with strong peaks at 1269MHz and 1208MHz: see
>>>attachment #4. But the experience with GLONASS suggests the advertised
>>>properties of these systems should perhaps be received with caution.
>>>
>>>So in short, 20cm observing Parkes and Narrabri is being badly affected by
>>>a new source of RFI for up to two or three days a week from morning till
>>>late afternoon. The RFI may also be posing a risk to receiving equipment,
>>>and may be spilling into the 20cm protected band. The culprit appears to
>>>be a satellite or satellite system as yet not positively identified. In
>>>particular it is not known whether the emissions are part of some
>>>commissioning phase, or the tip of an impending operational iceberg. The
>>>latter prospect is not a happy one.
>>>
>>>Any relevant info welcome!
>>>
>>>Cheers,
>>>John R<P6220241.JPG><s22021.gif><s2205.gif><Compass144.gif><f2_0102.gif>
>>
>>
>
Received on 2010-06-23 12:14:14