Performance of H Maser During the EOC Week – 29 July to 03
August
ALMA Technical Note Number: 6Status: FINAL
Prepared by:

Organization:

Date:

Anthony Remijan (EOC Program
Scientist for Extension andOptimization of Capabilities)

ALMA03 August 2014

Atacama Large Millimeter/
Submillimeter Array
Alonso de Córdova 3107
Vitacura - Santiago Chile

MEMORANDUM
To: DSO/ADE Teams
From: Anthony Remijan, ALMA Program Scientist (EOC), APP Team
Date: 11/16/2014
Subject: Performance of H Maser during the EOC week – 29 July – 03 Aug
Background:
The installation of the H maser provides a new 5 MHz standard for ALMA and enables anotherlarge step toward VLBI capabilities with ALMA. Prior to the activities reported in this memo,
the H Maser installation and testing plan has progressed well, with the following
accomplishments (all performed in coordination with the APP, ADE, DSO and EOC teams):
1. The seismic rack to house the maser in the ALMA LO room at the AOS was installedon May 10, 2014, including all connection for power.
2. On May 11, 2014, the H maser was installed in the maser rack, powered on and testing
began. Testing quickly revealed a faulty micro-controller board, and a new one wasshipped from the manufacturer. The thermal systems on the maser were left poweredon so that the maser could reach thermal equilibrium in the LO room.
3. From June 4-8, 2014, the faulty board was replaced and the maser was brought fully online for testing. During this period, the maser was observed to meet all specifications.
Figures 1 and 2 show the short term stability and phase noise of the maser observed at
this time and the long-term drift with respect to GPS measured over a month. As
shown in Figure 1, some adjustments were required to remove the linear drift in themaser 1pps signal, and some optimization for VLBI may yet be required.
4. Since the June 4-8 campaign, the maser has been monitored daily by the APP team at
MIT Haystack and at the NRAO NTC in Charlottesville. The points/tests that havebeen constantly monitored include: internal and external temperatures, power draw,hydrogen usage, and phase-lock parameters of the 5/10 MHz maser outputs. Over thecourse of the past 6 weeks, there have been no deviations of any of these monitorpoints/tests from the nominal values.
Given the monitoring and apparent stability of the maser over this time, the decision was madeto integrate the maser into the ALMA system during the EOC week starting 29 July. The
decision to integrate at this time was to provide a long period of monitoring the stability of themaser before the start of the long baseline campaign starting in September 2014. In addition,
the integration of the maser should not affect any Early Science observations over the course ofthis time so additional tests were performed to ensure the maser performance on ESscheduling blocks.

Figure 1: Long term comparison of Maser-derived 1pps and GPS 1pps. Colored values show the offset in time
between Maser and GPS 1pps ticks after the drift rates shown have been removed. Diurnal variations are due toionospheric changes that affect GPS signal propagation. Times marked by ‘#’ characters indicate when the maser
synthesizer was adjusted to remove the measured drift rate. At the current drift rate, the maser will deviate fromGPS by less than 7 ns per day.

Figure 2: Short term stability and phase noise of the Maser compared to an Oscilloquartz 8607 crystal. (left)
Allan Deviation plot showing adev ~ 1.3e-13 at 1 second integration time. (right) Phase noise plot showing -122
dBc/Hz at 1 Hz from the 10MHz Maser signal. Both values are within VLBI specifications. Data taken 9 July 2014.

Test Plan and Results:
On Tuesday, 29 July 2014, the APP team with support from EOC, ADE and ADC integrated
the new H maser into the ALMA system. A detailed hourly test plan was reviewed and enacted
by members of the APP/EOC/ADE and ADC teams 1. As part of the maser integration test
procedure, three distinct tests were done before and after the integration to test the initial
performance of the maser. They are listed below:

1

Hourly integration plan can be found at:https://wikis.alma.cl/twiki/pub/AIV/EOCMemos/EOC_Memo10_Jul25_FINAL.pdf

1. DelayCal.py was run in TDM mode on 3c279 (or comparable quasar with adequate fluxdensity) over the course of ~30-45 mins to look at the overall phase stability vs. time.
2. DelayCal.py was run in a high resolution FDM mode on the v=1, J=2-1 transition of SiOtowards VyCanis Majoris to determine if there is any evidence of line broadening.
3. A similar, high spectral resolution observation of an ES program was run to test the“end to end” performance of the maser. A thorough QA0/2 was performed on thedataset to ensure the data quality.
Full instructions to run both the DelayCals and the ES observation are available on the EOC
weekly top priority page available at: https://wikis.alma.cl/bin/view/AIV/29July05Aug%2c2014. Furthermore, the uids of each test are recorded in the work log of thefollowing JIRA: http://jira.alma.cl/browse/CSV-3107. Below we summarize the results.
DelayCal on bright quasar:
Data obtained using the Rubidium Standard:
DelayCal.py -b 6 -P 4 -d 600 -r 3 -s 3c279 --wvr --wvrSkyCoupling <-- NB: 3c279 notobservable; replaced with J0522-364

