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Preventing electrical noise

Electrical noise in modern homebuilts seems to a common problem. Probably due to all the digital stash put into them. Googling this I found a great site (I think) with lots of simple suggestions of how to prevent it. It’s not aircraft electrical, but I would think the principles are the same?

The site is https://www.ia.omron.com/support/guide/22/further_information.html, and the noise thing starts about half way down. What is a surprise to me was the use of twisted wire for everything, also the supply.

The elephant is the circulation
ENVA ENOP ENMO, Norway

If you are trying to cut down on electromagnetic emissions from a power supply, it is certainly best to use a twisted pair for the output cables, because it minimises the area of the radiating loop

That is common practice when getting a piece of your equipment through the CE emissions lab tests – you wire everything up using the tour de force approach even when everybody knows that the end user won’t

It would be better to filter the power supply output better, but that costs money…

However I don’t think this is the main issue in homebuilt avionics in “plastic planes” which have no bonding so e.g. an RV is fine but a Lancair is not. The main issue in the latter is that nothing is really grounded. The only thing resembling a ground is the collective effect of the shields of the various cables, plus any ground plane which one has (has?) under the base of any antenna.

It’s a bit like in PCB layout… about 25 years ago, it became quite cheap to have 4-layer PCBs so you used a solid copper plane for the ground (and another for the +5V, and then the two outside layers carried the signals). Before that, 2-layer PCBs, meeting EMC regs with anything that contained a CPU was a nightmare, but pre-EU (CE) almost nobody cared anyway…

If I was building a “plastic” homebuilt I would spray the entire inside of the airframe with a zinc coating, like this (not cheap), and bond the various parts with cables like they do in certified planes which have a metal mesh in the composite.

For power connections, even better to use a coax, or a twisted pair with an overall shield, with the shield going to the (metal) airframe. I have done this with USB chargers, many of which radiate like hell, killing VHF comms on some frequencies. But sometimes the issue is so bad that nothing works well enough. The other problem is that you never know which frequency has been wiped out. It could be some ILS one… One would need to do a sweep with a spectrum analyser. Of course no GA aircraft manufacturer does any of this…

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Shoreham EGKA, United Kingdom
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