Post by Roy LewallenBut 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.
That's another reason why I prefer the separate elements for multi
band use, vs the single wire.
I generally prefer the normal dipole pattern on most of the bands
I use.
Post by Roy LewallenIt'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?
It's been so long since I did that, I forgot exactly how I came to
that conclusion.
But I think I was using my resonant coax fed dipole as the load,
and pretty sure I had dual watt meters. One before the tuner,
and another after the tuner. The tuner has an antenna switch
to bypass the tuner.
I believe what I did was measure the power on both meters with
the tuner bypassed, and then tried using the tuner as a "line
flattener", more than an actual tuner, being the system was
already resonant.
I tried various settings of the tuner, trying quite a few variations
in inductance vs cap settings to see if I could notice much loss
with the tuner inline. The radio was my old IC 730 and I used
full power for the tests. The meter after the radio was used to
verify the appx power from the radio, and it stayed fairly constant
in all the tests. The meter after the tuner was used to check
the power at that point in the line.
In all cases, the tuner would indicate a "flat" match with all
the various settings, so any variation in the output of the
radio should have been small, and the meter after it verified
this.
But the meter on the other side of the tuner could vary
anywhere from about 20% less, to almost unnoticeable
difference, depending on the inductance setting of the tuner.
This test didn't tell me much about the losses using
non resonant loads fed with ladder line, but I suspect that
the loss would still be greatly defendant on the inductance
setting.
I would think the loss would greatly vary just depending
on the load at the moment. Could be high, as if feeding a
half size dipole with a T network tuner, or pretty low with
other longer wire lengths.
I didn't try to worry about the exact loss in numbers, but
I could see the problem cropping up fairly easy if one were
lazy about using the least inductance setting, or if using a
tuner with a tapped coil that was not the optimum setting.
My tuner uses a roller inductor, which lets me tune to
exactly the best spot on the coil, but some tuners tap
and switch the coil position. With some of those, loss
could be more noticeable if it's compromise setting was
way off from optimum.
Another thing I noticed that was it didn't take a whole
lot of extra inductance for the losses to begin to show.
Basically, I found there is only one tuner setting that
will give you fairly low loss in such a case. The one
using the least inductance to get a usable match
for the radio. All the other settings would show quite
a bit more loss, and it didn't take too much more
inductance to start seeing 10-15-20 % decreases in
output from the tuner. And all these settings show
a perfect match to the radio.
But if using the least inductance in such a case, the
meter reading was so close as to almost be the same
vs bypassing the tuner.
So you can use a tuner and have low loss if you
are careful about tuning.
Sure, even 20% won't make much of a difference on
the other end, but I'd prefer not to lose it none the less.
I'm usually on the noisy lower bands, and I rarely run
an amp anymore. That's why I insist on every drop.
In the summer, I usually need every drop.. :/
I also prefer coax anyway just due to the convenience.
But if I run ladder line, I run ladder line the whole way.
I don't like running coax to ladder line. I either use
one or the other.
