I want to make something clear. I never said that is practical to match any
load with an antenna tuner. In fact if you have an "anti-resonant" antenna it
is a lost cause.
I was simply debunking the notion that an antenna tuner only protects the rig
from a high SWR and it does not change the currents or voltages in the antenna.
I used E.F. Johnson transmitters in my earlier years and they were capable
of matching a large range of "mis-matched" antennas, even some random length
length long wire antennas. In those days an SWR meter and antenna tuner were
luxuries that a lot of us could not afford. We tuned up the rigs to for a dip
in the
plate current, adjusted loading to get the dip to the proper current. That was
it.
The G5RV was "invented" before I was born, almost 70 years ago. There was
not even a 15 meter band then. And most relied on the variable (swinging link
coupling in the plate, possibly a
series capacitor to match their dipoles. The G5RV is a dipole in fact and there
is an attempt create multiple resonances by combinations of antenna length and
feedline length.
I am an engineer, retired now. And have had over 50 years experience with RF.
Said enough.
Good luck guys.
Maybe some of you should sit in on my class on resonance and why we use
resonant antennas and impedance matching networks.
73
Bill wa4lav
________________________________________
From: Fuqua, Bill L
Sent: Monday, April 27, 2015 12:23 AM
To: towertalk@contesting.com
Subject: Re: G5RV vs 40M dipole
Not everyone knows that a tuner only protects the rig. That is the job of a
dummy load.
In fact the tuner matches the impedance of the antenna system to the rig and
not only that,
by doing so providing the antenna with a conjugate match, that is to say the
antenna's radiation
resistance is matched and its reactance is also matched by the equal and
opposite reactance thus
making the antenna system resonant. If the antenna has a radiation resistance
of 10 Ohms and
a capacitive reactance of 100 Ohms the antenna tuner matches it with 10 Ohms
real resistance and
an inductive reactance of 100 Ohms thus providing maximum energy transfer.
While at
the same time it provides 50 Ohms resistive load for the transmitter.
Resonating the antenna system with a tuner is equivalent resonating the
antenna. The only difference
is that there may be some additional losses within the tuner and transmission
line which are generally
minimal at HF frequencies. Also, there is a reduction in bandwidth of the
antenna system.
Yes it does change the currents and voltages in the antenna. The G5RV was an
antenna developed back
when we had tube transmitters with a PI network output that could accommodate a
broad range of
impedances. It also was made to work on 5 bands.
Just about every AM broadcast antenna system has an antenna matching network.
It is a shame that
they don't work.
73
Bill wa4lav
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