VHF Radio Interference from Outboard

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Stormin Norm

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10 May 2002
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My radio suffers from interference from my 90hp 2 stroke Mercury outboard, a rapid click,click,click, type of noise. It does not really interfere with the reception when listening to someone else broadcasting but it is a bit annoying. Is there any filter or suppression gadget I can fit the sort this out? Thanks.
 
I have been told that spark plugs can cause this if they are not of the surpressed type. I cannot verify this but it could be a cheap place to start.
 
Hi Norman - I was going to reply to your request as I have done a lot of work on RFI/EMI over the years and whilst I was searching for metal spark plug shrouds and braided earthing covers to sit over the HT lead as found on military vehicles, I found this link which you might find interesting.

All the salient points can be applied to your problem as I suspect you only really get interference when listening to AM broadcast stations and to a lesser extent when listening to marine VHF transmissions:

http://www.ultralightnews.com/pilotslounge/ignition_shielding.htm

Hope it helps in suggesting a way forward for you?
 
Also, you will probably find that the outboard motor cover is made of plastic? You can buy (metal) screening material which can be stuck to the inside of the plastic housing to act as a screen.

Each piece of screening material would need to be bonded to the other and then bonded to the metal engine block to get best effects.

Basically you are embarking upon a very difficult journey when you try to eliminate all RFI and really there is no hard and fast method which will guarantee 100% success

Let us know how you get on. /forums/images/graemlins/smile.gif
 
are you charging from the outboard, if so it may be coming through the wiring. To prove if this is the case disconnect the charging and see if it still does it.

Steve
 
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