Wednesday, May 22

Chapter 11: Eliminating Noise Interference

Now that you have your SSB station completely installed, it’s time to turn it on and start listening to the bands. Your antenna tuner system is automatically set close enough on receive that you should hear plenty of signals. Notice that there is more atmospheric noise on the lower frequencies than the higher frequencies. With your engines and other motors turned off, the noise is the usual type of background racket prevalent on every band until a signal appears.

Strong signals will usually completely mask out noise. Weak signals on 2 and 4 MHz will only quiet the noise by about 50 percent. The more sensitive your receiver, the more atmospheric noise you are going to pick up—this is normal. Poor receivers don’t pick up background noise!

Atmospheric noise is always there—on any frequency, but louder on lower frequencies. It can not be filtered out—to do so would also cause your distant radio signals to fade away.

The noise that can be filtered is electrical noise generated by the ignition system of your engine, plus noise from other motors onboard. Fluorescent lights also create noise that is usually heard on the lower frequencies. Other noise sources: fans, refrigeration, battery voltage monitors, inverters, computers and battery chargers.

Onboard noise sources should be filtered at the spot they are generated. There are filters for alternators, and filters for fluorescent lights. You can put resistor spark plugs on your gas engine, and electronic tachometer filters on your electronic tachs. Fuel pumps can be quieted down, and bait tanks silenced, with specific filters designed for each individual interference source.

Tune in a relatively weak signal on your SSB set, and then start the engine. If the signal is still there, your interference noise problems are few. However, if the signal completely disappears—you will need to get some filters for each noise interference source.

For noises and interference external to your boat, such as a passing skiff with an outboard that can be heard clearly on your SSB set, simply turn on your noise-blanker switch on the front of your radio. This will cancel out the repetitious popping sound almost completely. It may also help on your fluorescent lights. Although the noise-blanker built into your set is one way of dampening repetition-type noise, noise filters at the source of the noise are the best way to go. Like plugging leaks, you must methodically get every single one.