<html>
<head>
<meta content="text/html; charset=GB2312" http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#FFFFFF">
Bob,<br>
<br>
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?<br>
<br>
Karl<br>
<br>
<div class="moz-cite-prefix">On 2/4/2013 1:49 PM, Bob Simon wrote:<br>
</div>
<blockquote cite="mid:51101EDE.3020801@nrao.edu" type="cite">
<meta content="text/html; charset=GB2312"
http-equiv="Content-Type">
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 moz-do-not-send="true" 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>
</div>
</blockquote>
</div>
<br>
</div>
</div>
</div>
</blockquote>
</div>
<br>
</div>
_______________________________________________<br>
Pafgbt mailing list<br>
<a moz-do-not-send="true"
href="mailto:Pafgbt@listmgr.cv.nrao.edu">Pafgbt@listmgr.cv.nrao.edu</a><br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://listmgr.cv.nrao.edu/mailman/listinfo/pafgbt">http://listmgr.cv.nrao.edu/mailman/listinfo/pafgbt</a><br>
</blockquote>
</div>
<br>
</div>
</blockquote>
<br>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Karl F. Warnick
Department of Electrical and Computer Engineering
Brigham Young University
459 Clyde Building
Provo, UT 84602
(801) 422-1732
</pre>
</body>
</html>