Checking the Calibration of your SWR meter

Checking the Calibration of your SWR meter and constructing a dummy load.

There is a simple way to check if your SWR bridge is working correctly.

You will need a 5 watt resistor, not wire wound, of 75 ohms and 100 ohms.

If you cant find a 5 watt carbon or metal film resistor, parallel up 3, 390ohm 1 watt units with 2, 360ohm units to make a 75.4 ohm resistor and 5, 500ohm resistors to make the 100ohm unit.

Solder each resistor into a PL259 plug so you can attach either of them to the back of your meter. If your using paralleled units, solder a coax fly lead to your bundle keeping all leads short. Too much coax will also affect the readings. Or build it using the dummy load construction technique as described in the article linked at the end of this note.

Turn your rig to its lowest power setting, hopefully lower than 5 watts and key the transmitter.

A 75 ohm resistor will indicate 1.5:1 and a 100 Ohm resistor will indicate 2:1 – simple !

I stress the need for carbon or metal film resistors since a wire wound unit adds significant inductance that will skew the result.

For more detailed instructions on building multi resistor dummy load, read this excellent article by K4EAA…