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Electric fence school

Radio frequency interference (RFI)

Radio frequency interference (RFI for short) is nearly always caused by the fence rather than the fence controller. RFI does not mean the faint click usually heard on most barn radios if there is an electric fence close by, but very loud radio or television clicks, often accompanied by disruption of a clear picture.

 Causes of radio frequency interference

What happens is this: there is a small spark somewhere along the fence wire, such as at a bad loop splice. This spark acts as a transmitter, with the fence wire becoming the antenna. This combination is quite capable of transmitting all over the neighbourhood, which is illegal.

There are four main causes of interference.

Poor splices

Make certain that all your wire splices are of the 'western union' type (see below), or if you have a high-tensile fence, then of the reef or figure-8 knot style.

A good splice

Loop splices after a year or so are extremely prone to causing radio interference. Even a good splice, if made with rusty wire, can be potential trouble.

Cracked insulators

Cracked insulators, especially porcelain ones, can cause a small spark, mainly at corners. You can usually detect a cracked insulator by placing your ear next to a suspected insulator (careful!) or looking at it at night.

For more information, see Types of insulators.

Poor grounds

A poor connection at the ground rod(s) is a common cause of RFI. A loose piece of grounded wire near a live one is another. For example, a loose strand of a rusty woven-wire fence on the opposite side of a post from an electric fence.

For more information, see Grounding tips.

Too powerful a fence charger

Using a fence controller that is capable of powering 50 miles of fence to operate a 100-yard feed lot can create problems. Using a less powerful fence charger, or if the fence charger has various voltage taps, using a lower tap might be your only solution.

 Detecting the cause of the interference

A small AM transistor radio comes in handy. With the radio turned on but tuned between two AM stations, walk along the fence. The clicks in the radio usually become louder when you reach the trouble spot.

Remember, it is illegal to cause radio interference.