Assignment 1
Transmission line circuit representation diagram
Role of RF lines on TV and radio transmission
RF is one of the most important sections in a TV or radio system. Its functions are many but we will just discuss the in passing. Radio frequency, or RF, is a frequency or rate of oscillation within the range of about 3 Hz and 300 GHz. This range corresponds to frequency of alternating current electrical signals used to produce and detect radio waves. Since most of this range is beyond the vibration rate that most mechanical systems can respond to, RF usually refers to oscillations in electrical circuits.
1. RF AS MODULATOR
RF modulators are used for coupling an audio signal into an audio system via its radio tuner when an auxiliary input to the audio system is not available. Radio frequency modulation techniques are used for transmitting information on a carrier signal, e.g. sound information on a carrier radio wave. Frequency modulated (FM) signals are widely used in many communication devices, such as two-way portable and mobile radios, for communicating messages and other types of information. RF modulation apparatus modulates video and audio signals supplied from a video apparatus to enhance a television broadcast. The modulator modulates the accessory audio signal according to the modulation scheme used by a radio reception band of the radio tuner so that an auxiliary input in the audio system becomes unnecessary.
2. RF POWER AMPLIFIER RF
power amplifiers are commonly used in numerous applications, such as base stations used in wireless communication systems. Amplifiers produce from an input signal, an output signal having an increased magnitude. gain. An amplifier produces a constant output power at a higher level. Different amplifiers are known and produce various types of gains. Power amplifiers are classified into different groups: class A, class B, class AB, class C, class E, class F, and class D sometimes referred to as digital amplifiers. The different classes of power amplifiers usually signify different biasing conditions. Each of these types of amplifiers, however, has significant problems when operating in the RF range. Modern wireless communication base stations transmit and receive radio frequency signals through the use of RF power amplifiers. Radio frequency signal is an electrical signal conveying useful information and having a frequency from about 3 kHz to thousands of GHz range, regardless of the medium through which such signal is conveyed.
3. RF & MICROWAVE ATTENUATOR
3. RF & MICROWAVE ATTENUATOR
An attenuator is a device that passes an input signal while operating to attenuate the signal by a precise amount. Attenuators are used in applications that require signal level control. There are many applications for attenuators. These applications include not only communications satellites, but also other communications systems, measurement instrumentation, and electrical apparatus such as televisions and radios. In many microwave systems attenuators are required for automatic gain control of receiver and transmitter systems. Attenuators are also used for amplitude weighting in phased array radar and for temperature compensation of microwave amplifiers. An attenuator is an electronic device which attenuates electromagnetic energy. Radio receivers accept and process RF transmitted energy signals to yield, generally, audible or visual information. To avoid variations in gain, the gain is intentionally attenuated during an initial period. Various signal processing functions may occur at the intermediate frequency (IF) level, including signal attenuation as may be necessary to prevent the signal from exceeding a threshold level. The degree of attenuation is controlled by an input signal. Attenuation may be performed on a received signal to cancel a number of distortion products gained during transmission. A microwave attenuator may be implemented as a fixed attenuator or a variable attenuator. A variable attenuator allows the level of attenuation to be adjusted.
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