Ardufox RDF transmitter V1

It’s been a long time coming but now, it’s here!

Ladies and gentlemen, I give you the ArduFox V1!

ArduFox V1 hiding from the hunters

The ArduFox is an all in one RDF foxhunt transmitter. It’s easy to build using only a few simple components and outputs 10mW (25mW for the HP version) in the 70cm band (434.650MHz which is also an ISM band licence free frequency in the UK). Power comes from a single 9v battery which keeps it running for around 6 hours. The code is based on Mark Rodgers, KC8GRQ, excellent Foxhunt IDer which also contained code by KB3VCQ. See the full code for credits. I’ve tuned it for use with an on board NTX2 and added various functions to refine it for my needs.

It’s super simple. You just need:

1 x Arduino Uno (or clone)
1 x Radiometrix NTX2 module (on 434.650MHz)
1 x 3.3V Low Dropout Regulator
1 x 0.1uF capacitor
1 x Arduino protoshield.
1 x 9V battery snap
1 x Power connector to fit the Arduino

I don’t think anyone will need a schematic to build this as it’s so simple but if you want one then please send me an email. Follow these simple build notes and you should be ok.

  • Read the code before you start to build. It’s going to be easier if you follow the default pin layout rather than choose your own. The code is well commented so it should give you a better understanding of what’s going on.
  • The Arduino runs at 5v whilst the NTX2 module needs 3.3v. Use the Low Dropout Regulator to step the 5V down to 3.3v for the NTX2 module. I used a 0.1uF cap to smooth the supply.
  • I’ve played with different antennas and even a small dummy load and have found that a short 8cm antenna gives a good mix of range vs ease of finding when close up. You can see from the images that I also added a small coiled ground wire.
  • The code has a “found” function. You can add a (normally open) switch between pin 2 and the 5v rail if you want to use this function. When the switch is closed it will force the fox to send it’s ident followed by a series of musical tones. We will be using this function on the next “fox” which will be a treasure chest for hunting the pirate booty! The switch will be connected so it closes the contacts when the lid is opened and sends the “found” tones.

We (the G0HRS club) use the fox for engaging the public at special events, JOTA and other publicity opportunities. We have 2 small 70cm handhelds complete with small loop style antennas which we give to anyone who wants to try and find the fox. With some simple instruction, most find it within 30 minutes, have great fun and we find it’s a great introduction to the hobby.

Our fox is actually a fox. We place the ArduFox inside a toy fox and hide it. It’s a lot easier and more engaging to tell the public to look for a fox rather than a plastic box with an antenna.

Code and images below. Let me know if you need more details and if you build one, please post back here in the comments section.

Download the code here – ArduFox-V1

ArduFox V1 assembled

ArduFox V1 close

3 Replies to “Ardufox RDF transmitter V1”

  1. hi,
    it’s very interesting what you have built.
    I need a schematic to build this, because I think it’s easier.
    thank you.

  2. It’s nice i want to build this but i nedd the schematic..if you dont mind please sent it to my email.. ?

  3. There is no scheatic. It’s a very simple circuit that powers the NTX2 via a 3.3v LDO regulator using a 5V feed from the Arduino.

    Let me know if you are having problems and I’ll find the device and hand draw a basic diagram for you.

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