HF radio ignition noise

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Aug 26, 2003
Beaumont, Texas
I have installed an HF mobil radio in my cruiser and am trying to get rid of ignition noise. I have done a test to locate the really hot spots which are reradiating RFI and the two most troublesome areas are the distributer and spark plug wires and the ECM unit under the passenger side dash. I have installed ferrite rf chokes on the four sets of wires right at the plugs, and then I ran copper braid ground strap from the chasis of the ECM to the metal kick pannel. However, I am still getting the spark noise from the ignition system. I have run ground strap from both hinges on the hood to the front quarter pannels, and strapped all four doors to the body, including the rear hatch to the body. Additionally, I have run solid 2.5" copper straps from the four corners of the full length roof rack to the body via the screw holes left from the factory rack. I have done everything I can think of except changing the ignition system.

My question is this... Are there spark plugs I could install (like the resistor type) that would help improve this situation in addition to perhaps a better protected spark plug wire set? I have also read that it might be a good idea to replace the distributor cap but isn't the spark electronically controlled therefore eliminating poor contacts?

Please anyone help to suppress as much of the interference as possible.



I don't have the answers to your questions :(, maybe you could also try asking on one of the amateur radio sites (e.g., eham.com)?

Cheers, Hugh
well I did do that and I even received a copy of a letter from Toyota concerning the installation of HF radio communication transceivers, and they were pretty general about the subject. They suggested the obvious such as not running any power or antenna leads along side of any vehicle wiring harness etc. I have followed all recommended installation procedures, including running ground strap from the exhaust pipe to the frame.

What I really need to know, is there a better type of noise suppressed spark plug that I can use or should I just replace them with the OEM plugs? I also wanted to find out if there was a higher performance set of plug wires to replace the OEM's? And also, can I replace my distributer cap and possibly improve some there or since the engine is electronic spark controlled, does that mean there are no actual contact points to be replaced???
The OEM sparkplugs, 90919-01176, are resistor plugs. In addition, OEM wires and cap and rotor are difficult to improve upon.

Do you know what plugs are in it now? They may not be OEM. Also, the over-all condition of the secondary ignition components could be less than optimum.

You may want to consider fresh plugs, cap, rotor and wires.

Greetings Mark -

You sound like you've covered all bases, but there are two things you did not specifically mention in your post...

1. If you are using an ext speaker, wrap several turns of the audio output-to-speaker wires around a ferrite core;

2. Use shielded power cables (DC to the radio), grounding the shield at both ends;

3. Install bypass caps at the power source (battery...).

You may find the experience of this chap quite helpful...
http://www.qsl.net/ka6wke/ (Follow the "HF Mobile" link)

BTW, what brand of transceiver are you using?

Cheers, R - K6RG
Those sound like good improvements I can make and will do so. How do you suppose I can get an 8-10' #8 pair shielded? Could I try and strip the outer jucket from say 213 coax, and ther pull the center dielectric with center conductor out and run my power cables through the braid?. I am running an Icom 706 MKIIG with the remote head up front and the rig in the back side compartment. My antenna is a Hamstick on the rear hatch, and I am getting ready to install a HI-Q screwdriver type with a 5'' coil for 80m on the roof rack toward the back. I am then going to work on getting a Metron or Ameitron hf mobil amp but I will need to go ahead and do the dual battery upgrade before I do that.

What value cap should I use at the battery bypass? I imagine I can find that in the handbook or something because it seems I did run across that before.

Also, one more thing that I forgot to mention and that is with regard to the electronic fuel pump. I can hear it start up when the key is turned on so I imagine it too is contributing to the overall noise level. I wonder what the best way would be to suppress the rf there, perhaps if I can find where the wires come out of the tank or wherever the pump is, I could place some ferrites there as well.

Thanks for your help.

Mark - N5LPT
I think the fuel injectors can be a source of RF as well. Have you tested this setup with some other antenna setup that is not attached to the rear hatch? Are you using a high quality coax to the antenna?
What could be done to help shield the injectors? Would it be possible to make up some sort of shielding using foil on some form to help maintain its shape, and then just bond it to the frame? I think you may be right though about the injectors adding to the mix since they are electronically controlled. I'll look into these areas and will be sure to keep everyone posted on my progress. I have been sort of doing the same thing in the house for my station there. It is starting to drive my wife crazy as I try to track down all RFI and a/c power interference.

Hey also, I remember seeing somewhere on thhe forum where someone had built something out of wood which fits in the rear quarter pannels and provides a good mounting space for stereo amps and equipment. Does anyone know where that thread was or does anyone have other suggestions? I suppose I could go to one on=f the custom stereo shops and see what they might be able to come up with.


That looks great. Please do post how things turn out, I'm very interested as well. I've noticed that the Icom 706 has dropped in price by ~30% - maybe in response to the new Kenwood.

Cheers, Hugh VE3HMC
Which new Kenwood is that Hugh. It is hard for me to keep up with these new rigs. I guess they all pretty much do the same except for a few features. I would like to check out the new Kenwood that you mentioned though.

Here it is: http://www.kenwood.com/i/products/info/amateur.html..looks like a nice radio, although it's now about 2X the price of the Icom 706 in Canada!

PS, I think the guy's name with the 'box' in the back of his truck is John IIRC - this may help with a search.

Cheers, Hugh

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