Beat frequency oscillator

A beat frequency oscillator or BFO in radio telegraphy, is a dedicated oscillator used to create an audio frequency signal from carrier wave transmissions to make them audible, as they are not broadcast as such. The signal from the BFO is then heterodyned with the intermediate frequency signal to create an audio frequency signal.

Example

A receiver is tuned to a Morse code signal, and the receiver's intermediate frequency (IF) is "Fif" = 45000 Hz. That means the dots and dashes [also known as dits and dahs] have become pulses of a 45000 Hz tone, which is inaudible. To make them audible, the frequency needs to be shifted into the audio range, for instance "Fbaseband" = 1000 Hz. To do that, the desired frequency shift is "Fbfo" = 44000 Hz, and the desired BFO output waveform is "cos(2π 44000 t)". When the signal at frequency "Fif" is multiplied by that waveform, it shifts the signal to two other frequencies: "|Fif − Fbfo|" and "(Fif + Fbfo)". The "difference frequency", "|Fif − Fbfo|" = 1000 Hz, is also known as the beat frequency. The other frequency, "(Fif + Fbfo)" = 89000 Hz, can then be removed by a lowpass filter, such as an ordinary speaker (which cannot vibrate at such a high frequency) or the human ear (which is not sensitive to frequencies over approximately 20kHz).

BFO works only linked with ADF , in some old contry like INDIA if you want to use ADF frequency on your RMP you must select also BFO to keep the frequency

Notes

#By varying the BFO frequency around 44000 Hz, the listener can vary the output audio frequency to suit his/her preference. That is particularly useful for tuning in single sideband voice.
#The waveform produced by the BFO is sometimes said to "beat" against the IF signal, thus the name BFO. However, the actual beat frequency is produced by the mixer, not the BFO.
#"Fbfo" = 46000 Hz also produces the desired 1000 Hz beat frequency. These techniques are distinguished by the terms high-side and low-side injection. The term superheterodyne applies to either one, because historically, "super" just stands for "supersonic". However, a neologism has apparently begun to creep into modern usage, such that the prefixes super- and sub- would be associated with high and low injection, respectively.
#For a radio signal with more bandwidth than Morse code, low-side injection preserves the relative order of the frequency components. High-side injection reverses their order, which is often desirable to counteract a previous reversal in the radio receiver.


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • beat — beatable, adj. /beet/, v., beat, beaten or beat, beating, n., adj. v.t. 1. to strike violently or forcefully and repeatedly. 2. to dash against: rain beating the trees. 3. to flutter, flap, or rotate in or against: beating the air with its wings …   Universalium

  • Crystal oscillator — A miniature 4 MHz quartz crystal enclosed in a hermetically sealed HC 49/US package, used as the resonator in a crystal oscillator. A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal …   Wikipedia

  • Intermediate frequency — In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier… …   Wikipedia

  • Local oscillator — A local oscillator is an electronic device used to generate a signal normally for the purpose of converting a signal of interest to a different frequency using a mixer. This process of frequency conversion, also referred to as heterodyning,… …   Wikipedia

  • BFO — • beat frequency oscillator …   Maritime acronyms and abbreviations

  • BFO — Beat Frequency Oscillator (Academic & Science » Electronics) Beat Frequency Oscillator (Academic & Science » Amateur Radio) * BestFoods (Business » NYSE Symbols) * Buffalo Range, Zimbabwe (Regional » Airport Codes) * Balanced Forearm Orthosis… …   Abbreviations dictionary

  • BFO — Beat Frequency Oscillator (Oscilador de Frecuencia de Batido) …   Diccionario español de neologismos

  • BFO — • Beat Frequency Oscillator • Buffalo Range, Zimbabwe internationale Flughafen Kennung …   Acronyms

  • Superheterodyne receiver — A 5 tube superheterodyne receiver made in Japan around 1955 In electronics, a superheterodyne receiver (sometimes shortened to superhet) uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency, which… …   Wikipedia

  • Heterodyne — This article is about waveform manipulation. For the use of the term in poetry, see Heterodyne (poetry). For the webcomic characters, see Girl Genius. Heterodyning is a radio signal processing technique invented in 1901 by Canadian inventor… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.