MINUTES OF JOINT RECEIVER DESIGN GROUP (JRDG) MONTHLY TELECONFERENCE

2001-Apr-26

Chair: John Payne

Attendees: Emerson (NRAO), Harman (RAL), Lamb (OVRO), Lazareff (IRAM), Payne (NRAO), Webber (NRAO), White (NRAO), Wild (RUG)

Total Power Stability Issue

Members should have read memo 131 before attending the meeting. Payne believes this is one of the most difficult specifications set by the ASAC. Payne wants the JRDG to make a formal recommendation to the AEC on this issue. Wild reminds us that the 10^4 is not a specification but an ASAC desire and we need to make a clear definition of this in the specifications. The question remains, "what would be a good number?" It is hard to set. Webber states that to set the specification we need numbers for several time scales. The group agrees. Payne suggest that we send a recommendation to the AEC stating:

In view of the fact that the total power stability desired by the ASAC is likely to affect both the difficulty and expense of producing the front ends for ALMA the JRDG would like to request the following:

  1. That a more precise definition of what is required be produced. It would be desirable to have the astronomy requirements stated clearly and from these and estimates of atmospheric contributions come up with the desired power spectrum of the total power fluctuations. Maybe all these things are buried in the project documentation somewhere but if so are poorly documented and this needs to be clarified.
  2. That the project management allocate the resouces to investigate the ALMA front end stability experimantally. This is difficult to achieve as any experiments need to be as close to the final ALMA recievers as possible. Nevertheless useful information could certainly be gathered by a series of carefully planned experiments. We would not care to begin even the planning of such experiments without a committment from the AEC that such a course of action would be supported.

Group agrees that this is a good statement to send to the AEC. Members want to make sure that the AEC ask the ASAC to do the necessary research for the desire and that the AEC allots enough resources to do the correct measurements to be able to set the specifications. The desire (science they want to see at the end) of the ASAC should be known, but they should allow the Front End engineers to state how this is going to be done.

Emerson joined the meeting to try and explain where the ASAC 10^4 desire had originated. He also noted that these numbers will vary depending on the atmosphere in this frequency. Emerson answered questions from the JRDG members. He also stated that the ASAC sees this specification as very important for specific types of observing.

More information is needed before the JRDG can actually make a decision.

TBD Items

Wild revised the Front End assembly specifications according to our previous meeting. To review what has been added/changed, review the change record at the beginning of the specification.

Miscellany

There is no currently scheduled meeting for May.

Minutes recorded and submitted by Carolyn White