Low SWR is not the be-all end-all!

How many times have I heard ‘well, my SWR is 1:1, but I can’t seem work anyone’ ?  It’s important to remember that just because the SWR meter shows a low SWR does not mean the antenna is radiating.  Remember, a dummy load has a 1:1 SWR!

Conversely, just because the SWR is high does not mean the antenna is not radiating.  Here are a couple points to keep in mind:

  • Because modern radios will start to reduce output power at SWR levels above 2:1 in order to protect the finals, it is important that the transmitter “sees” an impedance close to 50 ohms.
  • An antenna tuner does this by placing an an “equal and opposite” impedance at the rig end vs. the antenna end.
  • An antenna tuner at the transmitter DOES NOT reduce the SWR on the feedline between the tuner and the antenna.  If it was 10:1 without the tuner, it is still 10:1 with the tuner.
  • The antenna tuner simply makes the transmitter “happy”.
  • High SWR on the feedline (depending on type) compounds the power lost in the feedline.
  • The best improvements in antenna system efficiency are gained by trying to present a near-50 ohm impedance to the feedline at the antenna end.

I find the ARRL Antenna Book to be a great resource for antenna builders.

73,

Chris

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