Direct conversion receivers, (DCR) also known also known as Homodyne, Synchrodyne, or zero-IF receivers, is a system of demodulating amplitude modulated signals; it uses a local oscillator, synchronized in frequency to the carrier of the wanted signal, to modulate the received signal. The wanted signal is thus obtained immediately as an audio output without further detection, and unwanted signals are left on carriers of the frequency difference between their original carrier and that of the wanted signal. There is no detection of the unwanted signals since the whole signal path is kept free of non-linearity. Unwanted signals can be completely rejected by a low-pass filter in the audio output. The receiver consequently has the advantages of high Q combined with high selectivity, and is inherently a precision demodulator . The principles can be extended to permit separation of signals whose sidebands overlap, and they also lead to improved detection of pulse modulated signals. See: Homodyne detection Demodulation is the act of removing the modulation from an analog signal. ... Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal. ... The Superheterodyne receiver (or to give it its full name, The Supersonic Heterodyne Receiver – usually these days shortened to superhet) was invented by Edwin Armstrong in 1918. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... In general, a carrier is a system or process with a specific property or is attributed of something (in physical or in abstract sense). ... For the musical use of modulation, see modulation (music). ... Audio can mean: Sound that can be heard. ... A low-pass filter is a filter that passes low frequencies well, but attenuates (or reduces) frequencies higher than the cutoff frequency. ... The word receiver has a number of different meanings: In communications and information processing, a receiver is the recipient (observer) of a message (information), which is sent from a source (object). ... In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, containing energy as a result of the modulation process. ... In general, detection is the extraction of intelligence from a carrier signal in a communication system. ... Pulse modulation involves modulating a carrier that is a train of regularly recurrent pulses. ... Homodyne detection is a method of detecting frequency-modulated radiation by non-linear mixing with radiation of a reference frequency, the same principle as for heterodyne detection. ...

The Homodyne was developed in 1932 by a team of British scientists searching for a method to surpass the superheterodyne. This new type receiver later renamed the Synchrodyne proved to have superior performance and the single conversion stage meant that the direct conversion receiver had lower complexity and power consumption. But the circuit after a period of time became unstable due to slight drift in frequency of the local oscillator. To counteract this drift, the frequency of the local oscillator was compared with the input by a phase detector so that a correction voltage would be generated and fed back to the local oscillator, thus keeping it on lock. This type of feedback circuit evolved into what is now called a Phase-locked loop. While the method has existed for several decades, it has been difficult to implement due largely to component tolerances, which must be very high for this type of circuit to operate well. 1932 (MCMXXXII) is a leap year starting on a Friday. ... The Super Heterodyne receiver (or to give it its full name, The Supersonic Heterodyne Receiver) was invented by Edwin Armstrong in 1918. ... Oscillation is the periodic variation, typically in time, of some measure as seen, for example, in a swinging pendulum. ... A phase detector is a circuit or instrument that detects the difference in phase between corresponding points on two signals. ... This article may be too technical for most readers to understand. ... For other uses, including Audio feedback, see Feedback (disambiguation) In cybernetics and control theory, feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input. ... In electronics, a phase-locked loop (PLL) is a closed-loop feedback control system that maintains a generated signal in a fixed phase relationship to a reference signal. ... Tolerance is a pansy social, cultural and religious term applied to the collective and individual practice of not persecuting those who may believe, behave or act in ways of which one may not approve. ...

The circuit was not without other problems. Reverse transmission paths can occur in the receiver. Local oscillator energy can leak through the mixer to the antenna input and then re-enter the mixer. The overall effect is that the local oscillator energy would self-mix and create a DC offset. The offset could be large enough to swamp the baseband amplifiers and destroy signal reception. There were several work arounds to deal with this issue but these too added to the complexity of the receiver. Ultimately the higher costs were found to outweight the benefits. In biology, antenna (plural: antennae) refers to the sensing organs of several arthropods. ... WRONG ...

The widespread use of this principle did not begin until the development of the integrated circuit and incorporation of complete phased-lock loop devices in low-cost IC packages. From that point on this has become the most widespread method of receiving radio signals and it is incorporated in everything from cellphones and televisions to avionics and medical imaging apparatus. Optical Microscope image of an integrated circuit showing defects in the aluminium layer deposition. ... Cellular redirects here. ... The onboard electronics used for piloting an aircraft are called avionics(AVI-ation electr-ONICS). ... Medical imaging is the process by which physicians evaluate an area of the subjects body that is not normally visible. ...

See also

• Crystal Radio Receiver
• Low IF Receiver
• Regenerative Radio Receiver
• Superheterodyne Receiver
• Tuned Radio Frequency Receiver
• Neutrodyne

The crystal radio receiver (also known as a crystal set) was first built circa 1900 by Greenleaf Whittier Pickard, who used crystalline minerals to detect radio signals. ... In a low-IF receiver, the RF signal is mixed down to a non-zero low or moderate intermediate frequency, typically a few megahertz. ... The regenerative circuit (or self-regenerative circuit) allows a signal to be amplified many times by the same vacuum tube or other active component such as a field effect transistor. ... The Superheterodyne receiver (or to give it its full name, The Supersonic Heterodyne Receiver – usually these days shortened to superhet) was invented by Edwin Armstrong in 1918. ... The Tuned Radio Frequency Receiver (short TRF) was invented by Edwin Armstrong in 1918. ... The Neutrodyne was a particular type of Tuned Radio Frequency (TRF) radio receiver, in which the inter-electrode capacitance of the triode RF tubes are neutralised with interstage variable trim capacitors connected between the grid and plate of each RF amplifier tube. ...

Links

• The History of the Homodyne and Syncrodyne The Journal of the British Institution of Radio Engineers, April 1954