From: <brett.reid_at_email.protected>
Date: Tue, 26 Apr 2005 13:58:34 +1000

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Hi Dave,
I have not been involved in seeing correlated data from 2 dishes at all
before, so I do not know if I have it right. I did send a later message
regarding coherence of the Kiwi system and added this message in response
to a message from Richard with the same concern you raise. I did not
include vlbiobs in the reply so you may not have seen it.

At L band the Kiwi receiver running on their Rubidium produced a
coherence tone at 5 MHz that drifted 1 cycle over a couple of minutes.
The drift was steady, without jitter. When we ran the receiver from the
maser the display was rock solid steady.

Here is what we did as detailed in the later message:
>Adjustment of the rubidium rate was not made since the initial adjustment
>on Friday (maybe it was Thursday). During Saturday we monitored the maser
>10 MHz and the rubidium 10 MHz. The drift was again less than 1/4 cycle
>over 3 hours. Sergei can confirm the actual drift. The drift was always
>in one direction only, with the rubidium running slower. I calculate that
>it is it is losing 0.1 microseconds in 12 hours or 1 second in 13,690
>years!! The unit as originally calibrated was running about 12 times
>slower when it arrived in Hobart. It remains to be seen what the trip
>back to Auckland does to it.
>
>During the coherence tests mentioned above, the 5 Mhz displays were rock
>solid with no drift when running everything on the maser. We then synched
>the AUT receiver and 2nd LO to the Rubidium 10 MHz keeping the injected
>sky tone synched to the maser. The display then drifted slowly and would
>probably take a couple of minutes to drift by one cycle. This slow drift
>looked constant, in one direction and was without jitter.

Now that both you and Richard have raised concerns, I wish we had put a
srew driver in the AUT rubidium again to see if we could freeze the
coherence display, especially since it always was slow and constant and
not jittering.

As I said I haven't been involved with correlating data. If the
rubidium's rate is known and reasonably constant, as demonstrated by our
tests, then hopefully this can be taken into account?

There would be some value in setting up PPS from Rubidium and PPS from
GPS and monitoring the offset over the weeks to the May test, I suppose,
to determine the rate of the clock after the trip back to Auckland.

Regards,
Brett.

==============Original message text===============
On Tue, 26 Apr 2005 12:55:20 +1000 David.Jauncey_at_csiro.au wrote:

Dear Brett,

Thanks for your e-mails. In regard to the "drift" of the NZ Rubidium I
still have a couple of concerns, as your 180 degree (= pi radians)
"drift" in 2 hours corresponds to 200 pi radians in 2 hours, or about 2
pi radians per minute at 2 GHz.

Your thoughts/comments would be most welcome.

Cheers and many thanks for spending so much time working with Steven and
the Kiwis,

Dave

-----Original Message-----
From: owner-vlbiobs_at_atnf.csiro.au [mailto:owner-vlbiobs_at_atnf.csiro.au]
On Behalf Of Brett Reid
Sent: Friday, April 22, 2005 10:47 PM
To: Phillips, Chris (ATNF, Marsfield)
Cc: vlbiobs_at_atnf.csiro.au; stingay_at_astro.swin.edu.au
Subject: Re: Progress toward New Zealand VLBI

Hi Chris,
On Fri, 22 Apr 2005 20:37:53 +1000 (EST) Chris Phillips wrote:

>Hi Steve,
>
>A couple of questions:
>
>- Were you using the NZ rubidium on the 14m?

Yes. Then we switched the 14m back from the rubidium to a common 5 MHz
synch (maser) and the fringes on the 5 Jy source were just a little
stronger.

>- Did you do a test of the phase stability of the Rubidium compared
>to Hobarts masers?

Yes. First off the rubidium 10 MHz drifted 36 degrees in 5 minutes. Then
after a few slight twists of a trim pot the phase drifted only 180
degrees over 2 or more hours. This was viewing both 10 MHz waveforms on
a
dual trace cro. No jitter was visible.

regards,
Brett.

Brett Reid
Observatory Manager, Radio Telescopes
University of Tasmania
School of Mathematics and Physics
phone + 61 3 6248 5285
email brett.reid_at_utas.edu.au
web http://www-ra.phys.utas.edu.au/~breid/

===========End of original message text===========

Brett Reid
Observatory Manager, Radio Telescopes
University of Tasmania
School of Mathematics and Physics
phone + 61 3 6248 5285
email brett.reid_at_utas.edu.au
web http://www-ra.phys.utas.edu.au/~breid/
Received on 2005-04-26 14:00:06