IF BW EXPANSION PROJECT

Purpose:
 
   Provide a parallel IF/LO system for the large telescope, with
   instantaneous BW of 4 GHz, tunable to provide overall coverage
   from approx 2 GHz through X-band.  This system is needed to take
   good advantage of the impending 4-8 GHz receiver as well as other
   planned telecope improvements in the future.
   
   The existing IF/LO system will remain in place for the indefinite
   future as backup and to satisfy the needs of those users who are
   reluctant to switch horses in mid stream as well as of those users
   of the lowest-frequency receivers.
   
   NOTE: This project as defined for cost/labor estimates includes
   getting a collection of six 3-5 GHz signals down from the dome.
   What happens to the signals next is addressed by a separate
   discussion hereunder (Tail End Matrix...).

Current Status:

   NOTE: One significant change has occurred to the architecture
   of the WBIF system, inspired by Phil's suggestion.  Instead of
   operating in full parallel with the legacy system, the WBIF will
   now operate as a switch-selected alternative to the front end of
   the legacy system.
   
   The necessary redesign and analysis of the upstairs portion of
   the system has been completed.

   Just about all of the RF components for the upstairs portion have
   now been ordered and most of those parts are on hand, with the
   remaining ordered parts expected to arrive within a couple of
   months (most sooner).  

   Additional thought and analysis has been given to the seemingly
   unrecognized downstairs portion of the WBIF system, but the
   detailed design has not yet commenced.  I'm effectively treating
   this as a sort of skunkworks project.  It's identity seems to
   have gotten lost in translation between the material I submitted
   for the supplemental proposal and what eventually came back as
   supported projects.  At the moment I'm concentrating on getting
   things to the point where our new technician can begin building
   the upstairs part.
   
Remaining Tasks Breakdown:
   
   > Identify a workable location & physical configuration in the
     dome.  NOTE: a small portion of this system is expected to
     share space in the existing "RF selector switch" chassis
     (really a 'converter selector').
     In its currently-unused "6th position" this switch will switch
     the RF signal into the new WBIF system.
     
     I am all but convinced that the best route will be to put most
     or all of the upstairs system in the left-hand blue rack in
     order to minimize RF cable lengths.  A minimum goal is to put
     everything through the 2nd mixers in the left-hand side.  The
     reflection coefficients of available components (even "high
     quality" attenuators) at the RF & 1st IF frequencies are high
     enough to lead to appreciable passband ripples, and I want to
     make these as coarse as possible through cable delay control.
     
     See appendix 1 ("Rearranging the Blue Racks")
     
     I am currently in the early stages of doing trial layouts (in
     CAD) of the RF components in realistic chassis models in order
     to convince myself that it will all really fit.
     
   > Build a thermal test chassis to verify that my thinking about
     how to adequately cool the 2nd mixer chassis is valid.  This
     chassis includes three power-hungry frequency synthesizers
     for the 2nd LOs, and must dissipate something like 100W total.
     
   > Choose/order remaining parts: RF cabling, power, cooling, and
     packaging-related.  Specifying RF cables and finding a quality
     vendor is likely to be a particularly time-consuming aspect of
     this.
     
   > Develop a power monitoring scheme.  I think it's perhaps time
     to do something new here to replace the expensive Agilent power
     meters that we currently use for such purposes.  I'm thinking
     of COTS ICs whose outputs are measured with a small A/D
     converter (probably part of a common microcontroller chip).
     
     As I see it there is little need for high accuracy- I view this
     as a system to get the levels in the ballpark, with final
     deternmination for setting being done by checking the A/D levels
     in the individual backend (rDBE, PUPPI, or whatever).   
     
   > Design the control hardware for two step attenuators and for
     the three 2nd LO synthesizers and the level monitoring A/D.
     
     This is a subtask beyond my current capabilities, for which I
     must assume support from someone like Luis Quintero.
   
   > Build, test, and revise (if needed), the "upstairs" portion
     of the system in the lab.   

