underground dog fence

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KE0YRP, Dec 13, 2019.

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  1. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    "RF Overload" of the cheap BCB radio front end.

    Any radio can be overloaded given sufficient signal strength/proximity.
     
  2. KF5LJW

    KF5LJW Ham Member QRZ Page

    You are welcome, just know from first hand experience. What you say and thought about sound waves is absolutely true in air or an atmosphere. In solid rock and water, this great big ball we live on, is a different story. What we think of RF does not penetrate water or dirt. It takes much lower frequencies like ultrasonic fish locators and all the variants of ultrasonic. Instead of thinking of RF energy think Magnetic and Magnetism. The earth has a magnetic field and you can send magnetic waves through the earths magnetic field.

    Somewhere in Michigan the USN operates a VLF radio. Its location is special because the soil has very poor conductivity. Last place you would dream of putting up a large radio system to communicate around the world. It takes two huge massive electrodes buried deep in two different locations with the transmitter between the two locations. They send a modulated AC current between the two electrodes which produces a huge magnetic wave that travels through the earth. In effect, they modulate the earths magnetic field. just like sound waves compress air. FWIW the communication is just one-way shore to ship.

    The dog fences at 7 to 10 Khz just produce a very weak EMF that can only be detected within a few feet. EMF is generated by a lot of devices like transformers and can be detected with a GAUSS METER built right into the dog collar. I feel a disturbance in the Force. :cool:

    To prevent accidental detection and causing false operation, like a TV or your toaster oven, they modulate the signal with either AM or FM signal in very short burst with timing of on/off ratio. Think of it like Morse Code. When the Gauss Meter detects a specific pattern, triggers and you get a YELP out of the dog when he close enough.

    The Fence is really pretty simple. A long wire acts like an inductor, and when you apply a small current produces a magnetic field we can detect. Think of an AF amplifier, and we take the speaker leads, connect one to a rod, and the other a long wire around the yard. We now run a 8 Khz signal at full volume. We will produce a 8 Khz AC current flowing in the earth we can detect.
     
    Last edited: Dec 14, 2019
    NH7RO likes this.
  3. NH7RO

    NH7RO Ham Member QRZ Page


    Now this 8KHz dog thingy finally makes sense to me---but I bet the switching power supply for it is the real RFI culprit. Thanks again!
     
  4. WA3CUJ

    WA3CUJ Ham Member QRZ Page

    The PetStop fence uses Digital Modulation (I am not sure which type FSK, PSK, or ASK).

    Thanks for the discussion, I found it very interesting.
     
  5. WA7F

    WA7F Premium Subscriber QRZ Page

    You are Ok as long as you don’t install a BOG receive antenna. This could result in BOG-DOG coupling.
     
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  6. KF5LJW

    KF5LJW Ham Member QRZ Page

    You are welcome. You just got hung up on sound wave energy instead of electrical energy. You can do the exact same thing without a fancy name like Invisible Pet Fence. Take one of your AC circuits in you house, and just run a line conductor from your main breaker panel outside and bond it to a Ground Rod pounded in the ground. Turn the Breaker on, and basically nothing happens that you can tell initially. But if you measured current, you would find a few amps of current flowing through dirt. In fact have done this many times teach Grounding and Bonding to Engineers and Electricians to demonstrate why you cannot use dirt as a conductor. The 15 amp fuse does not operate because there is not enough current to make it operate. However if you had a Gauss Meter, you would have a strong magnetic field coming off the wire you ran from the breaker box and get a very high reading within a few feet.

    Years ago I got contracted to do a Grounding Audit and RFI Investigation in a large office complex. Three employees CRT screens were heavily distorted and doing weird things. Took me less than a minute to find the problem. The three employees were side by side in a row along a wall. As son as I sen the screens I asked what was on the other side of the wall? I was told the Electrical Room. Walked into the Electrical Room and found what I was looking for immediately. A Transformer up against the wall right where the employee on the other side of the wall. EMF was interfering with the CRT's causing distortion of the electron beams in the CRT screen. Easiest $1000 I ever made.
     
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  7. NH7RO

    NH7RO Ham Member QRZ Page

    Or if you employ a LOG as well as a BOG and have a dog, well, consider the tangled-up barking-its-head-off mess that might ensue...
     
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  8. NH7RO

    NH7RO Ham Member QRZ Page

    Roger that---I get it now---I was too focussed on AF/ RF and couldn't see the electromagnetic forest for the EMF trees...!
     
  9. KF5LJW

    KF5LJW Ham Member QRZ Page

    Me like.
     
    NH7RO likes this.
  10. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Title: "Underground dog fence"

    I'm still waiting to hear about this underground dog! :)
     
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