interesting question

is the wire a single insulated conductor or is it some kind of shielded
or multiconductor cable?

do you have acess to both ends and the break is in the middle of the
loop someplace?


i guess you could connect an AM signal gen to eac h end and follow it
with a portable AM radio

Mark

In article . com, "Mark" wrote:
interesting question

is the wire a single insulated conductor or is it some kind of shielded
or multiconductor cable?

All the electronic dog fences I've ever seen use a single insulated conductor.

do you have acess to both ends and the break is in the middle of the
loop someplace?

Obviously he has access to both ends -- they're connected to the control unit.

i guess you could connect an AM signal gen to eac h end and follow it
with a portable AM radio

He already has an AM signal generator connected to each end -- the control
unit. All he needs is a radio, as I described in another post.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Your FIRST step should be to join the Varmint Hunters Association, and
open your place up to them, for a little clean-up.

It's OPEN SEASON for varmints, you'll recall.

This should work of course, but it would be best to capture
the gopher responsible and make him show you where he committed
his crime.

Doug Miller wrote:
In article . com, "Mark" wrote:

interesting question

is the wire a single insulated conductor or is it some kind of shielded
or multiconductor cable?


All the electronic dog fences I've ever seen use a single insulated conductor.

do you have acess to both ends and the break is in the middle of the
loop someplace?


Obviously he has access to both ends -- they're connected to the control unit.

i guess you could connect an AM signal gen to eac h end and follow it
with a portable AM radio


He already has an AM signal generator connected to each end -- the control
unit. All he needs is a radio, as I described in another post.

Mike Berger wrote:
This should work of course, but it would be best to capture
the gopher responsible and make him show you where he committed
his crime.



.........and sue the little bugger for damages.




Doug Miller wrote:
In article . com, "Mark" wrote:

interesting question

is the wire a single insulated conductor or is it some kind of shielded
or multiconductor cable?


All the electronic dog fences I've ever seen use a single insulated conductor.

do you have acess to both ends and the break is in the middle of the
loop someplace?


Obviously he has access to both ends -- they're connected to the control unit.

i guess you could connect an AM signal gen to eac h end and follow it
with a portable AM radio


He already has an AM signal generator connected to each end -- the control
unit. All he needs is a radio, as I described in another post.

On 8/26/2005 11:29 AM US(ET), Mike Berger took fingers to keys, and
typed the following:

This should work of course, but it would be best to capture
the gopher responsible and make him show you where he committed
his crime.


Rub his nose on the broken wire?
Or, put collars on all the gophers and put them outside the perimeter,
so they won't come back onto the property.


Doug Miller wrote:

In article . com,
"Mark" wrote:

interesting question

is the wire a single insulated conductor or is it some kind of shielded
or multiconductor cable?



All the electronic dog fences I've ever seen use a single insulated
conductor.

do you have acess to both ends and the break is in the middle of the
loop someplace?



Obviously he has access to both ends -- they're connected to the
control unit.

i guess you could connect an AM signal gen to eac h end and follow it
with a portable AM radio



He already has an AM signal generator connected to each end -- the
control unit. All he needs is a radio, as I described in another post.



--
Bill

In article ,
Doug Miller wrote:
In article . com, "Mark" wrote:
interesting question

is the wire a single insulated conductor or is it some kind of shielded
or multiconductor cable?

All the electronic dog fences I've ever seen use a single insulated conductor.

do you have acess to both ends and the break is in the middle of the
loop someplace?

Obviously he has access to both ends -- they're connected to the control unit.

i guess you could connect an AM signal gen to eac h end and follow it
with a portable AM radio

He already has an AM signal generator connected to each end -- the control
unit. All he needs is a radio, as I described in another post.

--
Regards,
Doug Miller (alphageek at milmac dot com)


The other day while jogging I passed an electrician truck,
with the guy there too retrieving some part -- and I
started a conversation.

I was asking about ground-rods, and how you could tell
if the cable going to them was perhaps open -- and
that led to discussing longer wires underground that
might have a break.

He said there was some kind of device they could attach
to *one* end and it could tell you how many feet down
the wire the break was.

He didn't know how it worked, he said.

My probably-incorrect guess is that it broadcasts some microwave
frequency down the wire, and vary the frequency transmitted
and see if you can get a resonance -- and do that for several
frequencies (relatively prime to each other? -- I make this
up as I type it in) and if there is some cheap computer
hooked to it, maybe it -- well -- tries to disambiguate
how long the resonating part is????

Something like a physicst or musician sending a continuous
tone in one end of eg an organ pipe that's got a blockage
somewhere, and by tuning the sound for a singing-in-the-shower
kind of resonance, dope out where the blockage is?

(Assumes that they're blind, or have no flashlights,
and no long pieces of wood to stick down until
it hits the blockage ... :-) )

Oh well, it was a try.


