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Author Topic:   Noise Filter for Lowrance
floater88 posted 06-01-2013 06:17 AM ET (US)   Profile for floater88   Send Email to floater88  
I have a Lowrance HDS 7 on my Revenge I use for fishing. When trolling with the kicker, or using the main, I am getting interference on my SONAR screen. The power wire is connected to the electric panel and the transducer cable is away from any other electrical wires. I have two batteries on board; the panel is fed from the main engine battery; when trolling, the kicker is charging its own battery, but not the battery the Lowrance is powered from. Is there a filter of some kind I could get that would reduce this interference? Thanks
jimh posted 06-01-2013 08:52 AM ET (US)     Profile for jimh  Send Email to jimh     
Move the wiring for the SONAR transducer away from all other electrical cables. On many older outboard engines the safety lanyard circuit or KILL circuit operates at a rather high voltage. It can induce noise into the SONAR transducer wiring. There is really no way to filter this; you have to physically isolate the two wires. Run them by different paths to the helm.

Since you report you still get interference on the SONAR even when the battery that it is powered from is not connected electrically in any way to the engine that is running, it does not sound like the interference is being introduced on the power wiring.

jimh posted 06-02-2013 10:56 AM ET (US)     Profile for jimh  Send Email to jimh     
If a particular device is creating electrical noise in the power circuits, the best approach to suppressing the noise is to put a filter in the power circuit of the device that is creating the noise. The filter will block the noise from the device from being carried back to the power source and being distributed to all the other devices. This is more effective than trying to put a filter on the power leads of all other devices that are being affected by the noise.
floater88 posted 06-03-2013 08:28 AM ET (US)     Profile for floater88  Send Email to floater88     
Thanks jimh. I'm gonna go and talk to the guys at Radioworld up here in Toronto. They should be able to sell me something that would help. The sonar cable is away from all other sources but as you say the interference may be coming from the motor. Thanks
jimh posted 06-03-2013 09:08 AM ET (US)     Profile for jimh  Send Email to jimh     
A good test to see if the interference is conducted into the SONAR on the power wiring is to temporarily remove the power wiring of the SONAR from all boat circuits, and connect it to a temporary 12-Volt battery source. Run the SONAR with its power wiring made very short and connected to a small 12-Volt battery--maybe something borrowed from a lawn mower or other smaller device. This should eliminate the power wiring on your boat as a source of the interference.

If the SONAR still shows interference when running on the completely isolated battery, the conclusion is the interference is being conveyed into the SONAR by the transducer or its cable.

floater88 posted 06-03-2013 06:23 PM ET (US)     Profile for floater88  Send Email to floater88     
Great idea. I have an ice fishing lowrance with a 12 volt I can use. Thanks

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