Frequency modulation is used in telecommunications and signal processing, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency.
This is in contrast with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant.
Frequency modulation can be regarded as phase modulation where the carrier phase modulation is the time integral of the FM modulating signal. FM is widely used for broadcasting of music and speech, and in two-way radio systems, in magnetic tape recording systems, and certain video transmission systems.
FM signals can be generated using either direct or indirect frequency modulation. Direct FM modulation can be achieved by directly feeding the message into the input of a VCO.
For indirect FM modulation, the message signal is integrated to generate a phase modulated signal. This is used to modulate a crystal controlled oscillator, and the result is passed through a frequency multiplier to give an FM signal. Is also used at intermediate frequencies by all analog VCR systems, including VHS, to record both the luminance (black and white) portions of the video signal. Commonly, the chrome component is recorded as a conventional AM signal, using the higher-frequency FM signal as bias.
FM is the only feasible method of recording the luminance ("black and white") component of video to and retrieving video from Magnetic tape without extreme distortion, as video signals have a very large range of frequency components — from a few hertz to several megahertz, too wide for equalizers to work with due to electronic noise below -60 dB.
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Crossed from: Inside Circuits | Clicks: 17801 | Votes: 1 | Comments: 0 | Rating: 10 | Rank: 10
FM radio with TDA7000
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An FM radio on a single chip requiring only a few simple peripheral components. In particular the ship requires only one simple coil and alignment is very easy. The chip includes an RF input stage, mixer, local oscillator, IF amplifier/limiter, phase demodulator, mute detector and mute switch. The output will directly drive a crystal earpiece or could be used with a TBA820M to form a complete portable radio...
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Crossed from: Inside Circuits | Clicks: 18602 | Votes: 0 | Comments: 0 | Rating: 0 | Rank: 10
FM IF Subsystem with CA3189E
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TheCA3189E is a comprehensive FM-IF system designed for high fidelity FM tuners. It includes a three stage FM-IF amplifier/limiter configuration with level detectors for each stage, a double-balanced quadrature FM detector and an audio amplifier that features the optional use of a muting circuit. The advanced circuit design includes desirable special features such as delayed AGC for the RF tuner, an AFC drive circuit, and an output signal to drive a tuning meter and/or provide stereo switching logic. In addition, internal power supply regulators maintain a nearly constant current drain over the voltage supply range of +8V to +16V. Distortion is primary a function of the phase linearity characteristics of the external detector coil...
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Crossed from: Inside Circuits | Clicks: 2729 | Votes: 3 | Comments: 42 | Rating: 10 | Rank: 10
TV and FM jammer schematic
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The Jammer is a very small circuit and can fit inside a small plastic box with 9V battery inside. It can be very illegal if you attach an external antenna so don't. adjust frequency by turning trimmer...
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Crossed from: Inside Circuits | Clicks: 14410 | Votes: 0 | Comments: 4 | Rating: 0 | Rank: 10
FM surveillance BuG Transmitter
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The Circuit shown can transmit voice to exceptionally good range. Tune trimmer to hear the signal to your near radio. Frequency range is 88-108 MHz. Max current consumption is 30mA. You can power the bug with a 9Volt Battery, or you can plug a power supply to feed in 9-12 Volts. ..
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Crossed from: Inside Circuits | Clicks: 14293 | Votes: 0 | Comments: 14 | Rating: 0 | Rank: 10
2 Watts FM transmitter
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This is a nice 2 Watts FM transmitter. It has a Super-Sensitive pre-amplification with BC109 and BC177 with more than 100% signal modulation. The job finish the 2N2219 by Motorola. For the Coils you should use 1mm wire(enameled), L1= 3 turns - 10mm diameter, L2= 1 turn - 10mm diameter. R9 trimmer controls the modulation gain. The tunning is easy by controlling C9 trimmer (88-108 MHz). The RFC J should be the VK220J with ferrite (VK200 is not suitable). ..
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Crossed from: Inside Circuits | Clicks: 2041 | Votes: 0 | Comments: 4 | Rating: 0 | Rank: 10
1W Linear FM Booster
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That RF Amplifier is for boosting small fm transmitters and bugs. It use two Philips 2N4427 and its power is about 1Watt. At the output you can drive any linear with BGY133 or BLY87 and so on. Its power supply has to give 500mA current at 12 Volts. More voltage can boost the distance but the transistors will be burned much earlier than usual.! In any case do not exceed the 15Volts. ..
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Crossed from: FM Transmitter | Clicks: 19516 | Votes: 0 | Comments: 0 | Rating: 0 | Rank: 0
FM Beacon Transmitter circuit
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This circuit will transmit a continuous audio tone on the FM broadcast band (88-108 MHz) which could used for remote control or security purposes. Circuit draws about 30 mA from a 6-9 volt battery and can be received to about 100 yards. A 555 timer is used to produce the tone (about 600 Hz) which frequency modulates a Hartley oscillator. A second JFET transistor buffer stage is used to isolate the oscillator from the antenna so that the antenna position and length has less effect on the frequency. Fine frequency adjustment can be made by adjusting the 200 ohm resistor in series with the battery. ..
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Crossed from: RF Receivers | Clicks: 8448 | Votes: 0 | Comments: 0 | Rating: 0 | Rank: 0
Pocket Radio AM / FM circuit
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Earphones, batteries are sold separately. AM / FM seems to be a common mold. But stamping is different. AM / FM E193577 UL94V0 board with the AM / FM etching printed circuit board manufacturers are the same. Shape is considered to be shared. (Design, sharing the production process design?). Radio FM transistor S9014, IC LA1800 is used. 100 AM, FM Radio and 2W IC Amp substrate incorporated into the case. Variable capacitor is used for the junk FM · AM variable condenser 2. FM section, and turned the proximity variable capacitor, AM has a distance as a measure of the local oscillator wrap, leads unavoidably variable capacitor, Sorudatoru (desoldering wire), and with the shield. Radio low-frequency portion, FM ANT has converted part of the circuit. Radio is the height of perfection impressed.??..
