About RFI interference

RFI interference is something that is common on boats.  If you want to understand troubleshooting the problem of Radio Frequency Interference (RFI) on your electronics such as depth sounders, instrumentation and fishfinders, as well as your marine SSB, HAM and VHF radios and the GPS, then you have to understand the causes. The average boat has several RFI noise sources.  These noises are often classified as Radio Frequency Interference (RFI) or Electromagnetic Interference (EMI). They are an insidious enemy of communications and electronics systems. It corrupts the GPS position fixes, makes a mess of your communications and generally causes electronics performance degradation.

What is RFI Interference?

Essentially RFI interference and noise is superimposed as a disturbance or a voltage transient either on the equipment such as the radios or even the whole boat electrical power supply, or on the data and signal lines that carry your GPS or navigation data between each other. This noise is then processed along with all of the good data, which then corrupts or degrades the processed information. 

The Voltage Transient

The voltage transient is probably the most damaging and has it’s source in many locations. Probably the best known effect is the corruption of your GPS position data where the equipment power is taken off an engine starting battery.

What happens is that when a significant load is applied to the battery, such as starting the engine, a momentary voltage drop is created and what is often called a brown out condition occurs. This is then followed by a sharp voltage increase. This under-voltage disturbance can exceed 100 volts in some cases, which is very damaging to the equipment power supplies, and causes wiping of the memories or corruption of the data.

The same problem also applies to dual battery systems where the house bank supplies power to items such as the electric toilets and other large current equipment such as a windlass. The starting battery voltage can experience a 3 to 4 volt dip on a motor starting. Transients are also caused by the variation or interruption of current in the equipment power conductor. 

What is Induced Interference?

The second common RFI noise source is called induced interference. Electrical fields are radiated from all cables and equipment. This can be induced into other closely located cables or equipment such as radios or GPS or your depth sounder. The most common cause of this is where cables running parallel or within the same cable bundle, and this is also called mutual coupling.

More on Induced Interference?

Always make sure they are installed so that are laid so that power supply cables and data cables are kept separate and make any cable crossovers at 90º. Always install power cables to any sensitive equipment completely separate to the main power cables so as to reduce inductive and capacitive coupling to the data and signal conductors. Solve noise and interference on your GPS unit and save on radio repair costs.  More great information for fishing and boats.