Standing Wave Ratio (SWR)
The ratio of the amplitude of a StandingWave at an Anti-Node (minimum) to the amplitude at an adjacent node (maximum). (188) Note 1: The standing wave ratio (SWR ) in a uniform transmission line is given by:
where is the reflection coefficient. Note 2: Reflections occur as a result of discontinuities, such as an imperfection in an otherwise uniform transmission line, or when a transmission line is terminated with other than its characteristic impedance.
- SWR means Standing Wave Ratio, it is basically how much of the power you are sending to the antenna is getting reflected back. The signal gets reflected back when you dont have an exact match between the 50ohm cable and the antenna, no antenna is exactly 50ohms(which would be a 1:1 SWR), but the closer it is the more of the power will be radiated. It is hard to tune 2.4Ghz antennas because SWR meters for it are really expensive and you most likely wont have access to them, the best why to do it is simply to tune it (by trimming or moving your driven element) until you get the best signal strength. Normally if your SWR is too high such as when an antenna is not connected and you transmit it can damage the radio. Due to the fact that I havent heard anyone omplaining about their card dieing and have done some stuff that would result in a high SWR myself I do not think that this is really an issue with 802.11b cards. The transmit power is rather low to begin with, and the cards not likely know not to transmit, lower their power or switch to the internal antenna when there is to high of an SWR. -- JessH
SWR really is not an issue at .25 watts which is proxamitely what kind of power were talking about here. It's really only something you need to worry about when you're doing bigger stuff at transmitions more like 100 watts. --CompuDroid
SWR is always an issue, no matter what the power is. An antenna with a 1:1 SWR is more efficient, allowing for better radiated power. Better radiated power == higher range. At a quarter watt you are correct to say that a high SWR would probally not kill a transmitter, but overall it would be ideal to have some type of swr benchmark for antenna tuning. -- ChristoAllermann
- A higher SWR also results in more loss in the coax that you have running to it. -- JessH