Carilli's notes VLA-VHF PDR, January 28, 2005 Charge to committee, Agenda and presenations can be found at: http://www.aoc.nrao.edu/~ccarilli/VHF.shtml These notes only capture the discussion and questions and recommendations of the committee. 1. Intro - Carilli - introduce folks 2. Charge - Ulvestad - emphasized evaluating impact on EVLA/NRAO 3. Overview - Greenhill: a. science D array - 50 hrs for (admittedly unlikely) cold IGM, then large proposal for warm IGM. Notes collecting area = MWA. Ulevstad pointed out that delivery date of mid Feb ffor first 2 units may collide with moving modcomps, for which the array is down from Feb 14 - 17, so we gotta coordinate. Pat says it might remain difficult for two weeks but ken says it should be ok. Blundell said it is probably OK, since initial testing and installation may not require connection to modcomps. b. technical and interface Kimberk presented design overview and VLA interfaces Thunborg - Why remove paint? answer: better mechanical connection Napier - UV performance of dielecr - Kim - very good Napier - peter asked about the (possible) switch for shorting dipole to (possibly) mitigate affect on P band, and how it is activated. Merteley says there are two free cables to focus barrel. Sowinski says that there is a free controlable bit that could be used for this purpose. Napier recommended testing the effect of shorted dipole on P band in lab at SAO. Owen expressed concern that the 10% effect on P band was not acceptable. Owen also said that a permanent mounting was vastly preferable for a number of reasons, scientifically so that we can switch quickly between 74 or 190 or 327. Durand asked about VLBA compromise = extendable dipole or spacer - not desirable, since performance is lousy at both frequencies due to focus losses. blundell - could get 2 sets of dipoles - one shorted, one open SAO bench testing - LNA, noise diode stability, gain stability, beam pattern, pol purity, couple ant-Rx, DNR, power, RFI Napier - bandpass filter after LNA? tong says should be ok Clark - changes necessary for EVLA antenna? signal path transparent, but are levels same? Someone noted that other bands will have same problem. Butler - problem is will we get EVLA back into array before D array - could be down to 23 antennas. Greenhill says that the first D array is really test for large proposal, and to rule-out cold IGM. so probably OK. Sowinski - lightning protection. Kimberk - they talked to NRL folks, and use same solution as 74MHz. there is diode at input to LNA. Durand - wants 1 spare in lab at all times for testing in case something goes wrong in field etc... he also wants to repeat some basic bench testing in lab here before installation, and to get documenations on SAO testing. 4. Testing: manlift work at night - no prohibition clark - be good to have shorted dipole or switchable right off to avoid having to repeat testing for effect on P. Napier -- can we take feed on/off telescope without going into barrel - Kimber - yes, but gotta watch electrical contacts, and push wire back into tube. Perley - can we get the subreflector further back? no debate: does feed move with subreflector? yes + barrel perley - can adjust various spacings to possibly get best performance? possibly? Napier - big issue is finding test time - old days could steal antennas, no way now. can we fit it in? how feasible to have eg EVLA and this in parallel? eg. collide in control room and using vla computers. answer: Sowinski - single dish OK. interferometer - line vs continuum mode might be issue -- we will have to be flexible. Clark - why do we need to do interferometry for P/L tests? on/off on cygnus a with S/D - G/T change (source/system) question - stability over 1hr. Perley says probably too hard with S/D Owen - detailed accounting of testing time required. Napier - how many test sessions at night with access to correlator? van buskirk - 3hrs sometimes available, but cannot commit Owen/Napier - both recommend strongly that we present results at test meetings, and in test memos, and eventually in observational status summary so as NRAO can properly evaluate, and for future use by user community. Thunborg - want is weather protection of SAO connectors (20yr field lifetime, and can they fit through the tubes -- noted the bolts on the end. Kimberk says removable, but are the bolts there for a reason? --------------- End - my take on main issues so far: 1. scheduling test time around EVLA, astronomy- cannot remove ants from array. 2. P band effect: on/off with/without short - send 2 dipoles 3. SD vs interf tests 4. Thorough memos on test results and eventually OSS input in particular for go/no go decision 5. single dish tests - hard but possible 6. scheduling issues: getting the test time is main issue 7. Staffing - Add RFI engineer for RFI testing/analysis 8. Strapping S/A on antenna over night is OK + 1 engineer day 9. NRAO wants 1 spare in general 10. NRAO wants 1 or 2 days in lab to plug it all in and make sure it works with SAO engineer - repeat some of the basic bench tests 11. NRAO wants some documentation on SAO bench test results ---------------- Committee summary and discussion: 1 All conclude -- NRAO should try to make it work. Exciting stuff and sound proposal/plan. 2 no show stoppers, but very challenging 3. techinical looks ok (like P,4) -- main issue is impact on other bands, in particular at P band (0.5 bd not good) recommend - do the lab test with short/switch and deliver set shorted and normal dipole 4. SMA connector - weather protection of demountable connection (20 years), and clearance through tube 5. test plan looks good and thorough Main concern - availability of VLA test time? need: more detailed test plan with hard numbers: example test plan -- Greenhill, Carilli, and VLA scheduler Can we slip testing later - won't help unless go to June? or extend B by week? what is fastest we can do this: 1 or 2/maint day can we install on non-maint days? test plan is 'success oriented' - prioritize tests can SAO come up with 20k for hiring techs to install? hit it hard in CnD to avoid schedule conflicts, but then bottle neck is cherry picker, and ant mechs. 6. implementation - reasonable - operational spare (debugging) - man power - success oriented (no redesign or retesting) - main risk - may take longer, not go down - 40 hrs overtime techs/mechs 7. turnover to NRAO: - need proper MOU w. top level statements - want to see through to completion w/o SAO pulling out, once go decision is made. who makes go/no go decision -- NRAO and SAO - what is cost of operating new band? -- not critical -----------------------