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<p>responses in line below.....<br>
</p>
<pre class="moz-signature" cols="72">Research Associate
Aerospace Systems Lab
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305</pre>
<div class="moz-cite-prefix">On 5/14/2018 3:45 PM, Phil Karn via
Ground-Station wrote:<br>
</div>
<blockquote type="cite"
cite="mid:311cecdb-dee7-a6ce-b1df-c773df540d9e@ka9q.net">
<pre wrap="">On 5/14/18 15:21, Zach Leffke via Ground-Station wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Quick reply....haven't ingested everything yet.
For Transmit, 10 GHz: (not practical for balloon due to weight/cooling,
but maybe as a reference, or at least inspiration)
</pre>
</blockquote>
<pre wrap="">Is this inherent to the design? There's no way to build a smaller and
lighter version of the transmitter? What's the mass?</pre>
</blockquote>
Pretty sure it mostly has to do with the aluminum case its mounted
into....possibly for thermal reasons.....<br>
<br>
Mass of the upconverter is 310g / ~0.68 lbs.<br>
Mass of the heatsink (that we used) is 800g / ~1.76 lbs.<br>
<br>
The heatsink could probably replaced by something 'smarter'. The
version we used is pretty traditional style fin design, relying on
air flow to move the hot air away (not much air to move at
altitude). I've seen nifty 'radiator' designs for balloons that
move heat to the 'non sun' side of the payload to radiate the heat
away towards 'colder' sky, but those were pretty sophisticated
systems that had yaw control. The heatsink was also intended for
use with Kuhne's HPAs, so was probably overkill in this
application. The upconverter doesn't get nearly as hot as the PAs
do, so something 'minimal' might be sufficient for a couple hours of
flight......or no heatsink and duty cycling if that fits the overall
conop.<br>
<br>
I'm pretty sure someone on this list could come up with their own
design and fabricate it that is 'purpose built' for this type of
thing and places a premium on efficiency / weight......not me
though.<br>
<blockquote type="cite"
cite="mid:311cecdb-dee7-a6ce-b1df-c773df540d9e@ka9q.net">
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">I'd be very interested in how the phasing of multiple LNBs plays out.
</pre>
</blockquote>
<pre wrap="">I'm not up on what you/they are trying to do here, but are you
considering locking all of the converters to a common frequency source
and processing each feed independently with a SDR to do software beam
forming and steering?
I think this is the next major step for ham radio now that basic SDR
technology has become widespread. I've been thinking of doing it on HF
since even large directional HF antennas have relatively few elements
compared to, say, 70cm. But if we can do it on X band, great.</pre>
</blockquote>
For me the problem with SDRs and phased array systems seems to be a
limit on the number of synchronized receive chains. I have a
complete bias (that I acknowledge and have accepted :-) ) towards
Ettus products. For me the hurdle I run into with phasing things
with their stuff is that at best you can get 4 synchronized
channels, at a cost of about $15k (X310 + two TwinRX daughtercards),
enough to experiment with monopulse designs (for receive only).
They have a new product called the N310 (~$10k) that has 4 TX and 4
RX channels, but there is this 'nifty' feature of the UHD driver
that causes a random phase offset that has to be calibrated out each
time you change frequency or start a flowgraph (even if on the same
frequency). The N310 is pretty new though, so there may be
solutions that I just haven't heard of yet. For the X310 + dual
TwinRX, I've 'heard tell' that the phase issues have to be
calibrated out only once (look up table style) and then each time
you restart the flowgraph you are good to go, but have yet to play
that game myself.<br>
<br>
I've heard of nifty ways to gang RTL-SDRs together by sharing the
TCXO from one to many....but again never tried it.<br>
<br>
<br>
<br>
-Zach<br>
<br>
<blockquote type="cite"
cite="mid:311cecdb-dee7-a6ce-b1df-c773df540d9e@ka9q.net">
<pre wrap="">
73, Phil
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</pre>
</blockquote>
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