Thread: Induction loops
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Old February 24th 18, 01:48 PM posted to
Indy Jess John
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Posts: 1,307
Default Induction loops

On 24/02/2018 12:44, NY wrote:

I remember encountering this when I was about to record the speeches at my
sister's wedding. I'd made up a long length of screened cable with 3.5 mm
socket/plug to extend the output cable of my electret microphone that was on
the table, so the camera could be a reasonable distance away. I'd tested all
this just before and everything was fine. At the end of the meal, when the
speeches were about to start, I turned on the camera and got a horrendous
buzzing which was only present if the camera was powered from the mains and
not if it was powered by battery.

This could have been a problem with the power supply for the camera.
Some years ago I bought a second-hand laptop which I networked to a
desktop via a pair of "Powerline" ethernet across the mains units. It
communicated fine. Until the laptop battery started to run a bit low so
I plugged in the power supply which came with the laptop. This wasn't
the original power supply but a supposedly compatible equivalent. The
moment I powered on the power supply the Powerline pair dropped carrier.
If I switched off the power supply, communication was restored.

I have had other laptops since then and none of their power supplies
interfered with the Powerline communications, so it was just that
particular power supply which was radiating so much interference that
nothing near it worked. But if one power supply was such a nasty
product, I imagine there might be other similar problematic power
supplies in use.


PS I no longer use the Powerlines, having run a CAT5e from one room to
the other.