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webby21
07-01-2008, 10:45 PM
I have Cruisecraft with lowrance sounder, gps, vhf, 27meg and cd radio in dash.
Turn sounder on and interference in AMradio is NBG........can't listen to Aussies thrash the Indian's for the noise. Not as bad with GPS. Both marine radios have interference with 27meg worse. FM radio is fine! Where do I start?
All electrics are coming from a common buzz bar. 27meg & AM/FM use splitter. VHF has its own arial. Once again where do I start? Thanks.

oldboot
07-01-2008, 11:58 PM
First of all you need to understand that you can only reduce interferance (noise) to ann acceptable level.

second it will be a multi pronged attack.

it all about detail & hygene.

As long as all your electrical is done in a workman like manner I think you would have minimal noise comming up the supply.

the sounder for a start produces large amounts of noise so the tranducer cable needs to be run on the oposite side of the boat to all your other wiring and as far away as possible from your radios.

those 27MHz/ am/fm splitter are nptorius for being lossy & dodgy..... try without it for 27Mhz and a seperate aerial

make sure your areials and their wiring is as far away as posible from your sounder and its wiring.

All of these devices are some form of radio transmitter or reciever so you will always have some sort of interaction.
FM radio has very strong inherant noise rejection, unfortunatly AM does not.

anything with a screen like sounders & gps will produce hash from the screen and the computer inside.

physical seperation is probly the most effective solution.

This sort of problem can be a head scratcher for the best of us.

Oh BTW
your DC wiring is good and heavy with good joints... isn't it?

cheers

finga
08-01-2008, 11:14 AM
First try without the splitter doova.
Then I'd be checking all power connections (especially from the busbar to batteries) before anything else that's too dramatic.
Don't forget the black wires. They're just as important as the red ones.

frank100
08-01-2008, 11:36 PM
Weby21, G'Day,
The first thing to do is switch off your equipment one at a time (except the radio ) to confirm it is your sounder is the culprit. If it is it's probably due to the cabling to the transducer inducing noise (does this because of a magnetic field) into your other wiring. It really should not because the neg. should act as a shield (ie shielded cable) so check the negative to your sounder is well connected (not corroded). Do not disconnect the transducer cable with the sounder on, that's liable to damage the sounder.
I posted a thread sometime ago describing how to connect a "capacitor" across you bus bar to reduce interference / noise, I strongly recommend doing that. (if you can't find the post let me know).
The main reason I did it was because my Lowrance died after 2 yrs. and I was told it was probably due to elect. spikes, probably from starting the motor.
Anyway I did some tests & found that the capacitor reduced the noise on the power supply to a tenth of what it was without it. Not bad for about $1.00.

Ther are lots of "surge" & noise protection gear on the market, but the capacitor is far cheaper.
Frank

frank100
08-01-2008, 11:40 PM
Weby21,
Fogot to mention, it could be your aerial connections from the spliter are crook, check the outer and inner of your cable from splitter to radio are nice & clean, as well as from the aerial to the splitter.

Frank

TheRealAndy
09-01-2008, 06:48 AM
There is a device you can buy called a tranzorb. These things are awesome at stopping spikes. I dont know how easy they are to buy but i know that prime electronics sell them (bowen hills qld). I will look up some suitable parts tonight. These will stop a lot of spikes and may help noise, but wont stop it. In my experience, the best way to stop noise is to stop it at the source. franks method of isolating each device is the way to find the source problem.

outsiderskip
12-01-2008, 06:22 AM
i use a second batteryfor all my electrics
make sure you use heavy wire from batt to buzz bar
and only use tinn wire and solder all fittings
have no interference sounding at 60klm per hr

pete

webby21
12-01-2008, 09:01 AM
Thanks all for the advice. Firstly I have checked and cleaned all contacts, wires from battery to buzz bar. Cleaned all contacts on backs of all electrical appliances. By the way they were already in prestine condition without any signs of green! Now resoldering splitter contacts. I really didn't want 3 aerials. 1 for VHF 1 for 27meg/AMFM only unless I can put a short aerial inside the cabin. The VHF has some distortion but nowhere as much as other. Do I install any size capacitor? Do I move the transducer cable only? I will do all this and report my progress. Regards, Webby

TheRealAndy
12-01-2008, 09:39 AM
Thanks all for the advice. Firstly I have checked and cleaned all contacts, wires from battery to buzz bar. Cleaned all contacts on backs of all electrical appliances. By the way they were already in prestine condition without any signs of green! Now resoldering splitter contacts. I really didn't want 3 aerials. 1 for VHF 1 for 27meg/AMFM only unless I can put a short aerial inside the cabin. The VHF has some distortion but nowhere as much as other. Do I install any size capacitor? Do I move the transducer cable only? I will do all this and report my progress. Regards, Webby

Found out what is causing the noise first, then go from there.