   > Modify the "RF selector switch" chassis in the dome (may not be
     needed, depending on how things fit otherwise).
 
   > Install and commission the added "upstairs" portion of the
     system.
   
   
   
"TAIL_END" IF MATRIX SYSTEM:

Purpose:

   This is the "skunk works project" referred to above for doing
   something with the six 3-5 GHz IF signals brought down from the
   dome by the "IF BW Expansion Project".  

   This system will handle distribution of IF signals from various
   sources (various receivers on the 305m system and however many
   12m UDCs we have) into all sensible signal "sinks" (WAPPS/PDEV,
   PUPPI, rDBEs, etc) considering bandwidth requirements etc.
   
   See 'Main_IF_Matrix_8-rDBE.pdf' for a (strangely-musical) drawing
   depicting the possible interconnections, with colored dots
   indicating those cross connections that seem sensible to me.
   Also see 'IF_Matrix_Explanation.txt' for more info about how
   the paths are to be formed.
   
   Some of the paths are "straight through" in the sense that they
   do not require frequency conversion; however many other paths do
   require frequency conversions (generally including bandpass
   filtering as well). 
   
   Note: while I think it's important to design this pretty thoroughly
   in one blinding flash of effort, the implementation could probably
   be piecemeal as needs (and suitable backend hardware) arise.  This
   is how one might keep a fairly low profile budget-wise.  
   
Current Status:

   I have prepared the aforementioned 'musical-looking' interconnection
   diagram which attempts to empower the determination of needed
   signal paths.  
   
   I have also put together a spreadsheet based on a very quick design
   effort (done for the supplemental proposal) to the component level
   of detail, so I could make some meaningful estimate of parts costs. 
   I emphasize that this is not yet a polished design.  I attempted to
   include sufficient complexity and detail to avoid the most obvious
   traps and leave some room for tweaking without risking big surprises
   in the cost department.  
   
Remaining Major Tasks (excluding the 'WB IF -> WAPPS/PDEV'):
   
   > Design detailed RF system, specify/choose/order parts.
     NOTE: Estimated parts cost is ~$70k
   > Determine where it will fit (WAPPs room?), devise packaging and
     cooling scheme, and specify/order those parts including power
     supplies. 
   > Design & program local controllers for RF switches, attens, &
     synthesizers.
   > Build hardware.
   > Test/revise system.
   > Install system.
   > Perform software integration of this system into the observatory

  
  
APPENDICES

1. Rearranging the Blue Racks 

     Last week (approx 24 Oct) I studied the situation in the dome
     at length, and the first thing I found was that there is no way
     to do this without considerable rearrangement of existing stuff.
     I propose to move most or all of the relay drivers and other
     non-RF chassis over to the right-hand rack.  Still allowing for
     running 2nd IF (3-5 GHz) across racks, this will fill up the
     right-hand rack and will also require deleting JHU/APL's RF
     power meter (used during our special S-band transmissions to
     illuminate the moon for LRO).  Even so this is all going to be
     a tight squeeze and may require locating power supplies for the
     WBIF stuff outside the blue racks.  This would be a headache
     from the RF shielding perspective, but is at least straight-
     forward in theory.
     
     Doing this will require extensive recabling of GPIB and other
     cables in the two racks.  I plan to do this with a series of
     cable extenders so that these may be checked out ahead of the
     big move, then preinstalled in the shielded guide now running
     between the racks.  The idea here is to do the rearrangement
     in a series of sufficiently small steps that each may be
     easily done in a single day's maintenance period with very
     little risk of leaving the observatory inoperative at the end
     of the day.
     
     An important precursor to all this will be to clean out the
     incredible rats nest of overly-long existing non-RF cables in
     the back of the left-hand blue rack.  I'm convinced that a large
     part of the mess comprises AC power cables, and these should
     be replaced by new cables of minimal length and minimal wire
     gauge.  Again, this can be done in little bits and pieces so
     as to avoid risking observatory operational integrity at the
     end of each working day.  I'd like to see this effort commence
     ASAP.