So using an SWR meter to 'tune' an antenna isn't really very practical. Does that mean that all them thousands of people tuning an antenna with an SWR are wrong?
Yep. Think about it.
I have thought about it, and you
are wrong. The SWR meter is a perfectly sufficient tool to
tune such an antenna.
What is the object of tuning an antenna? To present a load impedance to the transmitter that
is close to the load it was designed for.
What does an SWR meter measure? How close the impedance is to 50 ohms (or whatever the
impedance the SWR meter is designed for.) When the SWR is 1 : 1 on 50 ohm coax, the load
impedance must be exactly 50 ohms resistance with zero reactance
. Any other impedance
will give you a different SWR.
So here you have a device that tells you how close you are to the best match to the transmitter.
You use it to adjust the antenna to get the best match. What are you proposing as an alternative -
something that doesn't
give the best match? Why would anyone in their right mind want such
In this case the antenna is a base-loaded whip with the feedline tapped up the coil for impedance
matching. It is designed so that, with the proper length of whip to resonate on 27 MHz it gives a
good match to 50 ohms. Now we are shortening the antenna to make it resonant at 28.5 MHz.
To do so we adjust the whip for the lowest SWR - that tells us that we have the best possible
match for that particular antenna. Because the frequencies change is small, the impedance
matching is still very close, and we expect that the SWR will be low. (Clearly in this case the
ground plane it is mounted on had a very large effect on the impedance, but it could still be
tuned for minimum SWR by adjusting the whip.) So if you adjust the whip for minimum SWR
the transmitter sees as close to its design impedance as you can get.
If the SWR meter gives you the best possible match, what could do any better?
[And before you go off on a tangent about resonant antennas, be sure to read , reflect, and digest
some of the articles available on the internet about how important - or not - resonance actually is
to antenna performance, and the fact that a pure resistance at some point on the feedline doesn't
guarantee that the antenna is, in fact, resonant.
Such as these:http://www.vk1od.net/antenna/iobr/http://www.cebik.com/content/a10/trans/x.htmlhttp://www.vk1od.net/antenna/arrm/index.htm
This is to help save you from sticking your foot any further in your mouth than you have already.]