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How to Calculate a Coaxial Cable's VSWR

SWR stands for "Standing Wave Ratio." In many applications, especially ham radio and CB, the SWR reading is important to ensure the highest transmission of power. It is the ratio of power transmitted to power reflected back. Low SWR will transmit the highest amount, while high SWR will not, and in some cases cause damage to your transmitting equipment

Things You'll Need

SWR meter
Calculator (if needed)
Small piece of coaxial cable

Instructions

Measuring SWR
- 1
  Take note of commonly accepted levels of SWR. While an SWR of 1.5:1 is best, under 2:1 will be sufficient. If it is any higher, changes to your system will most likely be needed.
- 2
  Set the SWR meter up, between your antenna and transmitter. Connect the small piece of coax between the radio and the meter, and your current coax from the meter to antenna. Typically, the meter will have the connections labeled for you (i.e. "Radio" and "Antenna," and the like).
- 3
  Before testing SWR, check your old piece of coax for any issues including fraying or wear. This could be the cause of high SWR issues. Also check connection points. Loose connections can also cause problems.
- 4
  Follow the instructions included with your meter to measure the SWR. Some meters will give two measurements, forward and reflected, requiring you to figure out the ratio on your own. Others will do this automatically. It will vary based on your meter.
- 5
  Take measurements at different points on a given band, or on CB on Channels 1, 19, and 40. At each point, depress the transmit key on your radio and record the reading given.
- 6
  If the reading is below 2.0:1, no further action is needed. If the reading is above 2.0:1, consider changing out the coax and retest. Newer as well as better-rated coax can also possibly alleviate the problem.

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