From: <Jim.Lovell_at_email.protected>
Date: Thu, 03 Sep 2009 15:15:23 +1000

Hi everyone,

Some results from recent Cd-Ho VLBI tests. The attachment shows phase
determined from 0.1 s integrations as a function of time with the
Agilent (on 3c273) and the Wiltron (last night, on 1921-293) at 6.7
GHz. There's obviously an improvement with the Wiltron, so I think we
should stick with it for the LBA run, but it still doesn't look as
good as it should.

Data were collected using RtFC and tweaking the delays until the phase
went flat across the band. The phase data were then averaged across
the band. Constant rates were also applied to account for maser drift.
It's a crude method but given the connectivity to Ceduna, the best we
can do at the moment. We're obviously concerned that those 50-100 deg
changes on 1 min timescales might be real and not just noise in the
data or something introduced in the rather crude processing. However,
that change of ~200 deg in phase over 2 min does look real.

Cheers,
Jim

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>

<div>


Received on 2009-09-03 15:16:02