Band-Rejection Filters
A band-rejection (band-stop) filter is used to
reject or block a band of frequencies from being
passed. This filter allows all frequencies above and
below this band to be passed with little or no
attenuation.
The band-stop filter circuit consists of inductive
and capacitive networks combined and connected to
form a definite frequency response characteristic.
The band-stop filter is designed to attenuate a specific
frequency band and to permit the passage of all
frequencies not within this specific band. The
frequency range over which attenuation or poor
transmission of signals occurs is called the
“attenuation band.” The frequency range over which
the passage of signals readily occurs is called the
“bandpass.”
The lowest frequency at which the
attenuation of a signal starts to increase rapidly is
known as the lower cutoff frequency. The highest
frequency at which the attenuation of a signal starts to
increase rapidly is known as the upper cutoff
frequency. The basic configurations into which the
band-reject filter elements can be arranged or
assembled are known as the L- or half-section, the
T-section, and the Pi-section configurations. These
configurations are shown in figure 10-14. For a more
in-depth discussion on the various filters discussed in
this chapter, you should refer to NAVSHIPS
0967-000-0120, (EIMB), section 4.
BONDING
Learning Objective: Identify purposes and
techniques of bonding.
Aircraft electrical bonding is defined as the
process of obtaining the necessary electrical
conductivity between all the metallic component parts
of the aircraft. Bonding successfully brings all items
of empennage and internal conduction objects to
essentially the same dc voltage level appearing on the
basic structure of the fuselage. However, bonding for
radio frequencies is not quite so simple. Only direct
bonding between affected components can
accomplish the desired results at all frequencies.
Only when direct bonding is impossible or
operationally impracticable should bonding jumpers
be used. Regardless of its dc resistance, any length of
conductor has inductive reactance that increases
directly with frequency. At a frequency for which the
length of a bond is a quarter wavelength, the bond
becomes a high impedance. The impedance of such a
resonant lead becomes greater without limit as the dc
resistance becomes lower. Multiple bonding using
the same length of bonding jumper increases the
impedance at the resonant frequency, but also tends to
sharpen the high-impedance area around the resonant
frequency. This sharpening is done by the rapid fall
of impedance on each side of resonance.
PURPOSES OF BONDING
Bonding must be designed and executed to obtain
the following results:
l Protect the aircraft and personnel from hazards
associated with lightning discharges
. Provide power-current and fault-current return
paths
l Provide sufficient homogeneity and stability of
conductivity for RF currents affecting transmission
and reception
. Prevent development of ac potentials on
conducting frames, enclosures, cables of electrical
and electronic equipment, and on conducting objects
adjacent to unshielded transmitting antenna lead-ins
Figure 10-14.-Examples of band-reject filter circuits
10-14
