One thing I have noticed with the built-in tuner on my radio is that all
it does is make the radio happy.
The radio shows a 1:1 SWR, but the meter past the radio still shows a
high SWR, so if there is loss on the line, even though the radio is
happy, the loss is still there. I think the tuners just give us a false
sense of security. 73
Tom W7WHY
On 4/26/2015 9:23 PM, Fuqua, Bill L wrote:
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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