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Troubleshooting SWR Aerial Problems

What is SWR? - Standing Wave Ratio is matching an aerial to a radio.

If the SWR, measured on the highest channel, is worse than the SWR measured on the lowest channel, the aerial is too long.   If the opposite is the case, the aerial is too short.

So, the procedure is as follows:-

  1. Select the lowest channel on your radio, put the SWR meter in line and check the weather (as if conditions are damp or wet, false readings will be obtained)

  2. Select the Forward, FWD, CAL or Calibrate function on the SWR meter.   (The exact marking depends on the meter being used).     

  3. Key the mic and adjust the control on the SWR meter to set the reading to the Set or CAL mark.    

  4. Now switch the meter function to REF or SWR.    

  5. Key the mic and make a note of the SWR reading obtained.

  6. Select the highest channel on your radio and repeat steps 2 to 5

  7. Now apply the rule to the two readings obtained and decide whether the aerial needs to be shortened or lengthened and adjust the aerial accordingly.

If this figure is much too high at the extremes and OK on the middle channels, the aerial is too tightly tuned for your frequency range - try a different type of aerial.

If the SWR is too high on ALL channels, the possible causes are:-

Earthing arrangements for your aerial are poor or incorrect. (check earth connections)

Your coax is confusing the SWR meter (change the cable)

There is an obstruction very close to your aerial. (possibly relocate the aerial)

Your SWR meter, patch lead, coax or aerial are faulty (try replacements for one component at a time)

The ground plane (Mobile Aerials!) is too small

On half wave and 5/8 wave aerials it is vital that the mounting pole does not protrude at all above the mounting bracket.  

3" of the pole above the top of the bracket can produce a SWR of 2.5:1 which refuses to be affected by any amount of aerial adjustment.

Correctly carried out this operation is worth every minute of the time it takes, the benefits are less interference, greater range and longer life for your transmitter.