Glendora Emergency Response Communications

ANTENNA TUNERS

WHAT IS AN ANTENNA TUNER?

Get maximum power to your antenna by learning how to hook up and use a tunner properly to "trick" your rig!


Yes, TRICK YOUR RIG!

WHAT IS AN ANTENNA TUNNER?

You have to learn how to hook them up to your tranceiver properly and tune them correctly to make your radio think that it is feeding it's signal into a "perfect or near perfect 50 ohm load called your antenna.
An antenna tuner, (transmatch), doesn't really TUNE your antenna OR ANY PART OF IT!

What an antenna tuner or transmatch does do, however, is transform the impedance at the antenna feed output at the radio to a value that your transceiver can handle, (typically 50 Ohms. When thinking about antenna tuners and SWR, it's important to remember that the tuner has no effect whatsoever on the SWR between itself and the antenna. It's the SWR between the transmitter and the tuner that is changed with the tuner controls.

In layman's terms, all a tuner does is act as a kind of adjustable impedance transformer between the radio and the antenna. It takes whatever impedance the antenna system presents, up to the design limits of the tuner, and attempts to convert it back to 50 Ohms--or something reasonably close to that value for the transceiver. When the transceiver "sees" a 50 Ohm impedance, it is able to load or produce it's maximum designed RF output into the system because it is designed to operate into a 50 ohm load. Your rig thinks it's seeing a 50 ohm antenna on it's output! That power is transferred through the antenna tuner, to the feed line and, ultimately, to the antenna--minus any losses incurred along the way. If you have high loses and a poor excuse for an antenna, you will have a poor excuse for a good signal no matter how well your tuner "tricks" your radio. Most of the power will be lost as heat in the tuner and very little will get to the other station!

These losses are the reason that the highest efficiency feed-line for each individual case is desirable and why some amateurs use ladder line on HF, which has the least loss per foot, which means maximum power at the input terminals of the antenna.

HOW TO HOOK UP AND USE

HOW TO HOOK UP AND USE

So now that you have a better understanding of what an antenna "tuner" actually does,
let's hook one up in a typical HF station. In the block diagram (see photo) we have typical Hf station setup consisting of:

An HF Transceiver
A Linear or power amp
Low Pass Filter
Swr/Watt Meter combo
The Antenna Tuner
A Dummy Load

The MOST IMPORTANT PART......THE ANTENNA!

Take a look at the block diagram above and notice where the antenna tuner and SWR meter are in relation to the flow of the RF signal coming from the transceiver.
PLEASE DISREGARD THE LINEAR AND LOW PASS FILTER FOR THE MOMENT! (Your station may not use them) You will notice that.... first, from left to right, you have the transceiver, Swr/watt meter, ANTENNA TUNER and then the antenna on the output. The rf moves from the transceiver to the SWR/WATT meter, then finally thru the "tuner" and out to the antenna. You just learned how to hook it all up! Just remember that our goal is to make the transceiver think all is well, and in order to "read" the SWR and Power out pertaining to "all is well"......at the radio's output....the meter must be between the radio and the tuner. NOT ON THE ANTENNA SIDE!

NOW LET'S LEARN TO TUNE THAT TUNER!

Most antenna tuners have an inductance rotary switch and two capacitors. (refer to photo at top of page) The capacitors are often labeled ANTENNA and TRANSMITTER. In some antenna tuners the inductance switch is replaced with a continuously variable inductance, popularly known as a roller inductor.

Let's assume you're using a tuner with an inductance switch, because they are the most common.
Place both capacitor controls at their mid-range positions. Don't trust the knob markers if this is your first experience with the tuner; if you are comfortable with it, remove the cover and turn the knobs until the moving capacitor plates are only half meshed with the stationary plates. If the knobs are pointing to half scale, consider yourself lucky. If not, loosen their Allen nuts and rotate the knobs so that they point to mid scale. Replace the tuner cover and you're ready to go.

Turn the radio on and tune receiver to an un-used frequency on the band you desire, listen for a few seconds, with the ANTENNA and TRANSMITTER controls at mid scale, crank the inductance switch until you hear the loudest noise or signals coming into your radio. Then, rotate the ANTENNA and TRANSMITTER controls until you get to the absolutely loudest noise or signal level on the radio. This should be close to your best tuning spot.

With your rig set to low power, send an ID then transmit a continuous carrier while you tweak the ANTENNA and TRANSMITTER controls for the lowest reflected power reading with the highest output power as read on the SWR/WATT meter. You may find that you have to vary the position of the inductance switch a position or two either way to get your best match. Play it safe and un-key before turning the inductor switch....un-key first....turn the switch...key up....repeat as needed until lowest SWR and maximum output.
Be gentle to your radio; keep the key-down periods as short as possible. Depending on the impedance at the antenna input (and the overall design of the tuner) you may not be able to obtain a flat 1:1 SWR on all frequencies and bands. Also important to remember is that your Swr will change, go up, as you tune further away from the frequency you used to "trick" your radio! So re-check and re-tune as needed as you move around the band.
You can get an idea of your SWR bandwidth by starting with your original frequency, and using the procedures above with low power, (don't move any knobs or switches after best setting)....sweep or tune your VFO up and down the band while watching the SWR readings and note the frequency where the SWR reaches 2:1 at the higest and lowest frequency. Stop there! Example: If your on 40 meters at say...7.262mhz as your starting point, and your SWR is 2:1 at 7.292mhz and the highest going the other way is 2:1 at 7.259mhz, then your "safe tuning range" without retuning the antenna tuner would be about 60khz. Keep in mind to use very low power and ID because your signal may be heard for a split second as you tune across the band!
Remember your TRICKING your way around a good antenna!

Thanks to Ham Universe for the article

Ham Universe