Interference is the effect of unwanted energy due to one or a combination of emissions, radiations, inductions upon reception in a radio communication system, manifested by any performance degradation, or misinterpretation or loss of information which could be extracted in the absence of such unwanted energy.
Types of Interference:
- Natural phenomena adversely affecting the electromagnetic waves
- Static electricity
- Thermal shot
- Solar radiation
- Electric and mechanical appliances
- The effect of some components of electric light bulbs (fluorescent). When such components do not work efficiently, they produce electric spark resulting in negative impact on communications equipment.
- The impact of the rotary engines, causing random electromagnetic waves, interfering the telecommunication equipments.
- Non-Radio sources
- Examples of some unauthorized equipment violating Telecommunication Act of Kingdom of Saudi Arabia.
- Interference because of using the same channel by more than one use in the same area.
- Interference resulting from adjacent channels because of noncompliance with the technical parameters.
- Interference resulting from inter-modulation because of noncompliance with the technical parameters.
- Radio equipment malfunction interference.
- Interference due to overspill emissions.
- Receiver overloads interference.
- Out-of-Band interference.
- General RF noise interference.
Some common types of radio interference
- Receiver Overload
If a receiver is near a transmitting system, the RF from that system will be too strong for the first amplification stage to handle. The transistors saturate and the receiver sensitivity decreases. Additional inter-modulation products may be created within the receiver. Since many communications receivers have wideband front ends, they will be affected by strong out-of-band signals entering their antennas. This is not the same as out-of-band emissions from a nearby transmitter. There are some ways to avoid this type of interference.
- Out-of-band emissions from transmission systems close in frequency
All transmitters emit radio frequency energy at frequencies other than the exactly desired frequencies. This is known generally as out-of- band emissions. Since these undesired signals may be on the desired receive frequencies, they can only be eliminated by filtering the offending transmitter or moving the offending transmitter to another location.
- Inter modulation product Interference
If more than one communication system is installed on a single antenna, or if communication systems with high capacity are close to each other, the frequencies of these systems will be mixed with each other or their frequencies will be mixed with those of mixing circuits in the nearby receivers causing new frequencies, which can cause harmful interference in receivers. There are some ways to avoid this type of interference.
Some types of natural phenomena that affect electromagnetic waves propagation
Skip is a phenomenon caused by the ionization of gases in the ionosphere. The radio frequency is reflected for long distances through this layer and returns to earth, causing harmful interference between uses in areas separated by great distances. This phenomenon is much more prevalent at frequencies below 30 or 40 MHZ and is time dependent. The interference usually occurs more at night and in the evenings.
Ducting occurs when air of different temperatures and humidity forms layers in the lower atmosphere. Electromagnetic waves are reflected to all ranges at these layers and travel much farther than normal, causing harmful interference to frequencies similar or close in frequency to the long distances, and this phenomenon occurs early in the morning and ends by noon.
- General RF Noise
Devices other than radio equipment can cause radio frequency energy. Typical of items that can cause interference are arc welders, electric motors, faulty spark plug wires, lightning, and even rusty tower bolts. These types of problems can be tracked down and eliminated.