SWR Nomographs (1)+(2)

The relation between SWR, Forward Power and Reverse Power

On this page two SWR Nomographs are shown:

SWR Nomograph (1)
SWR Nomograph (2)

When installing communications systems and thereby also antenna systems it would be useful to be able to check that the systems work as they should. Which means that as much power as possible is dissipated in the antenna.

For this purpose you can use SWR Nomographs, which from the forward power and reflected power show the SWR that the transmitter can “see”.

Large drawing: SWR Nomograph (1) Forward Power: 0.5 -> 500 W Reverse Power: 0.2 -> 20 W

Large drawing: SWR Nomograph (2) Forward Power: 0.5 -> 500 W Reverse Power: 0.01 -> 1 W

SWR Nomograph (1) and (2) show the proportion between forward and reflected power. By entering these into a double logarithmic system of co-ordinates a linear SWR sequence is shown. The forward power is the power being transmitted into a system whereas the reflected power is the power being reflected because of a mismatch at the load.

The SWR can be found by using the SWR Nomographs if the forward power and reflected power are known.

SWR Nomograph (1) covers the forward power from 0.5 to 500 W and the reflected power at 0.2 – 20 W.

SWR Nomograph (2) covers the forward power from 0.5 to 500 W and the reflected power at 0.01 – 1 W.

Example:
SWR Nomograph (2) is used if a transmitter transmits with 25 W and the reflected power is 0.3 W. By looking at the intersection of the two numerical values in the Nomograph it can be noted that the SWR is 1.25.

The Nomographs are calculated on the basis of the following formula: