From: <John.Dickey_at_email.protected>
Date: Thu, 20 Aug 2009 19:06:12 +1000

Thanks, Hayley. We'll try to get another synthesizer out there before
the September run. That's pretty terrible.

cheers,
jd

On 20/08/2009, at 6:53 PM, Hayley Bignall wrote:

>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
>Fax: +61 (0)8 9266 9246
>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.
>>>>
>>
>>
><v311a_4min_1921-923.pdf>
Received on 2009-08-20 19:06:32