David

On Mon, 19 Sep 2005 05:55:54 +0000 (UTC), (David
Combs) wrote:


He said there was some kind of device they could attach
to *one* end and it could tell you how many feet down
the wire the break was.

It's called a Time Domain Reflectometer or TDR.


He didn't know how it worked, he said.

That's surprising, as one has to enter some parameters to get it to
work correctly and that generally requires some degree of knowledge of
how the process works.


My probably-incorrect guess is that it broadcasts some microwave
frequency down the wire, and vary the frequency transmitted
and see if you can get a resonance -- and do that for several
frequencies (relatively prime to each other? -- I make this
up as I type it in) and if there is some cheap computer
hooked to it, maybe it -- well -- tries to disambiguate
how long the resonating part is????

No, the TDR works like radar. It fires a fast rise time pulse down
the wire and times the reflection and measures the polarity. The
reflection is caused by a change in the characteristic impedance of
the line, such as a short or open. The time is the round trip travel
time. If the wire's velocity factor is known (one of those important
parameters), the instrument can turn the time interval into distance.
The polarity of the returned pulse indicates the type of fault - same
polarity is a short and reversed polarity is an open. The best
instruments even look at the reflected pulse's amplitude and can
compute characteristic impedance and indicate if the fault is
resistive or not.

A TDR can also check for proper far end impedance termination. A
properly terminated line won't reflect anything. The amplitude of the
reflection indicates the degree of mismatch.

John
---
John De Armond
See my website for my current email address
http://www.johngsbbq.com
Cleveland, Occupied TN

There's an interesting method used to find breaks in electric ceiling
heating wires buried in the plaster. It would probably work for this too.

I can't go very deeply into how it works since I only understand it well
enough to use it.

A radio signal is fed into each end. One end broadcasts a Morse code "N"
and the other end broadcasts an "A". At the point of the break, the signals
overlap and produce a steady tone. With a receiver and headset I've located
breaks narrowed down to the size of a quarter and was able to make invisible
repairs working from the top side.

I used the device several times successfully. It was on loan from the local
power company.

George Willer

"Neon John" wrote in message
...
On Mon, 19 Sep 2005 05:55:54 +0000 (UTC), (David
Combs) wrote:


He said there was some kind of device they could attach
to *one* end and it could tell you how many feet down
the wire the break was.

It's called a Time Domain Reflectometer or TDR.


He didn't know how it worked, he said.

That's surprising, as one has to enter some parameters to get it to
work correctly and that generally requires some degree of knowledge of
how the process works.


My probably-incorrect guess is that it broadcasts some microwave
frequency down the wire, and vary the frequency transmitted
and see if you can get a resonance -- and do that for several
frequencies (relatively prime to each other? -- I make this
up as I type it in) and if there is some cheap computer
hooked to it, maybe it -- well -- tries to disambiguate
how long the resonating part is????

No, the TDR works like radar. It fires a fast rise time pulse down
the wire and times the reflection and measures the polarity. The
reflection is caused by a change in the characteristic impedance of
the line, such as a short or open. The time is the round trip travel
time. If the wire's velocity factor is known (one of those important
parameters), the instrument can turn the time interval into distance.
The polarity of the returned pulse indicates the type of fault - same
polarity is a short and reversed polarity is an open. The best
instruments even look at the reflected pulse's amplitude and can
compute characteristic impedance and indicate if the fault is
resistive or not.

A TDR can also check for proper far end impedance termination. A
properly terminated line won't reflect anything. The amplitude of the
reflection indicates the degree of mismatch.

John
---
John De Armond
See my website for my current email address
http://www.johngsbbq.com
Cleveland, Occupied TN

I've been watching this trace for a while and remember seeing utility
guys tracing underground services with a device. Could it be like one
of these?
http://www.electrical-contractor.net...?source=google
It will detect services down to 10'.
This site also talks about detecting breaks in underground irrigation
systems and specificly about finding breaks."The
valve-locator/wire-tracker can be used to trace the wire path, locate
valves, locate splices, and locate damaged wires."
http://www.igin.com/Irrigation/groundwiring.html
For instance this unit uses a number of different frequencies:
http://www.professionalequipment.com...qx/default.htm
Richard

"George Willer" wrote in message
...
There's an interesting method used to find breaks in electric ceiling
heating wires buried in the plaster. It would probably work for this too.

I can't go very deeply into how it works since I only understand it well
enough to use it.

A radio signal is fed into each end. One end broadcasts a Morse code "N"
and the other end broadcasts an "A". At the point of the break, the
signals
overlap and produce a steady tone.

hence the old saying "you are on the beam" (when aircarft pilots were not
veering off to the left or right of the proper flight path).

With a receiver and headset I've located
breaks narrowed down to the size of a quarter and was able to make
invisible
repairs working from the top side.

I used the device several times successfully. It was on loan from the
local
power company.

