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blog (coffee shop)
by This weekend, I received a familiar call from my father. He was calling to request my services to help him troubleshoot issues with something electronic in his house. While I normally field calls for his PC (I haven't been able to convince him to switch) or other household electronics, this week's request was to help troubleshoot his invisible dog fence.
First, for those unfamiliar with invisible fences, they consist of a loop of wire, run under and/or above ground. A radio signal is sent down the wire (antenna), and if a receiver (dog collar) gets within range of the wire, they get an electric shock. The controller unit is a box that sits on the wall, with a dial which controls the transmitter power, and two LEDs which indicate power present and loop status. The system doesn't work without having the antenna loop being continuous from end to end.
Unfortunately, PVC insulation seems to be a favorite snack of rodents, and as such, the loop is frequently damaged. The manufacturer, obviously aware of this, has designed the unit to beep in the event the loop is broken, to avoid a jail break.
After a quick online search, and a trip to the store where the unit was purchased, I still had no answers other than to uninstall the existing loop and reinstall a new loop. As the perimeter of the yard is around 300 meters, this wasn't an ideal solution. While it did cross my mind that this was a perfect excuse to buy a TDR, I decided this would be a good time for some ingenuity.
My solution? Use a tone generator and inductive amplifier to follow the signal. When the sound stopped, I knew the problem was somewhere behind me. While my solution was not exceedingly elegant, it did work. Has anyone else had this sort of problem, and what other ideas can the group come up with?
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0 Nerd-Its
wireless dog fence
Dog fence such as wireless dog fence is really important for it keeps your dog within defined boundaries to set them aside from the areas where s/he needs to be protected. You have a nice site here! I will be saving this page to my favorites for sure. Thanks.
-Andrei
http://www.wirelessdogfence-4less.com
1 Nerd-It
low tech break search
Take an old transister radio with a dial, (no digital) and headphones. Dial to the low 600 frequency on the AM band, You will hear a certain tone when near a completed loop. May have to test on short loop. Walk the line on the perimeter. You will hear a change in the signal when near a break.
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I think I would use this as an excuse to experiment with simulating a TDR with a pulse generator and an oscilloscope.
I presume that it is a simple loop of one piece of wire buried shallow.
If there is still some current flowing in the loop, perhaps a compass might deflect near the break in the loop where the magnetic field would change.
another suggestion:
Apply a very high voltage to the ends of the loop - like say the HT volts from an ignition coil. You could use the spark plug lead from your lawn mower. The break is probably a fracture having a very small gap. The high voltage should cause a spark gap transmission which could be detected as a burst of static by a portable AM radio. Shield the radio on one side with some aluminium foil to make its reception directional. Tune it away from any local stations and hold it near the ground.
Someone would have to keep pulling the lawnmower starter while you run around with the radio, so it would be better to make a circuit that repeatedly opened and closed the primary of an ignition coil - like an old fashioned electric fence.