[evlatests] [evla-sw-discuss] L band tuning

[David Harland]

The SSS code is based pretty much on the values on the antenna block 
diagram. Looking again at that diagram for the L301, i see:

In red text, "Fout = 11.904 to 20.352".

On the other it has F=N * 512 ± 128 MHz, where 23 < N < 39.

If Nmin is truly 24, then 24 * 512 = 12,288. Using the "-" 128 MHz, that 
gets us down to only 12,160, not 11,904.

Luckily, if this needs to change, i can go to one spot and update it.

Unfortunately, though, things which we once thought were possible would 
not be.


Ken Sowinski wrote:
> There is a disconnect between LoIfSetup in the executor and
> the tuning algorithm in the OPT.  The executor enforces a
> minimum L301 setting of 12928 MHz, so that any LO leak through
> remains out of the downconverter input band.  But the OPT
> allows it to tune as low as 11904 MHz when deciding which
> Widar subband to use, leading to scripts which will not be
> tunable at observe time.
>
> If we set the OPT lower limit to 12928 MHz, and continue to
> avoid using the zero'th subband the lowest we can tune in
> L band is 1202 MHz.  This, I think, is unacceptable.  I have
> changed the lower limit in the executor to one notch lower,
> 12672 MHz, and suggest that the OPT enforce the same limit.
> This will allow a lowest L band tuning of 946 MHz which is
> more than we need.
>
> On the principle that the limit of 12928 MHz was set for a
> reason, we should have a careful look at L band observations
> to be sure that there are no adverse effects from LO leak
> through.
>
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