How to Search 500 Square Kilometres in 10 minutes

LoRa Relay – Part 1

Of all the LoRa programs I have written, the relay program is by far the most significant, the impact it can have on long range locating is monumental, and it’s a very simple program.6

At ground level a ‘lost’ tracker, be it a Radio Controlled (RC) model or high altitude balloon, could be just too far way to receive good signals. What can very significantly improve search range is increasing the altitude above ground of your receiver, even a 10M pole can make a big difference, especially in urban areas.

Its often not practical to put a large handheld LoRa receiver at height. A good location in an urban area for a receiver may well be on the roof of a house but how do you get all the kit up there ?

The simple answer is that you don’t have to, you put the relay ‘up there’ instead. The relay listens for packets coming from the ‘lost’ model or balloon and then retransmits them so you can pick them up on your normal LoRa receiver. The relay is small light, and self contained.

Using a bit of string and a weight, a small rubber ball is good a stone is not, its only a few minutes work to get a line over a house or tree and pull the relay up. If you carry a long extensible pole, also useful for rescuing models from trees, put the relay on that, the extra 10M or so of height can make a real difference.Part 1 - 2

With a low cost radio control plane or quadcopter, it’s possible to get the relay to 100M plus above ground very quickly. Take a look at the pictures, with a LoRa GPS tracker left running in my garden, once the plane was flown to about 100M I was able to pick up the trackers transmissions, and hence location, across 12kM+ of urban environment and countryside, C on the map below. In about ten minutes I had covered a search area of 500 square kilometres, imagine how long that would take to search at ground level !!!

Part 1 - 3

An alternative to using a RC model to get the relay to altitude is to use a kite, the relay is light enough.

The software for the relay is in the HAB programs folder on the dropbox, set the frequency and LoRa constants to match your normal tracker and receiver settings and turn it on. 

The next article will cover the building of the relay.

Not quite according to plan

Conditions looked good for a test of my easy build Pico balloon tracker. Picos are typically 36” foil party balloons filled with just the right amount of helium so that they rise to around 8000M and continue to float along at that altitude. CUSF Flight Prediction

The CUSF landing predictor suggested the balloon would from a Cardiff launch travel South, turn back North, circle back on itself, head North again and come back South over the Iceland and the West coast of the UK. It was not going to be quick but the battery would last around 6 days.



The tracker build for this flight was about as simple as it can get, just an Arduino Pro Mini, DRF1278F LoRa transceiver, UBLOX Max8Q GPS, PCBs, batteries, pin headers and some wire, no other additional components needed. The tracker board is multi-purpose, designed to be used as lost model locator, balloon tracker, remote sensor or a portable receiver. Extra components can be added for the audio uplink into habitat, powering from primary and backup supplies, components to switch on\off the GPS power and extra decoupling capacitors, if needed. There are connections available on the expansion header for an external serial or I2C GPS, a serial LCD display or a I2C environment sensor such as the BME280 or BMP280, you can even fit an independant watchdog supervisor.

Tracker Front

Tracker Rear

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Finding Lost Trackers

Once a balloon tracker has landed it will normally continue to send its GPS derived position. With your radio gear you can decode the FSK RTTY to a laptop or phone application. With a LoRa based tracker you can use a small hand held receiver which will tell you where the tracker is and how far and in what direction you need to travel to find it.

But what do you do to find your tracker if after landing the GPS has no reception or it has failed for some reason, or maybe its just not convenient to carry a rucsac of radio gear to pick up a FSK RTTY only tracker.

One possible answer is to use basic radio direction finding (RDF) techniques by listening for the trackers FSK RTTY transmissions. A UHF Frequency Modulation (FM) hand held such as the cheap Baofengs will detect these FSK signals but you don’t need to decode them as such, just listen to the audio.

If you turn off the squelch on the hand held so that you hear continuous background noise, you will notice that the background noise goes away when FSK RTTY is received. The FM hand held sees the signal, but there is no real FM content for it to decode so you ‘hear’ silence. The stronger the received signal, the quieter it sounds.

This quieting caused by the FSK RTTY is noticeable even when the tracker is a considerable distance away and received signals are very weak. With a directional antenna such as a Yagi or simple Moxon, you can get a good bearing on the tracker by moving the antenna around for minimum noise, when noise is at a minimum the antenna is pointing at the tracker.

Directional Antennas

Examples of directional antennas are shown below, the first is an Arrow yagi, this is robust, collapses well for transport and is quick to assemble.

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The MAX6369-MAX6374 Watchdog

This is a marvellous device to fit to a balloon tracker. It is a timed watchdog that needs no extra components to operate, you just provide a pulse every so often and it sits there doing not much at all.

If it does not see a pulse for the watchdog period then it will reset the tracker, recovering it from a possible fatal program crash.

Data Sheet is here

The watchdog timeout can be a range of values from 1 to 3mS up to 60Secs to 180Secs, depending on the particular device and how you connect 3 pins.

I use the 60Sec to 180Sec timeout, this is plenty for a tracker and has the advantage that even if the pulse to the watchdog fails, but the program is otherwise running, you have enough time to read the GPS and send the tracker payload before its reset.

The code I write for my trackers has the routines to pulse the watchdog already imbedded so all you need to do if you want a separate independent of the processor watchdog function is to fit this single device.

Easy Build High Altitude Balloon Tracker – Part 1

Today I am going show you how to build a low cost and low component count LoRa high altitude balloon tracker.

The tracker is powered by 2 x AAA Lithium batteries which will last in LoRa only transmission mode for around 25 days, half that with FSK RTTY transmissions enabled.


This balloon tracker is suitable for both small Pico (foil party type) balloons and the larger latex balloons. The tracker will send back its location using LoRa and FSK RTTY. The tracker operates in the UK license exempt 434Mhz region at 10mW power output. Line of sight LoRa reception ground to balloon will be 250-450km, depending on the altitude of the balloon.

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GPS Antennas and the effect on Tracker power consumption

For some time I have wondered if you could improve the battery life of PICO High Altitude balloons tracker if you used the GPS’s hot fix capability.

The common GPS for PICO HABing is the UBLOX MAX8 and if that is given a battery backup supply the GPS will save the down loaded satellite data in battery backed up memory when the GPS is powered off. It should then quickly acquire a new fix when its powered back on. The potential for power saving is clear, if you only want a new GPS fix every minute or so, why have the GPS powered up and running all the time, even if its in power save mode ?

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