In telecommunications, standing wave ratio (SWR) is the ratio of the amplitude of a partial standing wave at an antinode (maximum) for the amplitude at an adjacent node (minimum), in an electrical transmission line. SWR is usually defined as a voltage ratio called the VSWR, for voltage standing wave ratio. For example, the VSWR value 1.2:1 shows a standing wave of maximum amplitude is 1.2 times greater than the minimum value of standing waves. It is also possible to define the SWR in terms of flow, resulting in ISWR, which has the same numerical value. Strength of the standing wave ratio (PSWR) is defined as the square VSWR.
Practical implications of SWR
The most common one to measure and check the SWR is when installing and tuning the transmitting antenna. When the transmitter is connected to an antenna with a feed line, the impedance of the antenna and feed lines must be identical to the maximum energy transfer from the feed line to the antenna to be possible. Impedance of the antenna varies based on many factors including: the natural resonance frequency of the antenna on being transmitted, the antenna height above ground, and the size of conductor used to build the antenna.
When the antenna and feedline do not have a matching impedance, some of the electrical energy can not be transferred from the feedline to the antenna. Energy is not transferred to the antenna is reflected back to the transmitter. It is the interaction of the wave is reflected by the forward wave that causes the standing wave pattern. Reflected power has three major implications on radio transmitters: Radio Frequency (RF) energy loss increases, the distortion at the transmitter because the reflected power from the load and damage the transmitter can occur In telecommunications, standing wave ratio (SWR) is the ratio of the amplitude of a partial standing wave at a antinode (maximum) for the amplitude at an adjacent node (minimum), in an electrical transmission line.
SWR is usually defined as a voltage ratio called the VSWR, for voltage standing wave ratio. For example, the VSWR value 1.2:1 shows a standing wave of maximum amplitude is 1.2 times greater than the minimum value of standing waves. It is also possible to define the SWR in terms of flow, resulting in ISWR, which has the same numerical value. Strength of the standing wave ratio (PSWR) is defined as the square VSWR.
Practical implications of SWR
The most common one to measure and check the SWR is when installing and tuning the transmitting antenna. When the transmitter is connected to an antenna with a feed line, the impedance of the antenna and feed lines must be identical to the maximum energy transfer from the feed line to the antenna to be possible. Impedance of the antenna varies based on many factors including: the natural resonance frequency of the antenna on being transmitted, the antenna height above ground, and the size of conductor used to build the antenna.
When the antenna and feedline do not have a matching impedance, some of the electrical energy can not be transferred from the feedline to the antenna. Energy is not transferred to the antenna is reflected back to the transmitter. It is the interaction of the wave is reflected by the forward wave that causes the standing wave pattern. Reflected power has three major implications on radio transmitters: Radio Frequency (RF) energy loss increases, the distortion at the transmitter because the reflected power from the load and damage the transmitter can occur
Matching the impedance of the antenna to the impedance of the line feed is usually done using an antenna tuner. Tuner can be installed between the transmitter and the feed line, or between the feed lines and antennas. Both installation methods will allow the transmitter to operate at a low SWR, but if the tuner is installed in the transmitter, feed line between the tuner and the antenna will still operate with a high SWR, causing additional RF energy to be lost through the feedline.
Many amateur radio operators consider the problem serious impedance mismatch. However, this does not happen. Assuming the mismatch is within the limits of operation of the transmitter, radio operators only have to worry about power loss in transmission lines. Power loss will increase with increasing SWR, but this increase is often less than amateur radio may assume a lot. For example, a dipole antenna tuned to operate at 3.75MHz-center 80-meter amateur radio bands will exhibit approximately 6:01 SWR at the band edges. However, if the antenna is fed with 250 feet of RG-8A coax, loss due to standing waves only 2.2dB. Feed line losses usually increases with frequency, so antenna VHF and above shall be adjusted closely to the feedline. Mismatches at 06:01 for 250 feet of RG-8A coax would experience losses on 146MHz 10.8dB.
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