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Topic: Beat frequency oscillator

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Amplitude modulation

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	Single transistor dual mode crystal oscillator(U) - Patent 4859969
		A single transistor dual mode crystal oscillator circuit is described which may excite more than one C-mode frquency in a crystal simultaneously such as the fundamental, used as a clock driver frequency, and a beat frequency between the third harmonic and the third overtone frequency, simultaneously.
		The outputs of a crystal oscillator are amplified in a single-stage transistor amplifier circuit.
		Attached to the emitter of the transistor is a low pass filter, 116, which passes 121, the beat frequency between the third overtone and third harmonic of crystal 107; it should be noted that the third overtone frequency is different from the third harmonic.
	www.freepatentsonline.com /4859969.html (1647 words)

	FlashWebHost.com - Ham Radio BFO (Beat Frequency Oscillator).
		We have many modes of HF (high frequency) communications like CW (continuous waves) where the signals are transmitted in the form of morse telegraphy.
		A simple free running oscillator oscillating at the receiver's IF (intermediate frequency) beats with the incoming signals in either CW or SSB and the resultant audio frequency goes to the AF amplifier.
		Switch on the radio and adjust the core of the transformer on the BFO with a trimming device until you hear a hissing sound in the radio.
	www.flashwebhost.com /circuit/ham_radio_bfo.php (1211 words)

	BFO
		It consists of two RF oscillators, usually at about 100 kHz, one of which is fixed in frequency, the other of which employs the search coil as the tuned circuit inductor - so that when a metallic presence affects the inductance of the search coil, that oscillator frequency is slightly altered.
		Frequency jitter/warble in a BFO detector is almost certainly due to bad coil construction practices.
		Now, the answer to frequency drift problems elsewhere in radio theory is to apply AFC (Automatic Frequency Control) This is an electronically derived correction voltage, which is used to counteract the effect of the frequency drifting off the predetermined reference point.
	members.aol.com /omlcgm/detecknowledgy/bfo.htm (1640 words)

	Metal Detector build your own (Site not responding. Last check: )
		The second oscillator uses a much smaller coil of wire, and is usually inside the control box and is called the reference oscillator.
		By adjusting the oscillators so their frequencies are very nearly the same, the difference between them is made audible as a beat note, this beat note changes slightly when the search loop is moved over or near to a piece of metal.
		When the two oscillators are well matched it should be possible by adjusting the brass nut in or out to bring the beat note to a halt or null.
	home.clara.net /saxons/bfo.htm (1782 words)

	Theory of Operation (Site not responding. Last check: )
		In a superheterodyne receiver, the frequency of the incoming signal is "mixed" (heterodyned) to an intermediate frequency, amplified, and detected.
		A mixer takes two input frequencies, the RF signal from the antenna and the VFO (variable frequency oscillator), and "mixes" them to produce two other frequencies, the sum and the difference of the original frequencies.
		A panel mounted variable capacitor is used to change the frequency of the VFO to a frequency in the desired range.
	www.pan-tex.net /usr/r/receivers/ra01011a.htm (570 words)

	Beat-Frequency Oscillator
		obtained from an oscillator known as a beat-frequency oscillator.
		The bfo heterodynes at the detector and produces an af output.
		the difference frequency of 1 kilohertz is heard in the output.
	www.tpub.com /content/neets/14189/css/14189_57.htm (360 words)

	KWM-2/2A Transceiver
		The amplified tone oscillator signal is taken from the plate of V11B and coupled to the grid of the vox amplifier V14B to activate the vox circuits in CW operation.
		The input r-f signal is fed to the grid of V13B, and the high-frequency oscillator injection signal is fed to the cathode of V13B.
		Output from the high-frequency crystal oscillator is fed to the transmitter second mixer and to the crystal oscillator cathode follower.
	www.wa3key.com /kwm2.html (2424 words)

