[Pafgbt] Photos of shelf

[Karl Warnick]

Bob,

It sounds like we will need to add significant attenuation before our
receiver boards, or somehow turn off some of the gain stages in our
receivers. Any advice on how best to do this? 38 barrel attenuators, or
is there a smarter solution?

Karl

On 2/4/2013 1:49 PM, Bob Simon wrote:
> Hi Brian, Junming,
> I've spent a couple days looking at the power levels in the PAF, and
> making some measurements. There was a problem in that the block
> diagram didn't match the as-built hardware. I've updated sheet one of
> the block diagram to reflect the corrections. See:
> https://safe.nrao.edu/wiki/bin/view/Main/PafDevelop
> From measured data Roger took, the cryo amps have a gain of 40db. The
> gain in the 300K RF section just before the optical section is +32db.
> For matching, Roger planned a 2db pad between the cryo amp and the
> 300K section, but these aren't in place, and may not be needed, as the
> input match of the mini-circuits ERA-51SM+ amps is better than 20db.
> So we have 40+32=72db gain in front of the optical transmitter. I
> checked the input and output return loss of the unit, as well as the
> isolation. I can up-load this data to the wiki if anyone is interested.
> bob..
>
>
>
> On 2/1/2013 12:51 PM, Brian Jeffs wrote:
>> Bob,
>>
>> Just to elaborate on what Junming mentioned:
>>
>> In past operations with the 20 meter telescope and the Arecibo
>> telescope we have only had about 30-40 dB of LNA gain ahead of our
>> receiver boards. This matched the signal levels pretty well at the
>> ADCs. Since you now have much more gain ahead of the receiver cards
>> (I assume this is in order to put the signal above the noise floor in
>> the fiber link) we will need to attenuate by 40-50 dB at the output
>> of your fiber receiver before going into our receiver boards. At
>> least that is our current thinking so that we do not overdrive our
>> receivers. Before we buy attenuators (in-line MiniCircuits sma type)
>> we want to confirm the level calculations, and see if you had any
>> other ideas.
>>
>> Thanks,
>>
>> Brian
>>
>>
>> On Feb 1, 2013, at 10:15 AM, 刁俊铭 (Junming Diao) wrote:
>>
>>> Hi, Bob,
>>>
>>> I have a question for you:
>>> Our receiver board has 60 dB gain, which leads to too much power (10
>>> W) to ADC (ROACH). Can you tell me whether there is some methods to
>>> fix this problem.
>>>
>>> Thanks,
>>> Junming
>>>
>>> On Mon, Jan 7, 2013 at 5:21 PM, 刁俊铭 (Junming Diao)
>>> <diaojunming at gmail.com <mailto:diaojunming at gmail.com>> wrote:
>>>
>>>     Thanks, Bob! This is very helpful!
>>>     Junming
>>>
>>>
>>>     On Mon, Jan 7, 2013 at 2:34 PM, Bob Simon <bsimon at nrao.edu
>>>     <mailto:bsimon at nrao.edu>> wrote:
>>>
>>>         Hi,
>>>         Attached is the original order I did for the rack purchase.
>>>         I told you incorrectly; it was not Amco, but instead it was
>>>         IMS engineered products. I don't know your exact
>>>         application, but be aware that shielded racks are very
>>>         expensive compared to the non-shielded type.
>>>         Our racks are positioned over a forced air plenum. So, you
>>>         may need honeycomb RFI air filters for both intake and
>>>         exhaust air. Depending on heat generated, you may need
>>>         additional fans on the exhaust side to pull air out of the
>>>         rack. We purchase RFI air filters form either MAJR or East
>>>         coast shielding
>>>         http://www.majr.com/
>>>         http://www.eastcoastshielding.com/
>>>         You'll need to size the filters according your requirements.
>>>         Installation of these filters requires machine shop work to
>>>         insure proper fitting for RFI shielding.
>>>         Hope this helps,
>>>         Bob..
>>>
>>>
>>>
>>>
>>>         On 1/7/2013 3:35 PM, 刁俊铭 (Junming Diao) wrote:
>>>>         Thanks, Bob. Please tell me know the details of rack you
>>>>         buy from http://www.amcoenclosures.com/. I think this one
>>>>         is a good choice for us.
>>>>         Junming
>>>>
>>>>         On Mon, Jan 7, 2013 at 6:23 AM, Bob Simon <bsimon at nrao.edu
>>>>         <mailto:bsimon at nrao.edu>> wrote:
>>>>
>>>>             variety to choose from
>>>>
>>>>
>>>
>>>
>>>
>>> _______________________________________________
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>>> Pafgbt at listmgr.cv.nrao.edu <mailto:Pafgbt at listmgr.cv.nrao.edu>
>>> http://listmgr.cv.nrao.edu/mailman/listinfo/pafgbt
>>
>

-- 
Karl F. Warnick                               
Department of Electrical and Computer Engineering
Brigham Young University
459 Clyde Building
Provo, UT 84602
(801) 422-1732





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