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Q-talk 125 - Heard on the Q-List

Heard on the Q-List

Dave Dugas asked the Q-List about some radio noise he was having and I think the responses are worth reprinting here.

Dave emailed: I've been having trouble with interference since I converted the RevMaster heads to auto plugs. So much that my TruTrak autopilot won't stay booted up. And my transponder light looks like a timing light. Lots of noise on the com radio too. It was suggested that I install auto resistor wires into the mag to cure this problem, and that it's been a very successful cure. Has anyone else had the same problem with the RevMaster, and if so, how was it fixed? What brand of wires were used?

I've spent the last week rechecking and moving a few ground wires that looked like they could have been more directly grounded, but have made no progress with the noise.

Finally, I ordered some mag filters and a power buss filter from Lonestar Avionics. The power filter is called the Eliminator. I spoke with one of the techs before I placed the order, and he said that I've got a 90% chance of fixing the problem by using the filters. Only drawback is that the engine has to be unbolted to access the P-leads at the back of the mag to install the mag filters. I wondered if anyone else has used these filters with any success. I'll post the results...good or bad, when I've finished installing.

Can the type of spark plugs solve the problem? RevMaster sent resistor plugs with the new heads, which I'm using. The engine runs great except for the ignition noise. Someone told me that resistor plugs shouldn't be used with a magneto ignition system. I'm open to any suggestions and thanks in advance.

Rene Robertson reponded with: My plug wires are Aurora 8.5mm Red silicone resistor wires see:


The swap is not an easy one though. I recall I took the back case off the mag. removed the old wires, drilled the holes on the drill press to the right size for the Aurora wires, siliconed the wires into the caps after stripping the ends so they work with the mag insulators. I then took 1/8" aluminum pop rivets, removed the stems and crimped the hats onto the resistor core of the wire to simulate the way the original wires made contact inside the mag.

This took a couple of hours to convert one dual mag over. I also did this for Dr. Steve's mag. Both of us have had no noise issues, but neither of us run the TruTrak system.

Then Roger Isaksson wrote: Resistor wires do two things, makes less of a noise in any electronics, and gives a hotter spark. Resistor wires as opposed to copper metal core wires, consist of compressed carbon powder in a blend only known to the manufacturer.

When the charge is traveling down the wire towards the sparkplug gap, the charge is encountering somewhat of resistance. That will allow the charge to build up and delay before the charge discharges in the sparkplug arc. The delay is microscopical and the difference in timing is so small that it has no consequence when it comes to timing degrees, but the net effect is a hotter spark.

Metal cores will be shooting the charge straight out, and give a weaker spark, and it will thus be able to build up a very significant magnetic field, disturbing electronic devices. Metal core spark plug wires will hold up very well, and be able to perform even in very dire conditions.

When it comes to resistance spark plug wires, look on them as a consumer product, in the same way as windshield wipers, brake pads, belts, hoses and shock absorbers. They all will have a finite active life span.

As they are used, the wires will slowly increase its resistance, until it has reached a point where the charge can no longer be transported to the sparkplug gap, and if it does, the charge has no power behind it, and is unable to jump (spark).

I once bought a car, for very cheap, the last owner had tried "everything" , and had given up. I started the car, it came to life and spluttered. I said hmm...bought it, and went straight down to a auto parts store, got sparkplug wires. After replacing the wires, the car ran great, and it came with all those other new parts the previous owner had invested in.

Ignition noise is an electromagnetic energy.

Gamma, xRay, radio, microwave, visible light, infrared, ultraviolet, and a long line of other existing electromagnetic radiation is the same thing with the difference only in wavelengths, and energy.

They travel in photon packages.

Depending on energy, the photon package will be able to penetrate matter more or less. Glass airplanes are piece of cake to penetrate.

Metal requires higher energies to penetrate, (Oh yes it can be done, but generally not easily) and it is the matter of choice to shield most electromagnetic sources.

It's better to shield the source, than the source it is affecting.

Electronic magnetic field can be tamed with drossels ( basically a bolt on resistor), with a metal housing, with a metal sock, or with resistor cables, etc.

Old magnetos have the old style ignition contacts, opening and closing for each ignition pulse. A condenser is attached to one side, and should be calibrated so that no, or almost no arc will jump when the contacts are closing. (Who uses those old ignition systems today anyway, mechanical activated points, stone age! You can still have a magnetic ignition without the points, there are many systems out there today)

If you get a strong electromagnetic disturbance from the points, that means that it is a sparking point, and it will have a very short life span. The contact faces on the points will very soon erode and throw the ignition timing off.

If you already have an electronic triggering device, but no points and still get noise, the first cure is always to try to balance the system with resistors, drossels, etc. ( check manufacturer, for specs on your system) Secondly, shield the system. The ignition system will in itself be shielded from interference from outside sources, and all other electronics will be shielded from the ignition system.

Hope this helps explain what's going on.

Mike Dwyer added: I'm using an electronic ignition with resistor wires and no-resistor aircraft plugs and I have no ignition noise. I did have some noise from the mag on the other side until I installed a mag filter on my Bendix mag. So, I hope you are encouraged that a mag filter should help. I understand that mag filters on Slick mags changes the timing and are not recommended. The power line filter is unlikely to remove mag noise as the magnetos don't connect to your power buss.

Now there is another question. The Plead should be a shielded wire where the ground is only connected at the engine. If you connect the ground to the mag and also to your power buss, you just made a big ground loop that can do all kinds of bad things.

You could also try some ferrite beads that snap around your spark plug wires or p-lead. These devices suck up the RF that's getting transmitted to your radios. You see them on most USB cables. They are the type that just snap in place over your wires.

Jim Patillo concurred with Mike: Have you tried the clip on noise filters that Radio Shack sells for approx.$5.00 each? They snap on right around the spark plug wire. Mark Summers used them on his O200 when he had a similar problem and they worked.

Finally, Dave writes about his success: The problem was fixed by replacing the spark plug wires with automotive plug wires. Rene Robertson gave me the brand that he has, which fixed the RF noise, actually eliminating it completely. Aurora wires from Canada are what we have, and I ordered them from their website: www.auroraelectronics.com

You can order a printed copy of Q-talk #125 by using the Q-talk Back Issue Order Page.