Radio interference

Was out last weekend and had a prob that I've never had before. While trying to transmit on the VHF all I could get was what sounded like the engines ignition system on the thing. Never had this prob before. The only change to the boat that has been carried out is the fitting of a plotter. Anyone got any ideas!

Sounds like a bad earth on the power supply or maybe the aerial co-ax.


DM

I had the same problem on a previous rib. The sounder would interfere with the VHF. I made the mistake of fitting a noice screen to the VHF power lead and also cleaning all the earths. On eof the things fixed it ......don't know which one though!!! :rolleyes:

There are two possible problems here ,you could be picking up RI from the plugs,have you come across resistor plugs or resistor plug caps, dont go fitting them unless it is okayed in the engine manuel there may or may not be equalivent plugs for your motor not all ignition systems can cope with them.The problem is probably caused not by the introduction of the plotter,but the cables running in close proximity to the radio areial cable.If you ran a live wire beside the areial lead a voltage can be induced into it from the live wire, (positive).Without doing anything, try to seperate if it is done the new cables from the vhf cables, see if this cures the problem, try turning off plotter from its source, see if this cures the problem, finally with the VHF switched off disconnect the aerial connection, check if the outside braid of the coax is making a good connection to the outer part of the gland, this screen should only be connected at one end, and not to anything else which represents earth at the other end, ie A frame metalwork, or a metal mount which has a connection to earth.Check to see if the VHF has negative earth, this will be evident from the manuel ,it more than likely will have, take a jump lead from the battery negative and connect it to the outside of the VHF radio aerial gland and see if this provision of a new negative removes induced noise.

I've not touched the plugs in the engine, they are the same make and type that are recommended by the engine maker. The only new bit of equipment is the plotter. None of the power cables run anywhere near the vhf coax. I deliberatly kept them apart. The only thing that is remotly near (electrically speaking) the vhf is the power lead from the plotter goes to the same block of fuses. Never had a prob with the sounder giving any interference with the vhf before. I wiuld'nt have thought that the plotter would give any, as its a reciever and does'nt produce a "signal" like the sounder.

Its got me stumped!

What make of engine are you running?

JW.

try fitting an car stereo power suppressor to the radio positive cable. Only a fiver from you local halfords and that will eliminate any noise coming from the engine (in theory) and if the interference persists try looking more in depth at the vicinity and routing of you cabling as mentioned above.

If you pull the fuse from the plotter supply then at least you will know it's definitely that!