George Willer

"Neon John" wrote in message
...
On Mon, 19 Sep 2005 05:55:54 +0000 (UTC), (David
Combs) wrote:


He said there was some kind of device they could attach
to *one* end and it could tell you how many feet down
the wire the break was.

It's called a Time Domain Reflectometer or TDR.


He didn't know how it worked, he said.

That's surprising, as one has to enter some parameters to get it to
work correctly and that generally requires some degree of knowledge of
how the process works.


My probably-incorrect guess is that it broadcasts some microwave
frequency down the wire, and vary the frequency transmitted
and see if you can get a resonance -- and do that for several
frequencies (relatively prime to each other? -- I make this
up as I type it in) and if there is some cheap computer
hooked to it, maybe it -- well -- tries to disambiguate
how long the resonating part is????

No, the TDR works like radar. It fires a fast rise time pulse down
the wire and times the reflection and measures the polarity. The
reflection is caused by a change in the characteristic impedance of
the line, such as a short or open. The time is the round trip travel
time. If the wire's velocity factor is known (one of those important
parameters), the instrument can turn the time interval into distance.
The polarity of the returned pulse indicates the type of fault - same
polarity is a short and reversed polarity is an open. The best
instruments even look at the reflected pulse's amplitude and can
compute characteristic impedance and indicate if the fault is
resistive or not.

A TDR can also check for proper far end impedance termination. A
properly terminated line won't reflect anything. The amplitude of the
reflection indicates the degree of mismatch.

John
---
John De Armond
See my website for my current email address
http://www.johngsbbq.com
Cleveland, Occupied TN

He said there was some kind of device they could attach
to *one* end and it could tell you how many feet down
the wire the break was.

He didn't know how it worked, he said.

My probably-incorrect guess is that it broadcasts some microwave
frequency down the wire, and vary the frequency transmitted
and see if you can get a resonance -- and do that for several
frequencies (relatively prime to each other? -- I make this
up as I type it in) and if there is some cheap computer
hooked to it, maybe it -- well -- tries to disambiguate
how long the resonating part is????


Sounds like a TDR, they're used a lot in repairing computer networks in
large buildings. For something like this though a simple Fox & Hound would
probably work fine, we have one at work and it's nothing but a little box
you connect to one end of the cable and an inductive probe that picks up a
transmitted tone, run it along the wire until the tone goes away. Same can
be done with a radio and some sort of noise generator or oscillator. You
can't use the fence controller itself as they normally shut down when the
loop is open and you need it connected to only one end so the signal will
not be present after the break.

In article eSLXe.9183$fb6.2357@trnddc08, "James Sweet" wrote:

You can't use the fence controller itself as they normally shut down when the
loop is open and you need it connected to only one end so the signal will
not be present after the break.

Entirely incorrect. At least with respect to the Invisible Fence brand,
anyway. It does *not* shut down on an open loop, you do not need it connected
to only one end, and the discontinuity in the signal is *clearly* evident. I
just had to trace a break last week; the AM radio showed very strong signals
all the way along the wire, which abruptly stopped *directly* over the break.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

On Wed, 21 Sep 2005 01:15:52 +0000 (UTC), (David
Combs) wrote:

In article ,
Neon John www.johngsbbq.com wrote:
On Mon, 19 Sep 2005 05:55:54 +0000 (UTC), (David
Combs) wrote:


He said there was some kind of device they could attach
to *one* end and it could tell you how many feet down
the wire the break was.

It's called a Time Domain Reflectometer or TDR.
snippity
Man, that's pretty cool!

(Uh, what's such a thing *cost*? (just wondering))

Wide range. Little handheld units that display only footage and
designed for a specific application might run $500. A top of the
line Tektronix scope-based TDR might run $4k or more. Then there's
the "poor man's TDR". A fast risetime pulse generator and a suitable
oscilloscope with a delayed timebase or a digital scope. If that kind
of equipment is already on hand, the cost is little more than some
interconnect cables and the time involved.

One launches the pulse, times the return on the scope screen and then
computes the distance manually. In the good old days, with hand
prepared lookup tables or slide rule. Nowadays with a programmable
calculator or handheld computer like a Palm.

A scope-based TDR can convey all sorts of info beyond an open or short
and distance. Any impedance discontinuity causes a reflection. A
good unit like the tek can see the impedance upset in even a good
connector like a Type N. It can see coax bent too sharply or a staple
put in too tightly. It easily sees splices. One can even get a
pretty good idea of an antenna's match (SWR) by looking at how little
of the pulse is returned.

Stuff that's come along "since my time" :-) includes checking the
transmission line characteristics of digital buses on PCBs and the
like. Here's some good reading from the Tek site if you're
interested:

http://www.tek.com/Measurement/appli...lysis/tdr.html

Looks like they're building the TDR function into the higher end
digital scopes now. Slick. I still like my old analog Tek TDR
though. The eye is still mightier than the DSP for some things.

John
---
John De Armond
See my website for my current email address
http://www.johngsbbq.com
Cleveland, Occupied TN