Quantcast Narrowband interference

 

Click here to make tpub.com your Home Page

Page Title: Narrowband interference
Back | Up | Next

Click here for thousands of PDF manuals

Google


Web
www.tpub.com

Home

   
Information Categories
.... Administration
Advancement
Aerographer
Automotive
Aviation
Construction
Diving
Draftsman
Engineering
Electronics
Food and Cooking
Logistics
Math
Medical
Music
Nuclear Fundamentals
Photography
Religion
   
   

 

Share on Google+Share on FacebookShare on LinkedInShare on TwitterShare on DiggShare on Stumble Upon
Back
Figure 2-1. Typical interferences sources.
Up
TM-11-490-5 Army Communications Facilities Operational Electromagnetic Compatability Manual
Next
Figure 2-2. Transmitter spurious emissions for an AN/GRT-22.


TM 11-490-5
interference is most prevalent near densely populated
operation through transmitter frequency drift and lack of
areas and industrial districts, or within any other region
selectivity at the receivers). Note that, for the purpose
where  many  transmitters  and  other  interference-
of this discussion, a channel is defined as an assigned
producing equipments are operating simultaneously.
frequency range of a given portion of the RF spectrum
Also included in this category are such ancillary
and may include from 1 to 2700 audio channels.
equipments as electric motors and generators.  This
type of interference is grouped into two categories:
narrowband and broadband.
(b ) Harmonics of the transmitted frequency and
other spurious emissions. Harmonics of the transmitted
(1) Narrowband
interference.
Narrowband
frequency and other nonharmonic spurious emissions
interference sources consist of cochannel, adjacent-
are always present to some degree in the radiated
channel, harmonic, and other signals at distinct
output of a transmitter.  Well-designed transmitters,
frequencies as described below:
maintained in good operating condition and properly
loaded into antennas, will radiate only very low-level
spurious emissions.  Improper tuning, loading, and
(a) Cochannel and adjacent-channel operation.
maintenance, and faulty transmitter and antenna
A transmission from a distant station, although fully
elements  can  cause  normally  low-level  spurious
authorized, may become a source of interference if it is
emissions to increase to extremely high levels. These
unintentionally received along with a desired signal.
signals are primarily generated in the frequency
This situation is usually prevented by assigning
multiplier  or  RF  power  amplifier  stages  of  the
cochannel  frequencies  to  equipments  only  with
transmitter.
In  addition,  harmonics  and  other
adequate geographical separation.  Adjacent channel
nonharmonic spurious emissions of the transmitter local
operation may require some geographical separation
oscillator (LO) may be radiated.
An example is
also; however, receiver selectivity usually provides
presented in figure 2-2, which shows the transmitter
rejection  of  undesired  adjacent  channel  signals.
spurious emission measurements on an AN/GRT-22
Conditions which cause cochannel and adjacent channel
transmitter.
Frequently, interference is caused by
interference,  then,  include  unusual  propagation
spurious emissions from a transmitter, rather than from
conditions (which cause distant transmitters to appear to
a transmitter operating on the desired frequency.
be local RF sources); frequency spectrum crowding
Frequency  allocation  plans  usually  prohibit  two
(which may result in adjacent channels being occupied
transmitters operating on the same frequency if the
by transmitters at power levels that override receiver
antenna patterns and service areas are such that
selectivity); use of excessively high, unauthorized power
interference could be caused.
levels; and lack of proper maintenance procedures
(which can result in off-frequency
2-3


Privacy Statement - Press Release - Copyright Information. - Contact Us

Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business