Minutes of Joint Receiver Design Group (JRDG) Monthly Teleconference

15:00 UTC, 27 April 2000

Attendees: Andrey Baryshev (SRON), Viktor Belitsky (OSO), Matt Carter (IRAM), Charles Cunningham (HIA), Darrel Emerson (NRAO), Mark Harman (RAL), James Lamb (OVRO), Bernard Lazareff (IRAM), John Payne (NRAO), Dick Plambeck (BIMA), Marc Rafal (NRAO), Yutaro Sekimoto (NRO), John Webber (NRAO), Carolyn White (NRAO), and Wolfgang Wild (NOVA/SRON)

John Payne welcomed everyone to the meeting. He hoped everyone had had time to review the material that had been sent out.

Since the meeting in Charlottesville:

• The ASAC report was sent out. This stated that there will be four initial receiver bands. It also details a very tight schedule for the group to work on.
• Payne proposes that the group have formal monthly teleconferences. A firm agenda will be agreed to beforehand. Minutes will be kept; they will be distributed to members via email and published on the NRAO and ESO ALMA web sites.
• The group agreed to meet the last Thursday of every month at 1500 UTC.
• An email exploder is being set up for different groups for discussions that cannot be carried out in detail in these meetings. The list of possible exploders, along with instructions, will be sent to the entire ALMA group.

Update of Ongoing Work

Optics Design: The number of focusing mirrors on the cryostat includes one on the inside and one on the outside for access to bands 3-10. Bands 1 and 2 will need a flip-out mirror. The tolerances and losses seem to be tight, but reasonable, according to the first draft calculations made.

(Q)If the door is equal to 1 meter according to the figures shown, won't this be an awfully tight fit?

(A)The 1 meter figure for the dewar diameter was only a nominal figure given during the Charlottesville meeting. The actual size is closer to 975 millimeters.

(Q)In Charlottesville, the cartridge statement was 170 millimeters, now we are seeing a number closer to 150 millimeters. Why the change?

(A)The layout in the Charlottesville design was optimized to use the area fully. After some rework, we have tried to revise it and allow some room for adjustments.

(Q) Can we live with the 150 millimeters?

(A)Yes on both the European and U.S. sides; however, the Japanese design is tight. The feeling among the receiver group is the bigger the better.

(Q) Does the 1 meter space clearance take into account for hinges, etc.?

(A) Payne will review this again, but we believe so.

(Q)If the design of the cartridge allows for self-aligning, which is a novel idea, but uses up a lot of space, should we maybe use a simpler idea to reduce space? From the NRAO experience, once the 'rockets' are working, they rarely fail.

(A)The self alignment is a manufacturability benefit. Because this is such a large dewar, we will see a lot more radial contraction. This is more of a fundamental issue. Also, if we don't have the self-aligning links, then we will have to use something else. At the moment, we don't have anything else to use.

(Q)Costing question? From the diagrams and material it looks as if we need ~1600 links? What is the cost for this?

(A)It is approximately ~150 pounds/link. However, with some more optimization of the design, we will not need the whole 1600 links.

(Q)Are there ways of producing a non-thermal link? And have they been investigated?

(A)Other ideas have been considered, but we choose to use the thermal link.

(Q)With all the curves and turns, will this be expensive to manufacture?

(A)These are being manufactured and the companies describe it as an easy tooling job. Actually the mass quantity makes it less expensive per unit.

(Q)Will there be a design-in for lifting the dewar onto the antenna?

(A)Documents have been published, but work still needs to be discussed with the antenna division.

(Q)Does the receiver have to provide the calibration?

(A)This will need to be defined and should be added as an action item.

(Q)The ASAC report stated that the cold load should not become a driving force in the design of the receiver. Why are we placing emphasis on this?

(A)The current design has available two cold loads, but you do not have to use them.

Receiver Baseline Design:

The appendix to the agenda represents a change in receiver design. The following is proposed:

• We eliminate the provision for Martin Puplett interferometers in the dewar design.
• All cartridges may now be supplied with LO power through the bottom of the cartridge. In the case of the multiplier approach, the input will be W-band waveguide with the final multiplier at 15K. Optical LO insertion into a WG hybrid is another possibility.
• The baseline for lower frequencies is sideband separating mixers (with DSB mixers as a fall-back position), and for higher frequencies a balanced DSB configuration (with single-ended DSB mixers as fall-back position).
• The group agreed with these proposals and has formally agreed to eliminate the Martin Puplett interferometers in the dewar design.

Have 5 LO drivers for the cartridges. Some would be shared among other cartridges. Bradley at the CDL has been looking into this. The other possibility is to have one driver for each cartridge. The machining techniques have increased dramatically and should not be of concern.

Action Items

• Rutherford needs an accurate estimate of the heat loads on the various cryogenic stages.
  Who: Payne
  When: June 01, 2000
• The calibration question needs to be settled
  Who: Richard Plambeck
  When: June 30, 2000
• HFET performance: An analysis and report on the suitability of the amplifiers for ALMA.
  Who: John Webber
  When: June 30, 2000
• Thermal link justification report
  Who: Mark Harmen
  When: May 19, 2000

Dewar/Antenna Interface teleconference will be setup between the antenna group and a subset of the JRDG. Any questions, comments, etc., about the antenna/receiver interface should be directed to:
U.S. - John Payne
Europe - Wolfgang Wild

Minutes recorded and submitted by Carolyn White
27 April 2000