Microphone FM Transmitter Wireless Two Transistors Circuit

Microphone FM Transmitter Wireless Two Transistors Circuit

Please be warned if operating this circuit might violate the regulation of your country, because this FM transmitter circuit radiate strong radio frequency to the environment. This wireless microphone is very sensitive, pick up every sound in the 20m radius, and transmit the radio signal up to 2 kilometers in open air. The first transistor (Q1) is the pre-amplifier for the microphone, and you can ommit this circuit if you don’t want to transmit the sound picked up by the mic, for example you can can connect your mp3 player directly to C1. The core of this FM transmitter circuit is Q2, a modified Collpits oscillator that the frequency is determined by L1, C4, C6, and the transistor’s internal base-emitter capacitance. The antenna use 1/16 wave length to compromize between the efficiency and the size. If you want the microphone to be less sensitive, you can replace the R1 by a higher resistor, try 10k or 22k, and this might overcome the feedback problem if you use this wireless microphone FM transmitter for a public address system.

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Logic Gates FM Transmitter Circuit

Logic Gates FM Transmitter Circuit

This is a FM Transmitter circuit. This circuit uses logic gates. This transmitter circuit has a RF oscillator. This oscillator uses 10.7Mhz ceramic filter and inverter N2 to drive the parallel combination of N4 to N6 through N3. The output impedance will be low because these inverters are in parallel, so an aerial of 1/4h wavelength can be driven directly. There would be a lot of harmonics in the output of N4-N6 because the output of N4 to N6 is square wave. The 9th harmonics of 10.7Mhz (96.3Mhz) will hence be at the center of the FM band. As an audio amplifier, this circuit uses N1. It will amplify audio signals from the microphone and fed it to varycap diode. The capacitance of the varycap is varied by the signal that will vary the oscillator frequency that produce Frequency Modulation.

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Electronic FM Telephone Transmitter Circuit

Electronic FM Telephone Transmitter Schematic

The following schematics design pictures is a circuit diagram FM telephone transmitter that built on a PC board layout which is so small it can simply be fitted within the housing of a telephone creating it an instant pseudo-speak earphone. This circuit diagram FM telephone transmitter components connects in series with telephone line, steals power from it, and transmit at both sides of the conversation to an FM radio tuned between 90 and 95 MHz. Detailed information you can find it here at pdf FM telephone transmitter manual book guide:

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Long Range FM Transmitter Circuit

Long Range FM transmitter Circuit

The power output of most of these circuits are very low because no power amplifier stages were incorporated. The transmitter circuit described here has an extra RF power amplifier stage, after the oscillator stage, to raise the power output to 200-250 milliwatts. With a good matching 50-ohm ground plane antenna or multi-element Yagi antenna, this transmitter can provide reasonably good signal strength up to a distance of about 2 kilometres.

The circuit built around transistor T1 (BF494) is a basic low-power variable-frequency VHF oscillator. A varicap diode circuit is included to change the frequency of the transmitter and to provide frequency modulation by audio signals. The output of the oscillator is about 50 milliwatts. Transistor T2 (2N3866) forms a VHF-class A power amplifier. It boosts the oscillator signals’ power four to five times. Thus, 200-250 milliwatts of power is generated at the collector of transistor T2.

For better results, assemble the circuit on a good-quality glass epoxy board and house the transmitter inside an aluminium case. Shield the oscillator stage using an aluminium sheet.

Coil winding details are given below:
L1 - 4 turns of 20 SWG wire close wound over 8mm diameter plastic former.
L2 - 2 turns of 24 SWG wire near top end of L1.
(Note: No core (i.e. air core) is used for the above coils)
L3 - 7 turns of 24 SWG wire close wound with 4mm diameter air core.
L4 - 7 turns of 24 SWG wire-wound on a ferrite bead (as choke)

Potentiometer VR1 is used to vary the fundamental frequency whereas potentiometer VR2 is used as power control. For hum-free operation, operate the transmitter on a 12V rechargeable battery pack of 10 x 1.2-volt Ni-Cd cells. Transistor T2 must be mounted on a heat sink. Do not switch on the transmitter without a matching antenna. Adjust both trimmers (VC1 and VC2) for maximum transmission power. Adjust potentiometer VR1 to set the fundamental frequency near 100 MHz.

This transmitter should only be used for educational purposes. Regular transmission using such a transmitter without a licence is illegal in India

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Micro Power AM Broadcast Transmitter

In this circuit, a 74HC14 hex Schmitt trigger inverter is used as a square wave oscillator to drive a small signal transistor in a class C amplifier configuration. The oscillator frequency can be either fixed by a crystal or made adjustable (VFO) with a capacitor/resistor combination. A 100pF capacitor is used in place of the crystal for VFO operation. Amplitude modulation is accomplished with a second transistor that controls the DC voltage to the output stage. The modulator stage is biased so that half the supply voltage or 6 volts is applied to the output stage with no modulation. The output stage is tuned and matched to the antenna with a standard variable 30-365 pF capacitor. Approximately 20 milliamps of current will flow in the antenna lead (at frequencies near the top of the band) when the output stage is optimally tuned to the oscillator frequency. A small 'grain of wheat' lamp is used to indicate antenna current and optimum settings. The 140 uH inductor was made using a 2 inch length of 7/8 inch (OD) PVC pipe wound with 120 turns of #28 copper wire. Best performance is obtained near the high end of the broadcast band (1.6 MHz) since the antenna length is only a very small fraction of a wavelength. Input power to the amplifier is less than 100 milliwatts and antenna length is 3 meters or less which complies with FCC rules. Output power is somewhere in the 40 microwatt range and the signal can be heard approximately 80 feet. Radiated power output can be approximated by working out the antenna radiation resistance and multiplying by the antenna current squared. The radiation resistance for a dipole antenna less than 1/4 wavelength is

R = 80*[(pi)^2]*[(Length/wavelength)^2]*(a factor depending on the form of the current distribution) The factor depending on the current distribution turns out to be [(average current along the rod)/(feed current)]^2 for short rods, which is 1/4 for a linearly-tapered current distribution falling to zero at the ends. Even if the rods are capped with plates, this factor cannot be larger than 1. Substituting values for a 9.8 foot dipole at a frequency of 1.6 MHz we get R= 790*.000354*.25 = .07 Ohms. And the resistance will be only half as much for a monopole or 0.035 Ohms. Radiated power at 20 milliamps works out to about I^2 * R = 14 microwatts.

