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I'm looking in to vehicle trackers, the kind that allow police to track stolen cars such as Tracker (UK) or LoJack (US), and I can see there is quite a lot of variants out there.

The common consensus is that they seem to run on VHF since the claim is that this is more difficult to block as GPRS or GPS as these can be spoofed or blocked altogether.

Some are subscription whilst others aren't but my question is how do the VHF ones work? Paid subscription or not, trackers have to communicate with something to let someone know where thy are... To transmit a signal the length of a reasonable sized country will potentially require kilowatts of power (depending on terrain etc), they clearly aren't doing that!!

How do these work?

rclocher3
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cosmarchy
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    Can you provide more information (e.g. quote the documentation / specs) about the device(s) you're asking about? Most of us probably aren't familiar with “vehicle trackers” as a product category, and saying that a device “works on VHF” is sort of like saying a building is made of stone — it's a choice that constrains the rest of the design, but doesn't say how it works. – Kevin Reid AG6YO Oct 30 '21 at 22:26
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    How can my cell phone call all the way to Hawaii when it can't transmit the necessary kilowatts :) Maybe first try a search like How Does LoJack Work for lots of information, then come back here if you have detailed technical questions. – tomnexus Oct 30 '21 at 22:41
  • @KevinReidAG6YO here is an example https://www.tracker.co.uk/how-tracker-works - "most" advertisements for these devices seem to follow a similar marketing pitch in terms of capabilities... – cosmarchy Oct 31 '21 at 20:34
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    @cosmarchy Please [edit] your question to include relevant quotes. Links may break — especially to shopping sites, and on Stack Exchange questions are required to be able to be understood alone, without visiting other sites. – Kevin Reid AG6YO Oct 31 '21 at 22:05
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    Hello and welcome to ham.stackexchange.com! Please do edit your question to give us more specifics. – rclocher3 Nov 01 '21 at 21:31
  • "Tracker" in the UK and South Africa is based on the LoJack VHF system pioneered in the US. It's the original, there are now many other ways it's done. Search for LoJack instead of Tracker and you will find. – tomnexus Nov 02 '21 at 05:59
  • Both the Tracker and LoJack websites are very vague about how their systems work, @tomnexus. – rclocher3 Nov 04 '21 at 00:39
  • This question initially created a lot of confusion because there are many types of vehicle trackers. There is an amateur-radio-based system called APRS. Now that your question seems to be about commercial vehicle anti-theft systems, in my opinion the question is off-topic because it's not about amateur radio or the technology of radio. Just because such systems use radios is not enough to characterize the question as being about the technology of radio, in my opinion. Please feel free to edit the question after it has been closed; reopening the question is possible. – rclocher3 Nov 04 '21 at 00:54

2 Answers2

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Nearly all vehicle trackers use GPS receivers or one or more of the national variants. GPS only supports deriving location from received signals, and does not support transmission, so a secondary network of some sort must be used to report the position.

Amateur Radio vehicle trackers largely use APRS although several other protocols may also support GPS telemetry. APRS has a world wide relay network that has i-gates to relay it into internet. APRS digipeater relay coverage is not complete, there are gaps in it. The US VHF frequency for APRS is 144.390MHz. In city coverage of APRS usually allows it to function with 1w of power, but coverage on interstate highways in the US is in places sparse enough to require 50w to get a reliable signal into the network. More power than that likely would not help where coverage is lacking, as power does not extend range over the horizon significantly.

Commercial vehicle trackers most likely use data only cell phone modules, but there are satellite based relays for this as well. The Iridium satellite network supports this usage, although its cost makes it an unlikely first choice for most vehicle trackers.

user10489
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  • I was surprised regarding the marketing of some of these trackers. The claims are that they work when the vehicles are inside containers, underground carparks or where the GPS is jammed!! – cosmarchy Oct 31 '21 at 20:30
  • Some triangulation is possible from cell towers without gps, but it isn't very accurate. If you have spotty GPS, you can cover the gaps with inertial sensors and dead reckoning, which is accurate short term but has drift issues (which GPS fixes). Combining multiple sensors can get results more accurate than any single sensor, including gps. – user10489 Oct 31 '21 at 21:37
  • I think this question is about a different kind of vehicle tracker. Of course this answer was written before the question was clarified. – rclocher3 Nov 04 '21 at 00:54
  • Technically lojack is not a different kind of tracker...it's just a specific brand name. Since that is off topic, I'll not expand on it further. – user10489 Nov 04 '21 at 02:46
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There are roughly two kinds of consumer-grade tracking devices. One kind receives a GPS signal and then transmits its exact position to some sort of network: either a terrestrial VHF/UHF network, a mobile phone network, or a satellite network. A good thing about this kind of tracker is that exact position reports are sent. A disadvantage of this type of devices is that they depend upon GPS signals that occupy a fairly narrow band and are very weak, meaning that the GPS signals can easily be blocked in a small area by a jamming device (typically illegal, but not difficult to construct or import from another country). If the device doesn't receive signals from the GPS satellites, then the device can't broadcast its location. This kind of tracker is generally used for situations where jamming is unlikely, such as a mobile phone application designed to inform family and friends where the phone's owner is.

The other kind of tracker broadcasts a signal, either on a regular basis or when it is instructed to broadcast a signal. Such a signal doesn't encode the exact location, but the device can be approximately located by simple means, such as comparing the received signal strength from several different receivers. This signal is thousands of times stronger than the local signal strength from GPS satellites, even if it's only on the order of one watt, so it's harder to jam. Even putting the tracker inside a metal box may not be enough to prevent a detectable signal from leaking out of the box. This kind of tracker is commonly used for vehicle anti-theft systems.

rclocher3
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