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Roy Lewallen · January 8th 09, 06:31 PM posted to rec.radio.amateur.antenna

wrote:
On Jan 8, 7:50 am, "Ed Cregger" wrote:

The aversion to transmatches is a ham cultural trait that has no basis in
reality, just as the CB'ers are hooked on resonant 50 ohm antennas. It's a
characteristic of the culture(s) of both types of operators, with no basis
in practical operating engineering.

Ed, N2ECW

I wouldn't say that. As an example, I've done tests showing that no
matter how careful I am with the tuner, it's settings, decent open
wire feeder, etc, I could never quite equal the performance of a coax
fed
dipole when feeding the same antenna using the tuner and ladder line.
Quite close granted, and to many people a non issue, but there *was*
a difference. Of course, the coax fed dipoles I use would generally
be considered a single band antenna. But that's no problem here.
But if I have my way, I avoid tuners if possible. I'm trading the
ability of fairly efficient multi band use, for the slightly more
efficient
coax fed single band antenna. I want to radiate every drop of RF I
can.

There are actually a couple of different consequences to using a
non-resonant antenna, and they're often confused or lumped together. The
first is the potential for tuner loss. In many, but not all cases, it
can be made negligible -- after all, 25% power loss is only a little
more than 1 dB. But of course no argument can be made against someone
who considers "every drop" -- even a fraction of a dB -- important. The
rest of us can usually use a tuner without any perceptible reduction in
signal strength. We do need to keep in mind, however, that there are
cases where tuner efficiency can be truly bad, and avoid them when possible.

But amateurs tend to use multiband antennas without any thought at all
to radiation pattern. When the frequency gets considerably higher than a
dipole's resonant frequency, the pattern changes. So there's a good
chance that the pattern will have nulls in at least some directions
where you might want to communicate. In those cases, the difference
between a half wavelength dipole and much longer dipole can be striking.
People who don't understand the reason for the difference often
mistakenly attribute it to a change in efficiency rather than pattern.

Also the settings of the tuner are fairly critical for the most
efficient
use. I have a 989c also, and I have done extensive testing with it
using various settings vs efficiency.
I found with the usual T network tuner such as the 989c, you might
be able to tune a load with 25 or more settings. But only the setting
using the least inductance will be fairly low loss. All of the
settings
that use more inductance than required show more tuner loss.
Up to about 20% of your power is lost in a worst case scenario.
So that is another issue. Small, being as one can make sure to
use the least inductance, but it's just another thing to fuss with
when changing bands.
It's relatively easy to measure tuner efficiency when it's working into
a nice resistive load. But I'm curious about how you measured the power
the tuner was delivering to a more realistic non-resonant load
impedance. The only way I can think of to do it with any semblance of
accuracy is to connect two identical tuners back-to-back and measure the
power out of the combination. Is that how you did it? If not, how?

. . .

Roy Lewallen, W7EL

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