The relative truth of my statement is relative to the band you are on, its
characteristics at the time of day you happen to be on the air, the
propogation, and the combination of physical/mathematical gyrations involved
in radiating a given signal into any given antenna.
2:1 SWR is a relative notion giving you notice that all is not well, but
better than 2.5:1, not as good as 1.5:1. Standing Wave Ratio. If you think
of a Standing wave as a sine wave with both a voltage peak and a current
peak, you can visualize that by the time a sine wave completes, half of sine
wave is on the way back to its starting point. The results is heat/wasted
energy. On the other hand 80% of the energy has been radiated and doing what
it is you intended.
The reason it's particularly true on the top band is its characteristic need
to see a long length of friendly wire to cast its energy into the ether,
rather than have the nearby ground eat it up giving the nearby earthworms a
thrill. It would be the same if you were using a forty meter dipole to
transmit on 75 meters. Or, a 20 meter beam on 40 meters, you may find a low
SWR using a tuner, but the remaining energy will not be nearly as likely to
reach the ether as it would, were the antenna resonant.
There are lots of tricks to shortened antenna, feedline variations, matching
transformers, combination feedlines and baluns, but none of these gives you
a free lunch. Compromise antennas will not work as well as its longer
and properly fed counterpart without exception. If you use a compromise
antenna, you are sharing your lunch with whatever device you use to make it
appear whole. Some devices eat more lunch than others depending on the band,
power level, propogation and operator skill. There are no happy meals in the
physical world, only understanding the raw ingredients and how they mix will
give you the rules of efficient rf energy projection.
Its what makes hf ineteresting and challenging. If it were easy everybody
could do it.
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