BaoBeacon Fox Hunt Beacon

This is the BaoBeacon. An inexpensive fox hunting beacon (< £30). It is based around the Baofeng UV-5R which can be had from Aliexpress for as little as £10 but usually around £15. You can even get them on eBay for less than £20 and from reputable sites like MoonRaker and Amazon for £25.

You must have an amateur radio license to operate this beacon!

You do not however have to have a license to take part in a fox hunt if you are only listening.

The purpose of a radio fox hunt is to use directional antennas and handheld radios to take bearings and locate a hidden transmitter or transmitters.

It consists of an Arduino (I use a digispark) a 3d printed case, the radio itself and a 3.5mm audio jack.

Recently I did a fox hunt with my scout troop and we decided that we enjoyed it so much we would like some unattended beacons so that we can do it more often. Using a live fox (licensed radio amateur) is not practical in the long run as they have to sit in the same location sometimes for hours at a time. Most commercial beacons we found were £100 delivered. 

I am not the first person to come up with using an Arduino and a Baofeng radio but I might be the first to put it into a tidy complete package that anyone with minimal IT knowledge can reproduce.

The beacon alternates between playing a short tune and your callsign plus a beacon number for around a minute then goes silent for another 4 minutes. So it has a 1/5 minute cycle. 

The Arduino takes its power from the radio itself so does not need an external power source.

I mostly wrote the Arduino code myself but borrowed from:
Morse Code Project

I also had some help from OARC Discord members Perry (M0PYL) and Paul (M0TZO) who helped me into the wee hours of the night debugging why for loops weren't for looping. Thanks guys. 

Battery Life

Low power (1w) = 5 hours
High power (5w) = 2.5 hours

BOM

Baofeng UV-5R Radio
BAOFENG GT-5R Upgraded Walkie Talkie LEGAL Dual Band Two Way Radio, Long Range Handheld Amateur Radio with 144-146/430-440MHz, 128 Channels, 1800mAh Battery, Headset for Adults, Support CHIRP: Amazon.co.uk: Electronics & Photo
Small Arduino ( I use a digispark )
ATTINY85 Digispark Development Board Binghe 5pcs Attiny85 Digispark Kickstarter with 32u4 chip ATTINY85 Micro USB Development Board Support ESP32 Compatible with Arduino IDE : Amazon.co.uk: Computers & Accessories
4mm SPDT 2 position switch
sourcing map 30Pcs 4mm Vertical Slide Switch SPDT 2 Position 3 Terminals PCB Panel Latching : Amazon.co.uk: DIY & Tools
3.5mm Audio Jack
Mikikit 10pcs 3.5mm Male to Bare Wire Open End Connector, Headphone Adapter, Audio Cable, Speaker Adapter Plug Jack : Amazon.co.uk: Electronics & Photo
M3 x 8 screws
M3 heat set insert
2mm Toy screws (cut to 2-3mm length)
Solid core wire for battery contacts ( I use stripped twist ties)
Wire for power connections (You can just cut some off your audio cable)

Instructions

First you need to flash the code contained in the zip file to your Arduino. Near the top of the main code file you will see a string you need to edit to your call sign. Under the amateur radion license you must identify yourself at least every 15 minutes.

If you are using a different Arduino and using a different PWM pin you will also need to edit this line to reflect that.

If you are using a Digispark they are no longer supported by the Arduino editor by default you will need to add the following to you board URLs under preferences then install the Digispark boards.

http://drazzy.com/package_drazzy.com_index.json

Once you have the board library installed you should be able to flash the Digispark using the IDE. Press upload and it will ask you to plug in the Digispark and it should upload the sketch.

Once you have 3D printed all the parts you will need to put the m3 heat insert into the main body then feed the solid core wire through the holes on the battery nubs then twist them inside the electronics space to keep the tight. Then trim them to suitable length (you need to be able to solder to them)

Next you should complete all the soldering and wiring between the battery nubs, switch, Arduino and 3.5mm audio Jack. Note the nub on the right as you are looking down into the box is positive. The wiring diagram is below.

Now put screw the switch into the back of the bottom plate. 
Tape up and or hot glue connections so they do not short then use 2 M3 screws to put the cover on feeding the audio cable out the notch on the right.

Next use some kind of foam or rubber on the bottom of the top panel to put pressure on the bottom of the radio while the lid is on, this will stop the radio losing contact with the battery nubs.

Do not connect the mic ground cable, it will cause a ground loop and the vox will never stop transmitting even when there is no audio (figured this out the hard way).

You will need to set you radio to vox mode (menu item 4) then experiment with the vox threshold ( I have mine on 7 and it works fine).

Now you set your radio to the desired 2m frequency (after checking it is not in use then screw the lid on with the thumb screw (m3 screw glued into printed part). Plug the audio jack into the radio. Flick on the switch on the bottom front panel and you now have a functioning beacon!

It is best to use the 2m band so then you can use the 3rd harmonic as a weak signal when you get in close with your home made yagi antenna.

eg
145.300 < 2m frequency
435.900 < third harmonic

You can also use techniques suck as body block and horizontal polarisation to manually attenuate the signal (make it weaker). 

For more information on radio fox hunting look on YouTube, the RSGB website, The Online Amateur Radio Club or Facebook groups such as (7) Amateur Radio Direction Finding and Fox Hunting ARDF | Facebook.

It is a good idea to label your fox hunt beacon with basic information about what it is and your call sign in case it is found by a member of the public.