[mmaimcal] Sensitivities continued

[Steven T. Myers]

We are routinely getting noise temperatures of 12-14K over 10 GHz of
bandwidth at 32 GHz on both CBI and DASI now.  I think Al's estimates are
fine, though with the optics design one might expect as much as 8 K from
ground spillover (pessimistically).  Actually, I think this is the one
band where we DO have a good estimate of the performance, as there are now
more than 26 recievers out there using the NRAO HEMT (MAP) design.  

>  > 3) You use Trec = 14 K at 35 GHz. My impression is that no HEMT amplifiers
>  > have such a low noise
>  > at these frequencies. Furthermore, optical losses will most likely be larger
>  > at 35 GHz than at higher frequencies.
>  > I think we should use the 10 h.nu/k for that band.
> Roger.  Yes, without a real receiver design we don't have a good estimate
> for this band, for the bandwidth we want.  I called Marian Pospieszalski
> about this.  He thinks that over the 30-45 GHz band with cold horn, window
> and room temp. mixer, we should achieve 14 K or so.  So OK, let us add a
> few K for mirrors and perhaps something else.  10 hnu/k gives Trx=21K or so
> and the continuum sensitivity climbs to .02 mJy/min, with the line (1 km/s)
> sensitivity increasing to 5.2 mJy/min.  This is Tsys=38 K or so, and
> Carlstrom reported numbers as low as 34K for his BIMA/OVRO experiment over 
> narrower bands in the recent ApJ paper, so I think we are quite conservative
> with this.