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Page "Amplifier" ¶ 4
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RF and amplifiers
Stability is a major concern in RF and microwave amplifiers.
Vacuum tubes are still used in some specialist applications such as high power RF amplifiers, cathode ray tubes, specialist audio equipment and some microwave devices.
The power gain of an amplifier depends on the source and load impedances used as well as its voltage gain ; while an RF amplifier may have its impedances optimized for power transfer, audio and instrumentation amplifiers are normally employed with amplifier input and output impedances optimized for least loading and highest quality.
Class-B and-AB amplifiers are sometimes used for RF linear amplifiers as well.
The usual application for class-C amplifiers is in RF transmitters operating at a single fixed carrier frequency, where the distortion is controlled by a tuned load on the amplifier.
Of the two kinds of RF power amplifier, switching amplifiers ( Class D amplifiers ) cost less and use less battery power than linear amplifiers of the same output power.
Triodes continue to be used in certain high-end and professional audio applications, as well as in microphone preamplifiers, electric guitar amplifiers and high power RF amplifiers and transmitters.
Generally, two or three RF amplifiers are required to filter and amplify the received signal to a level sufficient to drive the detector stage.
Valved RF amplifiers are very different because the load resistance which a valve is designed to operate with is normally much greater, hence for power designs the circuit designs are often very different.
# A parallel resonant circuit can be used as load impedance in output circuits of RF amplifiers.
RF amplifiers are used at intervals to overcome cable attenuation and passive losses of the electrical signals caused by splitting or " tapping " the coaxial cable.
These technologies include data converters, amplifiers, radio frequency ( RF ) technologies, embedded processors or digital signal processing ( DSP ) ICs, micro-electromechanical systems ( MEMS ) and sensors, power management, and interface products.
The company ’ s RF portfolio includes TruPwr ( tm ) RMS power detectors and logarithmic amplifiers ; PLL and DDS synthesizers ; RF prescalers ; variable gain amplifiers ; ADC drivers, gain blocks, LNAs and other RF amplifiers.

RF and are
The fact that in equivalent baseband models of communication systems, the signal spectrum consists of both negative and positive frequencies, can lead to confusion about bandwidth, since they are sometimes referred to only by the positive half, and one will occasionally see expressions such as, where is the total bandwidth ( i. e. the maximum passband bandwidth of the carrier-modulated RF signal and the minimum passband bandwidth of the physical passband channel ), and is the positive bandwidth ( the baseband bandwidth of the equivalent channel model ).
A single class-B element is rarely found in practice, though it has been used for driving the loudspeaker in the early IBM Personal Computers with beeps, and it can be used in RF power amplifier where the distortion levels are less important.
In RF inductors, which are mostly air core types, specialized construction techniques are used to minimize these losses.
To reduce parasitic capacitance and proximity effect, RF coils are constructed to avoid having many turns lying close together, parallel to one another.
The windings of RF coils are often limited to a single layer, and the turns are spaced apart.
* Honeycomb coils: To reduce proximity effect and parasitic capacitance, multilayer RF coils are wound in patterns in which successive turns are not parallel but crisscrossed at an angle ; these are often called honeycomb or basket-weave coils.
The industrial, scientific and medical ( ISM ) radio bands are radio bands ( portions of the radio spectrum ) reserved internationally for the use of radio frequency ( RF ) energy for industrial, scientific and medical purposes other than communications.
RF magnetic fields above about 100 kHz can be shielded by Faraday shields, ordinary conductive metal sheets or screens which are used to shield against electric fields.
Clutter refers to radio frequency ( RF ) echoes returned from targets which are uninteresting to the radar operators.
Nodules are associated with a positive RF ( rheumatoid factor ) titer and severe erosive arthritis.
When RA is clinically suspected, immunological studies are required, such as testing for the presence of rheumatoid factor ( RF, a non-specific antibody ).
Like RF, these tests are positive in only a proportion ( 67 %) of all RA cases, but are rarely positive if RA is not present, giving it a specificity of around 95 %.
In a triode radio-frequency ( RF ) amplifier, if both the plate ( anode ) and grid are connected to resonant circuits tuned to the same frequency, stray capacitive coupling between the grid and the plate will cause the amplifier to go into oscillation if the stage gain is much more than unity.
The following essential elements are common to all superhet circuits: a receiving antenna, a tuned stage which may optionally contain amplification ( RF amplifier ), a variable frequency local oscillator, a frequency mixer, a band pass filter and intermediate frequency ( IF ) amplifer, and a demodulator plus additional circuitry to amplify or process the original audio signal ( or other transmitted information ).
Additionally, newer set-top boxes that sit at the edge of IP-based distribution networks are often called net-top boxes or NTBs, to differentiate between IP and RF inputs.
Digital television channels are the same for legacy reasons, however through multiplexing, each physical radio frequency ( RF ) channel can carry several digital subchannels.

RF and often
In all cases, microwave includes the entire SHF band ( 3 to 30 GHz, or 10 to 1 cm ) at minimum, with RF engineering often putting the lower boundary at 1 GHz ( 30 cm ), and the upper around 100 GHz ( 3 mm ).
In all cases, microwave includes the entire SHF band ( 3 to 30 GHz, or 10 to 1 cm ) at minimum, with RF engineering often putting the lower boundary at 1 GHz ( 30 cm ), and the upper around 100 GHz ( 3mm ).
The increase in conductivity is also taken advantage of in RF engineering at VHF and higher frequencies, where conductors often cannot be scaled by 6 %, due to tuning requirements, e. g. cavity filters.
The signal from the antenna is tuned and may be amplified in a so-called radio frequency ( RF ) amplifier, although this stage is often omitted.
Baseband can often be considered a synonym to lowpass or non-modulated, and antonym to passband, bandpass, carrier-modulated or radio frequency ( RF ).
: In order to access the components, a housing is typically made in sections ( such as a box and lid ); an RF gasket is often used at the section joints to reduce the amount of interference that leaks through the joint.
RF testing of a physical prototype is most often carried out in a radio-frequency anechoic chamber.
In radio frequency ( RF ) practice, this is often measured in a dimensionless ratio known as VSWR with a VSWR bridge.
* RF currents applied to the body often do not cause the painful sensation of electric shock as do lower frequency currents.
This is often used in BEAM robotics and in RF circuits where component leads must be kept short.
Galvanic and thermolysis are often combined in a method known as blend, developed by Arthur Hinkel in 1948, which uses both RF and direct current, combining many of the advantages of galvanic and thermolysis.
This may then be converted to RF with an external box known as an RF modulator that generates the proper carrier ( often for channel 3 or 4 in North America, channel 36 in Europe ).
Small-area Schottky diodes are the heart of RF detectors and mixers, which often operate up to 50 GHz.
For instance, they are often used as a source of RF for antenna analyzer bridges.
RF circuits by contrast are typically required to operate at high frequencies but often over a very narrow frequency range.
In any case, adding a preamp stage ( RF stage ) between the antenna and the regenerative detector is often used to further lower the interference.
In radio frequency ( RF ) transmission systems, in situ is often used to describe the location of various components while the system is in its standard transmission mode, rather than operation in a test mode.
Components often consist of a laptop or proprietary computer, software, RF receiver / transceiver, and external vehicle antennas.

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