Sunday, June 19, 2016

Fox Hunt Progress Update

In a series of previous posts (search this blog for "fox hunt"), I have described a fox hunt transmitter for simultaneous HF and VHF fox hunting.

I have made some slight changes to the code to select a VHF frequency based on serial number and made different recordings for the voice announcement on VHF that will identify the fox beacon code.  I have reduced the audio sample rate to 8 kHz and set the deviation to +/- 12.75 kHz.

I decided that given I don't have any experience yet with the VHF fox that I would put each  of them on a different VHF FM simplex frequency based on it's serial number.

SN 0 - 147.420
SN 1 - 147.435
SN 2 - 147.450
SN 3 - 147.465

Once I have some experience with locating a VHF fox, I may experiment with putting multiple foxes on the same frequency and staggering their announcements.

Here you can see my four little foxes ready for their fox den.  The eye bolts on the end will be attached to lengths of wire to provide both the HF and VHF antenna connections and a convenient way to hang the fox up in a tree or other hiding place.  The end caps are not glued in place, so they can be removed to facilitate repairs, firmware changes or battery replacement.  They will keep dust and rain at bay however quite nicely.

A standard 9V battery powers these devices for several days with only the HF beacon running on CW.  It remains to be seen how much the VHF FM mode reduces that battery life figure.

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