[mmaimcal] Band 9 CREs

[Al Wootten]

Folks,

As a result of the recently completed reviews, there are three change 
requests (Nos 164, 165 and 166) in for Band 9--to seek relaxation of 
cross-polarization specs, gain flatness and sideband gain ratio. 
Acceptance of these change requests will mean loss of a few per cent 
sensitivity.  I'll try to get a better estimate of the loss.  We will 
discuss this at the 21 Mar Science IPT telecon; the deadling for close 
of discussion will be 23 March (originally 16 March).  I think we must 
accept these if we are to have B9 receivers, but we need to understand 
the consequences.

Thee CREs deal with a change of specification to Band 9. Approving these 
CREs will result in the specifications being relaxed in Band 9's 
specification document, and also for Band 9 in the Front End technical 
specifications.

http://tinyurl.com/263t88
It is requested to relax the specification on the maximum allowable 
output power variation within 2 GHz sub-bands. At present, the maximum 
allowed output power variation at the output of the warm cartridge 
assembly is 6 dB peak-to-peak over the full 4-12 GHz band and 4 dB 
peak-to-peak within any 2 GHz sub-and of the 4-12 GHz band. It is 
proposed to relax these requirements to 7 and 5 dB peak-to-peak, 
respectively.

http://tinyurl.com/yntflv
It is requested that the sideband ratio specification for the Band 9 
cartridge be relaxed from its current wording:
“The side-band ratio shall be 3,0 dB or better across the IF band as 
specified under section 4.3.3.” (This IF band is 4-12 GHz.)
to read:
“The side-band ratio shall be 3.0 dB or better across 80% of the 
combined IF and LO frequency ranges specified under sections 4.3.2 and 
4.3.3.” (This LO band is 614-708 GHz.)

http://tinyurl.com/2a7olo
Description :
It is requested to modify the specification on the cross-polarization 
level of the Band 9 cartridge. The current requirement (Req. # 
FEND-40.02.09.00-00290-00 / T ) calls for the cross-polarization 
component of each signal channel to be at least 20 dB below the 
corresponding co-polar component for all angles within the main beam 
that hits the cartridge secondary. This is not feasible with the 
existing Band 9 optics design, and a change to the design at this time 
is not possible within the project schedule and budget constraints.

It is proposed to change this specification to:
??? “The cross-polarization level of each signal channel shall be at 
least 16 dB below the peak of the co-polar main beam, for all angles 
within the main beam that reach the telescope secondary mirror.”