Listening to Satellites: A Journey with My RTL-SDR V3

Listening to Satellites: A Journey with My RTL-SDR V3(moh53n.medium.com)

148 points by Asdrubalini 3 years ago | 20 comments

dekhn 3 years ago |

My grampa was a ham radio guy and he told me a lot of things. I was really amazed by shortwave and how radio could travel long distances by bouncing off the ionosphere. He also gave me a shortwave radio and I remember tuning into weird stations that would just say numbers in a funny voice ("numbers stations"). He even had a ham radio in his car and could dial phone numbers remotely through it.

I never really got into ham, I'm still not much of a radio person (I prefer wired) but I still had fun playing with RTL-SDR; listening to my car's tire pressure monitors and various other things in the ISM band. Antennas are still fairly spooky magic to me, though.

Taniwha 3 years ago | |

I was a radio ham in the early 70s used to hang out with some guys who were snarfing weather satellite data - essentially it worked this way - the satellites passed over and either spun along their axis or had a spinning sensor - that made a continual FSK signal (think a FAX signal, because it was intended to be downlinked to actual early fax machines) - we'd calculate the pass time and grab it on a big yagi steerwd manually (by listening to the noise floor).

In a dark room it would be played onto a TV screen with a very slow horizontal rate, vertical retrace would be done manually with a switch and the vertical increments were extracted form the signal. In front of the TV we'd place a bunch of cameras, we'd open the shutter at the start of the pass and close them at the end. At the end of the night we'd develop the film - the meteorology people who'd paid hundreds of thousands of $$ for ground stations were pissed that we were getting better quality images than their fax machines.

Also around midniught local time (in NZ) we'd pick up processed world images - 4 around each pole and 4 around the equator, with the country boundaries overlaid, and the communist countries carefully whited out

wkat4242 3 years ago | | |

Why were those whited out I wonder? It was just really lowres weather info.

I mean, today you can even see north Korea on Google maps :)

geocar 3 years ago | |

The tire radio was surprising! I was looking for my pool sensor when I found my neighbours car. Then I told my neighbour that his car told me his tire pressure was low and he said he had no idea his car was literally broadcasting what his tire pressure is (and serial numbers and so on…)

stevekemp 3 years ago | | |

For me too. I setup a couple of wireless 433Mhz temperature/humidity sensors in my flat (one on the balcony, one on the sauna).

Turns out the balcony sensor was just that little bit too far away to be regularly detected. However I noticed that I could get temperature readings from the car-tyres parked in the carpark to the side of my flat.

So I switched to using those instead for my "outdoor" temperature. Works a little better than my balcony would have done, as that is glazed and warmer than the actual outdoor temperature.

themodelplumber 3 years ago | |

Numbers stations are still pretty fun. Here's a video I got of the Cuban one, which is relatively easy to pick up in the US:

https://twitter.com/systematikk/status/1072960631916027904

Last I checked, they were using Windows XP freeware for data encryption.

There's also the shortwave radiogram and other interesting stuff if you go deep. The portable receivers and straight up SDRs they sell these days are pretty amazing in terms of sheer availability.

This receiver has been fun to use on the go:

https://www.youtube.com/watch?v=j3WQQn7rM3k

And the more consumer receiver stuff is now starting to ship with remote app control as well. A pretty awesome time for radio really.

wkat4242 3 years ago | | |

I'm surprised numbers stations are still a thing. Back in the cold war every serious traveler carried a world band receiver. But these days carrying such equipment would draw attention, most world stations have even been decommissioned.

mikub 3 years ago |

That's nicely written. Can't imagine how hard it must be building this stuff and getting all the components when you're living in Iran, it always reminds me that sanctions and such things are not only "hurting" the government but also, and probably most, all the normal people who just want to live a normal live.

blantonl 3 years ago |

One thing that is so critical in RF exploring is antenna design, and you can see where the author learns that very quickly.

It's kind of like the old adage in audio where you can have the best sources, AMPs, scalers, etc... but your speakers are the crucial component.

In RF, it's really is about the antennas.

procarch2019 3 years ago | |

Specifically selecting the right type of antenna and placing and orienting it correctly. Very easy for omni’s (mostly). Terribly annoying for spatial or directional.

Radios are fascinating. Optimizing and enhancing your radio capabilities is a black hole of time and money, but in return you gain knowledge and satisfaction.

ajsnigrutin 3 years ago | | |

It's interesting to me, that these things were almost impossible to do correctly in an amateur setting (equipment needed was a $10k+), and now with devices like NanoVNA, SDR dongles and some aliexpress shopping, you can do everything for a price of two prime steaks at a local restaurant.

NanoVNA to tune the dipole (1/4l), gain is fixed, autogain off, move the dipole around the antenna with sufficient attenuation on the transmitter (or even better, rotate the antenna itself), and you can get reasonably accurate radiation graphs. Also tuning an antenna with a NanoVNA is very easy and if the antenna geometry is simple enough, orientation is simple too.

10+ years ago, you needed a friend working at a local college to take you in at night to measure stuff :)

yuvadam 3 years ago |

It's amazing how RTL-SDR has ushered a new era of accessible RF hacking.

After many years of playing with SDRs I've actually went the other way around and got licensed as a ham radio operator, even though it's obvious that the old school rag-chewing is soon to be a relic of the past.

I'm super interested to see what the next generation of RF hackers and ham radio operators will look like, given the ongoing consolidation of RF applications into software.

procarch2019 3 years ago |

Originally I got interested in radios when I learned to deploy wifi for industrial applications. The big thing with industrial applications is interference and reflection. You typically have a lot of large structures made of metal or other materials that block the waves. Also, there’s a bunch or rotating equipment that emits emf as well (interferers). This can make antenna placement critical.

I wish I had gotten into it earlier, but I was discourage by a university professor who basically told my senior design groups that radios were too finicky for us to tackle.

Now I participate in amateur radio and I suggest anyone who finds the topics interesting to do the same.

pajko 3 years ago |

The 137 MHz band is sadly abandoned and the days of current satellites in the sky are counted. So if you are planning to experiment with satellite reception, HRPT is recommended at 1.7 GHz instead. Needs a more capable SDR device (however the RTL-SDR v3 might still fit if cooled properly), needs a more complex antenna, but the resolution is much better:

https://www.rtl-sdr.com/a-comprehensive-beginners-guide-to-h...

Actually even the HRPT streams are seem to be phasing out, but will be supported on the MetOp line for a long time (MetOp-B has been launched in 2012, the -C in 2018, and the satellites generally have a 15 years of lifetime). Future live streams will be transmitted in the 5 GHz+ range, which needs an even more complex antenna and probably a downconverter.

JKCalhoun 3 years ago |

I've seen these DSP radio receivers on AliExpress that have SDR, a touch screen — all in a small form factor. I'm not aware though if there are any intuitive, well crafted software for them that would allow a novice to play around with them, perhaps even call up satellite imagery like the blog post.

polalavik 3 years ago | |

There’s GNU Radio and PySDR. I’m not sure they are entirely intuitive but they are pretty good.

JKCalhoun 3 years ago | | |

My experience with GNU Radio was that it was a construction kit for creating receivers. But, yeah, that's not the kind of intuitive front end I was thinking of.

PySDR I'll have to check out.

binbag 3 years ago |

Really fascinating and impressive!

ge96 3 years ago |

some cool videos on this topic by saveitforparts on YT