[GMVAtech 76] Re: C231A VLBA Observer's Log {External}
Thomas Krichbaum
tkrichbaum at mpifr-bonn.mpg.de
Thu May 11 15:10:05 CEST 2023
Hi Jay,
sorry for the delayed reply.
Replacing 999.0 by an interpolated or smoothed TSYS value is not a good option.
As you can see in the example below, the short VLBI scan
! BR C231A 1156+295/0 124-23:20:00/124-23:23:00
does not get any LCP Tsys at all !!
############################
! BR C231A 1156+295/0 124-23:20:00/124-23:23:00
! 1 3mm B RCP 1 U 512.00MHz 128M 86076.00MHz 8.69
! 2 3mm D LCP 2 U 512.00MHz 128M 86076.00MHz 12.18
! 3 3mm B RCP 3 U 640.00MHz 128M 86204.00MHz 8.23
! 4 3mm D LCP 4 U 640.00MHz 128M 86204.00MHz 11.65
! 5 3mm B RCP 5 U 768.00MHz 128M 86332.00MHz 7.90
! 6 3mm D LCP 6 U 768.00MHz 128M 86332.00MHz 11.07
! 7 3mm B RCP 7 U 896.00MHz 128M 86460.00MHz 7.88
! 8 3mm D LCP 8 U 896.00MHz 128M 86460.00MHz 10.83
124 23:20.308 163.70 999.00 171.18 999.00 173.49 999.00 177.94 999.00 ! 23.28
124 23:20.900 165.67 999.00 171.79 999.00 172.93 999.00 176.58 999.00 ! 23.38
124 23:21.500 165.10 999.00 171.49 999.00 172.86 999.00 176.69 999.00 ! 23.47
124 23:22.100 165.15 999.00 170.89 999.00 171.58 999.00 174.63 999.00 ! 23.57
124 23:22.692 164.09 999.00 169.74 999.00 171.01 999.00 174.47 999.00 ! 23.66
!
! BR C231A NGC4278/0 124-23:24:00/124-23:30:00
124 23:24.283 170.88 244.77 178.28 239.74 180.21 228.17 184.18 226.08 ! 20.70
124 23:24.817 170.33 243.60 177.72 238.84 179.54 227.54 184.29 225.61 ! 20.79
.....
124 23:29.183 166.88 238.99 174.38 234.75 176.58 224.10 181.03 222.67 ! 21.47
124 23:29.717 164.91 237.39 173.37 232.94 176.49 224.31 181.69 223.25 ! 21.55
#############################
Quite often there is a ~3min time lapse, until LCP is recovered, I wonder
if there is a software timeout which enforces the second RDBE to come back, eg:
##############################
! BR C231A NGC4374/0 124-23:46:40/124-23:51:40
! 1 3mm B RCP 1 U 512.00MHz 128M 86076.00MHz 8.69
! 2 3mm D LCP 2 U 512.00MHz 128M 86076.00MHz 12.18
! 3 3mm B RCP 3 U 640.00MHz 128M 86204.00MHz 8.23
! 4 3mm D LCP 4 U 640.00MHz 128M 86204.00MHz 11.65
! 5 3mm B RCP 5 U 768.00MHz 128M 86332.00MHz 7.90
! 6 3mm D LCP 6 U 768.00MHz 128M 86332.00MHz 11.07
! 7 3mm B RCP 7 U 896.00MHz 128M 86460.00MHz 7.88
! 8 3mm D LCP 8 U 896.00MHz 128M 86460.00MHz 10.83
124 23:46.942 198.51 999.00 209.27 999.00 213.98 999.00 220.14 999.00 ! 11.80
124 23:47.500 197.70 999.00 208.96 999.00 213.38 999.00 219.80 999.00 ! 11.90
124 23:48.058 197.62 999.00 208.92 999.00 212.83 999.00 219.48 999.00 ! 11.99
124 23:48.608 195.64 999.00 206.99 999.00 212.10 999.00 219.07 999.00 ! 12.08
124 23:49.167 195.10 999.00 206.37 999.00 211.02 999.00 217.86 999.00 ! 12.17
124 23:49.725 194.92 999.00 206.16 999.00 210.76 999.00 217.22 999.00 ! 12.27
124 23:50.275 193.73 999.00 204.56 999.00 209.46 999.00 217.06 999.00 ! 12.36
124 23:50.833 192.96 277.50 202.28 268.99 208.94 263.78 217.23 267.23 ! 12.45 <--- RDBE2 comes back here
124 23:51.383 190.36 277.69 198.40 265.40 205.61 260.92 214.01 265.67 ! 12.54
##############################
Practically this means Tsys is available only for the last minute, which makes interpolation
difficult. For PI's who are interested in polarimetry, an accurate measurement of Tsys in
both polarisation is almost mandatory.
