The purpose of this writeup is to outline some sources of
interference: explain how to eleminate or reduce them and tells you how to
protect yourself againts RFI. Remember all cases of RFI involve two things the
source of the interference and the victim of the interference.
Generally speaking aside from thunderstorms and lightning
static, most interferance is man- made and can be located and suppressed. The
problem is finding the source and than applying the remedy. That's not so easy
RFI may originate within your own home, within your neighbor's house, from
nearby utility lines, or from unknown a thousand kilometers away. Bare in mind
RFI problems are found every day as our world becomes more complex and as we
invent electronic "black boxes" to perform new task for us.
What does RFI means? Radio frequency interference is a broad
term that covers any type of electrical signal capable of being propagated into
and interfering with, the proper operation of other electrical or electronic
equipment. Another term for RFI is electromagnetic interference (EMI) this
latter term is much favored by the military. But both terms, in essence, mean the
same thing. As already mentioned RFI can originated in almost anything that
uses electricity or that is conected to a power line.
The following is a partial list showing some potential
sources of RFI:
Fluorescent lamps and starters
Ignition System
Welding Set
Distribution system
Voltage stabalizer
UPS
Switching Power Supply
Cell Phone Charger
DC to AC Inverters
Computers
Power Lines & Poles
Food Mixers
Hair Dryers
Light Dimmers
Elecrtric Drill
Vacuum cleaners
Motorbikes
Washing machines more and more !
Natural Sources of Interference
Added to the unholy din of man made RFI must be the natural
sources of radio noise: static, lightning, atmospheric hiss, radio noise from
outer space, and the noise generated by the movement of electrons in the heart
of all the elctronic equipment. In short, our world is filled with RFI both
natural and man made and as our culture advances, the level will
increase-unless something is done about it now.
Noise limit the usefull operating range of all radio
equipment. Aside from man made noise, natural radio noise, natural radio noise
is all around us. A major source of atmospheric noise (statistic) is a belt of
continuous lightning activity around the equator from which interference is
propagated toward the rest of the world by ionospheric reflection .
Thunder-storms in the temperate zones creat additional radio noise : the
overall noise level depends upon frequency, time of day, season of the year and
geographical location.
A second sourse of natural interference is galactic noise
from outer space. A major generator of galatic noise is the sun and variuos
star group have been indentified as radio noise source. Precipitation static is
often found in the HF spectrum during a heavy rainstorm, showing up as a loud
hiss in the radio receiver or as "snow" on the screen of TV set. It
is caused by static electricity building up on trhe receiving antenna. Finally
there is a low level of thermal noise in all electrical equipment caused by the
thermal agitation of electrons in conductors.
All of these noise sources, plus man made noise, form a
"noise floor" in the communication spectrum below which the
sesitivity of the communication equipment is restricted. And in a long run, a
receiver's ultimate sensitivity, in the absence of man made noise, is determind
by natural noise.
The "WOODPECKER"
High Frequency radio communication has been plagued during
the past years with an annoying form of man-made interference termed the
woodpecker. The interference consists of a series of rapid pulses that ocupy
large spectrum. The pulses are extremely powerful and seeming move about at
random, knocking out communications over a wide swath frequencies. Examination
of the the pulses has led to the conclusion that they are generated by a
variable frequency backscater radar system located in the Soviet Union. The
purpose of that radar, it is assumed, is to detect the launch of
intercontinental ballastic missiles.The system seems to have two transmitters
located in the Ukraineand Siberia that transmit pulses over the North Pole
towrds the United States. The reflected pulses provide information on ionized
trails left by the launch of a surface missile.At present the woodpecker have
not heard through the HF spectrum. We never know what will happen next.
An RF Noise Source - The Spack Discharge
A partial list of equipment capable of creating RFI,
particularly of the Spack discharge type is given above. You can think of other
devices which fit this category.In addition to the spack discharge, there are
two other classes of RF noise generators : the electrostatic discharge and the
RF oscillator. Radio transmitters are included in this last class. Each class
of noise has its own pecularities and leave its own unique "noise print"
a fact that is helpfull in tracking down the source. Lets examine these sources
starting with spark discharge which is common to all neighborhoods. A natural
discharge is a lightning stroke. A good example of usefull spark discharge is
the ignition system and spark plugs in gasoline motor.
The charecteristic sound associated with spark discharge may
variously be describe as a buzzing rasping, popping noise similar to bacon
frying in a pan. Spark discharge seen on the TV screen appears as a band of
horizontal dot-dash
Ok nows lets look into how to cure the noise.
Ok example if you install your VHF/HF rig inside your car.
There is no problem when the engine is off. But if you have a problems when
your engine is on example the receiver will pickup a noise wiiiigg.....wingggg....and
its becomes louder if you press your excelerator. Check all the connections
tighten all the connections at the battery terminals, your lines fuse..supply
together with your VHF rig. And if the noice is still there its time to service
your alternator the carbon brush at the alternator maybe needs to be replace or
your alternator needs to be service. If you have a problem when you turn on your Air Cond in your car what you can do is just install a capacitor 0.001uF at the Condenser Fan which is located near your Radiator.
For those who works from base station make sure you have a good grounding system and avoid using a cheap type switching power supply. You may also install a line filter at your AC line. If you have space you can install a QUAD or a LOOP antenna this will help you to reduce the noise level.
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