Noise in Marine Radio - The Hull Truth

JBoggen · 03-03-2005, 08:16 PM

Have never had any problem with any noise being broadcast from my radio, until recently...everyone on the water said they could hear it bad....The only things that happened recently were - upgraded from 2 stroke to a new 4 stroke engine, changed from a neoprin atenna rail mount to a stainless steel rail mount - mounted to grab bar at center console, discovered a slight tear in the coax cable cover and outer mecsh wiring cover...enough to expose the inner core....any ideas on what might be causing the noise?....could it be the tear in the cable?

Sea_Dad · 03-03-2005, 08:52 PM

try swapping to resistor spark plugs.

hang on let me put away my hip shooter. how big is the tear in the shield?

JBoggen · 03-04-2005, 04:09 AM

bout 1/8" wide, goes 1/3 the way around....

Mumblerone · 03-04-2005, 09:57 AM

I don't believe in coincidence.* I'd replace the cable; do you have enough cable to cut off and reterminate?* I would also check for any corrosion on connector.* New motor?*

Sea_Dad · 03-04-2005, 10:38 AM

well I dont think thats enough to do it, but it's a simple test to wrap the cut with aluminum foil. Make sure the foil makes contact with the braid itself. If thats the problem it should make a marked difference.

But based on what you describe of the cut, I still would vote spark plugs.

rwells · 03-04-2005, 08:51 PM

Try transmitting with the engine off, that will let you know if the interference is from the plugs.

JBoggen · 03-04-2005, 10:07 PM

No interference at all when the engine is off.....so is this a for sure sign it is plugs???....Where would I be able to purchase the right plugs to eliminate this noise for a 2005 Merc 115 4-stroke....??

baypro21 · 03-05-2005, 07:52 PM

Just because it quit making the noise when motor is off doesn't mean the motor is causing the problem. It's going to be a process of elimination. Repair or replace coax, go back to old antenna or mount, check power connections to radio, try a buddies radio on your boat, try his antenna too, try your radio on his boat, ok - starting to ramble.

Sea_Dad · 03-05-2005, 08:27 PM

What plugs are spec'd for the motor?

baypro, sparkplugs are excellent transmitters. It is the sole purpose of resistors in the plugs to limit that ability.

JBoggen · 03-07-2005, 08:10 PM

I have replaced the entire cable/antenna with a new antenna...still has the problem...Manual specs out a NGK LFR6A-11 plug...any idea if they are resistor?

baypro21 · 03-07-2005, 09:53 PM

S D - Yes, I know. If the plugs are resistor and it is making the noise then JB will need somewhere to start. I believe you are more of an engineer, I, as a technician, merely pointed out a few basic troubleshooting tips. JB - Let us know what the problem was.

N3NFX · 03-08-2005, 08:21 AM

How do you have the radio grounded and are you sure it's spark gap noise?

JBoggen · 03-09-2005, 07:20 PM

The radio is connected to an accersory...I never had this problem before....until....I had a new 4 stroke put on instead of the 2 stroke...at the same time I switched to a stainless steel antenna mount (from the nylon mount), and lowered the antenna base below the level of the radio...The noise only occurs when the engine is running...??

rwells · 03-09-2005, 07:38 PM

The next step should be to determine if the interference is being broadcast by the 4 strokes or if it is traveling thru the electrical system. If you have a multi-battery setup and can temporarily isolate the VHF power source from the engine electrical system or perhaps use a separate battery for testing. If the interference is still there when on separate power it is probably the plugs or ignition wires. If the problem is gone when on separate power you can probably solve it by using a noise filter (ferrite beads) on the power and ground feeds to the radio.