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CICADAGreenBankSpectrometer2015Feb10
(2015-02-10,
RichardPrestage
)
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TGBT14A_912_69 - continued bank discrepancy tests on real VEGAS
Setup
Setup
Start 8:10am
run into Manager problems (loading old BOF). Finally get started around 10:30am.
This BOF seems to have too much fixed digital gain, causing filtersnap_nogain to clip
setting input power to -28dBm causes filtersnap_nogain power to be -12dBm, just beginning to hit +/- 127.
Deduce we want 16dB less fixed digital gain. We have to do powers of three, so select 15 dB less gain.
Randy goes off to build a new BOF file; stop testing for now.
Start again with BOF 119 at 1:45pm
Now input power of -28dBm causes filtersnap_nogain to be -30dBm. We seem to have lost 26dB of gain!
digital gain seems to need to be around 2**26.3, or 90000000. Keep it fixed at this value throughout the test.
various scans to check the procedure is correct.
run checkLinearityBalance, with a VEGAS balance to get CM rack, but then lbw_gain set to 90000000.
run over target ranges (-36, -6, 2), start with Scan 3
Note: VEGAS doesn't seem to balance as good as +/- 2dB (as in the spec)
e.g. target -32 gives: -32/35, -32/32, -28/28, -34/34.
for target of -10dBm, CM13 and 14 fail, but
BankE
is the one that looks off.
But converter racks are running out of attenuation here. Also, filtersnap is also clipping.
Finishes with scan 17
Note: they have changed from KFPA to L-band! Run the test again with L-band configured.
Now using Banks A,B,C,D
Run checkLinearityBalance again, (-36,-6,2)
starts with scan 18
These numbers seem even more bogus - looks like KFPA was in focus after all (despite Antenna Monitor screen).
Now seems like we need a lbw_gain of around 2**25 = 33554432
revert to old system. For many attempts, VEGAS will not balance, but then fixes itself. Very wierd!!!!
Scan 33 - eso558_vegas just to do a test scan - looks fine.
--
RichardPrestage
- 2015-02-10
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Topic revision: r4 - 2015-02-10,
RichardPrestage
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