Ground Loop

From Honda Trail Bike Wiki

All electrical circuits have two sides; positive and negative (or earth, or ground).

Typically equipment that is added to a bike, is powered from the bike, which is easily done. However, if that equipment also connects into the bike's intercom there can be issues with buzz being introduced into the audio. This can be as little as a hum, or so loud that the audio is completely covered.

This is know as a ground loop, and is a result of multiple routes to earth, ie earth via the power lead, and also via the audio lead and intercom. To stop the problem, one of the routes to earth must be broken. The way this is done really depends on the need to power the epuipment from the bike; if there isn't a need, simply disconnecting the power will break the loop and cure the problem.

However, with something like a GPS, it's likely that power in and audio out will be required, so the only way to break the loop is on the audio side.

There are two ways of doing this, cut the earth cable, or use a ground loop isolator.

Cutting the audio earth cable will achieve the desired effect, but it means that the audio will get it's earth through the power side of the GPS, which may damage the unit. It's better to break the earth with a ground loop isolator.

The ground loop isolator breaks the earth by using two coils of wire to inductively couple the ground, ie, it's physically broken, but electrically sound. The makers of intercoms normally supply these isolators at vast expense, but they can be purchase from ebay and work well.

(Construction article to follow)

The only downside to this method is that audio quality may be slightly affected.