- microprocessors
- SSB radios
- TV and satellite tracking antenna direc-
tion sensors - VHF radios
So when equipment misbehaves, how do
we find the source of interference? I have two
tools I like to use.Tools of the Trade
Even though EMI and RFI are considered syn-
onymous, for the purposes of troubleshooting,
I divide them into two categories: RFI, which I
can hear; and EMI, which I can’t hear, but I
can measure. I use two tools—one somewhat
sophisticated, and the other extremely unso-
phisticated—to search out the potential for
EMI/RFI emissions to create problems. To
measure EMI, I use a gauss meter. To listen to
RFI, I use a simple transistor radio. Using both
of these two tools is extremely easy.Transistor Radio
Let’s start with the transistor radio. Pull out the
antenna if it has one and turn up the volume as
high as you can. Set it to the AM band and
tune it to just off the scale, either high or low,
so that no sound can be heard other than per-
haps some low-level static. That’s it—now you
are ready to try it out. Here’s how:1 Turn on a battery charger or use the alter-
nator on your car.
2 Gradually bring the radio closer to the
charger or alternator; you will clearly hear
static getting louder and louder.
3 Move the radio back and forth and all
around the interference source to be sure
you don’t miss any leakage noise.90 electrical systems troubleshooting
I use an AM/FM transistor radio that I picked up for $8
at Wal-Mart to listen to RFI emissions in both the kHz
range and part of the MHz spectrum.4 After you get the noise to peak, gradually
move the radio away from the source. The
distance at which you no longer hear the
interference becomes the minimum safe
distance (the separation distance or zone)
from the unit that you should mount sen-
sitive equipment.
5 Repeat this procedure with any interfer-
ence source on the boat.