How to Use a VSWR Meter

The Voltage Standing Wave Ratio, or VSWR, is an indicator of how good an impedance match an antenna is with a radio transmitter. The better the match, the more efficient the antenna will be when sending out the radio signal. A worse match means less efficiency and indicates how much of the signal will be reflected back to the transmitter. In tube-based transmitters, a radio operator could tune the antenna in a crude fashion by watching the output tubes glow more or less red as they were heated by reflected power. As radio manufacturer SGC notes, however, this leads to premature tube failure.

Things You'll Need

Short (about 3 feet or less) coaxial cable (RG-8, RG-58) with compatible connectors (usually PL-259)

Transmitter operating at antenna's frequency

Instructions
Using a Single-Needle VSWR Meter
1.Connect the antenna cable to the VSWR meter "Antenna" connector, and the VSWR meter "Transmitter" connector to the transmitter output using the short coaxial cable. If available, set the power range switch to the minimum range allowed by the transmitter.

2.Set the VSWR meter to "Cal" (calibrate) and transmit with just enough power so that you can adjust the meter to place the needle in the "Cal" or fully forward position.

3.Change the VSWR meter setting to "SWR" and transmit again, observing the reading. Unless the antenna is far out of tune, this is your SWR reading, which should be 2.0 or below.

4.Repeat the calibration and measurement steps after each antenna adjustment. Many modern transmitters will adjust output power based on VSWR, so any change in VSWR may require recalibration.

5.Disconnect the VSWR meter and connect the antenna directly to the transmitter for regular use for best performance. You can leave the meter in place to monitor the antenna for changes due to weather or other environmental factors or accidents to protect your transmitter. If you transmit on other nearby frequencies, you can observe how much the VSWR changes with frequency.

Measuring VSWR with a Two-Needle VSWR Meter
6.Connect the two-needle VSWR meter between the antenna and transmitter using the short cable.

7.Set the meter to the minimum power range, if available. Adjust the transmitter to transmit in that power range and get a needle deflection about halfway across the meter where the VSWR reading scale is located.

8.Measure VSWR with a two-needle VSWR meter by observing the crossing of the forward and reflected power needles and reading the value, such as 1.5, at that point. Setting the meter to "Cal" is not necessary because the two needles work together.

9.Repeat VSWR measurement as needed for antenna adjustments. No adjustment of the meter is necessary.

Tips & Warnings
These procedures are for an antenna designed for a specific frequency, not a "random wire." An antenna tuner device can be used with a random wire to put it in the right frequency range before measuring VSWR.

High SWR values may cause the transmitter to reduce power output, and may also make it difficult to tune to "Cal" and make an accurate measurement.

When tuning the antenna, you will be transmitting on air. Remember to follow all legally required procedures.

VSWR meters generally cover a broad frequency range, but make sure that you are using a meter which covers the frequency of the antenna and transmitter.

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