	Class Definition for Class 331 - OSCILLATORS
		The vibration or oscillation is of the molecule itself and not that due to the translational motion of the molecule as a whole.
		The fundamental elements required by an oscillator system are: (1) a frequency or period determining element, such as a resonator or timing means, (2) a driving system for the frequency or period determining element, and (3) means for deriving a useful output from the oscillator system.
		A frequency determining means comprised of substantially pure reactances of opposite signs (i.e., mass and compliance in a mechanical resonator or inductive and capacitive reactance in an electrical resonator) wherein the phenomenon of resonance (i.e., when the positive and negative reactances are equal) is relied upon to determine the frequency of the generated waves.
	www.uspto.gov /go/classification/uspc331/defs331.htm (4602 words)

	Untitled Document
		When the two oscillators are well matched it should be possible by screwing the slug in or out to bring the beat note to a halt or null.
		Then the frequency could be adjusted carefully over a wide range by a brass ring that was a snug fit on the outside of the tube, this was an excellent method.
		The BFO detector suffers from drifting due to falling battery voltage and the effects of temperature on the coils.
	www.sas.org /E-Bulletin/2003-06-20/labNotes/body.html (810 words)

	History Of The General Radio Company - Products
		A Beat-Frequency oscillator was used to modulate a Standard Signal Generator to provide the antenna input to the receiver under test.
		General Radio pioneered in the development of quartz-crystal frequency standards, which were combined with multi vibrator dividers, heterodyne multipliers, and various modulation meters, etc. as complete monitoring assemblies for the nation's 200 or so radio broadcasters.
		Frequency measurement was simplified in the 50's and 60's with the advent of frequency counters and synthesizers.
	www.teradyne.com /corp/grhs/products_radio-broadcast.html (224 words)

	[No title]
		The BFO is intended as an audio source for the testing of audio equipment, and it produces sine waves from 10 cps to 13 kcs at variable amplitudes.
		The main oscillators are 6J8G triode hexodes, with the triode as the oscillator and the hexode as a buffer.
		The frequency response of the BFO is from 10 cps to 13 kcs whereas the modern oscillator is 10 hz to 1 mhz.
	www.shlrc.mq.edu.au /~robinson/museum/AWA_BFO.html (1411 words)

	Pavek Theremin Page
		Thus a greater decrease in frequency of the oscillator circuit is obtained when the pitch control circuit is close to the oscillator circuit in frequency than when it is a greater frequency difference.
		The amount of the difference is dependent on the frequency of the variable pitch oscillator the frequency of which is determined by the position of the hand in relation to the pitch control rods The frequency of the fixed pitch oscillator does not change while playing.
		This causes an audible frequency difference between this oscillator and the fixed pitch oscillator, the frequency of this note depending on the position of the hand.
	www.pavekmuseum.org /theremin/theop.html (744 words)

	Radio Receivers
		In a situation where a carrier frequency of 800 kHz is modulated with a 5 kHz (5000 Hz) tone, the sum of the carrier and the audio frequency results in the Upper Side Band (USB) of 805 kHz.
		This frequency is obtained by deducting the RF input from the tuned circuit from that of Local Oscillator Frequency.
		The BFO is used to introduce a 'Local Carrier Frequency' (frequency of the carrier is 10 to 20 Hertz within that of the transmitter carrier frequency which is suppressed at the transmitter of the ham radio station willingly in order to save power).
	www.qsl.net /vu2msy/receiver.htm (2227 words)

	KWM-1 Transceiver
		The output frequency is amplified by two amplifier stages (V3 and V4) and the driver stage (V2) and applied to the grids of the two 6146's in parallel (V23 and V24).
		Mixer V5 combines the 3.9- to 4.0-mc signal with the high-frequency oscillator signal and inverts the side-band to produce the desired upper sideband output frequency.
		Its operating frequency of 3.445 to 3.545 mc is controlled by a permeability-tuned coil.
	www.wa3key.com /kwm1.html (2041 words)

