On 5/6/2014 1:33 PM, Paul Christensen wrote:
"But the antenna tuner does not change the feedpoint impedance of the
antenna which in my view would be actually "tuning" the antenna."
It does however change what the rig sees as the antenna impedance. (R,
L, and C). So whether you change the antenna height or length, or stick
a "tuner" in the line the results are the same, so call it what you
want, The results are the same.
An antenna does not have to be resonant to radiate otherwise 5/8th
radiators would not work. It's a radiator and will eventually radiate
all the power getting to it although some may make the trip up and down
the feedline a number of times.
With the tuner at the antenna (matching network) the loss is less
because the trips up and down the coax are fewer.
With low loss coax, the loss is less because there is less loss per trip.
Where ever you put the matching network, antenna tuner, line tuner or
what ever you want to call it don't forget there is loss in that network
and for low impedance antennas the loss may be considerable. A matching
network, a 4:1 balun, what ever, the low impedance antenna will lose
power in the matching network.
Put a 160 dipole at 30 or 40 feet for 20 or 30 ohms R and that coil in
the network can get mighty hot and that is all lost power. You can lose
a substantial amount of the power going to the antenna in the matching
network. That is why, all matching networks are limited in power at low
impedances. Look at the limits for the (legal limit MFJ 989 series) They
will not handle the legal limit at low impedances. You, You may be able
to match it with the legal limit, but thy get noisy in a hurry because
that rotary inductor gets hot and will have a short life!
Look up the power limits for high to low impedances for any tuner. Even
my AT5K tuner is substantially limited at low impedances although it'll
still run the legal limit.
73
Roger (K8RI)
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