[mmaimcal] comments on Al's revised rx specs (and some Stephanes comments)

[Al Wootten]

Thanks for the comments, Steve.
 > > 3.4 Receiver noise performance.
 > > I think that this should be more specific.  Stephane proposed:
 > > '1)  Receiver noise temperature should not exceed (NUMBERS GIVEN FOR Freq.
 > > below 370 GHz) for Single Side Band receivers, 6 h.nu/k averaged over the 
 > > best 80 % of its nominal bandwidth, and 10 h.nu/k at any place in the 
 > > nominal bandwidth for Double Side Band receivers, these numbers
 > > should be halved
 > > ...
 > >  What about sub-mm frequencies. Would 10 h.nu/k be acceptable, conservative
 > > or too difficult ?'
 > > I agree.  In our memo on sensitivity goals, Bryan and I used an equation:
 > > TrxSSB= A * (hnu/k) + 4 K
 > > And for current technology, based on the review at the URSI 99 meeting:
 > > with A = 3 below 500 GHz
 > >      A = 6 for band 9 (602-720 GHz)
 > >      A = 12 for band 10 (787-950 GHz)
 > > 
 > > We suggested goals for these future receivers of:
 > >      A = 3 below 500 GHz
 > >      A = 4 for band 9 (602-720 GHz)
 > >      A = 8 for band 10 (787-950 GHz)
 > > 
 > > I believe that there should be specifications and goals, with achieved receiver
 > > performance to fall between the two.  I think Stephane's proposals are
 > > acceptable for specifications, though I feel fairly confident that better
 > > results may be achieved.
 > 
 > How about:
 >                            SSB hv/k inner / max
 >   Band 1-6 (below 275 GHz)   Spec: A =  6 / 10          Goal: A = 3 / 5
 >   Band 7-8 (275-500 GHz)     Spec: A =  8 / 12          Goal: A = 4 / 8
 >   Band 9 (602-720 GHz)       Spec: A = 10 / 15          Goal: A = 6 / 9
 >   Band 10 (787-950 GHz)      Spec: A = 10 / 15          Goal: A = 8 / 12
 > 
 > I split off bands 7-8 as I think there are still some difficulties doing
 > this compared with the lower mm bands.
Good point.  I think this is right, at the cause of a little complexity.
 > 
 > I like the idea of having the tougher specs in some inner part of the band
 > (Stephane's 80% seems reasonable) - I figure we can live with 50%
 > degradation on the outer bits.  I worry that pushing the 8 GHz bandwidth
 > will be hard enough as is - should we relax the A values a factore of
 > two in those outer 20% even?  Im happy with x1.5 there...
Well, as scientists we should push, so let's go with x1.5.
Tony Kerr thinks that these are very reasonable targets also.
 > 
 > > --------------------------------------------------------------------
 > > Sidebands, IF bandwidths and Simultaneous operation of bands
 > > 
 > > This seems too unspecific to me.  The Munich PDR
 > > (http://www.cv.nrao.edu/~awootten/mmaimcal/ALMA-DesRevRec4.html) said:
 > > In addition to the baseline IF bands of 8 GHz Upper and Lower Sideband, 
 > > receiver designers are free to select any of the following
 > >        alternatives: 8 GHz Single-Side-Band, Upper or Lower, 8 GHz 
 > > Double-Side-Band or 4 GHz Upper and Lower Sideband. In all cases, dual
 > >        polarization for a total of 16 GHz IF band width. Sideband separation 
 > > in DSB-mode will be possible for integration times in multiples of 1 sec.
 > >        Depending on the choice, and maintaining the currently proposed LO 
 > > coverage, this might lead to some loss of frequency coverage. The impact of this
 > >        should be evaluated by the Science Group.
 > > 
 > 
 > It seems you are suggesting the following:
 > 
 >     SSB  1 x SB  2 x Pol = 2 x 8 GHz   ( sideband rejecting )
 >     
 >     SSB  2 x SB  2 x Pol = 4 x 4 GHz   ( sideband separating )
 > 
 >     DSB          2 x Pol = 2 x 8 GHz
 > 
 > Do we allow?
 > 
 >     SSB  2 x SB  1 x Pol = 2 x 8 GHz   
I don't think so.
 > 
 > Is sideband or polarization separation easier at the higest bands?
 > 
 > Also, we should state our goal explicitly:
 > 
 >     SSB  2 x SB  2 x Pol = 4 x 8 GHz   ( sideband separating )
 > 
 > which is what the IF system is designed for!
 > 
 > -------------------------
 > 
 > Looks like we are on the right track...
OK.  I'll revise my notes in accord with your suggestions here--thanks!

Al