[evlatests] test observations with IF pairs > 4 GHz apart

[David Harland]

Gustaaf,

With respect to Notes 1 and IF 1 having the higher frequency in AIPS: 
the AC / BD swap was probably done by the script generation logic that 
the OPT calls.  For bands K, Ka, and Q the logic looks to see if the 
conversion path through the T303 is needed.  (That logic will say to use 
the conversion path when the IFs are separated by about 3GHz, which is 
the case here.)  For these bands, if the conversion path is required, 
the software switches the IFs into legal positions -- that is, w/ A/C 
being higher than B/D.

What surprises me is the statement about scans 7 & 8 not being 
observed.  I would've expected them to have their IFs swapped, w/ the 
results being the same as scans 6 & 4, respectively.  K, Ka, and Q use 
the same block of logic and it looks like scan 3 had its IFs swapped.  
Can you reconfirm the failure of those scans?

With respect to Notes 2, i don't know what the cause is.  Perhaps you 
could forward a copy of the script (if not to everyone, then to me, 
Brian T., Bryan B., Ken, and anyone else you think could help diagnose 
this).

Thanks,
David


Gustaaf Van Moorsel wrote:
> During software time I tested tuning the IF pairs more tha1n 4 GHz apart.
> During 30 minutes I observed the following scans in spectral line, BW
> code 1, 25 MHz bandwidth, 1.56 MHz channel width.  The schedule was
> created using the OPT.
>
> 1 - dummy scan at X-band, continuum
> 2 - reference pointing determination, X-band, continuum
> 3 - K-band, AC at 20.5 GHz, BD at 25.5 GHz
> 4 - Ka-band, AC at 36.0 GHz, BD at 30.0 GHz
> 5 - Ka-band, AC at 38.0 GHz, BD at 28.0 GHz
> 6 - Q-band, AC at 49.0 GHz, BD at 42.0 GHz
> 7 - Q-band, AC at 42.0 GHz, BD at 49.0 GHz
> 8 - Ka-band, AC at 30.0 GHz, BD at 36.0 GHz
>
> The observations were successful: scans 1 - 6 were observed, whereas scan
> 7 and 8 were not; not surprising since they (on purpose) violated the 
> req-
> uirement that the AC frequency has to be greater than the BD frequency.
> The OPT should probably check for those constraints.
>
> Notes:
>
> 1 - In scan 3 (K-band) the system accepts freq(AC) < freq(BD) but AIPS
>    labels the higher of the two frequencies as IF 1, an the lower as IF
>    2.  How do we make sure the right data is attributed to the right IF?
>
> 2 - AIPS labels the IF pairs with a slightly different frequency than 
> req-
>    uested in the OPT.  For instance, in scan 4, AC requested is 36.0 GHZ,
>    AIPS labels it as 36.00078125 GHz, a difference of half a channel.  BD
>    requested is 30.0 GHz, AIPS labels it as 30.02421875 MHz, a difference
>    of 15.5 channels.  This needs to be sorted out.
>
> Gustaaf