Standing Wave Ratio (SWR) indicates the exact voltage or current produced by a radio and its accompanying antenna. Measured by an SWR meter, it defines the ratio between the output power generated by a radio transceiver, and the lowest voltage or current level that goes back from the antenna to the electronics. No power being reflected back to the radio’s transceiver electronics would equal an SWR of one to one. Defects in any component of the radio system, including cables, connectors, and mountings, can increase the ratio as measured by the SWR meter.
An SWR meter is most accurate when it is between the antenna and the radio. Coaxial cables are connected to the meter from both the radio and the antenna. Switches on the device allow it to read either reflected power or forward power, which is the combination of the power going out and that being diverted back to the radio. A digital or analog reading on the front of the SWR meter will indicate if the voltage standing wave ratio is too high, by showing the level entering an established red zone.
When an SWR meter registers too high, it could be due to a short in the connectors. The operator could also check how the mounting studs were installed or if they are working properly. Antenna mounts that are not grounded or cables not long enough could also cause the SWR to be high. The problem can be measured on different channels to understand it better. Operating the radio before fixing it could damage the system beyond repair.
Antennas and transmitters in a radio need to be connected by some kind of wiring. These wires and the associated coaxial connectors often lose some power, causing signals to be fed back to the transmitter. When the antenna and transmitter have the same power, they are said to match, and the level of this matching is the impedance. Rarely do both components have equal impedance so an SWR meter usually registers an imperfect ratio.
Many times the SWR does not cause any effects on the receiving end of the radios system. Unless the SWR registers over two to one, the ratio will not result in a power loss that anyone can recognize on either end. If enough power gets diverted back to a transceiver, electronics can get overloaded and short out. Power protection circuits can sense excess current and voltage and automatically lower the transceiver output to a safe range.