
Decoding radio telemetry heard on news helicopter video footage with GNU Radio - penneyd
https://www.rtl-sdr.com/decoding-radio-telemetry-heard-on-news-helicopter-video-footage-with-gnu-radio/
======
paulgerhardt
Highly recommend the “Advisory Circular Project”[1]. It takes ADS-B data
grabbed from a network of 3000 pi+gnu radios [2], analyzes them for aircraft
flying in circles(!), and tweets out the images[3].

This is better than FlightAware as you are getting raw unfiltered ADS-B/Mode
S/MLAT location data broadcast from the aircraft and aren’t filtering out
position only flights.

Here is an instance of the California Highway Patrol observation plane
circling downtown Oakland last night for some reason:
[https://twitter.com/skycirclessf/status/1268408145224720384?...](https://twitter.com/skycirclessf/status/1268408145224720384?s=21)

[1] [https://gitlab.com/jjwiseman/advisory-
circular/](https://gitlab.com/jjwiseman/advisory-circular/)

[2] [https://www.adsbexchange.com/](https://www.adsbexchange.com/)

[3]
[https://twitter.com/skycirclesdc/status/1268332759358947328?...](https://twitter.com/skycirclesdc/status/1268332759358947328?s=21)

~~~
jcims
This is really cool. Pretty remarkable how a relatively simple heuristic
captures the behavior so effectively.

Also, take a look at the timestamps for the most recent tweets from
@skycirclesla.

Would be cool if the adsbexchange project added some audio fingerprinting and
even skyward-facing cameras to start detecting and even identifying aircraft
that don’t sqwawk/squit/etc.

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jcims
Just because it takes a few clicks from the article to get there, Oona
Raisanen (aka windytan) did this originally.

[http://www.windytan.com/2014/02/mystery-signal-from-
helicopt...](http://www.windytan.com/2014/02/mystery-signal-from-
helicopter.html)

If this interests you at all highly recommend you check out her blog.

~~~
naavis
Oona has super interesting projects in the blog. Can highly recommend too!

~~~
jcims
Her 'sounds of dial-up' image is poster-worthy -
[https://oona.windytan.com/posters/dialup-
final.png](https://oona.windytan.com/posters/dialup-final.png)

~~~
DoingIsLearning
Pure curiosity but do you know what software was used to generate the
spectrogram in that poster?

The color scale used in it really looks like the old-school cathode ray
oscilloscope displays.

edit: found it, windytan actually mentioned it in the blog page. It was done
using 'baudline'. ([http://baudline.com/](http://baudline.com/))

~~~
jcims
She makes a lot of use of baudline.
[https://www.youtube.com/watch?v=YGdg_VC9LDI](https://www.youtube.com/watch?v=YGdg_VC9LDI)

Sometimes it's a pain in the ass to get it dialed in but once you do it's hard
to beat.

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graupel
I tried to do this years ago while working at TV station with a helicopter and
despite owning (well, leasing) the chopper and owning the microwave equipment
the vendor would not release a way to decode the lat/long data used to track
the video antenna, which I wanted to pull into a google map to show the
choppers position.

So instead I gave the pilot an early smartphone (this was 2006) set up to use
cellular to send back lat/long data and pulled it in that way, resulting in
this:

[https://techcrunch.com/2008/05/16/become-a-virtual-
newscopte...](https://techcrunch.com/2008/05/16/become-a-virtual-newscopter-
passenger-on-airfox-live/)

~~~
skeletonjelly
Very cool! Is there a copy of that video linked in the article somewhere? It
404s

~~~
graupel
I found a screenshot! [https://www.newscaststudio.com/wp-
content/uploads/2008/05/ai...](https://www.newscaststudio.com/wp-
content/uploads/2008/05/airfox.jpg)

~~~
dfee
Either you really did, 17min ago, or you just trolled us all with a “403:
forbidden” for laughs.

~~~
voidon
The site has referer check. Enter the url manually (not click via hn), and the
image loads fine.

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flyinghamster
I took a quick listen to the audio, and "Bell 202" immediately came to my
mind. It crops up carrying Caller ID on landlines in North America, and
railway end-of-train devices use it for sending their telemetry over
narrowband FM. It's very well-suited for any situation where you want to send
short, low-bandwidth bursts of data over an audio channel.

If you need to encode or decode Bell 202 or similar schemes such as V.23, the
SpanDSP library [1] is very handy.

[1] [https://github.com/jart/spandsp](https://github.com/jart/spandsp)

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haram_masala
This is great. I have one of those cheap RTL-SDR units, and it was well worth
the $8 to pull in and decode ADS-B signals from overflying aircraft. There’s
something exciting about obtaining data “over the air” in a way that
completely circumvents the Internet.

------
ChuckMcM
And this is why I'm enjoying the heck out of playing with SDRs.

