[Ground-station] 10GHz Remote Receiver - update, and how best to do the web interface?

Tue May 29 15:22:30 PDT 2018

Attached is a screenshot from rtlsdr_scanner (
https://github.com/EarToEarOak/RTLSDR-Scanner) and some other photos of LNB
on a Stick. This is a DirecTV LNB mounted on a mast and received on an
RTLSDR. The RTLSDR is run by an Odroid which is reachable by WiFi link.

LNB on a Stick is intended to be a remote receiver looking for things like
balloons and payloads (and people!). Right now, the receiver is pointed at
the local 10GHz beacon here in San Diego and is successfully receiving it.
The beacon is the spike towards the middle of the screenshot. This is a
half-watt 12dB gain beacon 23 miles away over terrain.

Yes, you get even more gain with a dish, but then we lose that cool 40
degree beamwidth. Think of this as more like a spotting scope. Additional
gain can come on board when remoting, reporting, and processing functions
are nailed down.

If you're looking at the screenshot and wondering why it's at 618MHz, it's
because that's the IF frequency received by the RTLSDR from the DirecTV
LNB. The beacon is on 10,368.36 MHz. The IF is 9,750 MHz. The signal sent
to the RTLSDR is at 618.36 or so. The beacon does drift. The RTLSDR is not
calibrated (yet). The LNB is a PLL version and that does help. Further
stability can be obtained by aligning the received bandwidth with a locally
generated stable tone. We have several synthesizer boards that can be
pressed into that service and are working on that angle as well.

We want to be able to turn this receiving station around and point it north
(or wherever) and ask the SBMS etc. to yell down at it just as soon as a
not-completely-janky way of recording/sharing/showing the receiver (on the
web) emerges. I want them (and anyone else) to be able to transmit and see
whether or not they are heard at the receiver. To hear LA I might have to
move the receiver higher than where it is in Carmel Valley, but I think we
should try it a couple of times as-is and see. A simplistic link budget and
what I know about the stations that have participated in the tune-up
parties in SoCal makes it look like the link can close.

So - easily seeing the receiver on the web is the pressing question.
Currently, in order to see anything at all on this receiver, you log in
from the local LAN using VNC (and ssh port forwarding) and start gqrx or
rtlsdr-scanner or whatever. This works. However, that’s like a sysop
approach. What I’m after is a receiver interface on the web that anyone can
reach.

rtlsdr_scanner (running on the Odroid) can produce .csv files for scanning
runs. With rtlsdr_scanner running, I can stash the scan results in a .csv
file and then post that to a website ever so often. But - there’s got to be
a more elegant way that gives immediate results along with storing/posting
the historical archive of the scanner runs (the .csv files).

Is there some magical HTML5 approach? Packages we should be looking at? Let
me know? This is a solved problem? Adding immediate visual feedback of
successful receive is the goal. I wanted to ask around before picking
something not-quite-right.

This prototype is the foundation of remoting the full-blown Phase 4 radio,
so getting the right ideas worked out for simpler or narrower bandwidth
applications (like the 10GHz balloon and some satellite payloads) I think
will pay off in the long run.

So far, the odroid+rtlsdr+LNB+biasT+wifiDongle in a sprinkler box on a mast
is hanging in there and working well. Odroids do seem to run hot and being
in a box has resulted in temperatures from 65C up to 75C - so far. This
Odroid does has a fan and it does run. This box does have downward-facing
holes for ventilation.

The VNC isn't exactly robust (Using Chicken of the VNC here). It drops with
"protocol errors" and "rectangular problems" and sometimes it just drops.
Also, the entire thing is AC powered and not, say, powered from a solar
panel. In other words, it's not off-grid or Burning Man Ready - yet.

But if it was battery/solar powered, and if the backhaul wasn't wifi, but
perhaps cellular or something else, then LNB on a Stick would be very
grab-and-go.

Future stuff? Tracking an APRS-revealed signal (like a balloon or person or
vehicle). Trying phased arrays of LNBs. Receiving live video. Experimenting
with adaptive coding and modulation in DVB-S2/X.

More soon!
-Michelle W5NYV
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