Lost Model Locator

[Dodgy Geezer]

A fellow modeller I know (free flight) had a fly-away last weekend, and the conversation raised the topic of remote location...

You can buy small onboard transmitters with associated trackers, but he thought that they were expensive, and questionably legal....

I wondered about a 5.8GHz FPV transmitter - these can be bought for about £15. They claim amazing ranges - but I suspect that this is line-of-sight, while locators have to work at ground level in a field of wheat... Nevertheless, it may be possible to get something working at a mile or so with a clever antenna...

I was wondering whether an ideal locator could be made cheaply? No need for a complex signal, of course, and the ground station could be quite cumbersome, since it would (we hope) rarely be needed. I don't know what the best mix of legality/frequency/power might be for the transmitter, or what kind of directional aerial would be most effective. But someone out there must have some ideas...

[bluejets]

Seem to be many LoRa based units around DIY on the internet.

[Dodgy Geezer]

Hmm....they look a bit complicated to me - I can't easily find out how much a working system would cost...

I was wondering about a simple beacon transmitter - operating for a variable percentage of the time so as to get a long battery life, and a simple receiver tied to a directional Yagi. I can't find circuits for one of those - but perhaps I'm not looking properly...

[bluejets]

It's simplicity really depends on ones ability.
What seems simple to one may be a right difficult can of worms to another, depends on experience.

Your explanation seems simple for example when you say it quick, but the is a lot to the combination you describe.

As previous, there are LoRa GPS systems DIY out there with varying claims of range etc. some with small battery life of 3 hours or so, some with 200 metres, some claim 2000 metres that will transmit GPS position using a relatively small Tx and Rx.
Largely depends on transmitter strength and whether open terrain or scrub and hilly country.

Best would be to do a search around on some of the RC sites and see what others have encountered.
If you want DIY it would be essential to have some degree of experience with Uc's and other electronics, with the option of buying some thing off the shelf.
If you have late model radios for example, you could use the RSSI feature most have all-be-it with a limit once again on range.

[Dodgy Geezer]

For Free Flight I suspect that we are talking about a range of 2 miles or more, with the model possibly upside down in dense scrub.

We would be talking about a battery life of perhaps a week, allowing the option of going home and coming back in a day or so with friends to do a recovery.

We would, I suspect, want to broadcast on a legal frequency. But one which is rarely used, so as to avoid false positive detections, or interference with other valid users.

I think the above spec makes a GPS system less attractive than a straight radio beacon, which I am sure would be simpler. The block diagram for the transmitter would simply be a battery, a timer switching on intermittently, and a carrier wave transmitter. The receiver would just be an aerial and a signal strength meter... But does this exist anywhere, even just as a circuit?

[Martin]

Lower transmission frequency is better for tracking, as the signal penetrates through vegetation and other obstacles better.

Here's a cheap home-build device, using 433MHz, that the poster used for direction-finding his cat, (and he has a photo of one attached to a tortoise). You need a 433MHz Yagi antenna, and a radio capable of monitoring the 433MHz band (one of the cheap Baofang 'walkie-talkies' will do). https://www.nutsvolts.com/magazine/arti ... et-tracker

Simplest/lightest is to use the existing (on some radio control receivers) 2.4 GHz telemetry signal - assuming that the crash isn't bad enough to disconnect the receiver power supply.

With a modern transmitter, you can log telemetry readings to an SD card. If you equip the model with a GPS and set up the telemetry to broadcast its position, you can log the latest valid GPS position to the SD card, say twice per second. Then, even if the model crash disconnects the battery, or blocks the signal, you'll have the last recorded position of the model before the crash stored on your transmitter.

[bluejets]

For Free Flight I suspect that we are talking about a range of 2 miles or more, with the model possibly upside down in dense scrub.

We would be talking about a battery life of perhaps a week, allowing the option of going home and coming back in a day or so with friends to do a recovery.

As I said before, say it quick and then try to sort out just how complex this can really be.
MacGuiver may offer up a two second solution but real life is completely different.

[Dave]

Biotrack Ltd was the maker of a rather expensive radio tracker used by free-flighters.

Very light weight using a fishing float battery I believe.And the battery would last more than a week!

An internet search revealed that Biotrack has been 'absorbed' by a Canadian company Lotek.

The 0.13-0.17g 'NanoPin' Tag is described here https://www.lotek.com/products/nanopin/

The Biotrack tags operated in an ISM 'Licence Free' Band around 170mhz.

There have been one or two threads on RC-Groups describing whatI I think might be described as a

'squegging' crystal RF oscillator but I failed to unearth them.

A friend with a Spectrum Analyser might be useful too!

[bluejets]

A friend with a Spectrum Analyser might be useful too!

Think you need to take a few giant steps back from there.

[Dodgy Geezer]

The ability to buy ready made tx and rx does seem to make it easy to create something. 433 mhz seems to be a garage door operating frequency - perhaps a bit high for long range. 170 mhz would be better.
Looking on ebay I see that you can buy 7 mhz tx for less than £5 - what they are for I have no idea. But I note that 7.5 mhz serms to be used for rectal probes.. !