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Hi Brian, Junming,<br>
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:<br>
<a class="moz-txt-link-freetext" href="https://safe.nrao.edu/wiki/bin/view/Main/PafDevelop">https://safe.nrao.edu/wiki/bin/view/Main/PafDevelop</a><br>
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. <br>
bob..<br>
<br>
<br>
<br>
On 2/1/2013 12:51 PM, Brian Jeffs wrote:
<blockquote
cite="mid:DD6EF64443A91A48BB206E89D2492BD8ED2B3C@CORN.byu.local"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=GB2312">
Bob,
<div><br>
</div>
<div>Just to elaborate on what Junming mentioned:</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>Thanks,</div>
<div><br>
</div>
<div>Brian</div>
<div><br>
</div>
<div><br>
<div>
<div>On Feb 1, 2013, at 10:15 AM, µó¿¡Ãú (Junming Diao) wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">Hi, Bob,
<div><br>
</div>
<div>I have a question for you:</div>
<div>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. </div>
<div><br>
</div>
<div>Thanks,</div>
<div>Junming<br>
<br>
<div class="gmail_quote">On Mon, Jan 7, 2013 at 5:21 PM,
µó¿¡Ãú (Junming Diao) <span dir="ltr">
<<a moz-do-not-send="true"
href="mailto:diaojunming@gmail.com" target="_blank">diaojunming@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
Thanks, Bob! This is very helpful!
<div>Junming
<div>
<div class="h5"><br>
<br>
<div class="gmail_quote">On Mon, Jan 7, 2013 at
2:34 PM, Bob Simon <span dir="ltr">
<<a moz-do-not-send="true"
href="mailto:bsimon@nrao.edu"
target="_blank">bsimon@nrao.edu</a>></span>
wrote:<br>
<blockquote class="gmail_quote"
style="margin:0 0 0 .8ex;border-left:1px
#ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">Hi,<br>
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. <br>
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<br>
<a moz-do-not-send="true"
href="http://www.majr.com/"
target="_blank">http://www.majr.com/</a><br>
<a moz-do-not-send="true"
href="http://www.eastcoastshielding.com/"
target="_blank">http://www.eastcoastshielding.com/</a><br>
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.<br>
Hope this helps,<br>
Bob.. <br>
<div>
<div><br>
<br>
<br>
<br>
On 1/7/2013 3:35 PM, µó¿¡Ãú (Junming
Diao) wrote:
<blockquote type="cite">Thanks, Bob.
Please tell me know the details of
rack you buy from <a
moz-do-not-send="true"
href="http://www.amcoenclosures.com/"
style="color:rgb(17,85,204);font-size:12.666666984558105px;font-family:arial,sans-serif"
target="_blank">http://www.amcoenclosures.com/</a>.
I think this one is a good choice
for us.
<div>Junming<br>
<br>
<div class="gmail_quote">On Mon,
Jan 7, 2013 at 6:23 AM, Bob
Simon <span dir="ltr">
<<a moz-do-not-send="true"
href="mailto:bsimon@nrao.edu" target="_blank">bsimon@nrao.edu</a>></span>
wrote:<br>
<blockquote class="gmail_quote"
style="margin:0 0 0
.8ex;border-left:1px #ccc
solid;padding-left:1ex">
variety to choose from</blockquote>
</div>
<br>
</div>
</blockquote>
<br>
</div>
</div>
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<br>
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