How to Use a Micronta Field Strength/SWR Tester

By Samuel Markings

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.

Step 1

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

Step 2

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

Step 3

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.

Step 4

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

Step 5

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.