Thursday, November 8, 2012


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
Switching Power Supply
Cell Phone Charger
DC to AC Inverters
Power Lines & Poles
Food Mixers
Hair Dryers
Light Dimmers
Elecrtric Drill
Vacuum cleaners
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.

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 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.
                                   Ignition type capacitor/condenser

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.
                                           AC LINES FILTER

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