[evlatests] [evla-sw-discuss] L band tuning (Expanded to ALL bands)

[Craig Walker]

The philosophy I use in SCHED and that might be considered here is to 
allow anything the hardware can do, but to complain loud and clear when 
the choices don't seem to make sense.  That way, advanced users can do 
what they want while less knowledgeable users are warned away from 
situations they probably don't want.  SCHED only prevents settings that 
are impossible.

Cheers,

Craig


David Harland wrote:
> Ken is right that we're heading for trouble because the
> OPT (spurred by user requests) is very liberal^ in what
> it allows, while it appears the executor is not.  This puts
> us in a position where the OPT will allow user configurations
> that will fail at time of execution.
> 
> To protect the average user while allowing for future
> freedom for more advanced users, we will restrict the
> values accepted by the OPT (while keeping the software model
> of the antenna electronics faithful to the actual design).
> This means we need to know any other situations where the
> executor is more restrictive that what the electronics would
> allow.
> 
> Here's the form we need this in:
> 
>   For each receiver band:
> 
>    + The minimum tunable frequency for the low edge of an IF pair.
> 
>    + The maximum tunable frequency for the high edge of an IF pair.
> 
>    + If either of the two values above vary by IF pair (eg, Ka's
>      A/C has higher min than B/D), then min/max per IF pair.
> 
>    + If any of the values differ by 8-bit vs 3-bit, a breakdown
>      of these values.
> 
> When we receive the above values, we'll use them to restrict
> the users' input.  We will do this work under JIRA ticket
> EVL-1137.
> 
> To keep the SSS model objects accurate, though, i would still
> like to get an answer on the lower and upper tunings of the
> L301s.
> 
> -----
> ^What The SSS Systems Do Now
> 
> Up until several weeks ago the OPT would not allow users to
> tune in a way that had any part of a baseband stray outside
> a receiver's 3dB limit.  The scientists who attend the SSS
> meetings found this limit to be arbitrary and too restrictive.
> We were directed to allow whatever the antenna electronics
> would allow.  This was done as part of JIRA ticket EVL-1043.
> 
> What the SSS system does in regard to tuning has been available
> in a test program:
> https://webtest.aoc.nrao.edu/dharland/evlaAntElec/evlaAutoTune.jnlp
> This program was first announced in April 2008 (w/ a request for
> input) and again in November 2008.  Among other things the values
> used for min and max LO settings are shown.
> 
> 
> David Harland wrote:
>> 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.
>>>
>>> _______________________________________________
>>> evla-sw-discuss mailing list
>>> evla-sw-discuss at listmgr.cv.nrao.edu
>>> http://listmgr.cv.nrao.edu/mailman/listinfo/evla-sw-discuss
>>>   
>>
> 
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     R. Craig Walker            Array Operations Center
     cwalker at nrao.edu           National Radio Astronomy Observatory
     Phone  575 835 7247        P. O. Box O
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