Data obtained using the H maser:
DelayCal.py -b 6 -P 4 -d 600 -r 3 -s J0522-364 --wvr –wvrSkyCouplingConclusion (Paraphrased from Sawada-san comments from CSV-3107):
Above are the plots from the 0522-364 datasets uid://A002/X88151d/X5 (after) and
uid://A002/X87f18c/X1f71 (before). The WVR-corrected phases of the channel-averaged
visibility in the baseline DA41-DA47 (102m) are shown; colors represent SPWs (basebands),
only polarizations XX and YY are shown among the four products. Obviously the phasestability is poorer in the data collected with the H maser compared with the Rubidium
standard. Perhaps it is accounted for the poorer atmospheric condition, although the plots
shown above are already WVR-corrected. Also shown are the WVR channel 3 amplitudes
which clearly illustrate the much more unstable conditions from the data taken with the H
maser. Therefore, the fluctuations in the phase vs. time are easily attributed to the moreunstable atmospheric conditions and not the H maser.
DelayCal on the SiO maser transition toward VyCanis Majoris:
Data obtained using the Rubidium Standard:
DelayCal.py -r 10 -b 86.2433e9 -d 300 -n FDM -w 16 -s 'vy_cma'
Data obtained using the H maser:
DelayCal.py -r 10 -b 86.2433e9 -d 300 -n FDM -w 16 -s 'vy_cma'Conclusion (Paraphrased from Remo and Tim’s comments from CSV-3107):
The data were analyzed before and after the installation of the H maser. The figure aboveshows and overplot of the SiO maser feature using the longest baseline (DV24-DV21). There isno evidence of broadening of the spectral feature before and after the integration of the maser.
The SiO spectral feature complex are reproduced with the same width, albeit with a slightly
lower amplitude after the install of the H maser compared to before. This is easily attributed
to a difference in amplitude gains (i.e. the data were not properly amplitude corrected). After
applying a constant factor of 1.2 the data with the new maser reproduces the feature almost
exactly. Furthermore, the data from all the other antennas were inspected and no evidence ofline broadening was found anywhere. Therefore, there is no evidence of spectral line
broadening with the new H maser standard and the amplitude fluctuations between the 2 daysis easily attributed to the unstable atmospheric conditions and the lack of proper amplitude
calibration.
High spectral resolution observation of an ES program:
In order to test the maser performance on an ES project, in coordination with DSO, EOC
observed the following SB: Name: g19.61-0_a_03_TE of Project: 2013.1.00266.S. This program
was chosen specifically for its LST range and for its high spectral resolution setup. The full data
reduction using the procedures for QA0/2 outlined for by hand data reduction were followed
and the data reduced in the standard way.

Data obtained using the Rubidium Standard:
40 minutes
Project: 2013.1.00266.SSB Name: g19.61-0_a_03_TE
ExecBlock uid: uid://A002/X87c075/X2cd9
Data obtained using the H maser:
40 minutes
Project Code 2013.1.00266.S
SchedBlock g19.61-0_a_03_TE
ExecBlock uid://A002/X883455/X12f

Conclusion (Paraphrased from Brian and Tony’s comments from CSV-3107):
The above figures show the spectral line profiles of the SiO J=2-1, v=1 transition (86.24337
GHz) and the 2-1 transition of CS (97.98 GHz) toward the high mass star forming region
G19.61-0.24A. Again, adjustments in the overall amplitude were required because:
1. the selected region to view the spectral profile were not precisely consistent between
the before and after maser installation datasets
2. the image was not cleaned and the beams were not identical for the before and after
maser installation datasets showing the spectral line profile.
3. the overall distribution of CS and SiO are much different which directly relates to thedifference in scaling factors derived for each dataset.
However, as previously shown, no line broadening or any other issues were found in these datathat can be attributed to the new H maser standard. Therefore, no issues in the ES collected in
the standard way using the CYCLE2_ON control software were found using the H maser.
Conclusions:
Since the initial tests, EOC has used the H maser standard for testing during the high frequency
campaign and to characterize the baseline lengths and other tests. In addition, ADC has beenusing the new H maser standard since Tuesday, 29 July for the subarray mission of the 2014.2
control software. During this time, the subarray mission has successfully performed tests using
4 subarrays and EOC has collected data using manual scripts to scheduling blocks ranging frombands 3 to bands 10. We have found no indication of any lack of performance or anomalies
found in the data that we can attribute to the new H maser standard.
Therefore, it is the recommendation of EOC and APP teams to DSO and ADE to leave the new H
maser integrated into the ALMA system as the new 5MHz standard from this point forward.