Attendees: Ellison (RAL), Harmen (RAL), Lamb (OVRO), Lazareff (IRAM), Payne (NRAO), Plambeck (BIMA), Rafal (NRAO), Sekimoto (NRO), Wade (ESO), Webber (NRAO), White (NRAO), Wild (NOVA/SRON)
- Heat Load Estimates - Report is almost finished. All felt the meeting in Rutherford went well. Payne sent Andersen the radiation load estimates. Harman is expected to conduct the provisional structural heat load test.
- Plambeck has submitted the Calibration Report - The ASAC has set the calibration to be 1%. Is this a reachable goal? Practically not, but should be we try anything else to become closer to reaching this goal? The ASAC did recognize that one percent was a bit aggressive.
Comments:
Could we have an individual tau measuring mean?
We need to look at the global problem of calibration. Compare both schemes in further detail. In my experience, I support Plambeck's conclusion to stay away from cold loads.
In the test run, assumptions included some gain compression on the SIS mixer.
Webber spoke with Kerr on this. Kerr believes this is also on track and is what would be expected.
If one suffered from gain compression, it may change your decision.
There may be problems with one dedicated device measuring the atmospheric temperature on all 64 antennas. No one is quite sure if the atmospheric temperature is the same across a 10 km array.
We need to decide how much effort the receiver group should put into trying to get to this one percent.
To what extent is tau related to water radiometry?
We have had extensive discussions on cold load. It will be better if everyone knows that it is built into the water vapor radiometer. However, it is still open for changes.
- HFET Performance Report - Webber has sent out. The report concludes: limits on timescales to 3 x 10^-4 in tenmillisecond; noise level is much higher (1 over bandwidth); and HFET is ten times more than SIS receiver.
In order to make progress, we need to: 1) Look at SIS receiver especially at wider bandwidth detectors; 2) in either scheme, the sensitivity is so much larger we need to tell ASAC to build a more complex receiver.
Has there been a fixed tune SIS mixer on the 3 millimeter band? And if this is true, we should go to the SIS mixer.
- Thermal Link Report - The draft thermal link report has been done. Will add some new items and figures and publish as a report. Expect to have results in testing done soon.
- Dewar - Changes in the dewar design include: refining the design with an optics scheme. Currently the design is coming in from the top. We are moving the window positions around. Will publish a new drawing in a couple of weeks.
Discussions on antenna interface have been on-going. We can get the proposed dewar through the door and rotate as well. We need to: 1) provide an up-to-date space requirement and 2) define the sets under the receiver and claim this area via an updated ICD.
- Optics - delayed.
- Cryogenics - A geometric model is being built with correct fixtures. Expect results from this in a couple of weeks. Need a nine-month lead and we should press on quickly.
Payne would like for us to revisit the reason why the pulse tube cryocooler is sticking our the side of the dewar. Discussions went on about this.
No cold load.
Optical alignment was discussed back in April. However, in the meantime changes were made. We need to look at how we are going to re-establish alignment.
- LO - Measurements on 80 GHz LO driver. Short-term phase noise and long term phase drift. There will be a memo out in two to three weeks.
Measurements of the first of a new series of frequency multipliers were carried out. This frequency doubler is nominally centered at 110 GHz input frequency. Since we do not yet have a power amplifier for this band (one is coming from JPL as part of our collaborative effort), the 110 GHz doubler was severely underdriven, resulting in low output as predicted by the model. Nevertheless, it produced peak power of >2 mW and produced sufficient power to drive a single-ended SIS mixer (in excess of 200 microwatts) from 204 to 232 GHz. Plans are being formulated to use this LO source with an SIS mixer in order to measure its amplitude noise characteristics.
Group is looking carefully at the LO multiplier technology. The JPL technology for multipliers above 300 GHz is extremely good, however their cycle time is too long (~1 year). Looking at other options. Have had discussions with Jack East of the University of Massachusetts. They can provide us with a similar product on a cycle time of about two months.
Good results from 25 - 110 GHz photo diode detector. Waiting to hook it up in Tucson to get true test results.
Next JRDG Meeting will be July 27.
Topics for the next face-to-face meeting will include optics. Possible date for meeting August 7-8.
HFET performance: An analysis and report on the suitability of the amplifiers
for ALMA
Who: John Webber
When: June 30, 2000
Review decision on cold load
Who: All
When: Immediately
Circulate table of contents for receiver chapter
Who: John Payne and Wolfgang Wild
When: ASAP
Carter to publish drawings with a designed out cold load
Who: Matt Carter
When: July 3, 2000
Plambeck to publish calibration memo
Who: Richard Plambeck
When: July 15, 2000
Coordinate with systems group on decisions that receiver group has made
Who: John Payne and Wolfgang Wild
When: July 27, 2000
Review independent tau measuring device
Who: John Payne and Wolfgang Wild
When: July 27, 2000
Specifications on the what the receiver needs to control and what it
does not need to control
Who: Brian Ellison
When: July 30, 2000
Draft Receiver Cartridge ICD
Who: John Payne
When: July 30, 2000
Polarization Issue: Analysis about the impurity on the mirrors.
Who: Peter Napier, James Lamb, Stafford Withington
When: TBD
Minutes recorded and submitted by Carolyn White