Listening to satellites for $30 | Hacker News Reader

Listening to satellites for $30

blog.nobugware.com

191 pointsmoises_silva36 comments

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 (English, no contact) 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

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

Great fun and great gift for hacker types.

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...

$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.

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/

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.

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.

How solid they are depends on the environment they're in. They primarily vary by temperature so if you're using them in an air conditioned room they're unlikely to have issues but if you leave them outside you'll notice the PPM value varying throughout the day.

This is pretty cool. Quite tempted to buy one and start messing around!

If you have the time but not the money, let me buy you one!

It might take a while to ship from China and your local customs might not like it though.

Thank you for the offer but it's the opposite way round! I'd only be distracting myself from my fifteen other hobbies. :{

But I caved and got the $7 one from aliexpress listed above.. :) It might take longer to arrive, but that's not really a bad thing as I won't have time to play with it at the minute anyway.

Thought so! Same here...

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...

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

Super super cool.

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

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.

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.

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?

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.

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.

Do you know what wavelength you were receiving? I would expect to see some clouds. Northern Scandinavia was a bit cloudy today.

http://oiswww.eumetsat.org/IPPS/html/MSG/IMAGERY/IR039/BW/WE...

Do you mean the frequency? I googled NOAA 18 and Wikipedia told me ~130Mhz.

May I ask what you've used as an antenna?

I used ANT500 [1] that came with HackRF One. I had to play with the angle a little to get a clear signal (horizontal worked for me).

[1]: https://greatscottgadgets.com/ant500/

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.

Author here, based on what you are trying to listen, different antennas may be better than others.

I use a discone antenna at home, but the picture you see on the blog was made with a wire antenna not especially dedicated to sats (a 2m/70cm wire JPole) outdoor.

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/

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.

You can use specialized beer- or even diet-dr-pepper-satellite-antenna https://v1.std3.ru/96/24/1443432707-96242a90aed02e25c975fc5c...

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

I'm assuming this is perfectly legal?

The downlink is analog (thus the calibration scales in the margins), and with this kind of hardware your image quality is limited by analog signal quality effects. At the source, though, APT ([false]-color pictures from NOAA satellites, as opposed to weatherfax charts) is 980px wide.

The satellites are a public service and privately owned receivers are nothing new, the RTL-SDR just made it a whole lot cheaper. The first time I saw this done at an amateur radio meet, the hardware cost many thousands of dollars and occupied a card table. The RTL-SDR is a bit magical in what it's done for hobbyist receiving.

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

I thought the easiest signals to pick up from weather sats are actually analog - 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...

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. ;)

See also http://mattg.co.uk/words/noaa_sdr/ from earlier this year

You can also get overhead plane positions using an rtlsdr:

https://www.youtube.com/watch?v=ZqBv_Jv2r84,

https://github.com/antirez/dump1090

My best one so far: http://imgur.com/a/rumWx

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