Hardware 101: Automatic Antenna Tuners

by John KI7LYP on 2020-07-25

Automatic antenna tuners: the magic box that makes everything great!  Before we get one and expect it to provide us with winning lottery numbers, the location of the Lost Dutchman mine, or the ability to talk to the International Space Station on your HT, let’s look at what it does.

The basic antenna tuners want to add inductance or capacitance to your antenna system, and why do we want to do that? For an antenna to be resonant and work the best, the physical length has to match the wavelength of the frequency we are transmitting.

If we put a random length of wire up in a tree as an antenna,

  • it is going to be too long for some frequencies (poor match),
  • it will be too short for some frequencies (poor match),
  • and it will be just right (resonant) on certain frequencies (good match).

By adding inductance or capacitance, we are able to fool the transmitter into thinking the wire is the correct length and matches the transmitter, and when the transmitting frequency matches the length of the wire, we don’t use the tuner.

So, keep in mind, if you are using an antenna that is already resonant or tuned for the frequency that you intend to use, a tuner may actually make things worse. As the old saying goes, “if it’s not broken, don’t fix it!” If you’re having trouble tuning or transmitting on your antenna, try bypassing the tuner; you may find the antenna is matched and your transmitter is now happy. But, if you do find yourself using a random wire as an antenna (mine is 53 feet long…), you will certainly want an antenna tuner to do the magic and make the wire appear to change lengths to match your transmitter frequency.

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