How to Use a Micronta Field Strength/SWR Tester

by Samuel Markings
A Micronta field SWR tester is needed to tune a CB radio.

A Micronta field SWR tester is needed to tune a CB radio.

A citizens band radio (CB) is a communication device that allows people to broadcast and receive messages over a range of approximately 20 miles. The CB radio needs an aerial to be connected, and a tuning procedure is needed for these devices to work. The tuning procedure can be carried out with a Micronta field strength/SWR tester, which measures the ratio of transmitted signal to that of reflected signal. A standing wave ratio of 1 means perfect transmission, whereas anything above 1 means part of the radio wave is being reflected.

Connect a short piece of coaxial cable between the SWR tester "Trans" socket and the CB radio output.

Connect the antenna to the "Ant" socket on the SWR socket.

Set the CB radio to channel 1, and select "Forward" on the SWR tester. Transmit a signal and adjust the calibration knob so that the needle on the meter aligns with the "Cal" marker.

Select "Ref" on the SWR tester and take a note of the output reading on the scale. Stop transmitting.

Change the channel on the CB radio to 40, transmit for a few seconds, and take a note of the reading. If the SWR reading on both channels is less than 1.5, then the CB radio is already tuned. If the channel 1 reading is greater than the channel 40 reading, then the antenna needs to be adjusted to a longer length. If the channel 40 reading is greater than the channel 1 reading, then the antenna needs to be adjusted to a shorter length. After adjusting, you should repeat the whole procedure until the SWR reads less than 1.5 on both channels.

Measuring field strength is generally a less useful way of checking power loss. However, the Micronta field strength/SWR tester can also be used to measure the field strength of your CB radio. To do this: 1) Connect the provided small antenna to the Micronta field strength/SWR tester. 2) Connect the CB radio directly to an aerial. 3) Transmit, and adjust the calibration knob so the meter reads 2 to 4 on the "FS" scale. 4) The antenna can now be tuned by varying its length and measuring the field strength directly during transmission.

Items you will need

About the Author

Samuel Markings has been writing for scientific publications for more than 10 years, and has published articles in journals such as "Nature." He is an expert in solid-state physics, and during the day is a researcher at a Russell Group U.K. university.

Photo Credits

  • photo_camera radio image by chanelle from Fotolia.com