Dan: We are talking about the method to deliver power to the antenna by
tuning the antenna SYSTEM to resonance. The system includes the antenna and
transmission line. If the antenna tuner is located at the rig will tune the
antenna SYSTEM to resonance and this is when the conjugate match is achieved
and maximum power is delivered to the antenna. It is NOT necessary for the
physical antenna itself to be in resonance as long as the SYSTEM is in
resonance. The antenna radiates all the power delivered to its terminals. Mr.
Walter Maxwell clearly explained all this in long proven and accepted
engineering terms in his series of articles in QST in the mid 1970's and later
book. It is NOT necessary for the antenna itself to be resonate as long as
the SYSTEM is resonate. That is what the antenna tuner accomplishes, a
resonate system. This has long been proven in commercial/engineering radio and
as an example, most a.m. broadcast antenna towers are not of themselves
physically resonant at their operating frequency. We are talking very large
amounts of RF power here. However, the antenna system is made resonate by a
matching or tuning device ususlly located at the base of the antenna tower.
Therefore, when the system is tuned to resonance, a maximum transfer of power
occurs in both the incident and reflected directions. ( I like to think of the
antenna tuner as the transmission system in your car. It permits the engine to
deliver maximum torque to the wheels at a very wide range of speed. Not having
a antenna tuner is like driving your car locked into fourth gear all the time.)
A conjugate match will not effect antenna characteristics like angle of
radiation or front to back ratio, etc. However, it will permit your
transmitter to deliver all its power to the antenna to be radiated and all the
received energy picked up on the antenna to the receiver. I suggest to go to a
library that has QST and read the articles; very eye opening!! An extreemly
large majority of hams clearly do not know what they are tal
ing reflected power, etc. Stop listening to all that bull s---t on the air
and start reading Mr. Maxwell's excellent articles or his book. - 73's -
sherrill k4own
>>> "Jim Reid" <kh7m@hsa-kauai.net> 11/07/00 07:11PM >>>
Dan wrote, in part:
> I still don't see no matter how much people try to come up
> with reasons to explain it that it could possibly improve
> things at the antenna itself.
Dan, The answer is the conjugate match. To understand
the conjugate match takes a bit of study. Try the latest
issue of QEX I referenced; or, if you can find one, a
copy of Walt Maxwell's first edition of "Reflections",
published by the ARRL. The conjugate match is also
written up in most recent earlier editions of the ARRL
"Antenna Book". For example, Chap. 25, "Coupling the
Transmitter to the Line", up to at least the 17th edition and
a few ahead of that one. I don't have newer editions, but
presume it is in them (it?) as well, hi.
In your example, the water that couldn't get in the hose,
falls to the ground. If all the power which is put out by the
rig, to use your analogy, is not radiated by the antenna, or
is not lost by heating lossy conductors in the tuner or in the
transmission line, where would you say it goes? Even
as little as 30 watts dissipated within your tuner or
transmission line could cause problems! Ever accidentally
touch an Ungar 30 watt soldering iron?
It certainly does not stay in the transmission line, else the
line would get very hot, very quickly; the solder within
the coax connectors would soon melt, hi. All the power,
then, which is not lost to heat in the tuner and line HAS
to be input into the antenna input terminals and RADIATED!
The power also does not get sent back into the rig, where
it would also soon cause havoc; my linear purrs along just
fine when my tuner is feeding full legal limit into a line
which has around 3:1 vswr at the output of the tuner
at the top end of the band. Why, because even with that
vswr, caused by the Z mismatch at the line/antenna terminals,
that system is "conjugately matched", and all the incident power
from the rig enters the antenna terminals
Where things can get warm, is trying to feed a short
vertical, real short, as when the vswr is 8:1 as Steve
Best uses in his analytic work on this topic. And yes,
it pays to get your antenna to within at least 3:1 or so
at the band edges. With much higher vswr and full power
out, it would be wise to have a fan in the tuner to blow air
across the inductor to keep from melting something there.
I managed to melt the plastic coil form within an MFJ tuner
once trying to center feed an 80 meter dipole while operating
on 160 meters at full gallon output! Not a wise thing to attempt;
to center feed a 1/4 wavelength antenna element, hi. But,
I thought I was desperate and could get away with it--not
so.
I know these ideas are not intuitively that obvious; I first
struggled with them when studying RF transmission lines
and circuits when back in engineering school, decades ago;
but the conjugate match theorem was even being taught
back in the 1950's, hi. Was even taught to the AC power
engineering students; the only way to get all the power
from the power house down into the homes/factories of the
folks of the city within the neighborhoods where even
60 Hz Z mismatches can happen, hi. Why do you suppose
you see banks of capacitors atop some power poles within
neighborhoods? Used to adjust the power systems "power
factor"; that is, performing an impedance match within
the distribution system! The problem occurs as many
homes/factories present way to reactive a load, too
high inductance, or high positive reactance: comes from
all the motors we use. So to match the load to the power
distribution grid, the source rig and distribution system
must be impedance matched to all that distributed
inductive reactance with the addition of those capacitor
banks. Then, the water flows into the load just fine,
even when it is very inductively, positively reactive
and not pure R at all. The load and the source generators
have been "conjugately matched".
Hope this explanation helps a little in understanding the
concept.
73, Jim, KH7M
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