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Electric fence noise

My neighbor has an electric fence for their horses. From there I have 30 kHz to ~8 MHz pulses on my antenna every second. Thankfully they are cooperative and let me have a look at the device and the fence.
I can't find anything wrong, its ground is proper and separated from mains earth, the fence looks ok. It was installed by an electrician so I assume everything is according to regulations.
Any tips how to reduce or get rid of those spikes without reducing the effectiveness of the fence?


  • Good place to start.

    Here I find when the grass grows up to the bottom of the fence that normally will get it going but also wires twisted together or just plain corrosion.
    I think it is any ark that will guarantee a broadband RF burst.

    Where I could not help fix the fence the noise blanker would actually do a decent job so long as I occasionally adjusted for the battery dropping.

  • Thanks, I will check the fence thoroughly. There is nothing growing to the height of the fence wires, maybe there is corrosion somewhere. Although the fence was newly built less than a year ago.

    The affected antenna wire is 55m in length, almost parallel to the fence in about 50m distance, some amount of interference will probably be unavoidable. Unless I add a low pass filter to the HV fence supply. But there will be a reason why the manufacturer doesn't do that from factory. Safety concerns if the HV pulse is too long?
  • I assumed the same, "inevitable" that there would be RF but saw a few fences for sheep installed that I had not spotted by radio, only by eye.

    Grass touching low wire was easy enough to track by ear and remove, then the noise blanker caught any clean regular pulse.
    I'm not quite sure of the physical process of (live - damp) grass touching, perhaps the flashover was a multiple event causing the field to be created and collapse enough times to induce radiation?
    I assume a long electric fence run has it's own inductance so should resist a very sharp edge, maybe that is why the breaks allow faster rise/fall and more RF + harmonic production.

    I don't have wire antennas so I could see that being more of problem but to me a clean pulse is just "NB" fodder and one of the easiest types of noise to cancel.
    There probably are rf filters on the devices but the quick rise time is, I assume, required for a good shock on a long run so they can't slug that too much.
    I don't think it actual RF coming from the fence energy source (unless it is faulty), I think it is how the voltage rise and decay is broken down by arcing.

    Happy to be corrected on any of that, hadn't really thought about it much until this came up.
  • Modern electric fence energisers have 'pulse shaping' which minimises noise from the energiser itself, so most problems are associated with arcing or insulation breakdown.

    One quick test is to disconnect the energiser and measure the resistance between the ground spike and the fence. This will usually indicate if there is any general degradation of the insulation to ground due to muck or moisture on the insulators. However it will not show up voltage breakdown or arcing when the normal high voltage pulses are applied, but you can often hear this acoustically (or sometimes see it) if you walk the length of the fence.

    The ARRL have some notes but other references can be found on-line.


    Martin - G8JNJ
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