[Ground-station] Ballon launch - lightweight inexpensive 10GHz transmit

[Zach Leffke]

responses in line below.....

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

On 5/14/2018 3:45 PM, Phil Karn via Ground-Station wrote:
> On 5/14/18 15:21, Zach Leffke via Ground-Station wrote:
>> 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)
> Is this inherent to the design? There's no way to build a smaller and
> lighter version of the transmitter? What's the mass?
Pretty sure it mostly has to do with the aluminum case its mounted 
into....possibly for thermal reasons.....

Mass of the upconverter is 310g / ~0.68 lbs.
Mass of the heatsink (that we used) is 800g / ~1.76 lbs.

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.

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.
>> I'd be very interested in how the phasing of multiple LNBs plays out.
> 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.
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.

I've heard of nifty ways to gang RTL-SDRs together by sharing the TCXO 
from one to many....but again never tried it.



-Zach

> 73, Phil
>
>
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