Electric fence in 50 Kw near field.

[wking601]

I'm looking for ways to limit RF burns from an electric fence close to a 50 KW AM array. I understand that Frank Berry might have some first hand info.

 

[frankberry]

Ground the fence through a capacitor. .01uf to .1uf at, perhaps, 2.5kv should work. Depending on the operating frequency of the station and the length of the fence, you may need to ground the fence in several places.

 

[davideduardo]

Ground the fence through a capacitor. .01uf to .1uf at, perhaps, 2.5kv should work. Depending on the operating frequency of the station and the length of the fence, you may need to ground the fence in several places.

Several items from experience at a 100 kw AM:

Fence wire on insulation-prone posts (wood or cement) may have wire junctions which are physical and not soldered. Make sure each stretch of wire is grounded and the joints may oxidize or be loose.

One piece of wire was a wavelength long. It did not like being touched. We insulated it at a random spot and grounded it.

A section of mesh fencing and a gate surrounded the entrance side of the property. In the construction process, the engineer had run a copper strap about 20 cm wide from the copper sheets at the tower base out to the entrance, and the fencing was connected to this with clamps that were then soldered since the ground was copper and the fence was whatever they made galvanized fences out of. That was mostly done to prevent maintenance people from getting RF burns as the lobe towards Buenos Aires was close to 200 kw.

 

[frankberry]

Several items from experience at a 100 kw AM:

Fence wire on insulation-prone posts (wood or cement) may have wire junctions which are physical and not soldered. Make sure each stretch of wire is grounded and the joints may oxidize or be loose.

One piece of wire was a wavelength long. It did not like being touched. We insulated it at a random spot and grounded it.

A section of mesh fencing and a gate surrounded the entrance side of the property. In the construction process, the engineer had run a copper strap about 20 cm wide from the copper sheets at the tower base out to the entrance, and the fencing was connected to this with clamps that were then soldered since the ground was copper and the fence was whatever they made galvanized fences out of. That was mostly done to prevent maintenance people from getting RF burns as the lobe towards Buenos Aires was close to 200 kw.

This is an electric fence. It can't be directly grounded.

 

[wking601]

The ampitude of the electric fence pulses must between 3KV and 7KV to overcome contact and ground losses. If I'm not mistaken the price for a capacitor that you mentioned is pretty stiff. I had understood that you had a similar problem in Tampa. At the site in question, there is no sign of such mitigation. The RF burns are pretty severe. Would it be possible to speak with you? As you can see speaking with some one is more efficient than E-Mail. It seems that David misunderstood me. This is not an ordinary fence, but an insulated wire that provides a shock to livestock.

 

[davideduardo]

This is an electric fence. It can't be directly grounded.

Ah, I missed that. I'm used to issues with "regular" fences either around the site or on very close by farms or properties. The most usual complaint is that kids or pets or farm animals get shocks. The animals are smart enough not to do it again, but the kids not so much.

Also have had a couple of cases of "singing fences" where the barbs on barbed wire act like a crystal set! I wonder if cattle become politically polarized if they have to hear Rush every day on the fence.

 

[K6JHU]

Maybe just accept the free power. Put a power resistor to the ground rod. Not wirewound and shunt some of the power to ground. Adjust the resistor until you measure 600-700 volts. Then you can turn off the fence charger and let the station power the wire ?

 

[wking601]

The fence "controller" provides a controlled duration pulse every second or so. This gets the attention of whomever or whatever comes in contact, without injury. The RF could conceivably burn someone. pretty badly. ( you probably knew that and I appreciate the humor).

 

[frankberry]

The ampitude of the electric fence pulses must between 3KV and 7KV to overcome contact and ground losses. If I'm not mistaken the price for a capacitor that you mentioned is pretty stiff. I had understood that you had a similar problem in Tampa. At the site in question, there is no sign of such mitigation. The RF burns are pretty severe. Would it be possible to speak with you? As you can see speaking with some one is more efficient than E-Mail. It seems that David misunderstood me. This is not an ordinary fence, but an insulated wire that provides a shock to livestock.

Wking601,

When I built the 50kW WQYK-AM transmitter plant, the entire tower field was fenced-in using 6' chain link. I had each link welded to it's adjacent link, a huge task. After the fence was installed, it was connected to the ground system in multiple locations. I did this to keep the fence from "singing" and producing a lot of rich harmonic energy. It worked.

You might also be able to break up the hot fence by cutting the barbed wire and installing RF chokes between the cut sections. This would permit the electrical fence pulses to pass while blocking the RF.

As for capacitors, you can find .001uf/2500 volt caps here:

https://mgs4u.com/product/transmitt...QYImJ64B1JtuDjt7kaApfZEALw_wcB&v=7516fd43adaa

.001uf caps will probably work if you install a number of them along the fence line. The total capacitance of the combined capacitors would be much greater than that of a single capacitor.
If you require a higher voltage rating, put multiple caps in series.

I will contact you via email.

Frank

 

[Kelly A]

But hold on here.. It's an electric fence. Who cares whether you get zapped by 7KV electrical or RF? It's supposed to hurt if you touch it.

If you want to breakup the RF, I'd put some "J" type torroid cores in series to each wire every 50 feet or so. Those torroids will block the RF, but pass the pulsed AC.

 

[frankberry]

I've spoken with the OP and discussed the problem.
Another thing to consider, the "hot" electric fence can radiate lots of harmonic energy due to loose, rusty barbs or splices.
It's important to solve the issue.

 

[davideduardo]

But hold on here.. It's an electric fence. Who cares whether you get zapped by 7KV electrical or RF? It's supposed to hurt if you touch it.

If you want to breakup the RF, I'd put some "J" type torroid cores in series to each wire every 50 feet or so. Those torroids will block the RF, but pass the pulsed AC.

But the fence systems I've seen do pulses, so there is no chance of an animal or person getting electrocuted. Otherwise, you have a real danger when it rains or if the land is naturally wet or moist.

 

[Kelly A]

But the fence systems I've seen do pulses, so there is no chance of an animal or person getting electrocuted. Otherwise, you have a real danger when it rains or if the land is naturally wet or moist.

I don't think anyone is talking about electrocution, but potentially getting burned by the RF. Still to me, unless the fence is re-radiating and screwing with the station's directional pattern, or causing NIER exposure levels to exceed amounts in a publicly "uncontrolled" environment, one isn't supposed to touch the fence. Either they get zapped with pulsing electrical or burned by RF. Whichever the result, touching the fence can be unpleasant.

 

[bulwnkl]

Electric fences are supposed to hurt, not harm.