From: <h.bignall_at_email.protected>
Date: Thu, 20 Aug 2009 16:53:14 +0800

Hi JD, all,

Attached is a plot showing 4 minutes of data on PKS 1921-293 (64 MHz
band, from v311a, observed in July at 22 GHz)

I think the Ceduna phase problem is as severe as in previous sessions.

It's hard to gauge what effect it will have on the 6.7 and 8.4 GHz
experiments scheduled for September. I think it depends on the
specific experiments - for example if targets are bright enough for
phase self-cal over a short solution interval (e.g. for TANAMI?),
there may only be a very small amount of decorrelation and reduction
in S/N. However for phase-referencing to detect weak targets it might
be a killer..

Regards,
Hayley

-------------------------------------------------
Dr Hayley Bignall
Curtin Institute of Radio Astronomy

Location: Brodie Hall Building 611, Room 106
          1 Turner Ave, Technology Park, Bentley
Phone: +61 (0)8 9266 9245
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Email: H.Bignall_at_curtin.<!--nospam-->edu.au

Post:
Curtin Institute of Radio Astronomy
Curtin University of Technology
GPO Box U1987
Perth, WA 6845
Australia

2009/8/18 John Dickey <John.Dickey_at_utas.<!--nospam-->edu.au>:
>Hi Folks,
>
>  Well, okay, I'll admit that there is something wrong with the phases to
>Ceduna, at least occasionally.  We've talked a lot about what could be
>causing it, and the most likely culprit is the Agilent Synthesizer.  We plan
>to remove the Agilent and send it back to Hobart for diagnosis, but I don't
>think we should try to do that before the September VLBI run.  Phil E says
>that the only scheduled experiments for that run are at 6.7 and 8.2 GHz.  So
>maybe the current status of the Ceduna system is going to be okay for those
>experiments.  Then we'll plan to send the synthesizer back to Hobart right
>after that run.
>
>  Does anybody have any problems with that?  We can reconsider if there are
>strenuous objections.
>
>cheers,
>jd
>
>On 17/08/2009, at 4:07 PM, Richard Dodson wrote:
>
>>Hi
>>
>> I am sure you guys know the system best .. but - as Hayley is saying
>>I think - there is detectable phase coherence (i.e. common to both
>>frequencies)  for the data at Ceduna, but it is rapidly (timescales on
>>the order of ten seconds) varying about 1 radian. Thus I don't think
>>it is thermal (as that should just be a random phase spread, not a
>>wander (correct?)).
>>
>>I note that V255 and V257 look pretty good.
>>
>>      Richard
>>
>>>> Below is a copy of the email I sent to Jim and Simon last Friday.  I
>>>>think
>>>
>>>it's quite possible that there are very short phase jumps that could
>>>cause
>>>the loss of gain at the high frequencies in the Ceduna data.  But since
>>>the
>>>phase is very stable long term at the lower frequencies (S band), then
>>>the
>>>phase must quickly return to the maser standard (on a time scale short
>>>relative to the correlator averaging time).
>>
>>
>>>As I see it the problem is not big phase jumps but low-level, rapid
>>>fluctuations.
>>>
>
>

<div>


Received on 2009-08-20 18:53:56