Configure the system as normal for VEGAS and the Spectrometer, and look at the respective backend inputs with a Spectrum Analyzer. Look for anything which looks anomalous between the two.
Take a cable (or cables) which normally connect the AFR to the Spectrometer, and either tee them off or connect them into the inputs of the VEGAS IF modules. Take tp with cal data (i.e. cal diode switching) either simultaneously, or consecutively with the Spectrometer and VEGAS. Compare the results.
Take data with VEGAS with the IF system configured for Mode 1, but trick VEGAS into running with Mode 4 (i.e. same IF configuration all the way to the VEGAS ADCs). Compare Mode 1 and Mode 4 results.
As above, but try different settings for the IF rack bandpass filter, from all-pass down to 20 MHz. Look at the converter rack attenuator settings to confirm Steve's point about bandwidth and variance.
Repeat above looking at the noise source in the IF rack
Physically swap some Converter Modules (not just the cables). See whether the results move around with the converter modules or not.
Repeat the tests were we drive some VEGAS IF modules with identical copies of a single converter module through a splitter, and others with their normal converter rack inputs. Compare the results.
(suggestion from Ray) - use a narrow band mode, and spread it across the wide band IF.
Set up at 8:00am
Ray needs to swap versions, Galen sets up Spectrum Analyzer
Weather is terrible; thick grey cloud, rain...
Spectrum Analyzer Checks
Run a tp spectrum to make sure system is configured correctly, and leave exactly this way for visual inspection.
VEGAS Mode 1
bank_gain_mode1_xband - Accidentally had A, not E - need to redo E.
balance - this does not seem to balance the IF rack! - fiddle around manually, with cleo, then run balance again
Scan 1: Track - but set up wrong. Decide we want to use the same converter modules for Spectrometer and VEGAS - A,B,C,D
bank_gain_mode1_xband_acs - confirms we will be using A,B,C,D
bank_gain_mode1_xband - hi cals running! Proceed with this anyway....