There are also cases where a VLBI scan does not get a LCP Tsys at all, eg:
###############################
! HN C231B NGC1052/0 126-19:36:25/126-19:40:25
! 1 7mm A RCP 1 U 512.00MHz 128M 42976.00MHz 6.76
! 2 7mm C LCP 2 U 512.00MHz 128M 42976.00MHz 8.88
! 3 7mm A RCP 3 U 640.00MHz 128M 43104.00MHz 6.22
! 4 7mm C LCP 4 U 640.00MHz 128M 43104.00MHz 7.91
! 5 7mm A RCP 5 U 768.00MHz 128M 43232.00MHz 6.26
! 6 7mm C LCP 6 U 768.00MHz 128M 43232.00MHz 8.12
! 7 7mm A RCP 7 U 896.00MHz 128M 43360.00MHz 6.50
! 8 7mm C LCP 8 U 896.00MHz 128M 43360.00MHz 8.41
126 19:36.667 145.14 999.00 146.46 999.00 150.91 999.00 152.22 999.00 ! 23.74
126 19:37.167 145.40 999.00 146.81 999.00 151.44 999.00 152.47 999.00 ! 23.67
126 19:37.667 145.48 999.00 146.82 999.00 151.44 999.00 152.83 999.00 ! 23.60
126 19:38.167 145.78 999.00 147.23 999.00 151.58 999.00 152.88 999.00 ! 23.53
126 19:38.667 145.87 999.00 147.34 999.00 151.55 999.00 152.76 999.00 ! 23.46
126 19:39.167 145.81 999.00 147.16 999.00 151.48 999.00 153.01 999.00 ! 23.38
126 19:39.667 146.11 999.00 147.33 999.00 152.03 999.00 153.06 999.00 ! 23.31
126 19:40.158 146.42 999.00 147.46 999.00 152.13 999.00 153.00 999.00 ! 23.24
###############################
I know that you and other VLBA experts are very busy, but I think the problem is not
so minor as one might think and perhaps a solution (or workaround) could be priorized a bit more.
kind regards, Thomas
PS: I cc to J. Park, whose projects BP261A&B (in /apr23) is affected by the same issue,
though not so often, as has they scheduled pointing scans less often. Also here, the missing
LCP TSYS will have an effect on the polarisation analysis.
On 09/05/2023 00:17, Jay Blanchard wrote:
> Good question, we have noted that the time it is out for is variable but I don't think we've confirmed that the Tsys always come
> back on the second scan.
> Note the data are ok even when the Tsys are not being calculated (i.e. are 999).
> Also AIPS is aware that 999(.0) is essentially a message saying "This TSYS was unknown and should be ignored".
>
> This if using AIPS to reduce your data and applying a reasonable smoothing for Tsys your calibration should be just fine. Which is
> why this isn't very high priority.
> Does that make sense?
> Jay
>
> On 5/7/23 04:43, Thomas Krichbaum wrote:
>> Hi Jay
>>
>> would it help to schedule a short dummy scan prior to each normal VLBI scan, eg a 5-10s scan using both RDBEs?
>>
>> This dummy scan then would suffer from the lack of good Tsys for LCP but the next (and longer real VLBI scan) should be ok, isn't it?
>>
>> best Thomas
>>
>> Am 07.05.2023 um 06:41 schrieb Jay Blanchard:
>>> Hiya Thomas, unfortunately I wouldn't count on this getting fixed at the
>>> RDBE level, there's simply no development being done there.
