[evlatests] [evla-sw-discuss] parameter simplification for the VHF receivers

[Frazer Owen]

Bryan Butler wrote:
> problem is, if we change this at the executor, MCAF will never know. 
> that's what i'm concerned about.  now, if it's *always* the same, then i 
> guess we could program it into MCAF but those kinds of hard-coded 
> solutions always concern me (and i know i'm not alone!).  i guess we 
> could overload the intents, yet again, and add one for this kind of thing.
>
> 	-bryan
>
>
> Michael Rupen wrote, On 6/29/12 12:48 PM:
>   
>> In the SDM, the Feed Table has separate rows for each Spectral Window.
>> Thus one can track the feeds & receivers independently for each SpW, which
>> is what we want. This would require a change in MCAF, which currently
>> assumes all SpWs in the same configuration use the same receiver. That's
>> not a big deal, except the Executor (or someone) has to tell MCAF which
>> SpW use which receiver/feed; or we embed the knowledge that 0-100 MHz
>> (say) is 4-band or whatever, in MCAF itself.
>>
>> Michael
>>     
    The situation is complicated. I would think the possibility of 
having two (or eventually three) receivers added together to produce one 
input band for the correlator probably never came up. The 4 and P-band 
part of Lowband have different power levels (although we are trying to 
get then to be close on the sky) and different  T_cals (~ 10X 
different). We probably will have one default observing set up which 
delivers both bands  in some number of subbands and channelization, 
e.g., one subband of 32 MHz with 1024 channels for 4-band and three 
subbands of 128 MHz with 512  channels. However, it seems clear that 
other choices would be made for some experiments.  So we can't just 
reserve certain subbands for 4 and others for P. Furthermore, since the 
T_cals are very different (as well as T_sys), more than one cal value 
seems necessary.  Furthermore the potential exist to add 2-band to the 
system (120-170 MHz) with a third set of parameters.  (see 
http://www.aoc.nrao.edu/~pharden/LBR/lbr.htm for more details)

    It also probably makes sense in some circumstances to use one IF for 
4band and the other for P-band. The possibility also exists, at least in 
theory, to observe with one IF for lowband and the other for one of the 
higher frequency, standard EVLA receivers. Jim Jackson and Chuck Kutz 
have written a memo about this. I am not sure this really makes sense 
but the NRL folks are very keen on doing this. See EVLA memo 155.

---Frazer


>>
>>     
>>> do they come through different receivers within the box?
>>>
>>> i'm concerned about being able to distinguish between them in the SDM.
>>>
>>> -bryan
>>>
>>>
>>> Ken Sowinski wrote, On 6/27/12 9:30 AM:
>>>       
>>>> Currently parmainator distinguishes between 75 MHz and 300 MHz for
>>>> band related paramters. The parameters of interest are subreflector
>>>> rotation and focus and band-dependent delays. Also there are T_cals,
>>>> which are now obsolete in the paramters DB, and tables of attenuator
>>>> settings, also obsolete.
>>>>
>>>> I suggest that we have only one band code "VHF" to select the low
>>>> frequency receivers. Receiver.java will transform any reference
>>>> to "75MHz" or "300MHz" to "VHF". This allows us to keep only
>>>> one set of parameters in the DB, rather than two identical sets;
>>>> prevents possible mistakes when two sets are maintains; more
>>>> accurately reflects the current hardware; and, eliminates the confusing
>>>> necessity of having to know whether the script selected "75MHz" or
>>>> "300MHz".
>>>>
>>>> The rational is that there is one receiver box containing all
>>>> receivers. Its single output (dual polarization) is conneted
>>>> to one T301 input. Regardless of which band is selected, the
>>>> hardware configuration is the same and the same wideband signal
>>>> is presented to the T304.
>>>>
>>>> Would doing this prevent anything that would be practical and useful
>>>> with the current scheme?
>>>> _______________________________________________
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>>>>         
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>>>       
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