Summary
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. In the most common application, two signals at frequencies f1 and f2 are mixed, creating two new signals, one at the sum of the two frequencies f1 + f2, and the other at the difference between the two frequencies f1 − f2. The new signal frequencies are called heterodynes. Typically, only one of the heterodynes is required and the other signal is filtered out of the output of the mixer. Heterodyne frequencies are related to the phenomenon of "beats" in acoustics. A major application of the heterodyne process is in the superheterodyne radio receiver circuit, which is used in virtually all modern radio receivers. In 1901, Reginald Fessenden demonstrated a direct-conversion heterodyne receiver or beat receiver as a method of making continuous wave radiotelegraphy signals audible. Fessenden's receiver did not see much application because of its local oscillator's stability problem. A stable yet inexpensive local oscillator was not available until Lee de Forest invented the triode vacuum tube oscillator. In a 1905 patent, Fessenden stated that the frequency stability of his local oscillator was one part per thousand. In radio telegraphy, the characters of text messages are translated into the short duration dots and long duration dashes of Morse code that are broadcast as radio signals. Radio telegraphy was much like ordinary telegraphy. One of the problems was building high power transmitters with the technology of the day. Early transmitters were spark gap transmitters.
About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related courses (3)
EE-519: Bioelectronics and biomedical microelectronics
The course covers the fundaments of bioelectronics and integrated microelectronics for biomedical and implantable systems. Issues and trade-offs at the circuit and systems levels of invasive microelec
MICRO-461: Low-power radio design for IoT
The basic function of an IoT node is to collect data and send it through a wireless channel to the cloud. Since the power consumption of an IoT node is largely dominated by the wireless communication,
EE-540: Optical communications
Situate and evaluate the potentialities, limits and perspectives of optical communication systems and networks. Design and dimension of photonic communication systems and networks
Related lectures (34)
Anonymous Authorization: Privacy Engineering Toolbox
Covers anonymous authorization, zero-knowledge proofs, attribute-based credentials, and practical issues in anonymous authentication.
Low-power Radio Design: Mixers Fundamentals
Explores the fundamentals of mixers in low-power radio design for the IoT, covering types, characteristics, and detailed analyses of the single balanced mixer.
Fiber Coupling with Laser Diodes
Covers basic laser operation, ultrafast lasers, and fiber coupling with laser diodes.
Show more
Related publications (106)