We all know that when an antenna resonates at a specific frequency, its efficiency is at its highest. When making or purchasing antennas, we often observe and adjust their resonance conditions (such as finding a lower VSWR value) by modifying the length of the antenna elements, among other factors.
We also understand that for the antennas used in our radio systems, a lower VSWR value is better.
But when does an antenna resonate or have the lowest VSWR value? The answer is when there is impedance matching between the components of the system, the efficiency is at its highest. The typical output impedance of our radio transmitters is 50 ohms. This means that if the entire system impedance, including the transmission line before the antenna and any amplifiers, is 50 ohms, the efficiency is at its highest, and the VSWR of the radio is minimized.
But what should we do if the system impedance is not matched, and the VSWR is very high?
That’s where an antenna tuner, often referred to as a “tuner,” comes into play. It is a device connected between the radio and the antenna, designed to help fine-tune the system to maintain consistent impedance levels, ensuring that the radio achieves a good VSWR.
However, does having an antenna tuner mean that the antenna itself is not important? There is even a common belief that “everything is an antenna,” implying that as long as you have a conductor and a powerful enough tuner, your radio can transmit. Is this correct? No, it is incorrect.
Impedance matching in the system ensures that the transmitter’s power can be efficiently delivered to the load, with very little power being reflected (resulting in a low VSWR). But this does not guarantee that the antenna will work effectively and radiate your signal. For example, if your load is a standard 50-ohm dummy load with a VSWR of 1, the radio can output power to it perfectly, but can it function as an antenna to propagate your signal? It cannot.
Similarly, a mismatched antenna, even with a tuner, regardless of how well it matches the impedance, will only ensure that the radio can gracefully transmit more power but does not guarantee that this power is radiated into the air.
An individual conducted a test involving a radio, an external MFJ tuner, and a SWR meter, with the connection setup as radio-tuner-SWR meter-antenna. They tuned to the 80-meter band (3.940 MHz), transmitted in FM mode, and the results were as follows: The external tuner displayed a VSWR of 1.2, but the SWR meter showed 8.16.
The external tuner’s display indicated that the entire feedline system, including the tuner, was well-matched for the radio, allowing for perfect transmission. However, the SWR meter reading of 8.16 suggests that when looking at the impedance from the radio through the tuner and beyond, there is still a mismatch, rendering the system unusable.
This test effectively illustrates a crucial point: a tuner is not meant to adjust the antenna itself; it merely ensures impedance matching for the entire system, enabling the radio to transmit power efficiently. Whether this power is radiated by the antenna depends on the antenna itself.
So, does having an antenna tuner mean that everything can function as an antenna?