LDG YT-100 Operation Manual - page 18
PAGE 18
perform a tuning cycle. When the tuning cycle is complete, control of the CAT interface is returned to
the PC.
This procedure is completely automatic, and is transparent to the user. Simply hook up a PC, and use
the rig control software as normal. Press the
TUNE
button on the YT-100 when tuning is desired.
THEORY OF OPERATION
Some basic ideas about impedance
The theory underlying antennas and transmission lines is fairly complex, and in fact employs a
mathematical notation called “complex numbers” that have “real” and “imaginary” parts. It is beyond
the scope of this manual to present a tutorial on this subject
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, but a little background will help in
understanding what the YT-100 is doing, and how it does it.
In simple DC circuits, the wire resists current flow, converting some of it into heat. The relationship
between voltage, current, and resistance is described by the elegant and well-known “Ohm’s Law”,
named for Georg Simon Ohm of Germany, who first discovered the principle in 1826. In RF circuits, an
analogous but more complicated relationship exists.
RF circuits also resist the flow of electricity. However, the presence of capacitive and inductive
elements causes the voltage to lead or lag the current, respectively. In RF circuits, this resistance to the
flow of electricity is called “impedance”, and can include all three elements: resistive, capacitive, and
inductive.
The output circuit of a transmitter consists of inductors and capacitors, usually in a series/parallel
configuration called a “pi network”. The transmission line can be thought of as a long string of
capacitors and inductors in series/parallel, and the antenna is a kind of resonant circuit. At any given RF
frequency, each of these can exhibit resistance, and impedance in the form of capacitive or inductive
“reactance”.
Transmitters, transmission lines, antennas, and impedance
The output circuit of a transmitter, the transmission line, and the antenna, all have a characteristic
impedance. For reasons beyond the scope of this document, the standard impedance is nominally 50
ohms resistive, with zero capacitive and zero inductive components. When all three parts of the system
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For a very complete treatment of this subject, see any edition of the ARRL Handbook for Radio Communications (previously the Handbook For
Radio Amateurs).