RF (Radio Frequency)

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As part of Project14 | RF (Radio Frequency): Win a Spectrum Analyzer for the Most Innovative RF Project!, I wanted an automated transmitter for my Antenna Radiation project.  Amateur radio folks use such a device for "fox hunting", a radio direction finding event where the transmitter is hidden and one has to find it.  I decided to go with one where an Arduino controls a handheld radio and plays a little segment that the radio broadcasts.  My inspiration came from Fox Hunt Transmitter – Whitecourt Amateur Radio.

The version I used for testing antenna radiation patterns was good enough - but I did want to improve it (sooner or later).  The schematic from Whitecourt had two wires reversed (dark brown and purple on the smaller plug).  The "schematic" below is correct.

Arduino Fox v1.0Arduino Mini Hidden Transmitter Assembly Schematic

Yes, that's a Velleman box.  The rubber band was to keep the lid on during the snow and sleet.  The blue thing is a 2000mAh cell phone charger for power and the whole system plugs into a $35 Baofeng UV-82 radio.

The relay controls the Push-To-Talk circuit.  When closed, the radio transmits.

D5 is the Arduino output to radio microphone input. The darker brown wire is also common / radio ground.

A0 allows for DTMF (Dual Tone Multi Frequency) input, but I'm not using that yet.


With the antenna radiation pattern testing complete, I wanted to upgrade the packaging of my fox - to make it more field ready.  The circuit did need to be modified slightly and I needed to change my Arduino code slightly.  The relay board above was active low and the relay used below will be active high.

Arduino Mini Fox With Transistor Driven Relay


1.  Protoboard that will fit in the project box

2.  Add headers and ground jumper

3.  Add relay

4.  Add relay driver circuit

5.  Add wiring that will connect to radio

6.  Add terminal connector for radio wiring & install Arduino

7.  Connect radio plug

8.  Project box

9.  Antenna jumper and installation hole

10.  Antenna jumper in hole

11.  Antenna installed

12.  Arduino fox with relay installed in project box, radio and battery added

13.  Arduino Mini Fox transmitting.  Not very flashy but will hide well.


I will need to add a notice on the side before I place it somewhere to test its range.  It wouldn't be good for someone to think it a nefarious device.  That is all for another day.


Forgot to add the files.