Using a manual antenna tuner can be a daunting task for someone who has never used one before. Before we begin using the tuner let’s take a moment to define what an antenna tuner is, and some of its most important parts.
Contrary to what it’s name implies, an antenna tuner does not “tune” an antenna. In fact, it does not modify your antenna in any way. It simply serves as an impedance matching device, or impedance matching network. Allow me to use a metaphor. The gears on a bicycle serve to connect the pedals to the wheel so that the person riding the bicycle can turn the pedals at an efficient speed, which is somewhere between 70-100 rpm depending on the rider. If you did not have these gears you would have to turn the pedals very fast when riding down hill, and very slowly when riding up hill. This is not efficient. The gears simply allow you to pedal at an efficient speed so that you can deliver maximum power to the wheel at all times. The antenna tuner serves a similar, albeit much more complicated purpose. Note that the gears on a bicycle do not change the way the back wheel works, they simply change how the wheel is connected to the pedals. The antenna tuner operates in the same way. It does not change the antenna. Rather, it modifies how the antenna is connected to the radio so that the radio can deliver maximum power to the antenna.
In almost every antenna tuner you will find capacitors and inductors. These capacitors and inductors can be wired in several configurations, but the most common is two capacitors and an inductor wired together in a “Pi” network. Take a moment to look inside your antenna tuner sometime and identify these components. See how they move when you turn the dials on the front of your tuner.
Now that you have an idea of the basic components inside your tuner, and the purpose a tuner serves, let’s take a look at the steps required to tune an antenna.
First, begin by setting the capacitors to their highest setting. Next adjust the inductor until the background noise in your receiver peaks meaning you see a rise in the S-meter. If you are not able to produce a peak in the receiver try reducing the settings of the capacitors to 90% of their highest setting, then adjust the inductor. If you are still unable to produce a peak in the recieved signal, reduce the capacitors to 80%, then 70% etc.
When you have found a strong peak in the received signal, you are close to you’re optimal tuning point. It should be noted that there are many tuning points which will produce a low SWR, but in order to maximize efficiency you’ll need to minimize the inductor setting and maximize the capacitor settings.
Next, put your radio in CW, FM, or AM mode. Do not use SSB mode because no power will be produced unless you are talking into the microphone. Make sure the output power setting is set to it’s lowest value. After making sure that you can legally transmit on the frequency you’ve selected, key the transmitter and observe the SWR on the tuner. Fine tune the two capacitors until a low SWR is obtained. Again, remember that there are many combinations of settings that will produce a low SWR, but combinations with low inductance and high capacitance will have higher efficiency and reduce losses in the tuner.
Once the SWR reads zero, and you are confident that the inductor is set to the lowest value that will produce an acceptable SWR, you are finished!