[Pafgbt] Photos of shelf

[Bob Simon]

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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