Subject:Re: OSF Holography Telecon, notes from meeting From:Jeff Mangum Date:Thu, 11 Aug 2005 14:22:21 -0400 To:Darrel Emerson Some action on my action items... Darrel Emerson wrote: > d) Jeff Mangum will look at the APEX holography measurements. > Reflections may be an issue - would this be better or worse > with a mountain top transmitter? Do we need 2 frequencies? > Communicate with the rest of the group, but especially to > Antonio. Robert and I have discussed the two-frequency question. Here is the answer (as I described it to Robert just a moment ago): I dug through the old (2000) CDR material for the prototype holography system. Looking at Larry's overview presentation (see http://edm.alma.cl/forums/alma/dispatch.cgi/2002pdrbackend/docProfile/100485/d20021106225052/No/t100485.htm), it says the following: "Two new requirements have been added since the PDR, and both make it necessary to operate on more than one frequency. First, we want to have a secondary frequency that is sufficiently separated from the first to allow verification that frequency-dependent effects in the data processing have been accurately taken into account. Specifically, this includes corrections for diffraction from the subreflector support legs and other antenna structures; and corrections for the fact that the transmitter will be in the near field. Second, since the transmitter will be at a relatively low elevation angle, we would like to have a way to remove the effects of multipath propagation. This can be done if the frequency is varied a few percent from nominal (see section 4.3.2, below)." So, this is what we have: 1. Since the data processing issues which necessitated the second band were checked during the prototype holography process, the need for the second band is eliminated. 2. Since we still may need to deal with reflection characterization, we still need the tuning capability about the single frequency band we will have. No word from APEX yet regarding reflection that they may have measured during their holography measurements. Cheers, Jeff > > e) Tower siting, assuming there will be a tower. Darrel > continues to work with Eduardo, with latest input from > Rick about the Vertex and Mitsubishi site facilities. > > f) Brian will make sure Robert Lucas knows about the > new holography data format. Robert will adapt his > analysis software to this. > > g) Dick Sramek will put into the PSI plan, the intention > to test the revised holography system at the ATF. > > h) Rick, Schedule and milestone plan. A continuing task, but > Rick will in particular get better information from > Antonio. > > i) For everyone: another telecon to confirm progress > will be held in about one month (i.e. end of August). > > > ...and to my remaining action item (regarding any noted reflections in APEX holography)... Darrel Emerson wrote: > > d) Jeff Mangum will look at the APEX holography measurements. > Reflections may be an issue - would this be better or worse > with a mountain top transmitter? Do we need 2 frequencies? > Communicate with the rest of the group, but especially to > Antonio. > Peter Schilke tells me the following: "As you know, we didn't have the same system as you, we observed with the subreflector, and had the main receiver in the receiver cabin. Reflections didn't seem to be important (we checked that by changing the focus), but of course were affected by diffraction by struts, subreflector, and entry hole into the receiver cabin." So, it seems that external (i.e. ground) reflections were not noted, but it still seems prudent to include the capability to investigate any suspected reflection signature by building frequency tuning capability into the production holography system. Cheers, Jeff