Page 270 - Concise Encyclopedia of Robotics

Radio-Frequency Interference (RFI)
Mobile robot
equipped with
Doppler radar
lower frequency
Transmitter
Receiver Outgoing wave: Barrier
Incoming wave:
higher frequency
Radar
RADIO-FREQUENCY INTERFERENCE (RFI)
Radio-frequency interference (RFI) is a phenomenon in which electronic
devices upset each other’s operation.In recent years this problem has been
getting worse because consumer electronic devices are proliferating, and
they have become increasingly susceptible to RFI.
Much RFI results from inferior equipment design. To some extent,
faulty installation methods also contribute to the problem. Computers
produce wideband radio-frequency (RF) energy that is radiated if the
computer is not well shielded. Computers can malfunction because of
strong RF fields, such as those from a nearby broadcast transmitter. This
can, and often does, happen when the broadcast transmitter is working
perfectly. In these cases, and also in cases involving cellular telephones,
citizens’ band (CB) radios, and amateur (“ham”) radios, the transmitting
equipment is almost never at fault; the problem is almost always improper
or ineffective shielding of the computer system.
RFI is often picked up on power and interconnecting cables. There are
methods of bypassing or choking the RF on these cables, preventing it from
getting into the computer, but the bypass or choke must not interfere
with the transmission of data through cables. For advice, consult the
dealer or manufacturer of the computer.
Power lines can cause RFI. Such interference is almost always caused
by arcing. A malfunctioning transformer, or a bad street light, or a salt-
encrusted insulator can all be responsible. Often, help can be obtained
by calling the utility company.
A transient suppressor, also called a surge suppressor, in the power cord is
essential for reliable operation of a personal computer or robot controller
operating from utility lines. A line filter, consisting of capacitors between

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