>>>
>>> We have attempted to work around this by setting up both RDBEs for the 7mm
>>> pointing scans, i.e. not letting that second RDBE go idle. Unfortunately
>>> we haven't had any luck with that yet (it's not something we've done
>>> historically, so a lot of systems expect only a single RDBE worth of data
>>> during pointing and get 'confused' for lack of a better word).
>>>
>>> We'll keep working it but it's fairly low on the list unfortunately.
>>> Jay
>>>
>>>
>>>
>>>
>>>> Hi Jim,
>>>>
>>>> thx for your response, I hope this issue can be fixed. In the past we
>>>> frequently got questions from the PIs about this issue.
>>>>
>>>> kind regards, Thomas
>>>>
>>>> Am 06.05.2023 um 18:23 schrieb Jim Ogle:
>>>>> Thomas,
>>>>>
>>>>> You are correct that it’s the 3mm scans after a 7mm pointing scan
>>>>> which are affected, the operator has it a bit backwards. It’s going
>>>>> from the single RDBE 7mm scans to the dual RDBE 3mm scans which runs
>>>>> into the problem of the second RDBE not getting set up and sending data
>>>>> right away, leading to those bad Tsys readings. This is a long-standing
>>>>> issue we’ve had with the RDBEs, Jay or Walter can probably provide a
>>>>> better overview of where we’re at with it.
>>>>>
>>>>> Jim
>>>>> VLBA Operations
>>>>>
>>>>>> On May 6, 2023, at 10:06 AM, Thomas Krichbaum
>>>>>> <tkrichbaum at mpifr-bonn.mpg.de> wrote:
>>>>>>
>>>>>> Hi Jessica,
>>>>>> thanks for your explanation, which is interesting. However when I check
>>>>>> the Tsys values in c231acal.vlba,
>>>>>> eg. for FD, I see the following (snapshot below):
>>>>>> at 124 23:16.792 to 23:18.933 there is a 7mm pointing scan on P-Leo,
>>>>>> using 2 MHz filters, all Tsys look ok.
>>>>>> The next scan is a VLBI scan on 1156+295. The scan begins at
>>>>>> 124:23:20:00 and lasts until 124-23:23:00. In this VLBI scan all Tsys
>>>>>> for RCP look good, but for LCP we get 999.00. for all entries. So the
>>>>>> VLBI scan is fully affected.
>>>>>> The next scan again is a VLBI scan on NGC4278 which lasts from
>>>>>> 124-23:24:00 until 23:30:00. In this scan the Tsys for RCP and LCP are
>>>>>> all good.
>>>>>> This behaviour repeats.
>>>>>> So my conclusion is that when a VLBI scan is preceeded by a pointing
>>>>>> scan, the Tsys for LCP are corrupted. When there is no preceeding 7mm
>>>>>> pointing scan, then the Tsys are ok.
>>>>>> I understand that you may not be able to fix this immediately, but it
>>>>>> is certainly a feature to look into after the session is over.
>>>>>> Apparently the DBE2 is not properly setup for 3mm Tsys measurement
>>>>>> when a7mm pointing scans is preceeding.
>>>>>> Here an excerpt from c231acal.vlba:
>>>>>> ! FD C231A P-RLEO/0 124-23:16:32/124-23:19:12 <--- 7mm pointing with 2
>>>>>> MHz BBC
>>>>>> 124 23:16.792 131.48 131.10 130.04 124.66 ! 49.10
>>>>>> 124 23:17.342 130.58 130.40 129.69 125.10 ! 49.21
>>>>>> 124 23:17.867 129.72 130.35 129.09 125.82 ! 49.32
>>>>>> 124 23:18.383 130.82 130.90 129.98 124.68 ! 49.43
>>>>>> 124 23:18.933 130.06 130.63 129.50 128.04 ! 49.54
>>>>>> !
