In
electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
, a Q multiplier is a circuit added to a
radio receiver to improve its selectivity and sensitivity. It is a
regenerative amplifier
In laser science, regenerative amplification is a process used to generate short but strong pulses of laser light. It is based on a pulse trapped in a laser resonator, which stays in there until it extracts all of the energy stored in the amplific ...
adjusted to provide
positive feedback within the receiver. This has the effect of narrowing the receiver's
bandwidth, as if the
Q factor
In physics and engineering, the quality factor or ''Q'' factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is. It is defined as the ratio of the initial energy stored in the resonator to the energy ...
of its tuned circuits had been increased. The Q multiplier was a common accessory in shortwave receivers of the
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
The type known as ...
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.
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.
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.
[http://www.historywebsite.co.uk/Museum/Engineering/Electronics/AJSSymphony/Symphony.htm ''The A.J.S. Symphony Seven Receiver - Inside Out'', retrieved January 31, 2018] 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.
See also
*
Q meter
A Q meter is a piece of equipment used in the testing of radio frequency circuits. It has been largely replaced in professional laboratories by other types of impedance measuring devices, though it is still in use among radio amateurs. It was d ...
References
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Radio electronics