Controller for a "fox" radio transmitter.
I built the FoxBox into a watertight plastic pistol magazine travel case, mainly because I was given one for free. It did work out nicely though as the foam inserts could be modified to easily fit the components. Many people use a metal ammo can for this purpose and more or less toss the components inside. This works well as it is also waterproof and has extra storage room for manuals or the like.
On my design, the radio is a cheap HT connected to a thru mount NMO connector. I went with this connector for its waterproofness, which was not really necessary. Do be aware that these type of mounts really expect to have a ground plane, normally the roof of a vehicle, which this plastic box does not provide. A metal ammo can may provide a bit of one. In practice, I'm not sure how much difference it makes, although I have the feeling that it does matter. Note that you can find NMO mount antennas that do not require a ground plane. I used this tiny little antenna simply for convenience, though I don't honestly think that it is a very good choice unless you are only hunting in a city park or something.
The software project is based on PlatformIO using the Ardunio platform. You can create a new PlatformIO project and git clone the project into it. The platformio.ini file should have everything that is needed to make this work from a configuration standpoint, such as defining the Arduino Nano board. Note that it also has two lib_deps enteries that point to two other classes of mine which provide objects for switches and timers.
See OPERATING.md for Operating Instructions
I have found no really definitive information on the Internet regarding which 2 meter frequency is best to use for ARDF/Fox Hunting. Some of the suggestions or practices that I have found are as following:
145.300 MHz (Someone claimed this is the national ARDF frequency, but I find no other reference to that)
146.565 MHz (Found 7 times on the Internet)
146.430 MHz (Found as secondary to 146.565 MHz)
146.520 MHz (3rd harmonic receive frequency of 439.56MHz)
146.535 MHz
146.550 MHz (Suggested use with a PL tone)
145.565 MHz (Found as secondary to 146.565 MHz)
146.580 MHz (3rd harmonic receive frequency of 439.740)
Stay away from 146.520 MHz
Based on the collection of data above, it seems that 146.565 MHz is the most popular option.
Any common simplex frequency other than 446.000. 446.0250 MHz would be fine
This varies depending on the desired difficulty of the hunt.
For easy hunts more frequent transmissions are desirable, whereas for experts longer pauses with shorter transmissions
would be the way to go.
Right now I am thinking that transmissions of about 15 seconds with a 1 minute pause is where I will start.
Notes on the wires within the official Baofeng earphone (Kenwood style).
- Blue and gold wires are connected to each other when the PTT button on the remote is pressed. These are the ones that would need to be connected via the relay to enable PTT.
- Green and blue are the wires connected to the speaker.
- Red and gold are the wires connected to the mic.
Wire colors connected to the HT connector
| Color | Pin Size | Use | Connection |
|---|---|---|---|
| Green | Small | Speaker | Tip |
| Blue | Small | Speaker | Sleeve |
| Red | Large | Mic | Ring |
| Gold | Large | Mic | Sleeve |
Schematic Mistake I have the battery listed as being 5VDC. In practice, I use a LIPO battery, which is actually 7.2VDC (I think). Anything within the VIN spec of the Arduino Nano should be fine as the Nano supplies the 5VDC that is used by the rest of the circuitry.
Schematic created on https://www.circuit-diagram.org/
Oddly to me, you don't need a common ground between the Arduino and the mic or speaker pins on the radio. Electrically, I don't know how this works, but it kind of does. However, the transmitted audio volume varies a lot depending on how the audio and mic wire are located in proximity to each other. I have found that grounding the sleeve of the audio/speaker plug (blue wire) seems to clear that up. In this case the speaker which is active and being monitored during the wait state looking for DTMF signals has a ground which is cool. Also, when the PTT relay is engaged, it then also grounds the mic input which seems to clear up the transmitted audio.
- Have an array of messages that can be transmitted either sequentially, randomly, or as time progresses. This could be just to spice things up, but it could also be to drop messages containing hints as the duration of the hunt becomes longer and longer.
- Add an overall watchdog type timer that shuts the beacon off if things go on for too long.
- Make time between beacons optionally random.
- Change time between beacons updatable programatically via DTMF. Im not certain this actually makes sense.
- Add a repeat count parameter to sendMessage to automatically repeat the message x number of times?
- Maybe switch to dash duration, end of word duration, etc. for code consistency.
- Possibly integrate a .mp3 player for pre-recorded audio.
- Maybe add back the buzzer/speaker for local sound. I couldn't do this as a seperate digital out as the tone() function built into the Ardunio library does not allow tone() to work on more than one pin at a time. I could possibly add it back by including a SPDT switch that sends the audio either to the speaker or to the mic in on the HT, thus bypassing the Arduino entirely.
- Fix the schematic to show that the battery voltage is actually greater than 5V.