>>>>>> ! FD C231A 1156+295/0 124-23:20:00/124-23:23:00 <--- 3mm VLBI scan with
>>>>>> 128 MHz
>>>>>> ! 1 3mm B RCP 1 U 512.00MHz 128M 86076.00MHz 13.05
>>>>>> ! 2 3mm D LCP 2 U 512.00MHz 128M 86076.00MHz 10.47
>>>>>> ! 3 3mm B RCP 3 U 640.00MHz 128M 86204.00MHz 13.06
>>>>>> ! 4 3mm D LCP 4 U 640.00MHz 128M 86204.00MHz 9.29
>>>>>> ! 5 3mm B RCP 5 U 768.00MHz 128M 86332.00MHz 12.35
>>>>>> ! 6 3mm D LCP 6 U 768.00MHz 128M 86332.00MHz 9.23
>>>>>> ! 7 3mm B RCP 7 U 896.00MHz 128M 86460.00MHz 10.50
>>>>>> ! 8 3mm D LCP 8 U 896.00MHz 128M 86460.00MHz 11.03
>>>>>> 124 23:20.308 150.40 999.00 154.31 999.00 148.92 999.00 135.04 999.00 !
>>>>>> 29.43 <------ LCP corrupt
>>>>>> 124 23:20.900 150.19 999.00 151.45 999.00 145.67 999.00 133.51 999.00 !
>>>>>> 29.55
>>>>>> 124 23:21.500 150.71 999.00 146.17 999.00 141.86 999.00 135.68 999.00 !
>>>>>> 29.67
>>>>>> 124 23:22.100 150.53 999.00 148.70 999.00 143.69 999.00 134.52 999.00 !
>>>>>> 29.79
>>>>>> 124 23:22.692 149.37 999.00 152.45 999.00 146.76 999.00 133.50 999.00 !
>>>>>> 29.91
>>>>>> !
>>>>>> ! FD C231A NGC4278/0 124-23:24:00/124-23:30:00 <--- 3mm VLBI scan
>>>>>> 124 23:24.283 156.26 142.43 160.12 136.82 154.28 147.99 139.95 170.67 !
>>>>>> 26.07 <--- LCP ok, when no 7mm preceeds
>>>>>> 124 23:24.817 157.39 140.45 158.98 137.15 152.68 149.48 140.00 169.99 !
>>>>>> 26.18
>>>>>> 124 23:25.358 157.34 137.45 156.02 137.52 149.86 150.73 139.58 167.72 !
>>>>>> 26.29
>>>>>> 124 23:25.908 155.49 137.83 156.25 135.35 150.07 147.86 137.95 167.35 !
>>>>>> 26.40
>>>>>> 124 23:26.458 153.96 139.66 157.25 134.50 151.45 145.71 137.59 167.56 !
>>>>>> 26.51
>>>>>>
>>>>>> ......
>>>>>> kind regards, Thomas
>>>>>>
>>>>>> Am 06.05.2023 um 14:06 schrieb VLB operators:
>>>>>>> Hi Thomas,
>>>>>>>
>>>>>>>
>>>>>>> I'm currently running part B of C231 and and after careful
>>>>>>> observation, I think I can explain the high values.
>>>>>>>
>>>>>>>
>>>>>>> The 7mm scans are set to only use DBE1, while the 3mm scans use both
>>>>>>> DBE1 and DBE2. During the actual recording scans of 3mm, Tsys for LCP
>>>>>>> at all VLBA sites look excellent. The problem seems to come in when
>>>>>>> the scans switch from 8-channel 3mm scans to 4-channel 7mm scans. Even
>>>>>>> though the setups have changed, Tsys erroneously continue to be
>>>>>>> calculated for 3mm, and since the last four channels (which are the
>>>>>>> 3mm LCP channels) are no longer being used, they get garbage readings.
>>>>>>> There is no actual recording happening during that time--though the
>>>>>>> Tsys values are still being logged--and as soon as the recording
>>>>>>> starts, it seems that all Tsys calculations "clear out" and are reset
>>>>>>> to calculate the correct 7mm values. I can also confirm that the
>>>>>>> 4-channel 3mm Tsys values also look normal.
>>>>>>>
>>>>>>>
>>>>>>> In conclusion, those high Tsys values are simply garbage are not
>>>>>>> associated with actual recording data. It just seems to be an odd
>>>>>>> setup quirk. I hope this is helpful, and sorry for the inconvenience.
