Our club is holding a fox hunt in a few months. We have a few portable UHF beam antennas but I thought I'd try a simple design that uses the phase difference between two sense antennas. It's called a HANDI-Finder and was described in QST in 1993.
It uses a CD4047 oscillator divider to make a nice square wave and two diodes to mix the incoming signals. In my case the oscillator is at around 600Hz. When the phase is equal no tone is heard, otherwise you hear the tone in a receiver tuned to the frequency you're hunting. Here's the board:
To try it out I used a NanoVNA to generate a CW signal. Here's a demo:
It's available as a kit but they kindly make the circuit easy to find here. See https://handi-finder.com/ for full information.
1 comment:
Similar ideas using 4-16 switched antennas mounted on the roof of cars were used in VK6 in the 70's and 80's for fox hunting.
One issue with fox transmitters that are more than say 500mW is that when you are close to the fox local fields get into the receiver input via secondary paths, reducing the null when you are off the correct direction.
73 Mark VK6WV
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