"Invisible fence" for dogs

Re: dog care, You just need enough room, :^) Our dogs are no more work than the cats, (maybe less... I'd rather do the ~one day spring clean up of winter dog poop, than the kitty liter box through the winter... Perhaps it's better there in the south.. (When there's no white stuff on the ground everyone poops in the field. Well except for the wife, kids and I.)

We've got some coyote, more predators to control the deer population would be good. Deer seem to be even more of a problem in the suburbs, no human hunters... and more coyote?

I'm totally a dog person. Cats are tolerated for their vermin control, funny antics are the gravy.

George H.

There are induced "currents" in the pipe.. With iron there can also be magnetic polarizations.... I'm not sure of the time constants involved.

If you are seriously going to try something, will you do copper and iron?

George H.

I have a 1000' perimeter, so that would be a bit of a nuisance. Thanks anyway. Bob

Ground. I.e., copper clad rods driven into the ground.

You can't leave a dog alone for a long weekend. We leave the cats in the house for a week to ten days, a couple of times a year, and have a neighbor (high school) kid look in on them once or twice a day and clean the (automatic) liter box once a week.

*Everything* is better in the South. ;-)

;-)

We have a lot of deer around. They munch on our plants and leave presents in the yard. They *love* the roses.

We're really dog people, too, but they do require more attention. Our cats have all been people cats (they sleep *on* my wife), so it's not like they're just sharing the house with their servants.

Huh? the current on the inner surface of the pipe will tend to cancel the current in the wire, but the current on the outer surface of the pipe will tend to match it.

--
  \_(?)_

sed

The 'current on the inner surface' is induced eddy current, because the pip e is getting magnetized. There's no current on the OUTER surface until the magnetization starts changing on the outside (dB/dt nonzero), and at high frequencies, that won't happen (there's a skin depth).

Eddy current heating of the pipe, and a whopping resistive + inductive impe dance as seen by whatever drives the buried wire, are to be expected,

Well, I rigged a miniature dog fence, a rectangle 400x300mm and fed it with 1MHz from my trusty HP3577, while sniffing around with a pick-up coil. I tried the bare wire and also with a 240mm piece of iron and then brass pipe around the wire along the long edge of the rectangle. Sort of like this (view with fixed-width characters):

--------------------- +-------------------------------------------+ | --------------------- | | pipe | | | | | | | | | | | | | | | | | | | +------------------------------------------|| signal in

Verdict: Bare wire or pipe, the signal as a function of distance is the same within a few dB.

I also tried back-tracking the wire along a larger perimeter,

580x480mm, bringing together and twisting the wires over some 200mm along one side. It's a bit hard to clearly show in ASCII art how the connections go, but basically, the current runs one way in the inner loop and back along the outer loop. +---------------------+ +------------------+ | | | | | | | | | | | | | +------------====================-----------+ | | | twist | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +----------------------------------------- + - | | \ \ | | \ \ | | \ \ | +-------------------------------------------------------+ +

Verdict: The signal has a clear drop, some 20dB, close to the twisted section. Elsewhere along the inside perimeter, the signal is a little weaker than before, ~6dB less @ 50mm, but still very present. On the other hand, in the area in between the inner and outer perimeter, the signal is about 6dB stronger than before. No surprise there.

So, as I've said, pipe does not work to shield the signal. Back-tracking and twisting the wires of some length *does* work.

Jeroen Belleman

You don't have to double loop the entire perimeter - just the section where you want to get fancy. Whether the feed for the doubled section is from the actual box, or from gap in the wire, the result is the same.

--
Grizzly H.

I have trouble visualizing what you mean. ASCII drawing please?

Jeroen Belleman

Yeah, if we go away the cats and dogs stay in the garage and a women down the road comes to care for them once a day.

I was going to add that the one thing I don't miss about the south is all the ticks and chiggers that the dogs bring back in the late summer.

George H.

Interesting, thanks for the experiment. What puzzles me is that I can use mu-metal to shield static and low frequency B-fields... so in my model of the world the iron should do something. Does one need "soft" iron?

George H.

Yeah I couldn't make it work "topologically" unless the wire went all the way around the perimeter.

George H.

Someone mentioned a transformer. So hook up a small ferrite transformer and adjust turns for best cancelling. Here's my thought, but I'm not to sure about it.

Mikek

Just take the single loop and run it around the perimeter. Break that loop at _any_ point(s) and construct a double loop.

|---------------------------------| | | | |----------------------| Feed |-----------------------| | | | |----------=====--------| | |---------| |--------| |---------------------------------| dog passage

--
Grizzly H.

this is an interesting problem.

Isn't the H field inside a loop nearly constant ANYWHERE inside the perimiter of the loop?

I think the operation of the fence is NOT due to the magentic H field alone,. If if was magnitic filed, then it would work in a similar fashion as those magnetic loop audio assist devices. Those work anywhere inside the perimiter of the loop, not just near the wire.

Since the dog fence operates only near the wire, it must not be purley H magnetic field operated, it is obviously not electric E field operated so it must be EM field.

So we need to shield or cancel an EM field, not an H field.

Am I wrong?

Mark

But how does the dog get too the passage without stepping over an un-cancelled section of wire. (Or to put it another way, your dog passage goes from outside the fence to outside the fence.)

George H.

Sorry, maybe I'm dense, but how would the dog get from its pen to the passage without crossing a singular wire at least once?

Jeroen Belleman

Huh, does that work? tying the output back to input?

George H.