
Listening to satellites for $30 - moises_silva
http://blog.nobugware.com/post/2015/listening_to_satellites_for_30_dollars/
======
apaprocki
Funny, I saw this posted on /r/amateurradio and the app works really well. I
just got my FCC license a few weeks ago and was inspired by some YT clips to
try to talk to the ISS. A guy in Italy made a home-brew arduino az/el mount
for his antenna so it tracks ISS as it moves across the sky so the radio can
do its job:

[https://www.youtube.com/watch?v=0kTBOxZUWrc](https://www.youtube.com/watch?v=0kTBOxZUWrc)
(English, no contact) [https://www.youtube.com/watch?v=59Ik-
xHzM_A](https://www.youtube.com/watch?v=59Ik-xHzM_A) (Italian, reception
worked)

Cool stuff. Any HNers into radio in NYC? With the RTLSDR you can easily listen
(and visualize) all the NYPD channels.. fun stuff:
[http://imgur.com/f77GsUC](http://imgur.com/f77GsUC)

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anc84
Linked is a specific model on Amazon but you can just use any rtlsdr stick.
They start at about 10$. [http://sdr.osmocom.org/trac/wiki/rtl-
sdr](http://sdr.osmocom.org/trac/wiki/rtl-sdr)

Great fun and great gift for hacker types.

~~~
ultramancool
Yeah, try aliexpress or ebay if you want to get a good price on one. They're
often identical devices, some of the ones you find on Amazon are just
companies who got their logo stamped on the same ones you can order off
aliexpress for less than half the cost. In fact I own one which looks
identical to the one pictured in the article but I think I got it for a lot
cheaper...

[http://www.aliexpress.com/item/USB-2-0-Digital-DVB-T-SDR-
DAB...](http://www.aliexpress.com/item/USB-2-0-Digital-DVB-T-SDR-DAB-FM-HDTV-
TV-Tuner-Receiver-Stick-
RTL2832U-R820T2/32313795742.html?ws_ab_test=searchweb201556_3_79_78_77_80,searchweb201644_5,searchweb201560_1)

$7.35 instead of $21.95... I think the antenna is a little nicer on the
NooElec one, but it's 3x the cost and neither is particularly good (as the
author of this article points out), you can probably find a much better one if
you look around.

~~~
makomk
The cheap ones off Aliexpress have fairly inaccurate crystals - they're 100
ppm or more off, which you can compensate for to a certain extent but that's
another step. By comparison, the rtl-sdr.com one looks particularly spiffy:
[http://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/](http://www.rtl-
sdr.com/buy-rtl-sdr-dvb-t-dongles/)

~~~
ultramancool
In my experience they're 30-70 ppm off, never seen one over 100, but it's
extremely easy to adjust and all apps pretty much support it, most tutorials
tell you right off the bat how to do it. Once you've got them configured
they're surprisingly pretty solid.

The rtl-sdr.com dongles there say 1-2 PPM, but that's only 1-2 PPM temperature
drift, right? The one I linked also uses the R820T2 tuner, which does seem to
be somewhat more accurate. You're still going to have to mess around to get
the right offset at first. Just less messing around for the first 5-10 minutes
while it heats up.

Honestly, if it's something you're really interested in and want to put some
money into I'd buy a HackRF instead, $300-400 but you'll be able to dump way
more spectrum and transmit.

~~~
makomk
I unfortunately don't have one of the rtl-sdr.com dongles (wish I did) but the
spec says there's a 2 PPM initial error plus 1 PPM temperature drift, which is
fairly reasonable for a cheap TCXO. My current dongle is a cheap one from
AliExpress with slightly over 100 PPM of offset, and finding a calibration
procedure that actually worked was... interesting.

