transmitter patch panels are interlocked with the
transmitter so that no open jack connection can be
energized and no energized patch cord can be removed.
This provides safety for both personnel and equipment.
Raise and lower antennas - raising and lowering
physically of antennas is associated with flight,
refueling or PMS operations. Extreme care should be
taken that all moving parts are in correct operating
conditions and the Officer of the Deck or
Communications Watch Officers know prior to the
physical movement of the antennas.
USE DIRECTIONAL ANTENNAS
Reception is defined as: when an electromagnetic
wave passes through a receiver antenna and induces a
voltage in that antenna. Further detailed information on
antennas, antenna use, wave propagation and wave
generation can be found in NEETS MODULES 9, 10,
Rotate For Optimum Reception
This is accomplished by both physical and
mechanical means of moving the antenna(s) to properly
align and tune the antenna.
Align For Optimum Reception
Using the correct antenna location (by rotation) and
the correct equipment for the system, you will bring the
antenna into alignment and be ready for the final step,
which is tuning.
Tune For Optimum Reception
There are two objectives of antenna tuning: (1) to
tune out the various impedances and (2) to match the
length of the antenna to the frequency radiated at its
Impedance: everything exhibits some
impedance, Even a straight piece of copper wire
3 inches long will offer some resistance to
current flow, however small. The characteristic
impedance of this same piece of copper wire is its
overall resistance to a signal.
The transmission line between an antenna and a
transmitter has a certain amount of characteristic
impedance. The antenna also has a certain amount of
characteristic impedance. This basic mismatch in
impedance between the transmitter and the antenna
makes antenna tuning necessary. Naturally, as
transmitters, transmission lines, and antennas become
more complex, antenna tuning becomes more critical.
Antenna length adjustment: When we tune an
antenna, we electrically (not physically)
lengthen and shorten it. The radiation resistance
varies as we vary the frequency of the transmitter
and tune the antenna. The radiation resistance is
never perfectly proportional to antenna length
become of the effects of the antenna height above
the ground and its location to nearby objects.
You will find that the better the ability of the
receiver to reject unwanted signals, the better its
selectivity, The degree of selection is determinedly the
sharpness of resonance to which the frequency-
determining circuits have been engineered and tuned.
You usually measure selectivity by taking a series of
sensitivity readings. As you take the readings, you step
the input signal along a band of frequencies above and
below the circuit resonance of the receiver; for
example, 100 kilohertz below to 100 kilohertz above the
tuned frequency. As you approach the tuned frequency,
the input level required to maintain a given output level
will fall. As you pass the tuned frequency, the required
input level will rise. Input voltage levels are then
compared with frequency. They can be plotted on
paper, or you may can view them on an oscilloscope.
They appear in the form of a response curve. The
steepness of the response curve at the tuned frequency
indicates the selectivity of the receiver, thus allowing
for the optimum reception.
RF SAFETY PRECAUTIONS
Although electromagnetic radiation from
transmission lines and antennas is usually of
insufficient strength to electrocute personnel, it can lead
to other accidents and compound injuries. Voltages may
be inducted in ungrounded metal objects, such as wire
guys, wire cable (hawser), hand rails, or ladders, If you
should come in contact with these objects, you could
receive a shock or RF burn. This shock can cause you to
jump or fall into nearby mechanical equipment or, when
working aloft, to fall from an elevated work area. Take
care to ensure that all transmission lines or antennas are
deenergized before working near or on them.
Guys, cables, rails and ladders should be checked
for RF shock dangers. Working aloft chits and safety
harnesses should be used for your safety. Signing a