Radio Frequency - General Informations

The laws regarding the use of the radiospectrum are actually fairly uniform, and established byinternational treaty, for the obvious reason that radio signals do notrespect international borders. The laws and regulations condinate the use of radio frequencies (frequencies, transmitting power etc.) and define the needed permission to use transmitters/receivers.Intentionally interfering with legitimate radiocommunications is illegal in virtually all countries. Generally a license is needed to operate a radio transmitter, unless you use a special radio system that is defined not specifically to need any special permit.Electromagnetic radiation is a wave that combines electric and magnetic fields, moving out from its source as an expanding sphere and having waves as the feilds alternate in value. This kind of radiation has different properties as its wavelength changes. We call this radio waves.Waves of a very long wavelength (low frequency), such as thousands of meters, tend to travel along the surface of the earth and even penetrate into the water. These are useful for communication with submarines. Radio, television, cellular telephones, walky-talkies, 2-way police radios, and other such communication/broadcast systems use electromagnetic radiation, or "Radio Frequency Waves". Each communication service uses a part of the spectrum that is suitable for its needs.A radio wave used to transmit audio signals is a complex signal that contains the carrier frequency of the broadcast station and the audio signal to transmit (usually from the microphone or audio amplifier source). The function of the radio receiver is to recover the audio signal that was modulated onto the RF carrier at the radio station, and apply it to the speaker, reproducing the sounds of the announcer. There are various ways to combine the carrier frequency and the audio signal together. This process is called modulation. The most commonly used modulation methods are amplitude modulation (AM), frequency modulation (FM), single sideband modulation (SSB) and phase modulation (PM).Also digital signals can be modulated to radio frequency carrier.When the signal is transmitted, there are many impairments on the way until the signal gets to the receiver: Typical impairments are:

• The absorption of radio signal power (air and surrounds absorb signal)
• Signal refelctions caused by the ground and obstacles (signal detected in the receiver is a sum of direct and reflected waves which can cause an effect known as fading)
• Co-channel interference (distant radio transmitters on the same frequency will disturb the reception)
• Intermodulation distortion (transmitters on different frequencies can disturb each other)
• Background noise in receiver (thermal noise generated by the receiver electronics itself)
• Atmospheric noise (bursty noises from thunder storms and similar)
• Industrial noise (RF noise from electronics, sparks)
Familiar forms of radio communications include such as AM/FM, short-wave, police/fire, radio, television, and so forth. These narrowband services, which avoid interfering with one another by staying within the confines of their allocated frequency bands, use what is called a carrier wave. Audio signals and data messages are impressed on the underlying carrier signal by modulating its amplitude, frequency or phase in some way and then are extracted upon reception. In receiving side the narrowband radio receivers are fitted with a front-end filter that prevents transmitters operating outside their reception bands from causing trouble.

 

General links on radio

 

• http://www.rfic.co.uk/ - RF and microwave design is a complex and large subject. This site gives you information and theory to understand it.   
• AC6V's Amateur Radio and DX Reference Guide   
• A very brief introduction to microwaves - By "microwaves" we mean the range of radio frequencies between about 1 GHz 300 GHz. For comparision.  
• Counterintelligence and Counterterrorism WWW Page - information about surveillance and countersurveillance  
• Doug Lung's R.F. Technology Page - Focusing on TV RF Broadcast Technology   
• Exposure Limits / Conversion Tables - information on limits for electric and magnetic fields   
• FCC Interference Handbook - electronic version of FCC Interference to Home Electronic Entertainment Equipment Handbook   
• FM-Transmitter.com Links - links to many radio sites  
• How Radio Scanners Work - This article will look at the basics of scanner operation, examine radio scanning as a hobby, and show you how to get started listening to public airwaves you may not have known existed!   
• How Radio Works - "Radio waves" transmit music, conversations, pictures and data invisibly through the air, often over millions of miles. There are many everyday technologies that depend on radio waves. This document will explore the technology of radio so that you can completely understand how invisible radio waves make so many things possible.   
• How the Radio Spectrum Works   
• Introduction to Scanning   
• Mobile commucation and cellular phone link   
• New Scanner Users FAQ  
• RF Design articles online   
• RF Energy Safety - Reprint from QST and the ARRL Handbook  
• RF Integrated Circuits - list of some commonly used types  
• Safety of Microwave Energy   
• Signals and Measurements for Wireless Communications Testing  
• The quest for the ideal rf amplifier   
• The RC Transmission! - text explains what kind of signals are sent from the TX to the RX of an "FM" radio control set, how they are decoded, and ideas about producing it yourself   
• The Radio Equipment and Telecommunications Terminal Equipment Directive (1999/5/EC) - On 9 March 1999, the Council and the European Parliament adopted a Directive, defining new rules for the placing on the market and putting into service of Radio Equipment and Telecommunications Terminal Equipment.   
• The Smith Chart - an RF engineering aid by Phillip Smith of RCA many years ago   
• Useful radio terms: A tutorial - This is a tutorial to decibels and other radio terms you might encounter in various radio applications.  
• Why my radio bought from USA does not work well in Europe ?
• System-Level Design Tackles Tough Soft Radio Framework Challenges - Recent design trends tends to add layers and virtualization even to high-rate and hard real-time systems such as wireless receivers. System-level design tools and high-level frameworks, such as the software communication architecture (SCA) developed within the Software Defined Radio (SDR) Forum, are serious threats to the "good old days" of "classical" C and VHDL programming approaches for DSP and/or FPGA/ASIC wireless systems.   
• ERO Frequency Information System - General Search for Radio Spectrum Utilisations   
• www.rfic.co.uk - RFIC and Microwave design tutorials   

Frequency allocation

 

• Allocation of Radio Spectrum in the United States - a list showing how the radio frequency spectrum is allocated to different users in the United States   
• Frequency Allocation Tables in USA   
• Some shortwave stations which can be listened in Finland - text in Finnish   
• United States Frequency Allocations   

Regulations

 

• FCC Part 15 - Radio Frequency Devices - Radio frequency devices regulations in USA.