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Veratyr
Someone else pointed out doing the same with the Russian Meteor-M N2
satellite. Also doable with an RTL-SDR but the images are much higher (12x)
resolution than the NOAA satellites: [http://www.rtl-sdr.com/rtl-sdr-tutorial-
receiving-meteor-m-n...](http://www.rtl-sdr.com/rtl-sdr-tutorial-receiving-
meteor-m-n2-lrpt-weather-satellite-images-rtl-sdr/)

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oxplot
OK, since I pack a HackRF One, I couldn't resist trying this. Inside my
apartment in middle of Sydney, this is what I got for IR imagery from NOAA-18:
[https://imgur.com/UbCBQd5](https://imgur.com/UbCBQd5)

Super super cool.

~~~
chillydawg
Isn't that Norway? How come you're getting pictures of Norway in Sydney?

~~~
oxplot
I'd assume this thing having been launched in 2005 has enough memory to hold
imagery for the entire planet so one wouldn't have to be in the region they
want data for. That's my assumption and it seems to agree with the data.

~~~
RX14
No, these satellites only send out the line of pixels directly below them. For
example if the satellite is moving south, your image is rendered from the top
down, but from the bottom up if the satellite is northbound.

These satellites are very basic, and that I find is part of the fun.

~~~
oxplot
OK, then in that case I managed to receive the signal from a satellite 800km
above but passing over the other side of the planet. How's that explained?

~~~
joushx
You got a very noisy signal without much information (the gray thing in the
background) with an random map overlay generated by wxtoimg. Try to hide the
map overlay and you should see the picture you really received.

~~~
oxplot
I am aware what I received (and it's not what you described). I was asking how
I could receive a signal with the entire planet blocking the way.

------
ubercow
Any advice on what type of antenna to use for this?

It says a "simple wire antenna" is good enough in most cases, but I'm sure you
could get a much clearer signal with something specialized.

~~~
wwkeyboard
A Yagi antenna is probably the easiest directional, high gain antenna to
build. There are a bunch of different ways to build them. Here is one using a
tape measure [http://www.instructables.com/id/The-Tape-Measure-
Antenna/](http://www.instructables.com/id/The-Tape-Measure-Antenna/)

~~~
RX14
Keep in mind that the signal from the satellite will be polarised, and that
the polarisation will change as the satellite moves through the sky. To get
the best results you will need to rotate your yagi to find the best
polarisation.

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cconcepts
This is quite impressive: does anyone know what resolution images can be
captured like this?

I'm assuming this is perfectly legal?

~~~
anc84
Absolutely legal. Resolution depends on the satellite (system). It's digital
data, so the resolution does not depend on _your_ hardware.

~~~
deutronium
I thought the easiest signals to pick up from weather sats are actually analog
-
[https://en.wikipedia.org/wiki/Automatic_Picture_Transmission](https://en.wikipedia.org/wiki/Automatic_Picture_Transmission)

It seems theres at least a Russian weather sat, which you can pick up which is
transmitting digital data - [http://www.rtl-sdr.com/rtl-sdr-tutorial-
receiving-meteor-m-n...](http://www.rtl-sdr.com/rtl-sdr-tutorial-receiving-
meteor-m-n2-lrpt-weather-satellite-images-rtl-sdr/)

~~~
anc84
Ah sorry, I meant the kind of data, not the transmission method. No idea if
this even makes sense. I meant that you get a image of pixels from them, the
resolution does not depend on your receiver. The image pixel quality itself
("color") will be subject to analog effects though. Not a scientist, just a
hobbyist with "dangerous semi-wisdom" typing this. ;)

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hoskdoug
See also
[http://mattg.co.uk/words/noaa_sdr/](http://mattg.co.uk/words/noaa_sdr/) from
earlier this year

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awqrre
You can also get overhead plane positions using an rtlsdr:

[https://www.youtube.com/watch?v=ZqBv_Jv2r84](https://www.youtube.com/watch?v=ZqBv_Jv2r84),

[https://github.com/antirez/dump1090](https://github.com/antirez/dump1090)

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joushx
My best one so far: [http://imgur.com/a/rumWx](http://imgur.com/a/rumWx)