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Crossed from: RF Receivers | Clicks: 1960 | Votes: 0 | Comments: 0 | Rating: 0 | Rank: 0
TDA7000 FM Radio
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This extremely simple FM radio receiver circuit is made possible by the special purpose TDA7000 IC. It integrates nearly all the functions necessary to build an FM receiver needing only a few external capacitors and a tuning circuit. Using a simple active RC filter made of only a single inductor, a few resistors and a varicap, this FM receiver will pick up broadcast radio between about 88 and 108 MHz. The mono output signal can then be used to drive a set of high impedance headphones, or feed a power amplifier...
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Crossed from: FM Transmitter | Clicks: 7428 | Votes: 0 | Comments: 0 | Rating: 0 | Rank: 0
Valve 45 watt FM trasnmitter
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The catering better it does not become at straight line from the network 220V but via transformer 220V/220V of isolation and safety 1A. When does not exist the R3, the force of expense is bigger, but respectively is increased also the hum 50Hz, because the simplicity of designing. The control (Audio In) can become from a kasseto'fwno or other powerful source. If it is microphone it will be supposed precedes amplifier so that it acquires a force of order of 8W roughly. Tendency of catering: 220V AC. Frequency of emission at FM: 88~108MHz. Force of expense: max 45W (without the R3)...
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Crossed from: FM Transmitter | Clicks: 17879 | Votes: 0 | Comments: 0 | Rating: 0 | Rank: 0
Phone line FM transmitter
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Here is a simple yet very useful circuit which can be used to eavesdrop on a telephone conversation. The circuit can also be used as a wireless telephone amplifier.
One important feature of this circuit is that the circuit derives its power directly from the active telephone lines, and thus avoids use of any external battery or other power supplies. This not only saves a lot of space but also money. It consumes very low current from telephone lines without disturbing its performance. The circuit is very tiny and can be built using a single-IC type veroboard that can be easily fitted inside a telephone connection box of 3.75 cm x 5 cm.
The circuit consists of two sections, namely, automatic switching section and FM transmitter section...
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Crossed from: Automotive Alarm | Clicks: 5197 | Votes: 0 | Comments: 0 | Rating: 0 | Rank: 0
Car wireless alarm
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This FM radio-controlled anti- theft alarm can be used with any vehicle having 6- to 12-volt DC supply system. The mini VHF, FM transmitter is fitted in the vehicle at night when it is parked in the car porch or car park. The receiver unit with CXA1019, a single IC-based FM radio module, which is freely available in the market at reasonable rate, is kept inside. Receiver is tuned to the transmitter's frequency. When the transmitter is on and the signals are being received by FM radio receiver, no hissing noise is available at the output of receiver. Thus transistor T2 (BC548) does not conduct. This results in the relay driver transistor T3 getting its forward base bias via 10k resistor R5 and the relay gets energised...
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Crossed from: Bugs | Clicks: 17749 | Votes: 0 | Comments: 0 | Rating: 0 | Rank: 0
High power bug
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My FM Wireless Microphone has been a very popular project with beginners and experienced constructors alike. It has been used inside guitars and as the basis of a remote control system. I do however, receive many requests for a higher powered circuit and better microphone sensitivity. Now I can introduce the new FM Wireless Microphone (v5), which also has a better frequency stability, over 1Km range (under ideal conditions) and is good on microphone sensitivity. This has been achieved by adding an RF amplifier buffer (with 10dB gain) and an AF preamplifier to boost the modulation a little...
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Crossed from: Bug | Clicks: 10647 | Votes: 0 | Comments: 0 | Rating: 0 | Rank: 0
wireless FM bug
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This project is a miniature, VHF FM (wideband) Wireless Microphone transmitter of the type that are commonly refered to as BUG's. Note that "BUGS" are illegal but "Wide-Band Frequency Modulation Wireless Microphones" (WBFMWMs) are not, as so many people have told me (including the RSGB!). Besides, the AF sensitivity of this transmitter prevents it from being an effective bug for eaves-dropping! I personally use one of these WBFMWMs plugged into my HF rig headphone socket so that I can "earwig" QSO's and nets when sitting on the toilet, washing the dishes, bringing in the coal, etc. ..
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Crossed from: RF Receivers | Clicks: 13280 | Votes: 0 | Comments: 0 | Rating: 0 | Rank: 0
VHF - UHF band reciever
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Here is a nice little receiver for narrow-band FM reception. It can also be used to receive FSK, RTTY and PACKET signals from the HF bands. Basic receiver sensitivity is in the region of 1uV PD and the receiver can be tuned to almost any frequency from 100KHz up to probably 120MHz. It is a bit big and cramped, but I think you will have no difficulties reading it. The receiver is built on a single- sided PCB, which is quite unusual for this type of circuit. I do have a PCB available, but more about that later. The RF transformers T1 & T2 and the capacitor Cy are chosen for the frequency you are interested in. As an example, using re-wound IF transformers (from Antique Electronic Supply, Tempe) the former is about 3.5mm Dia. and 10 turns (thin wire) plus Cy=33pf tuned 26MHz to 35MHz. This covers CB, 10-meters and the radio control bands...
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