VHF radio interference - alternator filters?

[singsail]

Help! I have just fitted a Silva DSC VHF set to my small outboard powered boat, and it's fine with the engine off - but once I start up I get a whine over the radio that stays fairly constant with revs, and is high pitched. I am guessing it is alternator. I have a Suzuki DF50 outboard, twin battery set up with the radio power supply from a main switchboard which also switches nav lights etc etc - any ideas please, especially in relation to what type of filter I should fit and where I can get it?

Thanks

 

[VicS]

The power supply for the radio should come dirctly from the battery (fused of course as close to the battery as posible) and run well away from other wiring. That should minimise the interference. Mine doesn't and my VHF is unusable with the outboard running. I would not like to say if the interference originates from the alternator or ignition system. Odd though that it does not vary with the revs.

You could try a suppressor capacitor across the rectified output from the alternator.

 

[DaveS]

I agree with VicS that it's odd that the interference doesn't change with speed. Another quick fix might be to clip split ferrites on to the wire(s) that are suspected of radiating, in this case presumably the battery charging leads. With a radio it should be easy (instant feedback) to see whether they're having any effect or whether re-positioning them or adding more does the trick.

 

[William_H]

It is very unusual to get interference from an alternator. Although I have no experience of O/B alternators.
It can be a sign of a dead diode in the recifier. So it may be worthwhile confirming the alternator is giving enough current.
Does the interference appear even if the motor is stopped but ignition is on? If that is the kind of set up.
it woulld be a good idea to run the radio off a battery which is not connected to the engine if the interfeence is still there it is not coming via the cable but rather through the air.

Suppressors can be in the pwer lead from the engine or to the radio or both.
The best suppressor is a filter with capacitor then iductor and another capacitor. The inductor can be several turns of heavy wire wrapped arounnd a ferrit etoroid (ring) or ferrite aerial rod out of an old radio. The capacitors to ground should be both high value like 10 microfarrad rated at a suitable voltage like over 20 volts and fitted positive to positive and a smaller capacitor (which has low inherent inductance) like .001 microfarrad in paralell.

good luck olewill