Electrical Interference – The hunt with my mate Billy.

I have had a problem of a really strong pulsating radio interference signal lifting my noise floor, the strongest signal were at 350Mhz, 521.5Mhz, 924.7 Mhz, 990.3Mhz, 1.802Mhz, 145.537Mhz and 145.000Mhz detected by my trusty AM radio, Billy.

SAM_5244 (Large)Billy the Fish with a broken gill.

Preliminary investigations walking around the house and outside pointed to it being the neighbours solar panels as when I got near to his garage where the inverter is located, Billy went nuts, it was as though it was radiating out everywhere, putting Billy over my buried radials in lawn amplified this signal up, even putting the radio near the earthed outside tap picked the interference up.

As I was convinced the interference was from outside of my house, the only way to prove this was to turn the power OFF to the house, so with Billy in hand, I turned the power OFF expecting the radio to go quiet, but it didn’t!

Looking around in the garage, where I turned the power off, for a source of the noise, I saw the UPS for the PC was ON, turning this OFF the noise reduced, but still did not stop, walking around with Billy the interference was still very evident.

Went inside the house and heard two other UPS bleeping, the first one is in a room directly above the garage and as soon as I turned this OFF the majority of the noise stopped.

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The next visit was to a room off my home office where my network kit is installed, the main UPS is fitted there, turning this off and the radio went dead quiet, so much for my theory of blaming the neighbours solar panels!!

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So now to start turning things back on, with all the breakers off, I turned the main power switch ON, and the radio stayed quite, turning the breakers ON one by one, I didn’t get very far until the radio kicked off again.

First breaker causing a problem was the garage sockets, turning the switches on the sockets OFF in turn, I came to one which stopped the noise when turned off, it was a 12v switched mode power supply for a camera causing the interference.

The next breaker to cause me a problem was the one to the house sockets, switching this ON, yet again caused the radio to detect interference, back into the house with Billy, the hunt was on!

It turned out to be right under my nose in the office, it was the Blitzortung lightning detection controllers power supply unit.

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I will investigate sourcing a low noise 5v DC linear PSU as well as making improvements to the controllers earthing as I don’t want to disable the unit.

I do have background hum from the power supplies feeding the Netgear switches and other small load items, but it’s nowhere near as bad as it was and I know what’s causing it, which is good, total elimination is the optimal solution, but proberbly unrealistic, so bit by bit I’ll chip away and get the noise floor as low as I can.

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2 thoughts on “Electrical Interference – The hunt with my mate Billy.”

  1. Hi Danny,
    Thanks for the link, the problem was a ‘wall wart’ type switch mode PSU, this was replaced with a highly smoothed linear unit off ebay and the results were dramatic, radio noise was reduced and the lightning detectors sensitivity gain has never been as high.

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