Standing Wave Ratio (SWR)
October 20, 2008 by Darren
How important is having a good SWR measurement?
SWR, or VSWR as it’s sometimes referred to, stands for Standing Wave Ratio. SWR is an important measurement because it shows how well your station, including antenna, coaxial cable or feedline, mount, and ground plane, matches the output of your transciever. A perfect match, where all the RF energy the radio is producing is transferred from the rig through the antenna, is considered a 1:1 match.
A high SWR reading (higher than 2:1) is a sign of reflected power (RF energy) going back to the radio. This means some of the power that is transmitting does not make it to the antenna. Besides signal loss, having a high SWR might also result in damage to the radio which of course equates to money spent with the radio repair man.
Keep in mind that while a high SWR reading is an indicator of a matching problem, a good reading does not necessarily mean that your antenna is radiating properly. An example of this is a dummy load. While a dummy load is able to achieve a perfect SWR it does not radiate a signal.
No Ground Plane antennas are also an example of this. These specialty antennas are designed to produce low SWR readings in tough grounding situations. Though their SWR match is good, their radiating pattern is very poor for mobile use. Instead of radiating towards the horizon, they tend to radiate skyward, thus limiting the distance you can transmit and receive with them.
What are some common reasons for high SWR?
- Insufficient ground plane
- Coax problems – Improper type, incorrect length, low quality, or damage
- Poor installation location
- Antenna not tuned properly
- Damage to the antenna
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