SWR or standing wave ratio is the ratio of the amplitude of a partial standing wave at an antinode (maximum) to the amplitude at an adjacent node (minimum), in an electrical transmission line. The SWR is usually defined as a voltage ratio called the VSWR, for voltage standing wave ratio. For example, the VSWR value 1.2:1 denotes a maximum standing wave amplitude that is 1.2 times greater than the minimum standing wave value.


The swr meter circuit schematic we present can be used to powers up to 100W rf and can help you obtain the maximum power to antenna. Usually a transmitter is adjusted to the maximum power at the output but it must be matched with the antenna.

SWR is an indicator of reflected waves bouncing back and forth within the transmission line, and as such, an increase in SWR corresponds to an increase in power in the line beyond the actual transmitted power. This increased power will increase RF losses, as increased voltage increases dielectric losses, and increased current increases resistive losses.

Matched impedances give ideal power transfer; mismatched impedances give high SWR and increased loss in the transmission line. Reflected power in the transmission line is re-reflected at the transmitter, and is eventually radiated by the antenna (minus cable loss). The higher voltages associated with a sufficiently high SWR could damage the transmitter. A very long run of coaxial cable especially at a frequency where the cable itself is lossy can appear to a radio as a matched load. The power coming back is, in these cases, partially or almost completely lost in the cable run.

Here you got the swr meter documentation + pictures and the swr meter schematic


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