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

Tue May 15 17:28:51 PDT 2018

>The thing that made me remember Mr. Myrick was no need to cut up the
RTL-SDRs.

Indeed.  The newer RTLSDRs from RTL-SDR have exposed unsoldered pad where
you can either take or receive clocking from other RTL-SDR dongles.
See

https://www.rtl-sdr.com/?s=daisy+chain

under "Feature 3" where they write
" An example of CLK daisy chaining is shown below. One dongles TCXO
is connected to two other dongles who have disconnected clocks. "

This would give you three RTL-SDR dongles all phased together.  Has anyone
tried this already?

Douglas KA2UPW/5

On Tue, May 15, 2018 at 12:38 PM, Michelle Thompson via Ground-Station <
ground-station at lists.openresearch.institute> wrote:

> There was a talk at GRCon16 that this discussion reminded me of.
>
> https://www.gnuradio.org/wp-content/uploads/2017/12/Wil-
> Myrick-GPS-Beamforming-with-Low-Cost-RTL-SDRs.pdf
> https://www.youtube.com/watch?v=lhZ2uMJNdjw
>
> Would this approach help us out in any way?
>
> It doesn't seem like we should be as limited as we are on synchronizing
> receive chains. This is high grade ore stuff that we should try and figure
> out. I'm familiar with rake receivers in CDMA.
>
> We have been assuming a synthesized tone to help with LNB/low-cost SDR
> setups, which can be considered, I believe, to be something like the signal
> of opportunity.
>
> There's another paper on synchronizing HackRFs, but it requires a hardware
> modification. The thing that made me remember Mr. Myrick was no need to cut
> up the RTL-SDRs.
>
> Needing the Jetson is a big deal, though. Can it be done with something
> much less expensive, today? I'll try and see what's happened with Mr.
> Myrick since this talk and report back.
>
> -Michelle W5NYV
>
>
>
>
> On Tue, May 15, 2018 at 9:47 AM, Zach Leffke via Ground-Station
> <ground-station at lists.openresearch.institute> wrote:
> >
> > 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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