Radio Noise from the MAC.

[Friendly]

I have a 72 MAC with Ricks CDI. I have installed muffers so now I can identfy some of the noise in the radio.
I use an I com 24 radio. I have a Softcom headset. The ignition sound of the motor drowns out the radio.
Any and all help is appreciated. How can I begin to solve this problem. I also have a new comptronic helmet but I had to order a patch cord to attact it to the Icom 24.

[dragonflyerthom]

Mark

You should be able to go to a radio shop ie Radio shack. Tell them you need an inline filter and they should be able to help you. You will need to put it in the antenna line. Do you have an external antenna?

Thom

[Rick Whittridge]

Mark, You might have to change your plug wires to a more shielded type. The Nascar guys have the same problems with there Hi output ignitions.

[Friendly]

Thom, I took the gyro and the radio and headset to Radio Shack. They said they did not know what to do, but the gyro sure brought them some walkin business. Radio equipped antenna is what I am using.

Rick, I am running the Accell 7MM spiral wire. Do you have a brand and part number? Don't I have to use the soild wire with your CDI set up?

[Harry_S.]

RFI can be a huge problem. I never used radio and/or instruments on my Bensen gyros, so...I didn't have the problems, the other early MAC users did have with radios.

My personal opinion is; to battle RFI, you must attack the cause, and the cause on a MAC powered machine is the lack of confining the interference?! The use of a finely woven metal shield and maybe a double layered shield, over the ignition wiring will be required. Do not ground this shielding to the airframe.

Like I said...this is just my opinion and...what do I know?!!


Cheers

[Friendly]

Harry,
I think you know more than I do about it. So far I think everyone is telling me to change the wires first.

I am all for that.

Has someone tried a particular brand of wires that work? I will check with a local electronic shop and see if I can purchase some sheilding to cover what I now have.

[Robert G. Stark]

Regular aircraft use fully shielded ing. leads. These are transmittion lines and the shield is connected to groung at BOTH ends. You would need shielded plugs too.

The RFI (noise) in on the same frequency as your radio is listening to. A filter in the antenna lead would stop the wanted signal as well as the noise. That is not the way to go.

Some engines (magnetos) are very hard to shield enough.

[C. Beaty]

Mark, resistor spark plugs might help if you can find them in 18mm size with the right heat range. You might also try carbon core spark plug wire. With CDI, starting shouldn’t be a problem with either or both.

Other than that, a shielded ignition harness is your only option.

[pwongkit]

Do not ground the radio ground (-)to the air fame.
pwongkit

[Friendly]

I will start with new wires tomorrow and post the results.

[Caribean_gyro]

use an external antenna. I have wire type cables and didnt have the nosie.

chuckP

[Rick Whittridge]

Mark, You must use a metal conductive inner wire for the CDI. Do not use carbon wires. The wire has to be better shielded than what you are using now. Do not use resister plugs with my CDI. There are wires out there that have a good shielding around the inner wire core. That is what you should try.

[Friendly]

Chuck B
Well I bought some wires and resistor plugs. Got home and did not have time to install.
Rick, I thought I remembered your instructions NOT to USE carbon wires with your system, so I purchased Accel 8.8mm 300+ Ferro-Spiral Race Wire.I also purchased DuroLast cables for a Ford CDI engine.
I installed the Accel wires and left everything else the same.
I am using a Champion D6 plug. I was sold some Autolite copper core 124 spark plugs. I asked for a comparison of the Champion Plug but they did not have one. I did not install the plugs as I wanted to look up the heat range first. The guy kinda stuttered when I asked if they were the same.

1st results is Accel 8.8mm 300+ Ferro-Spiral Race Wire and Champion D6
plugs has about the same static RFI as I had before.


The duro wires have no information on core or shielding. I would think they are carbon core.
I received an email that Aircraft spruce has the shielding for the cables. I guess this is my next step. Back to ordering. I will not try the resistor plugs and duralast cables. (Ricks recommendations for his CDI)

[Friendly]

Originally Posted by Caribean_gyro

use an external antenna. I have wire type cables and didn't have the nosie.

Chuck

Chuck,
Could you post a picture and more details of your set up? I was raised on comic books. I need pictures and captions

[C. Beaty]

Spark plug wires with a spiral wrap over a ferrite core are not shielded.

The spiral wrap provides a bit of inductance and the lossy magnetic core (ferrite=iron rust) is supposed to soak up the high frequency impulse noise from the spark.

Doesn’t always work though; Marconi spanned the Atlantic with a spark gap transmitter.

There is nothing wrong with carbon core wires; not as reliable as metallic wire but good enough for 50,000 miles in an automobile. If your Mac will start and run with carbon core wires, why not? They provide the most effective noise suppression short of shielding.

The low tension wires coming out of the magneto must also have noise suppression. In-line filters from Radio Shack, mounted as close to the magneto as possible, short leads and the filter ground lugs screwed to the magneto case will work here.