Monday, April 17, 2006

GPS - mount and audio

Some of you have probably seen the GPS on Brenda's Goldwing. We had it on the Enchanted Rock trip (April 1-2) but it had a couple of problems that are finally fixed.

First, it is such a large screen (5 inch diagonal) that I didn't really like it mounted on the handlebars where it was on April 1. So I moved it to front and center as you see here. The mount is just a simple plate that uses 1 inch spacers to stand off of the two screws beneath the key cover plate. A RAM mount is bolted in place along with two rubber jam nuts that provide support without scratching the plastic underneath.

The second problem was engine noise in the audio. The Lowrance iWAY500c has a built in MP3 player that hooks into the 1/8 inch stereo auxilliary input inside the left pocket of the Wing's fairing. It is really nice to have your music loaded into the GPS and not fret over radio stations and the like. And the AUX input plug makes it all simple and clean to use. But somehow the installation with the iWay coupled an engine whine into the audio that made both the music and the voice navigation instructions unpleasant to have in the headsets.

Since the engine whine varied with engine speed, I assumed that the noise was being coupled in on the power leads and bought a P.I.E. NF-5 noise filter (pictured above) and installed it. This is a simple filter that connects to the battery +/- and sends clean 12Volts DC out on the blue wire to your component. It will clean up any alternator noise and such that is coming into your component through the power source. In this case, the NF-5 had no affect. We still had this unbearable engine noise in our very expensive GPS/MP3 player.

There is only one other common source of audio noise, and that's a ground loop. The problem is that ground loop noise is usually a more random popping or hissing and not related to engine speed.

Never-the-less, I bought a P.I.E. EIS-ILNO (pictured above.) It's an omni-directional noise filter that plugs inline with the audio signal. I had to replace the four RCA plugs that come on this filter with two (one male, one female) 1/8 inch stereo plugs which takes a little soldering skill. Once I did that and plugged it into the connector in that left hand fairing pocket, the noise was gone. My theory is that the shielding on the goldwing AUX cable and the shielding on the GPS were causing the ground loop.

A ground loop is when a shield conductor (that braided silver or copper wire on the outside of a coaxial cable) is grounded in more than one place in a system. Being grounded in more than one place allows extraneous and noisy current to flow in a sort of circle. This current can be heard as audio noise. Ground loops cause all sorts of havoc, and in extreme cases can even couple in energy from lightening strikes in places like refineries or buildings, although I've never seen that happen in a vehicle. Ground loops can happen on any vehicle powered audio device including XM radio, MP3 players or CD players and can be very difficult to diagnose. They are even more likely to occur when the shield is also used as a ground for the audio signal like it is in the Lowrance iWay and Honda Goldwing.

The EIS filter is basically a set of one-to-one transformers that de-couple the electronics on each side of the system thereby breaking the ground loop. It will clean up any noise that is coupled into the system on the audio wires themselves, as opposed to the power leads. You can also fix ground loops by acutally finding the second (and third, fourth...) place that the shield is grounded and disconnecting the ground from those places. That can be a tough job though and the isolator works pretty well.

The EIS filter took care of my audio problem and if you are having audio noise problems with your bike, the chances are that one of these two filters will fix your problem too. Each of these filters is available on the web for $10 - $15 plus shipping.

E-mail me if you want to discuss this posting, or let me know if you've fixed an audio problem on your sled.

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