Electrical Noise

tim

As part of the original setup for the Trip, I bought an AutoCom ActivePLUS, which connected my iPod, my phone, and my UHF radio, and routed the sound through to my helmet. The other thing it did was feed all of that sound through to my helmet camera.

One of the things I’d hoped to do was capture some commentary of my own and radio chatter from the rest of the party as a way of narrating the video. Trust me… helmet camera footage is interesting for all of 30 seconds, music or no music.

One of the things that got in the way of that plan (and there were a few) was electrical noise. All the comms gear was powered off the bike, and all the helmet camera video I recorded was infected with a whining noise which changed pitch with the bike’s engine revs. I was aware of the problem before the Trip, and bought a noise supressor which was meant to resolve the issue. It didn’t.

Last weekend I bought a larger noise supressor, and started running some tests on gear powered off the bike. Using the AutoCom and the helmet camera, I ran a series of tests with various combinations of bike power and battery power. What I found was that, even with the filter in place, the helmet camera picked up a lot of noise when powered off the bike. The AutoCom itself seemed to remain reasonably clear on bike power, though the helmet camera (running off batteries) still picked up some electrical noise from the AutoCom.

Both these gadgets are designed to be fitted to a bike, so it came as a bit of a surprise that both would be so susceptible to electrical noise.

I started searching the ‘net, trying to understand the nature and cause of electrical noise, and found that the most common cause was a poor ground (or negative) connection. I started looking at the photos I’d taken when I first added the SAE cable that powers the tank bag, and I think I might have found a clue. The positive lead runs near enough to straight from the battery, so that should be reasonably clean. From there it runs to a relay behind the instrument panel. The trigger wire on the relay comes off the instrument backlights (which are always on when the bike is running). Again, this shouldn’t be a problem, since the switch side of the relay is isolated from the power it’s switching. The weak point, as expected, is the ground. Rather than go back to the frame, or all the way back to the negative terminal on the battery, I attached the ground to a negative wire off the back of the instruments. I can’t be sure, but I think that’s the weak point.

The next step is to rerun the auxiliary power on the bike, with positive and negative originating as close to the battery as possible. From there I’ll break out only for the relay, and use the same trigger source as before.

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