	Time and Frequency from A to Z
		An oscillator that uses the quantized energy levels in atoms or molecules as the source of its resonance.
		The principle underlying the atomic oscillator is that since all atoms of a specific element are identical, they should produce exactly the same frequency when they absorb or release energy.
		The national frequency standards developed by NIST derive their resonance frequency from the cesium atom, and use cesium beam or cesium fountain technology.
	tf.nist.gov /general/enc-am.htm (905 words)

	Electronics 37
		The blocking oscillator is closely related to the two-transistor or two-tube astable circuit, except that it uses only one amplifying device.
		The 4.7k resistor is to damp the oscillations when the transistor is turned off at the end of a period of conduction.
		The oscillation is very stable, the grid swinging from 0 to -15 V, and the plate only 8 V peak-to-peak.
	www.du.edu /~etuttle/electron/elect37.htm (1114 words)

	WS19 A set
		This set is equipped with a mechanical flick frequency arrangement which permits the pre-selection of any two frequencies in the band, change-over from one to the other being accomplished by the simple movement of each of the two tuning dials.
		C9A, one section of a four-gang assembly, tunes the transformer secondary to the signal frequency and C10A is the trimmer for this circuit.
		Oscillator frequency is varies within audible limits of the I.F. by means of the coupling coil L5C which is shunted by the rejector circuit L6A, C42A and R14A, R14A is centre-tapped and variable.
	www.rod.beavon.clara.net /ws19aset.htm (2362 words)

	ARRLWeb: Glossary of Key Words
		The BFO signal mixes with the incoming signal to produce an audio tone for CW reception.
		Frequency coordinator -- An individual or group that recommends repeater frequencies to reduce or eliminate interference between repeaters operating on or near the same frequency in the same geographical area.
		Such electromagnetic radiation with frequencies as low as 3 kHz and as high as 300 GHz are considered to be part of the RF region.
	www.arrl.org /qst/glossary.html (5737 words)

	Plural search frequency directional metal detector apparatus having enhanced sensitivity (US4255710)
		Further improvement is provided in that each resultant audio frequency difference rate is aggrandized so as to change at a rate, in hertz, which is far in excess of any change, in hertz, directly produced in each search fundamental frequency signal by varied object proximateness.
		The effect is to cause an apparent increased sensitivity, which is shown in one form so as to be variable, in the operation of the metal detector, while at the same time providing proximal resolution by way of a left-hand, or else right-hand, indication of the hidden object transversal path.
		A directional beat frequency concealed metal object detector apparatus adapted usually as a means for sensing the presence of an object, establishing the effectively right or left bearing of the object relative to the detector, and accurately spotting the location of the concealed object, said apparatus comprising:
	www.delphion.com /details?pn=US04255710__ (365 words)

	[No title]
		The BFO is intended as an audio source for the testing of audio equipment, and it produces sine waves from 10 cps to 13 kcs at variable amplitudes.
		The frequency response may not be completely equal (flat) across the whole range, as most speakers cannot reproduce very low frequencies or very high frequencies.
		The BFO is very useful for fixing valve radios and would be a useful addition to your radio test gear.
	www.ling.mq.edu.au /~robinson/museum/AWA_BFO_use.html (1475 words)

	Specific Use: Metal Detector (Site not responding. Last check: )
		Before we can start detecting changes to the oscillating frequency we need to have a reference frequency for comparison and we also need to determine if a change in frequency is large enough to indicate the presence of metal.
		It takes a frequency reading from the oscillator circuit, then calculates values for the two variables that are used to determine if the last frequency reading was large enough to trigger a response.
		The advantage of locating the oscillator circuit near the coil is that the wires going to the core module carry digital signals that are much more noise resistant than the coil leads and will not affect the oscillator if they are moved or touched.
	www.imaginetools.com /documentation/docs/manuals/MicroStarterKit/appmetal.htm (1584 words)

