[Gb-ccb] blank sky power spectra / r-factor correction

[Roger Norrod]

Brian,

Thanks.  Quite interesting.

There seem to be three solid and three dotted lines in each frame.  What do
the three colors represent?

Roger

At 11:23 AM 2/27/2006 -0500, Brian Mason wrote:
>
>Attached is the power spectrum from a 5 minute blank-sky drift scan with 
>the CCB collected on Saturday. Solid line is the power spectrum of the 
>differenced data, and the dashed line is the power spectrum of the total 
>power data; CCB input ports are J1-J4 (top, left to right), J5-J8 (next 
>row down left to right), etc.  Axes are log10(frequency) and log10(power 
>spectra density). Typical 1/f corner frequencies for the better channels 
>are 10^-0.5 - 10^-0.7 =0.2-0.3 Hz. The two first low frequency channels 
>(J1 and J5) show similar performance in total power and differenced power.
>
>With the working assumption that the 1/f we see is due to receiver gain 
>fluctuations multiplying an imperfectly balanced input load, we tried 
>applying the "r-factor" described in the Planck LFI papers by Seiffert, 
>Menella et al. The idea is to let
>
>  Diff Data = Sig - r * Ref
>
>and adjust r so that the mean difference is zero, which reduces the effect 
>of gain fluctuations. In effect this is a software gain-balancing made 
>possible by the fact that we measure total power not just the difference. 
>Doing this made no appreciable difference in the power spectra. We have 
>more drift scan and hot/cold load data that we need to analyze, and we 
>also need to look into the validity of the approximations made in our 
>simple r-factor correction (such as detectero zero levels). But on the 
>face of it this would disfavor offsets x imbalance as the cause of our 
>1/f, and suggest an actual pre-hybrid intrinsically variable offset.
>
>Several channels also have notable refrigerator microphonics (J10, J14; 
>J4, J8, J12, J16) and most have 60 Hz. These are more prominent than in 
>hot/cold load power spectra owing to lower overall noise levels.
>
>  Brian & Larry W.
>
>
>--------------------------------------------------------------------
>Brian Mason                           | office: +1(304)456-2338
>Associate Scientist                   | fax:    +1(304)456-2229
>National Radio Astronomy Observatory  | mail:   PO Box 2 
>bmason at gb.nrao.edu                    |         Green Bank, WV 24944
>http://www.gb.nrao.edu/~bmason/       |
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