Q multiplier

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In electronics, a Q multiplier is a circuit added to a radio receiver to improve its selectivity and sensitivity. It is a regenerative amplifier adjusted to provide positive feedback within the receiver. This has the effect of narrowing the receiver's bandwidth, as if the Q factor of its tuned circuits had been increased. The Q multiplier was a common accessory in shortwave receivers of the vacuum tube era as either a factory installation or an add-on device. In use, the Q multiplier had to be adjusted to a point just short of oscillation to provide maximum sensitivity and rejection of interfering signals. [1]

A Q multiplier could also be adjusted to act as a notch filter, useful for reducing the interfering effect of signals on frequencies near to the desired signal. In some receiver designs, the Q multiplier was made to also serve as a beat frequency oscillator by adjusting it to oscillate. This could be used for reception of single sideband or Morse radiotelegraphy, but in that case the circuit no longer provided improved selectivity. [2]

The principle of regeneration applied to radio receivers was developed by Edwin Armstrong, who patented a regenerative receiver in 1914. At least one console-model broadcast superheterodyne receiver used positive feedback to improve selectivity in a 1926 design. [3] Q-multipliers were common on shortwave general-coverage and communications receivers of the 1950s. With the advent of crystal and ceramic intermediate frequency filters, the Q-multiplier was no longer popular.

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<span class="mw-page-title-main">Amplifier</span> Electronic device/component that increases the strength of a signal

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<span class="mw-page-title-main">Superheterodyne receiver</span> Type of radio receiver

A superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency. It was invented by French radio engineer and radio manufacturer Lucien Lévy. Virtually all modern radio receivers use the superheterodyne principle.

<span class="mw-page-title-main">Heterodyne</span> Signal processing technique

A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called heterodyning, which was invented by Canadian inventor-engineer Reginald Fessenden. Heterodyning is used to shift signals from one frequency range into another, and is also involved in the processes of modulation and demodulation. The two input frequencies are combined in a nonlinear signal-processing device such as a vacuum tube, transistor, or diode, usually called a mixer.

<span class="mw-page-title-main">Intermediate frequency</span> Frequency to which a carrier wave is shifted during transmission or reception

In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called heterodyning, resulting in a signal at the difference or beat frequency. Intermediate frequencies are used in superheterodyne radio receivers, in which an incoming signal is shifted to an IF for amplification before final detection is done.

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<span class="mw-page-title-main">Crystal radio</span> Simple radio receiver circuit for AM reception

A crystal radio receiver, also called a crystal set, is a simple radio receiver, popular in the early days of radio. It uses only the power of the received radio signal to produce sound, needing no external power. It is named for its most important component, a crystal detector, originally made from a piece of crystalline mineral such as galena. This component is now called a diode.

<span class="mw-page-title-main">Crystal filter</span>

A crystal filter allows some frequencies to 'pass' through an electrical circuit while attenuating undesired frequencies. An electronic filter can use quartz crystals as resonator components of a filter circuit. Quartz crystals are piezoelectric, so their mechanical characteristics can affect electronic circuits. In particular, quartz crystals can exhibit mechanical resonances with a very high Q factor. The crystal's stability and its high Q factor allow crystal filters to have precise center frequencies and steep band-pass characteristics. Typical crystal filter attenuation in the band-pass is approximately 2-3dB. Crystal filters are commonly used in communication devices such as radio receivers.

<span class="mw-page-title-main">Regenerative circuit</span> Electronic circuit using positive feedback

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<span class="mw-page-title-main">Tuned radio frequency receiver</span>

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<span class="mw-page-title-main">Armstrong oscillator</span>

The Armstrong oscillator is an electronic oscillator circuit which uses an inductor and capacitor to generate an oscillation. The Meissner patent from 1913 describes a device for generating electrical vibrations, a radio transmitter used for On–off keying. Edwin Armstrong presented in 1915 some recent developments in the Audion receiver. His circuits improved radio frequency reception. Meissner used a Lieben-Reisz-Strauss tube, Armstrong used a de Forest Audion tube. Both circuits are sometimes called a tickler oscillator because the distinguishing feature is that the feedback signal needed to produce oscillations is magnetically coupled into the tank inductor by a "tickler coil" (L2, right). Assuming the coupling is weak but sufficient to sustain oscillation, the oscillation frequency f is determined primarily by the LC circuit and is approximately given by

Linear electronic oscillator circuits, which generate a sinusoidal output signal, are composed of an amplifier and a frequency selective element, a filter. A linear oscillator circuit which uses an RC network, a combination of resistors and capacitors, for its frequency selective part is called an RC oscillator.

In electronics, a frequency multiplier is an electronic circuit that generates an output signal and that output frequency is a harmonic (multiple) of its input frequency. Frequency multipliers consist of a nonlinear circuit that distorts the input signal and consequently generates harmonics of the input signal. A subsequent bandpass filter selects the desired harmonic frequency and removes the unwanted fundamental and other harmonics from the output.

<span class="mw-page-title-main">Communications receiver</span>

A communications receiver is a type of radio receiver used as a component of a radio communication link. This is in contrast to a broadcast receiver which is used to receive radio broadcasts. A communication receiver receives parts of the radio spectrum not used for broadcasting, including amateur, military, aircraft, marine, and other bands. They are often used with a radio transmitter as part of a two-way radio link for shortwave radio or amateur radio communication, although they are also used for shortwave listening.

Radio receiver design includes the electronic design of different components of a radio receiver which processes the radio frequency signal from an antenna in order to produce usable information such as audio. The complexity of a modern receiver and the possible range of circuitry and methods employed are more generally covered in electronics and communications engineering. The term radio receiver is understood in this article to mean any device which is intended to receive a radio signal in order to generate useful information from the signal, most notably a recreation of the so-called baseband signal which modulated the radio signal at the time of transmission in a communications or broadcast system.

<span class="mw-page-title-main">Reflex receiver</span>

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<span class="mw-page-title-main">Preselector</span> Radio signal filtering device

A preselector is a name for an electronic device that connects between a radio antenna and a radio receiver. The preselector is a band-pass filter that blocks troublesome out-of-tune frequencies from passing through from the antenna into the radio receiver that otherwise would be directly connected to the antenna.

A reed receiver or tuned reed receiver (US) was a form of multi-channel signal decoder used for early radio control systems. It uses a simple electromechanical device or 'resonant reed' to demodulate the signal, in effect a receive-only modem. The encoding used is a simple form of frequency-shift keying.

<span class="mw-page-title-main">Shortwave radio receiver</span> Shortwave radio

A shortwave radio receiver is a radio receiver that can receive one or more shortwave bands, between 1.6 and 30 MHz. A shortwave radio receiver often receives other broadcast bands, such as FM radio, Longwave and Mediumwave. Shortwave radio receivers are often used by dedicated hobbyists called shortwave listeners.

References

  1. Joseph Carr, Antenna Toolkit Elsevier, 2001 ISBN   0080493882, page 193
  2. Tony Dorbuck (ed.), The Radio Amateur's Handbook, Fifty Fifth Edition, American Radio Relay League, 1977 no ISBN, p. 259
  3. http://www.historywebsite.co.uk/Museum/Engineering/Electronics/AJSSymphony/Symphony.htm The A.J.S. Symphony Seven Receiver - Inside Out, retrieved January 31, 2018