	Delayed Automatic Gain Control
		The action of the rf amplifier, mixer, local oscillator, and IF amplifier is the same for both cw and AM; but the cw signal reaches the detector as a single frequency signal with no sideband components.
		If the intermediate frequency is 455 kilohertz and the bfo is tuned to 456 kilohertz or 454 kilohertz, the difference frequency of 1 kilohertz is heard in the output.
		When you vary the bfo control, you are varying the output frequency of the bfo and will hear changes in the tone of the output audio signal.
	www.tpub.com /neets/book17/74e.htm (872 words)

	Privateline.com: Radio Fundamentals
		Oscillator is Australian for "I'll see you later." :-) Actually, an oscillator or does what its name implies, it sets up an electrical current that races back and forth, oscillating, until it produces a radio frequency within the radio.
		Although beyond this discussion, a beat frequency oscillator is a sort of super oscillator, a variable type you can control.
		It's in addition to the normal oscillator that is always present in modern radio.
	www.privateline.com /radio/oscillator.htm (485 words)

	KNLS DX Definitions, Page Four
		Zero Beat tuning, also called ECSS tuning, is a method used by Dxers to increase the readability of a poor AM signal.
		Zero beat tuning is accomplished by carefully tuning in on the center of a station so that the tone goes down in scale, stopping just at the point where the tone disappears.
		Zero beating also allows measurement of the station’s frequency with the greatest accuracy because the zero beat is on the exact center frequency of the station.
	www.knls.org /English/trascripts/dxdef04.htm (3170 words)

	icom - Program to Control ICOM Receivers and Transceivers
		Since the setting of this switch is saved along with the frequency and mode in a channel and apparently cannot be changed using radio commands, the setting may have to be done manually.
		In these radios, the BFO frequency is shifted using a varactor and a network of diodes and resistors to generate the necessary BFO frequencies.
		This is done by adjusting the VFO frequency to compensate for the systematic LO error and individual BFO errors.
	www.eecis.udel.edu /~mills/icom (3210 words)

	Crystal Radios "Stay Tuned" Crystal Sets
		Tuning a BFO to the carrier of a weak DX signal raises the voltage of the signal to a region of
		The BFO is connected to the crystal set by attaching a clip lead to the OUT post and loosely wrapping the lead around the crystal set’s antenna lead-in wire.
		The BFO is very frequency-stable in the short term in spite of there being no supply voltage regulation provisions.
	www.crystalradio.net /crystalsets/bfo/index.shtml (1879 words)

	Fastest Wing Beat
		Using a beat-frequency oscillator as well as personal auditory analysis, Sotavalta (1953) found that a midge of the genus Forcipomyia (Diptera:Ceratopogonidae) attained a wing beat frequency of 1046 Hz.
		In asynchronous muscle systems (Hymenoptera, Diptera, Coleoptera, and Hemiptera), the impulses in the motor nerves and the mechanical activity of the muscles do not occur at the same frequency (Pringle 1976.) The arrangement of muscles in the asynchronous system is antagonistic which causes cyclic deformations of the thorax (Smyth 1985).
		One advantage for rapid wing beat is the ability of the insect to remain relatively stationary in air (hover).
	ufbir.ifas.ufl.edu /chap09.htm (644 words)

	[No title] (Site not responding. Last check: )
		Radio Frequency Identification (RFID) is a type of automatic identification system that enables data to be wirelessly transmitted by portable tags to readers that process the data according to the needs of a particular application.
		HD Radio, with a frequency response of 20 Hz to 18 kHz on the FM band, eclipses analog FM's bandwidth ceiling of 15 kHz.
		The beat frequency equals the difference or offset between the two frequencies.
	www.lycos.com /info/frequency--radio-frequency.html (618 words)

	Radio Terms and Abbreviations
		beat frequency oscillator: A receiver circuit that generates a replacement carrier to enable intelligible reception of CW, FSK, and SSB signals.
		critical frequency: The frequency at or near the MUF at which the maximum sky wave propagation range is obtained.
		frequency modulation: A modulation technique that varies the carrier frequency of a transmitter in accordance with the variations in the strength of the modulating audio signal.
	www.dxing.com /radterms.htm (5172 words)

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