>>>>>>>
>>>>>>>
>>>>>>> -Jessica K., VLBA Operator
>>>>>>>
>>>>>>>
>>>>>>> On 5/6/23 04:27, Thomas Krichbaum wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> I just looked at the Tsys in the c231acal file. I realize that the
>>>>>>>> Tsys for LCP is 999.9 for the first half of most VLBI scans at 3mm.
>>>>>>>> Can you check what is wrong and fix it ?
>>>>>>>>
>>>>>>>>
>>>>>>>> kind regards, Thomas
>>>>>>>>
>>>>>>>>
>>>>>>>> Am 05.05.2023 um 17:54 schrieb vlbaops at nrao.edu:
>>>>>>>>> VERY LONG BASELINE ARRAY OBSERVING LOG
>>>>>>>>> --------------------------------------
>>>>>>>>> Project: C231A
>>>>>>>>> Observer: Krichbaum, T.
>>>>>>>>> Project type: GMVA
>>>>>>>>> Obs filename: c231a.vex
>>>>>>>>> Date/Day: 2023MAY04/124
>>>>>>>>> Ants Scheduled: NL FD LA PT KP OV BR MK
>>>>>>>>>
>>>>>>>>> =UT-Time===Comment===============================================MF#===%AD==AMD=
>>>>>>>>> Operator: Alan Kerr
>>>>>>>>> 1600 Begin at EF (and other non-VLBA sites)
>>>>>>>>> 2253 Begin at NL
>>>>>>>>> 2313 Begin at FD,LA,PT,KP,OV,BR
>>>>>>>>> 2313-0003 *BR 7mm dead. WO-17253 FE 50 25
>>>>>>>>> 2335-2347 *BR out for Site Tech to work on antenna. HWA 100 12
>>>>>>>>> 0000 Date is 2023MAY05/125.
>>>>>>>>> 0003-1520 *BR 7mm and HVAC problems continue. Antenna HWA 100
>>>>>>>>> 917
>>>>>>>>> removed from observation.
>>>>>>>>> 0213 Begin at MK
>>>>>>>>> 0555 New operator: Jessica King
>>>>>>>>> 1338 New Operator: Paul Padilla
>>>>>>>>> 1520 End at VLBA sites.
>>>>>>>>> 1524 End.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Downtime Summary:
>>>>>>>>> Total downtime : 954 min
>>>>>>>>> Percentage downtime of observing: 8.5%
>>>>>>>>> Average downtime per hour : 5.1 min
>>>>>>>>>
>>>>>>>>> Total scheduled observing time (# Antennas): 11232 min (8)
>>>>>>>>>
>>>>>>>>> Notes:
>>>>>>>>> * = Entries where data was affected.
>>>>>>>>> % = Entries where data may have been affected.
>>>>>>>>> & = Entries where the site tech was called out.
>>>>>>>>> WEA = Weather entries.
>>>>>>>>> MF# = Maintenance form or major downtime category associated
>>>>>>>>> with a problem.
>>>>>>>>> %AD = The percentage of an antenna affected by a problem.
>>>>>>>>> AMD = Total antenna-minutes downtime for a problem.
>>>>>>>>> Tsys = System Temperature (TP/SP x Tcal/2)
>>>>>>>>> ACU = Antenna Control Unit
>>>>>>>>> FRM = Focus/Rotation Mount
>>>>>>>>> RFI = Radio Frequency Interference
>>>>>>>>> CB = Circuit Breaker
>>>>>> --
>>>>>> Dr. Thomas P. Krichbaum
>>>>>> Max-Planck-Institut fuer Radioastronomie
>>>>>> Auf dem Huegel 69
>>>>>> D-53121 Bonn
>>>> --
>>>> Dr. Thomas P. Krichbaum
>>>> Max-Planck-Institut fuer Radioastronomie
>>>> Auf dem Huegel 69
>>>> D-53121 Bonn
>>>>
>>>
--
Dr. Thomas P. Krichbaum
Max-Planck-Institut fuer Radioastronomie
Auf dem Huegel 69
D-53121 Bonn / Germany
Mail: tkrichbaum at mpifr-bonn.mpg.de
Tel.: (Germany +49)-228-525-295
Web : http://www.mpifr-bonn.mpg.de/research/vlbi
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