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

[David Harland]

I should have mentioned that the OPT is probably missing a test that 
would warn the user that the lowest A/C frequency for Ka band is 32GHz.  
I'll look into that and update the code if it is indeed missing.  --David


Gustaaf Van Moorsel wrote:
> During software time I tested tuning the IF pairs more than 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