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

[Gustaaf Van Moorsel]

David Harland wrote:
> 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
>   

Given that the OPT automatically swaps the IF pair frequencies if needed,
I guess this means that the test should be that one of the IF pair freq-
uencies has to be 32GHz or higher.

Gustaaf