"Invisible fence" for dogs

Perhaps the gap needs to be longer ??

You don't mention the brand, but it's likely not an RF system, but rather a medium-frequency AC current flowing through the wire, creating a simple magnetic field surrounding the wire, that's sensed by the electronic shock collar. Sorry, you cannot use electrostatic shields to block magnetic fields.

I don't know if its possible to have a fixed opening. Yes, you can create a non-functioning section: simply run the wire back on itself, creating a cancelling field. Twisting the two wires helps. Ahem, your problem is then what to do with this folded-back wire, to continue on a complete-loop path around your closed-in area, which blocks in the animal.

--
 Thanks, 
    - Win

You don't mention the brand, but it's likely not an RF system, but rather a medium-frequency AC current flowing through the wire, creating a simple magnetic field surrounding the wire, that's sensed by the electronic shock collar. Sorry, you cannot use electrostatic shields to block magnetic fields.

I don't know if its possible to have a fixed opening. Yes, you can create a non-functioning section: simply run the wire back on itself, creating a cancelling field. Twisting the two wires helps. Ahem, your problem is then what to do with this folded-back wire, to continue on a complete-loop path around your closed-in area, which blocks in the animal.

--
Thanks, 
    - Win 
============================================================ 

Wild idea, but if it's detecting the magnetic field could you run the wire  
through a 3 or 4' long piece of iron or galvanized steel pipe?  Maybe that  
would provide enough shielding to give you a 3-4' door.  I'm thinking 3/4"  
pipe, or maybe 1". 

----- 
Regards, 
Carl Ijames

Steel conduit? Bury deeper?

RL

** These devices normally use frequencies in the AM band, so shielding ought to work. That it does not indicates your grounding of the shield is ineffective - so it radiates just like the rest of the loop.

FYI:

Invisible dog fences are very controversial with many dog owners who have tried them strongly recommending against their use.

In NSW where I liven their use is illegal ( under the Prevention of Cruelty to Animals Act, 2012 ) unless accompanied by a real fence that effectively contains the animal.

.... Phil

It's a PetSafe brand, Yardmax model. I found a number of secondary sources that said it did use a magnetic field. That's also consistent with it needing both ends of the loop wire connected.

Yeah, completing-the-loop is a problem with that. I think that I'll try to create an opening by raising the wire there. It will be a question of how high it has to be.

Thanks, Bob

it's a loop. it's also near-field, so you're picking up the magnetic field coax will give electrostatic shielding, but not magnetic.

dig a deep trench or make a high catenary so that the dog need not approach the wire. or assuming the breach is for your back door run the wire along the roof-line or across the basement floor.

or you may find that a large metal plate gives suffifient shielding.

it'll be in an ISM band possibly 13.56Mhz or 25Khz

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  \_(?)_

It does when it is the return path for the current, but not in this case where it carries little to no current.

--

Rick

I would not expect the frequency to be very high. The first thing I would do is look at the signal and see what frequency is used.

Then assuming the frequency is reasonably low, I would connect a 1:1 transf ormer to the wire near where you want to suppress the signal. Now you can connect the secondary of the transformer to a loop of wire where you want t he signal suppressed. Connect a sense coil to your scope and arrange the n ew loop so the signal is minimized.

This assumes you can get or make a transformer that will work at the freque ncy.

So the first thing to do is to measure the frequency.

A friend and I did something like this to see if the field from high volt age transmission lines could be cancelled. We made a large loop using regu lar house wire , probably 12-2 with ground. Connected the wires so we had a three turn coil and feed that with voltage from a Variac. We could can cel out the field from the high tension wires. We thought about the proble m of the field from the high tension wires changing with the amount of powe r being used by the power grid, and figured we could design a system which would null the field, but never actually make such an apparatus.

Dan

No. Pipe or no pipe, the magnetic field at a given distance

Yes, that should work.

Jeroen Belleman

I had another thought that would be fairly easy to try and cost very little.

How about connecting another two wires into the circuit. So where you want no signal, there would be three wires each with 1/3rd the current. The wires would need to be spaced maybe two or three feet apart, maybe more.

You would still have the signal , but not as strong.

Dan

That is *not* what Ampere's law says. Even if it did, it only applies to static fields.

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Rick

It won't work, because the pipe would just be a lossy ferrite bead... it'll load the entire loop circuit, probably prevent normal function everywhere.

Oh boy, now I want an experiment. I would think that a nice iron pipe would concentrate the B-field locally and make it smaller up above the dirt.

George H.

There's a method on the Petsafe website speaking to that issue:

"How do I allow a place along the boundary wire where my pet can safely cross?

To create the layout that you need, a double loop layout format will be necessary.

First, run the wire around the perimeter. When you get to the end, make a U-turn with your wire and backtrack around the coverage area.

Be sure to keep the wire 3 - 5 feet apart where you want signal. When you want to cancel the signal, bring the wires together and twist them

10 times per foot."

I have a friend who wanted to allow free passage for his dog into the house and garage but keep him away from flower beds, mailmen and the like. Took a lot of wire for the double loopnbut it all worked after a fashion.

An elevated section worked most of the time but the dog got zapped when standing for a petting on the way to the play area a couple of times - not a good thing.

--
Grizzly H.

Balanced path, tightly bunched.

Jamie

Great... I was trying to picture some way to make one section a twisted pair, but couldn't make it work.

George H.

When you say you grounded the shield, Grounded it to what? M

One of the problems with invisible fences round here is that we have coyotes, and the poor dogs can't run away from them because of the invisible fence. A certain number get eaten as a result.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net