Mains interference

[Fredxx]

Are you a spammer?

Before replying to a 14 year old post through a broken website read this first.

[Brian Gaff (Sofa]

However mains interference has actually got worse over the intervening times but its radiating from wires everywhere, so its now pointless trying to use filters. Just move to a clean area, go off grid and then see what happens. Brian

[alan_m]

Wasn't it mentioned recently that one of the biggest problems with interference was "green" energy feeding into the grid? Many thousands of individual sources not 100% synchronised to (nominally) 50Hz.

[John Walliker]

They are most definitely 100% synchronised to the nominal 50Hz of the grid. Otherwise there would be a lot of melted inverters. They can, however, produce large amounts of switching harmonics.

John

[The Natural Philosopher]

That is not the issue. The advent of switched mode power supplies and inverters that enable light cheap and small transformation of voltages between AC and DC as well as changing voltage levels depends for efficiency on very high speed switching. And that in itself if not immediately damped down leads to an enormous amount of RF energy being slapped onto the grid. It wont for a typical domestic solar panel get past the transformer between the 11KV regional grid and the local 250V phase, but it still consists of a local 'hash'

Doing stuff properly would add so much to domestic solar and the like that it would make the whole exercise pointless

[The Natural Philosopher]

+1

[Brian Gaff (Sofa]

Its normally the inverters that kick out the crud, but even the humble 5V usb charger or psu is terrible and of course all those internet over the mains devices. They issue is that as mains wiring is so lossy due to appliances plugged into it, the powers involved to make it work mean that you can hear the ticking and screeching several hundrered yards away. Then there are little inverters in apparently low power devices like dvd players even line level amps to boost signals for hi fi have them. The result is completely useless AM bands. It used to just be TVs that put birdies everywhere, but now most of these use switch mode power supplies and sit on standby. Also so do most computers, and of course laptop chargers are well known for radiating crud. It would in fact be relatively simple to make more efficient power conversion circuits even switch mode ones, but most makers seem to not bother about the waste of power in creating crud in the rf spectrum. We had a power cut the other day, my little short wave portable was reborn for ten minutes... Brian

[Peter Able]

I don't think it is particularly related to cost or efficiency. Just about everything electronic I buy nowadays terrorises me with its interference potential - and yet, here I am, typing at a desktop fitted with a super-cheap (about £12) PSU and with a radio receiver on the same desk listening on the 80m band - and no problems. What's more, I can only recall one such cheap desktop PSU ever being a problem.

Of course, it helps that these PSUs do seem to be fitted with mains in-line filters, but there's more to it than that. My wife's recently acquired treadmill improved when fitted with such a filter - but only a bit. The remaining noise is coming off the cabling from the PSU to the display.

Yet this computer has 11 USB cables with the potential to radiate mush - so there's something more.

I think it might be the quality of the switch-mode PSU transformer. I suspect that some of them are not fully assembled - i.e. when the two core-halves are brought together grit forces a gap between the two halves, the resulting inductance thereby falls and the transformer rings.

Get a few well-performing and a few bad-performing switch-mode PSUs. Get an oscilloscope with a times one probe, clip the probe lead to the tip. For each PSU, load it with a representative load and use the oscilloscope wand to pick up radiation from the PSU.

Such test done here show an overwhelming correlation between saturating transformers and radio interference.

BTW, Brian, same here. During power cuts all you hear here are the occasional electrified fence ticks. Very nostalgic.

PA