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electrical question -non boating related

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electrical question -non boating related

Old 05-24-2010, 05:34 AM
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cjd
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I am puzzled, and I know someone here knows the answer


I put in an underground dog fence, and it has been working for three weeks. Yesterday the collar stoppped functioning, and would only zap if I held it right next to the line.

After much time wasted, I figured out the issue, but I am still puzzled. Turns out, when I installed some metal brackets to hold some poles, I trapped the wire between the wall and the bracket. here is where it gets strange. The collar worked for the 8 feet between the pinched line, and the transmitter, but would not work for the 600 feet of yard.

It is tempting to say that I severed the wire in the plastic case, but the loop showed perfect continuity the entire time. once I loosened the bracket, the fence worked again.

It is as if I had blocked an air hose by pinching it. I had no idea that you could do the same with current. remember, i did not break the line, i just pinched it against the wall.

Does this make any sense at all?
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Old 05-24-2010, 05:48 AM
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Sounds like the metal bracket pinching the wire was (effectively) grounding the antenna out. If the metal bracket was ground, the insulation would not have to be pierced to cause a problem. Just being pinched and the ground in extreme close proximity to the antenna conductor will run the signal to ground. I guess you know the 600' loop around the yard is your transmitting antenna??? It would be like getting a long wire with alligator clips on each end, clip 1 end to the tip of your VHF antenna and clip the other end to the metal case of the radio. If you checked continuity from the case (ground) to the antenna conductor it would not be shorted (except for inductors internal to the radio from signal to ground, that's a differant lesson) but you can imagine it wouldn't transmit very far.
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Old 05-24-2010, 06:20 AM
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cjd
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I figured it had someting to do wth the bracket being metal, though I would have thought that I needed to pierce the plastic covering for the grounding to kick in.

Thanks
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Old 05-25-2010, 11:08 AM
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You can have continuity with broken wires that are touching, means nothing, you have to test it under load, or range asw in your case. You may have a pinched wire or something has gone bad.
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Old 05-26-2010, 12:45 PM
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Metal surrounding a single conductor carrying current will actually increase the resistance (impedance) ofg the conductor. It acts as a "choke". A choke is an inductor designed to block (have a high reactance to) higher frequencies in an electrical circuit while passing signals of much lower frequency or direct current. I think this may be what happened in your case.
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Old 05-26-2010, 02:42 PM
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Wow KASKIND

So for my low end mind, the low frequencies allowed the current to run, (and look like I had a good connection) But the highre frequencies (the ones that make the collar go ZAP) where bottled up in the 6 feet between the tranmitter and the metal brace.


Sounds right - (but when we start talking frequencies and ofg, I am trying my best to look like i get it). Sorry I was an english major.
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