Home >> Science & Nature >> Science

How to Reduce VSWR

Citizen Band (CB) radios are portable communication devices that require an aerial in order to function. Aerials can range in size from small table-top varieties to large poles that are placed on roofs or in gardens. The voltage standing wave ratio (known as VSWR, or more commonly, SWR) is a measure of the ratio of power transmitted from an aerial to the power that is reflected from an aerial. SWR values of greater than three indicate an inefficient transmission whereas values below three are acceptable. In order to reduce the SWR, a special device known as a SWR meter is needed.

Things You'll Need

CB radio
CB aerial
SWR meter
Coaxial cable

Instructions

- 1
  Connect the coaxial cable coming from the aerial in the "ANT" terminal on the SWR meter.
- 2
  Connect a small piece of coaxial cable between the CB radio's antenna terminal and SWR meter's "TRANS" terminal
- 3
  Set the function on the SWR meter to "CAL.' Turn on the CB radio and transmit a signal. The needle on the SWR meter should rotate to the right. By rotating the "CAL" knob on the SWR meter, you'll align the needle with the "CAL" mark on the meter scale.
- 4
  Set the function on the SWR meter to "SWR."' Transmit a signal. The needle on the SWR meter will rotate to the right. Read off the value of the SWR. Any SWR value below three is acceptable. If the the value of SWR is above three, the aerial length needs to be modified.
- 5
  Change the length of the CB aerial by loosening the grub screw holding the two metallic rods in place and moving the inner rod with respect to the outer rod. Check the SWR value for a range of different aerial lengths. You should find that the SWR changes significantly with aerial length and it should be possible to get the value to less than three. If changing the aerial length does not allow the SWR to be brought to a value below three, check all coaxial cable connections. Ensure that the plugs on the ends of the coaxial cables are secure. If necessary, replace all coaxial cables with new ones.

Science