3-2
the transmitter is located inside a radio room and its associated antenna is mounted on a mast. A
transmission line is used to connect the transmitter and the antenna.
The transmission line has a single purpose for both the transmitter and the antenna. This purpose is
to transfer the energy output of the transmitter to the antenna with the least possible power loss. How well
this is done depends on the special physical and electrical characteristics (impedance and resistance) of
the transmission line.
TERMINOLOGY
All transmission lines have two ends (see figure 3-1). The end of a two-wire transmission line
connected to a source is ordinarily called the INPUT END or the GENERATOR END. Other names
given to this end are TRANSMITTER END, SENDING END, and SOURCE. The other end of the line is
called the OUTPUT END or RECEIVING END. Other names given to the output end are LOAD END
and SINK.
Figure 3-1.—Basic transmission line.
You can describe a transmission line in terms of its impedance. The ratio of voltage to current
(Ein/Iin) at the input end is known as the INPUT IMPEDANCE (Zin). This is the impedance presented to
the transmitter by the transmission line and its load, the antenna. The ratio of voltage to current at the
output (Eout/Iout) end is known as the OUTPUT IMPEDANCE (Zout). This is the impedance presented to
the load by the transmission line and its source. If an infinitely long transmission line could be used, the
ratio of voltage to current at any point on that transmission line would be some particular value of
impedance. This impedance is known as the CHARACTERISTIC IMPEDANCE.
Q1. What connecting link is used to transfer energy from a radio transmitter to its antenna located on
the mast of a ship?
Q2. What term is used for the end of the transmission line that is connected to a transmitter?
Q3. What term is used for the end of the transmission line that is connected to an antenna?
TYPES OF TRANSMISSION MEDIUMS
The Navy uses many different types of TRANSMISSION MEDIUMS in its electronic applications.
Each medium (line or wave guide) has a certain characteristic impedance value, current-carrying capacity,
and physical shape and is designed to meet a particular requirement.
