Sometimes even a loud lost-model-alarm isn't enough, when you're beyond 200m or so in a noisy environment it can be impossible to still get a fix, worse, the energy drain driving the loud buzzer means you only have a couple of hours to find it.

As an alternative, I've started designing a RF beacon which can be tracked using a suitable receiver and antenna.

The beacons use a 433MHz ISM band.

The current design uses a self contained lipo which will be charged by the normal receiver power, if the plane's power dies the beacon will still continue to operate for days afterwards.

As an additional assistant in location, I've made it possible to have a small buzzer on board to help with the last 10m or so of locating, where RF tracking is quite a bit harder.

The beacon transmitter is only 1x1" in size.

The cost of the units has yet to be fully determined but it'll be ~$50 for the beacon transmitter. The receiver and antenna have yet to be worked out but the electronics for the receiver will be cheaper. I'm trying to come up with an ideal simple antenna for this system and so far a 3-element Yagi looks to be a good compromise.

Paul.

I forgot to add in more details;

The one version of the tracker that I'm planning will have a lipo management chip built in as well as a low-voltage alarm for the lipo (audiable). The lipo management chip is a proper device which is a good reassurance for those who are a bit concerned about lipo safety. I'm also planning to see if I can cram in the ability to use a 4-cell NiMH pack (something like Enerloops would be great).

Paul

Sounds great Paul, We've tried those cheap hand held Ebay ones but the will only work on relative flat ground with no trees/long grass in line of site. So hopefully it will be able to work in such areas(usually found around most slopes).

Cheers, Paul.

Paul

would this tx have the ability to be upgraded to supply lat and long if a gps such as the fpv osd's are using was installed and a different receiver used. The gps would just be an additional aid because if the plane was in a bad position the gps may not aquire any satalites.

Tony

scatcat,

A lot will depend on the antenna used on both ends. I can source some very nice proper rubber-duckie/stub antennas specifically for 433MHz but they do add a bit to the price (and the fact that you have to run coax) and they're heavier than a simple 17cm length of 26AWG wire.

Using the Yagi antenna should help a lot, improving sensitivity by a few levels. It's not the most 'elegant' option but it does provide superior pickup.

Paul.

* Design has just been updated to allow it to work with NiMH packs as well - though unfortunately they'll have to be separate builds.

Tony,

Originally Posted by Tony Finn

Paul

would this tx have the ability to be upgraded to supply lat and long if a gps such as the fpv osd's are using was installed and a different receiver used. The gps would just be an additional aid because if the plane was in a bad position the gps may not aquire any satalites.

That's a good question, realistically it'd be a bit of a complete redesign to facilitate a GPS system, in fact, an entirely different transmitter product, other than the transmitter. In fact, for that sort of thing, I'd just bundle a GPS module + transmitter which would work out around $90~$100 depending on the type of GPS module used.

Paul.

Paul
I'm sure that you have thought of this already, but just in case.
Most 2.4GHz systems have a failsafe in the receiver, so the age old technique of looking for missing pulses would not work with these systems.
Would your system be able to work such that if the attached chanel goes to the failsafe position (1ms or 2ms pulse) that the alarm is activated.
Thre user would need to set up the radio so thatin noral use the channel attached to the alarm was between these two limits.

Kaindub,

Yes, this "problem" has cropped up a few times with the normal PLD-LMA's - but once people set their failsafe positions to the 1ms area it works fine. I'm also working on a no-change alarm too (eg, for throttle/rudder etc if there's no spare channel).

Paul.

Paul

perhaps you can use a pair of pins, bridged or open to set whether the lmt is looking for receiver signal or is just on all the time. Would the output of the lmt tx be a problem for the 36mhz or 2.4ghz receivers if it was continuously on.

Tony

Tony,

I could indeed put a switch on the board to select the mode... the trick is to find a space... when I started out with the 1x1" board I thought I had no end of room, by the time I added the buzzer, lipo management, NiMH option, LED and a few other things it's finally run out of space :laugh: (fear not, I will find some).

The 433MHz ISM band should not induce any interference with either 2.4 or 36MHz gear.

Paul.

I just realised something... if I have a battery backup on the beacon, how does it know when to turn off - rather than thinking that the RX has died and it has to keep on transmitting.

Paul

when we are safely back with our loved one, we unplug the battery.

Tony

Mmm... but what happens when we accidently forget

Fortunately, because I will be monitoring the voltage level of the lipo, I can make the system move into a shutdown type mode which hopefully won't draw more than 0.1mA, though that only leaves you with about 2000hrs before your lipo gets killed (fortunately not in a volatile way).

Attached is a partial image of the tracker transmitter board. I did manage to cram in the switch to select between modes of operation.

This unit can be built in so many ways; it can be run purely off the RX power, or have its own backup battery, of which can be lipo or Ni* ( in fact, anything up to 5~6V ).

Now, the fun bit... getting them fabricated.... aaah sweet cashflow, where art thou!

Paul

Its burning a hole in my pocket, cant wait.

Tony