Positioning Without Satellites Or Base Stations | Hackaday

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We’re all used to satellite navigation systems such as GPS or GLONASS, sheer magic in which the combination of a set of reference transmitters and super-accurate timing information can be used to calculate a position to an astounding precision. They had land based predecessors such as LORAN and Decca Navigator which worked in a similar fashion but with fixed land-based reference transmitters. Terra is an attempt to do the same thing without a network of dedicated transmitters, instead using FM broadcast transmitters as its fixed points.

This might seem like an impossible task without access to the transmitters, but they have a workaround using the Internet as a backhaul. Instead of transmitting their timing information like the systems mentioned above, they rely on a set of reference receivers sharing it online to the client’s receiver software. So far they have a demo running in Denver.

The interesting thing about this system is that it’s open-source, and requires only a relatively inexpensive software defined radio receiver and a computer to operate. Now anyone with a group of internet-connected friends to set up reference receivers can have their own positioning system, it’s no longer the exclusive preserve of governments. We like this idea, and we look forward to seeing it being tested more widely.

If you’d like to know where we’ve come from, we’ve taken a look at LORAN before.

33 thoughts on “Positioning Without Satellites Or Base Stations”

Presumably this is much harder to jam as instead of a low power satellite a long way away, it’s using high powered transmitters much closer?

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APRS, by Bob Bruniga. Problem solved.

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There is big big big money If they can get rtk grade accuracy (put up your own transmitters). Lot of high $$$ markets for private location services in gmss denied areas

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You know, it would be totally possible to add a signal to commercial broadcast stations specifically for this kind of LORAN-lite solution.

Over the years we’ve encoded quite a lot of auxiliary information into broadcast signals for a variety of uses, it ought to be possible to add a simple timing tick to produce a reasonably accurate navigation signal.

I the modern world where GNSS jamming is a real thing, having a backup that was as good as old school LORAN would be nice.

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What you’d want to do is synchronize their digital transmission starts: you can’t really add an additional timing signal because you need more bandwidth for that than you’d think – if you think about a 1 PPS signal, it’s transmitting way more information than 1 bit/s, it’s just that most of them are zero. Ideally you’d want to synchronize the carrier, which would give you more precise timing (this is true with GPS as well).

You’d still be more limited than GPS just due to the frequency difference.

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If most of the bits are zero, you don’t need that much extra bandwidth to transmit them.

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No, because it’s the timing that matters, so it’s really symbols/sec.

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Some countries are already deploying fiber backbones to provide accurate time information to transmitters.

For cell towers (mobile phone towers).

Since some weeks (IIRC), we not only know that Russia is jamming GPS and BaiDou in Europe, but which Russian satellites exactly man the GNSS signals.

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The Obama administration oversaw the shutdown of LORAN without any definative plan to replace it, despite global reliance on easily jammed GPS. Work was supposed to start on a new one in 2021.

That said, it needed to happen since the LORAN sites were giving all the Coast Guard members living under the antennas all kinds of rare cancers. The high voltage vacuum tubes were producing x-rays. Never mind living at the base of an absurdly powerful HF tower.

Its a shame considering how accurate you could be with LORAN lines on a chart and an analog RDF reciever. Always thought they should expand and enhance the VOR beacon network used for aviation to ships and ground traffic. Just need to find a solution to it being line of sight VHF. Maybe NVIS bounce?

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x-rays could cause cancer but being exposed to radio waves can, at worst, slightly warm your body (particulary at microwave frequencies). extra credit for that moment of thanking Obama!

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HF antennas can cook your eyes and reproductive tissues with comparatively little exposure.

Antennas on military ships have bright red lines painted around them with e posure warnings. Aircraft aren’t allowed to energize certain radios while on deck for the same reason.

Coast Guard ETs have to keep a radiation expoaure log for all the time they spend near energized systems. Once they fill that card up they’re not supposed to go near operational antennas...