While actual RF design is quite difficult, understanding basic RF concepts is amazingly straightforward. For those of you delving into the world of RF for the first time, when you finish this article, you will have a clearer understanding of how signals are transmitted and received in an RF environment.
APPLICATION NOTE AN-00100RF 101 Information for the RF Challenged®WIRELESS MADE SIMPLE
INTRODUCTIONFor those of you with previous RF experience or a TThhee TTrraannssmmiitttteerrgood grasp of RF basics, skip this tutorial. Its The function of a transmitter is to take an analog orsimplicity will probably insult your intelligence. For digital signal and, through an antenna, deliver it intothose of you delving into the fearsome world of RF free space. A simple transmitter is illustrated below. for the first time, however, read it fully and with care. AntennaWhen you finish you will have a clearerunderstanding of how signals are transmitted andreceived in an RF environment, and perhaps a RF Amplifiernewfound admiration for the unseen world ofwireless intelligence that swirls around us. Data InThis application note goes to great lengths toremove the mysteries of RF. Please don't mistake Oscillatorthe ease with which you may grasp these basic Figure 2: A Simple RF Transmitterprincipals for the effort required to actually execute You will notice the transmitter has three primaryan RF design. Nooo, noooo, kiddies, don't try this at components: a frequency source (the oscillator), ahome. At least not if your job's on the line. The gain stage (the amplifier) and a free space couplerscience of RF is unlike any other area of discipline (the antenna). The oscillator generates thein electronics. Proficient RF design requires frequency at which the transmitter will operate. Thissophisticated test equipment, years of experience, frequency is called the Fundamental. In order forlots of money, and a big smile from Above. the fundamental frequency to be transmittedFortunately, while actual RF design is quite difficult, effectively through the resistance of free space, it isunderstanding basic RF concepts is amazingly necessary for the signal to be amplified. This is thestraightforward. purpose of the gain stage. WHAT IS RADIO FREQUENCY? Once the oscillator's frequency has been amplified,Radio Frequency (RF) does not refer just to radio it must transition from being a frequency containedbroadcasting but rather encompasses all of the within conductors (called transmission lines) intoelectromagnetic spectrum. RF energy is classified free space. This is the function of the antenna. Theaccording to frequency. The range of frequencies is transmitting antenna allows the RF energy to becalled the Radio Spectrum. While there is no efficiently radiated from the output stage into freeprecise beginning or end to frequencies making up space. It is, in essence, a bridge between a guidedthe RF spectrum, Figure 1 shows the generally wave and free space. accepted ranges and class designations. WHAT IS MODULATION?HOW IS THE RF HARNESSED? Now that you have a basic understanding of how aIn order for a signal to be transmitted wireless, it is signal finds itself delivered into free space, you maynecessary for the signal to be conveyed into free be wondering how any useful information could bespace then recovered and restored to its original represented by that signal. The answer isform. Two devices are used to accomplish this task: Modulation. Modulation is the process whereby athe transmitter and the receiver. carrier medium is impressed with content. The
MW HF VisibleELF VLF LF (MF) (SW) VHF UHF SHF EHF IR Light UV X-Ray
14 16 17 18100 10 100 1 3 30 300 1 30 300 10 10 10 10Hz kHz kHz MHz MHz MHz MHz GHz GHz GHz Hz Hz Hz Hz(1000 MHz)Figure 1: The Electromagnetic SpectrumAN-00100RF 101 Information for the RF Challenged Page 2
frequency to be controlled is called the Carrier. A on-board frequency source called a local oscillator.carrier is like a moving truck. Just as you might This converts the signal to a new lower frequencyplace the contents of your house on the truck, so called the Intermediate Frequency or IF for short.the information you wish to transmit is loaded onto The detector then strips out the IF frequency anda carrier. That signal, which has been impressed leaves present only the original information. onto the carrier for "transportation", is called theProgram or Control Signal. In the case of digital Antennadata transmission, a carrier frequency is modulatedwith a control signal consisting of binary data. ... [download for more]
