Antenna Tuners do not tune the antenna! They are RF Transformers that match the (usually) 50 ohm output of the transmitter to some unknown load presented by the antenna coax or twinlead at the frequency in use. They are sometimes called a “Transmatch.”
So they do “tune” the antenna system.
You can of course spend many $$ and buy a commercial unit, and some modern transceivers can be had with built-in tuners. But if you do not have such a transceiver or do not want to spend big bucks, build your own. They are very easy to construct and require a minimum of mechanical or electronic skills.
There are many designs – C-L-C, Z-Match, Balanced line, T-Match and more. The ARRL has many, many articles about these, going back to the 1920’s. You must be an ARRL member to read these, found in the QST selection of the “Technology” section. Also, Mr. Google knows all about the subject.
The simple “T-Match” circuit, and some variations on it, is probably the most common circuit used by Antenna Tuners. It is very versatile and should match the antennas that we amateurs are likely to encounter. My homebrew one has matched the xmtr to any antenna I’ve tried, including a 137′ Inverted VEE (a multiband doublet).
A “Google Search” will provide several day’s worth of reading on the subject and likely leave you with some confusion as to which design is best for you. Just go with the T-Match.
My recommendation? KISS. Select a simple design and build it Read VK5AJL’s instructions as to how to use one to find the settings needed for each band. These are found at the end of his webpage.
In my experience, you can also use a sensitive Field Strength Meter to find settings that produce the best level of radiated power, but use VK5AJL’s instructions first.
Don’t try to determine the settings while applying full power!
For example, I use a 137′ inverted VEE antenna fed by about 65 feet of 450 ohm #14 twinlead (a.k.a. “ladder line”). This is attached to a 1:1 T-200 core current balun within the T-Match tuner.
This simple device provides a 1:1 match on 80 through 10 meters. The antenna was not designed to be used on 160 meters but if both ends of the twinlead are shorted together and the balun is omitted, the tuner will use the twinlead and antenna as a T-shaped antenna and a match will be found. I don’t operate on 160 meters so it’s not a problem for me.
If you are using a twinlead-fed antenna it is essential to insert the 1:1 Current Balun just in front (antenna side) of the tuner. Don’t skip this and make sure it is a Current Balun, not a Voltage Balun.
If you already have a 4:1 balun in place, and everything works OK, just leave it!
If your antenna system is coax-fed, don’t include the balun.
Below are links to some basic Antenna Tuner designs, theory and other interesting articles that I have found. If you find more, please send me the info! And Google the subject to your heart’s content.
I suggest reading the articles about SWR found on this website’s Antenna page, so you can better understand what the SWR meter is doing, as you find the correct settings on your tuner, for each band.
DJ0IP’s website provides ARRL information comparing the efficiency of the different brands and models of commercial matching devices.
Here is some good information on the T-Match antenna tuner, which is probably the simplest and most versatile manual tuner one can have; and perhaps the cheapest.
T-Match Tuners: A web page by VK5AJL that provides a lot of detailed information about designs, layouts and tables of values likely to be encountered.
L Networks (C-L or L-C) are extremely simple and can often be all that is needed to provide a good match between the xmtr and the 1:1 balun attached to the antenna twinlead, or directly to the antenna coax.
A Balanced-Balanced Antenna Line Coupler. This one allows balancing each side of a twinlead-fed antenna system. If you put a 1:1 current balun in front of another tuner design, you will not need this, but it’s a neat idea.
PG1N’s Antenna Tuner page, which lists many different designs, can be found here.
AD5X provides a comprehensive page about Z-Match Antenna Tuners.
W8JI provides an extensive analysis of the famous Johnson Matchbox Antenna Tuners. These tuners were old designs but his analysis is well worth reading.
Have all these tuner articles confused you enough? Just build a junkbox T-Match unit or a C-L, L-C unit and it is almost certain that your antennas and transmitters will be happy together.