[evlatests] L304 RLS

[Keith Morris]

Bryan:

The change to the L304 LO Reference Receiver consists of (1) a calibrated
optical power monitor, and (2) a programmable attenuator on the 512MHz LO
reference.  The optical power monitor allows optical levels to be set
without visiting the antenna, and the programmable attenuator allows the
LO reference level to be set without visiting the antenna.  This LO power
level is set to be within the range required by the L305 clean-up PLL.

The level of the LO distributed within each antenna is set by the output
level of the L305 clean-up loop oscillator, and is constant within each
antenna, and consistent from one antenna to another.  As such, this change
does not affect (presumably IF) power variation from antenna to antenna.

Presently, without this modification, we set the 512MHz power level
manually, with a fixed attenuator, and once the right level is achieved,
it is left alone (unless the fiber LO reference power level changes again
and the PLL input level requirement is not satisfied).  This is generally
only done after an antenna moves to a new pad, as that is generally the
only time the level is subject to change and requires resetting.  The
level-setting loop must be initiated deliberately, and does not auto-level
in response to power changes without being commanded to do so.

Under the new scheme, which we propose to test on antenna 13, the level
will be set automatically with a detector/attenuator loop, much like in
the T304, and this too will only be done once.  After the proper LO
reference level is determined and set, there is no further reason to
adjust it (again, unless there is a catastrophic change in the fiber LO
level, and such an adjustment would need to be commanded explicitly).



>
> i have to admit i knew nothing about this.  did it get discussed at a
> meeting that i missed?  i thought the problem with level setting was the
> variation from antenna to antenna in a given band?
>
> 	-bryan
>
>
> Vivek Dhawan wrote, On 7/29/14 18:51 :
>> Hi Eric,
>>
>> the level setting is disabled after it is done, right? i.e. it does
>> not keep adjusting during operation
>>
>> On 07/29/2014 03:53 PM, Eric Chavez wrote:
>>> Hello,
>>>
>>> I would like to install an L304 with remote level setting (RLS) into
>>> Antenna 13 when it moves to the master pad tomorrow. Are there any
>>> objections?
>>>
>>> RLS is outlined in electronics memo 247.
>>>
>>> http://www.vla.nrao.edu/memos/elec/
>>>
>>> Thank you,
>>>
>>> Eric
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