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

[Steven T. Myers]

> --------------------------------------------------------------------
> 3.2 Polarization
> The ASAC report at
> http://www.cv.nrao.edu/~awootten/mmaimcal/asacreport/node12.html
> needs to be made more specific.  Steve Myers has put work into this, and
> his draft recommendations are located at:
> http://www.aoc.nrao.edu/~smyers/alma/polspecs-imcal.txt
> We invite comments on this document.
> --------------------------------------------------------------------

These specs are essentially those proposed by Larry, with goals and 
spec separated.  Please do look these over and make sure I got things
straight...

> 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.

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...

> --------------------------------------------------------------------
> 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   

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...

  -steve