~~~
arminiusreturns
Do you have any suggestions on a good full duplex sdr to start with? The last
one I remember wanting was maybe the lime something? ADS-B data is cool, but
my main goal was/is to demonstrate use as a bug finder and maybe do some other
spectrum fun with my pc accessories and tv, wlan, etc.

~~~
ChuckMcM
Depends on how cost sensitive you are. Currently the LimeSDR[1] is the best
value (even at $300 and no case) because it is not only full duplex, it also
supports MIMO operation. While the latter is intended to support things like
4G LTE it also gives one the ability to do direction finding as multiple
receivers clocked by a phase locked LO allows you to do phase analysis of
incoming signals.

The Ettus USRP B-series[2] is very well supported for about $1000.

The ADALM-PLUTO[3] at $150 is a bargain for a full duplex SDR but a range of
325 MHz to 3.8GHz leaves a lot of interesting spectrum out. That is less of a
problem if you get a mixer and RF signal generator because you can up/down
convert the HF/VHF/UHF bands up to 1 GHz as an IF and play with them there.
There are some off the shelf solutions for this like the 'Ham it Up'[4] but
you are at the mercy of their TXCO.

I have all of these solutions except for the USRP and find that when I reach
for a radio to look at a signal I usually grab the LimeSDR.

[1] [https://www.crowdsupply.com/lime-
micro/limesdr](https://www.crowdsupply.com/lime-micro/limesdr)

[2] [https://www.ettus.com/product-categories/usrp-bus-
series/](https://www.ettus.com/product-categories/usrp-bus-series/)

[3]
[https://www.digikey.com/products/en?keywords=PLUTO](https://www.digikey.com/products/en?keywords=PLUTO)

[4] [https://www.nooelec.com/store/sdr/sdr-addons/ham-it-
up-304/h...](https://www.nooelec.com/store/sdr/sdr-addons/ham-it-up-304/ham-
it-up-plus.html)

~~~
prashnts
Any recommendations for softwares to play around with?

I got a NooSDR (€30 ish on amazon). I agree so much that its 1090MHz(?) leaves
so much to explore, but I didn't have much luck other than decoding TV/FM/DAB
using CubicSDR, GQRX, and VLC.

I am more interested in using it with Python/GNU Radio so didn't bother
installing those super cool web based tools yet. Since I'm just starting, I'd
like to get a feel of using it with a general purpose "summary software"
first. Essentially something that can lookup the frequency databases, etc. to
tell me: what is it that I'm looking at; if its LSB/USB/FM, and these sorts of
things. Overall, I quite enjoy CubicSDR for this, but I'd appreciate if you
have suggestions or resources I could check out. Thanks for the info above!

~~~
ChuckMcM
I found gnuradio companion to be useful for just poking around. Assuming the
radio has a gnuradio compatible driver then you can do a lot of basic things
like tune it around various spectra and get a feel for its sensitivity and
selectivity. You can try out lots of different things quickly with it.

Lately I've been looking at front end selectors and their impact on radio
performance. I have been using pysignal to process snapshots of iq data from
the radio in my test setup.

~~~
prashnts
Thanks for the tip, this definitely narrows down problem space to poke around
with.

------
ccostes
I'm wondering where the raw video from the helicopter came from originally. My
guess is that this isn't something you can do with an SDR and hobbyist
equipment, but I would love to be proven wrong.

~~~
skeletonjelly
[https://www.youtube.com/watch?v=2MprHxarmOI](https://www.youtube.com/watch?v=2MprHxarmOI)

The footage is direct from the news organisation. I'm guessing this is footage
from their FLIR mounted camera, maybe captured streaming to their HQ. Is that
what you mean?

