: davefr wrote:
: > I installed a 2-3 acre section of undergound electronic
: > Fence several years ago. On those several acres are several
: > gophers.
: > Today one of those thousand gophers ate one of those thousand
: > wire and I'm getting the fault alarm.
: > The radio fence manual is rediculous. It says to start at
: > way point and patch back to the control unit and keep doing
: > the broken section is located. That would take me several
: > several thousand feet of patch cords. Beside that I can't
: > the flags (gophers ate those too!)
: > I want a scientific method of pinpointing the break however I
: > want to invest $1000's in a TDR (time domain reflectometer).
: > I do have some old signal generators and I heard there's an
: > method.
: > Anyone have any tips at locating the break. The dog doesn't
: > need it anymore but I want to preserve it for future
: > TIA
: Our Invisible Fence has occasionally had a break. Here's how
we locate it.
: Take one of the collar units off the dog.
: Hold it (by the collar) at about dog height.
: Walk to where the fence is.
: If it chirps then you have signal there so move to a different
: If it doesn't chirp then you're in the right area so move to a
: Repeat until you have two spots with chirps and a space between
with no chirp.
: Your break will probably be in between the two.
That's sure worth a try, but it didn't work for me.
Without current flow, the Rx wouldn't pick up anything anywhere
except right up at the Tx. I had a literal break though; maybe
it works for a short ckt to gnd; was that what you found?
Nope, it was a clean break (made it myself with a shovel that I just stuck in
the ground while doing something else at least 2 feet away from the fence
location). But there was another case where that did not find the break and we
ended up getting our Invisible Fence Man to materialize with his magic equipment
that did more. I don't recall what the problem was -- that was 2 houses ago.
"The career politicians are keeping the elevator at the penthouse
floor and not sending it down for the rest of us." - Kinky Friedman
If the wire is not broken but was a short to ground You can use a
arrangement to locate the ground.
The two ends of the loop tie to two ends of a potentiometer, Put one or
two volts to the
two end connections of the loop and measure from the wiper and ground.
the potentiometer for minimum voltage. Then the ratio of the two parts
of the pot.
is the same as the two parts of the loop.
:I installed a 2-3 acre section of undergound electronic Radio
: Fence several years ago. On those several acres are several
: Today one of those thousand gophers ate one of those thousand
: wire and I'm getting the fault alarm.
: The radio fence manual is rediculous. It says to start at the
: way point and patch back to the control unit and keep doing it
: the broken section is located. That would take me several years
: several thousand feet of patch cords. Beside that I can't
: the flags (gophers ate those too!)
Well, that's actually pretty standard advice in that manual, and
actually does work well. It's called the "rule of halves".
If you start with 1,000 ft of wire for example and use the rule:
-- you get 500' the break could be in.
-- then 250'
but you'll find the break at about the 8' point because you can
eliminate the parts of the wiring not in the ground easily.
To estimate where the wire is buried, a cheap portable AM radio
will usually suffice. It may not do a lot to locate where the
break is because most wires are transformer driven and the
voltage will exist on both sides of the break, but it can locate
where the wire is buried reasonably well.
If you used the metal flag poles, you might locate the buried
portions of them with a cheap metal detector if you know they're
actually still there and not just mowed/dragged away.
If you have access to a "good" metal detector, it might locate
the actual wire too, depending on how deep it's buried.
Once the wire's located, you could also use the "shorting across
the break" trick to locate the break too, using the rule of
halves and the dog's receiver to tell when it starts working
Short 500' and if Rx works, it's in that 500', else it's in
the other 500'. Then 125' and so on.
An afternoon would surely take care of this for the size field
you have once the wire is located.
The worst case scenario is that there are more than one break in
the wire. Only the rule of halves and looping back to the Tx
would work in that case. Had any heavy equipment or serious
ground movement in there lately?
Thanks for the replies.
At first I tried an AM radio but barely heard the signal caused by
the fence. Part of the problem was that there was a radio station
broadcasting at about the same frequency as the fence.
Next I tried an old signal generator and connected the RF Output leads
to each end of the wire loop. I tuned the radio and signal generator
to about 600 khz where there wasn't any radio station.
I taped the radio to a yardstick. It turns out the radio had the be
aligned perpendicular to the underground wire to get the signal.
It was easy. I just walked the fence line until the output dropped
off. Then I went past it until I re-intercepted the signal again.
That distance was only a few feet. Within inches of the center point
in the null area was a fresh gopher hole and that's where the fence
You don't need a TDR. A simple underground wire tracer will do. This
thing puts a low level RF signal on the line. You track it with a
receiver. Maybe you can rent one or perhaps find someone with the
phone or power company to come out and search.
I have a very old, antique cable locator made by Western Electric. It
consists of little more than a vibrator type induction coil. It feeds
several hundred volts into the wire. The receiver is nothing more
than several tens of thousands of wire wound into a coil and attached
to a set of headphones. The phones register a clicking sound, louder
the closer it gets to the wire. This is something you could make at
Now the question arises, what are you going to do about the gophers
before the next time.
John De Armond
See my website for my current email address
You can buy an electric signal tracer at many of the larger hardware
stores. They are under $50 for most. You hook they device on the end
to the wire. Then you follow the path of the wire with another
handheld device and either listen to a tone or watch for flashing
These are made for wiring in a building. Dont know if it will work
Method #2: This method requires you purchase an "RF-Choke" from Radio
Shack (Catalog item # 273-102) and use an AM Radio. Once you have these,
follow these procedures:
1. Disconnect the boundary wire from the terminals on the transmitter.
2. Wrap the boundary wire around the choke leads
3. Connect the choke leads to the terminals on the transmitter. The
choke has now completed the loop as far as the transmitter is
4. Turn the range adjustment knob up 1/4 to 1/2 turn.
5. Take the transistor radio and set it to AM 600. Stand outside the
structure where the twisted wire exits and listen for the
pulsating static of the transmitter.
Gently swing the radio back and forth across the front of your body and
follow the wire out to where the loop begins. Pick either direction and
continue until the pulsating stops for a 4-6 ft area. In this area is
That's what we did. We got pretty good at it!
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