[mmaimcal] B7 Change Requests

[Al Wootten]

Folks,

Last week we discussed pending change requests for B7m which were not
available on edm.  I put copies on the agenda.  They are now available in
edm, and a comment by Lazareff has been made to No. 171.  Tomorrow morning 
at about 1530 UT there will be a general discussion between IPT leads on these
changes.  Please send me your comments as I will need to formulate a science
ipt response.  I think the response to 170 will parallel that already submitted
for a similar CRE to B9 (http://tinyurl.com/2nck3o) except that we have
tighter requirements for calibration for B7 and the atmosphere is more generally
benign at those frequencies.

171.  	Band 7 cartridges: Image band suppression

CRE Number : FEND-40.02.07.00-092-A-CRE


Description :
Specification FEND-40.02.07.00-00190-00/T can be met marginally, which significantly impacts the production yield and therefore cost. We argue in attached documents that this specification
a) Might be significantly relaxed without any impact on the scientific performance of the instrument;
b) Is formulated in an unnecessarily restrictive way that either impacts the production yield or calls for frequent RFW's;
c) Impacts the production yield and cost of Band 7 cartridges.
As an indication, we propose a base level of \u20138dB image gain, with \u20137dB allowed in 10% of the frequency span of any IF band.

See: http://tinyurl.com/24hr9h

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170.  	Band 7 cartridges: IF power variation
CRE Number :FEND-40.02.07.00-093-A-CRE


Description :
The pre-production cartridges generally do not meet specification FEND-40.02.07.00-00210-00/T. The first clause of that specification, i.e. ±2dB in any 2GHz portion of the IF band, is the most problematic.
With the understanding that this specification has a direct impact on the efficiency of the digital correlator, we have designed, tested, and proposed IF bandpass equalizers that would allow us to meet the specification in its present version. We also also heard of active equalizers developed in the back end IPT.
Because neither of these two developments has an official status as far as we know, and because we cannot commit to a specification that cannot be met (see attached document), we ask for the following relaxation of the specification:
\u2022 ±3dB (6dB peak to peak) in any 2GHz portion of the IF band
\u2022 ±3.5dB (7dB peak to peak) across the whole IF band

See: http://tinyurl.com/2xtfdh

Clear skies,
Al
Al Wootten
Interim Project Scientist
ALMA, 40 El Golf, Piso 18
Las Condes, Santiago, Chile
Tel: +1 434 296 0329
Al Wootten Cell +14342424713