[evlatests] 3-bit tests, Tsys vs. bit levels.

[Rick Perley]

    Indeed so.  This can be reconciled to my report by noting that 
although the 'PDif Compression' remains about the same for all three 
3-bit combinations, this is a global statement.  For any one antenna/IF, 
there are significant differences, which lead to the different claims of 
system temperature. 
    As usual, the 8-bit PDifs look good, except for ea07, where a very 
slight 'PDif compression' can be seen ...

   

Vivek Dhawan wrote:
> Another note on this: the Tsys is a function of which 3 bits we
> select!
>
> I compared corresponding subbands (at the same frequency) from
> the 3 paths, A1C1, A2C2, BD.
>
> When using the lowest bits, the antennas/basebands/pol show the
> 3-bit Tsys to be equal or lower than the 8-bit Tsys, by ~0-10%
> across the array.
>
> Using the higher bits usually (but not always) raises the Tsys
> of the 3-bit paths, so they spread -10 to +20% on either side
> of the 8-bit Tsys.
>
> The explanation must lie with the gain compression/expansion of
> Pdif. The scans on/off 3C84 show the Pdif compression, but I have
> not tried to fit the numbers.
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