A different kind of Foxhunt

Home

11 January 2025 | by John VE7TI | Share | | Leave a Comment (0)

Suitable for the urban fox

From the January-February 2025 SARC Communicator

If traditional foxhunts don't work well for your club or organization, this one might...

The last few months, I've been thinking about a different way to do a Foxhunt. My vision was to have a Foxhunt available whenever you want, especially this time of year. Not everyone lives in town, and everyone's busy shopping and might not be able to dedicate an afternoon on a specific day for a group search. But what if the fox kept calling you out for a few minutes here and there, whenever you had a chance? No pressure, just try it out and see what you can find with your gear, experimenting with different antennas to get the best results. Go get that Fox!

Where to start with my build? You guessed it: Google and YouTube. The first step was to make a Fox using things I had in my toolbox. I got a Baofeng radio, Arduino UNO, batteries, a waterproof box, and a Drok buck converter. Simple enough, right?

I first searched using Miss Google and came across this: https://www.hackster.io/nfarrier/auto-keyer-for-radio-fox-hunting-e89b99 "Cool, I can do this," I thought, so I did. After putting it all together, I programmed the Arduino UNO using the Arduino software with the code from that website. I set up the CW message, and everything tested just fine. My vision was starting to come true!

My power supply was an 18 volt 5.0 Ah Lithium-Ion Battery (Makita BL1850b) feeding in the Drok Buck Converter to reduce the voltage to 7.4 Volt for the Radio and that voltage was also perfect to feed the Arduino Uno as it has a 12 volt connection with its own regulator to supply 5 volt to the board.

Tested everything, and boy was this great! One watt output from the radio gave good range. I packaged it all up and headed outside. I found a good hiding place for the Fox, with easy access and safety in mind.

I could hear it from the east and west side of town. All was good darn... a few days later I couldn't hear it anymore until I was right beside it. I took the Fox home and discovered the TX (transmit) wasn't putting out power anymore, even though the battery was still good. My Fox SX5 Mosfet transistor must have failed. It must have been spending too much time in TX mode. So, I replaced the radio and changed the transmit message, reducing the time by almost 50 percent.

I put the Fox back in its den, and it was happy again, calling everyone to get searching. Darn... a few days went by, and once again, it stopped transmitting. I figured it must be the batteries. Out it came, and yes, the batteries were depleted. However, the Fox SX5 Mosfet transistor also failed again.

There goes the fox hunt, second radio blown. How disappointed you all would be! I talked to a fellow ham about Baofeng radios. He uses them more often than me, and he showed me in the manual that the duty cycle is very small, 03/03/54 minutes (RX/TX/Standby). My fellow ham had a spare radio he wasn't using, so I bought it from him.

I did a few more programming changes to adjust the duty cycle. I also decided to add "MORE POWER!" (à la Tim Allen) So, I added a second Makita battery for a longer stay in the den.
I relocated the fox to be closer to home, just because I know I'll need to replace the batteries in a few days. For those of you in the area, I hope you all get a chance to find the Fox.

Happy Fox Hunting! 73,

~The Silver Fox VE3BQM

AmateurRadio.com