Reference: Radiation impedances of wire and rod antennas.

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50-300mW FM Transmitter With TX300

50-300mW FM Transmitter With TX300 Schematic

Here it is a cast new TX300 FM transmitter. The amplifier has absolutely the aforementioned architectonics as TX500 with the aberration that TX300 has alone one date capricious VHF amplifier. It is a beautiful schematic that was fabricated for all of you who capital article alike simpler than TX500 and with not as abounding all-important parts. It is a absolute ambit for transmitting your music about the abode and yard. Interesting affection is a accretion ascendancy P1 that lets you acclimatize your adapted achievement ability and distance. If in case you appetite to alter Q2 with added able transmitter like 2n4427 or 2n3866 you will accept to alter P1 with a resistor due to the college all-important current. For abundant added advice go to TX500's page.

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200mW High Quality FM Transmitter With TX-200

200mW High Quality FM Transmitter With TX-200 Circuit

FM Transmitter With TX-200 Part List

Here is the latest and abundantly bigger TX200 VFO/VCO FM transmitter. The best able transmitter to date that can be angry into aerial allegiance stereo PLL based 200mW FM transmitter. It is a absolute ambit for transmitting your music about the abode and yard. TX200 uses alone two coils; one in the oscillator and the added one in the 200mW VHF amplifier so it should be adequately accessible for anyone to build. It additionally includes congenital pre-emphasis and C5 for added complete quality. While accumulating the transmitter affliction charge be taken to accomplish abiding that C1 is anon affiliated to L1 and C9 to L2. These caps annihilate the distortions anatomy the DC accumulation and advance the complete affection greatly. 9V voltage accumulation is additionally actual important because it provides the exact bulk of accepted to Q1 to aftermath loud and bright complete quality. I achievement that you'll accept as abundant fun as I had while architecture this transmitter.

VHF Power Meter:

TX200 comes with congenital LED based ability meter. This is a actual accessible apparatus that will acquaint you if your transmitter's oscillator is alive properly. If RF arresting is transmitted the LED will illuminate. Besides that, it will additionally accord you a quick beheld way to analysis how abundant ability is actuality transmitted. I awful acclaim that you accept the transmitter and ability beat on the aforementioned PCB. If you like to agreement a lot, you will acknowledge this bargain but evidently accessible addition.

VHF Power Meter

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Single Chip FM Transmitter Circuit

Single Chip FM Transmitter Circuit Schematic

A simple FM transmitter links your home-entertainment arrangement to a carriageable radio that can be agitated about the abode and into the aback yard. For example, you can comedy music on the CD banker in your active room, and acquire to it on a carriageable radio by the back-yard barbeque.

IC1 is a voltage-controlled oscillator with chip varactor. Its nominal abundance of cadence is set by inductor L1, and a 390nH amount places that abundance at 100MHz. Potentiometer R1 again lets you baddest a approach by affability over the FM bandage of 88MHz to 108MHz. Output ability is about -21dBm into 50 (most countries acquire emissions beneath 10dBm in the FM band).

The home system's larboard and appropriate audio signals are summed by R3 and R4, and attenuated by the (optional) potentiometer R2. R2's wiper arresting serves as a aggregate ascendancy by modulating the RF frequency. Signals aloft 60mV acquaint distortion, so the pot attenuates bottomward from that level.

In the absence of a accepted FM radio antenna, 75cm (30 inches) of wire will answer as a transmitting antenna. For best reception, it should be army alongside with the accepting antenna. The IC operates on a distinct accumulation voltage in the ambit 3V to 5V, but you should adapt the activated voltage to abbreviate abundance alluvion and noise.

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Stereo PLL FM Transmitter With BH1417

Main blocks of BH1417 chip are; pre-emphasis, (audio level) limiter, stereo encoder (MPX), PLL circuit, oscillator and RF buffer.

BH1417 Block Diagram

Stereo PLL FM Transmitter With BH1417 Schematic

This is the latest BH1417 FM Transmitter architecture from RHOM that includes a lot of appearance in one baby package. It comes with pre-emphasis, limiter so that the music can be transmitted at the aforementioned audio level, stereo encoder for stereo transmission, low canyon clarify that blocks any audio signals aloft 15KHz to anticipate any RF interference, PLL ambit that provides bedrock solid abundance manual (no added abundance drift), FM oscillator and RF achievement buffer.

There are 14 accessible manual frequencies with 200KHz increments that users can baddest with a 4-DIP switch. Lower bandage frequencies alpha from 88.7 up to 89.9 MHz, and high bandage frequencies alpha from 107.7 up to 108.9 MHz.

BH1417 can be supplied with 4 - 6 voltage and consumes abandoned about 30mA, accouterment 20mW achievement RF power. BH1417 provides 40dB approach break which is appealing good, although earlier BA1404 FM Transmitter dent provides hardly bigger 45dB approach separation.

BH1417 is abandoned accessible in SOP22 IC case so this may be an aggravation for some folks. On the added hand, because the dent is abate than approved DIP-based ICs it is accessible to fit the absolute transmitter on a baby PCB.

BH1417 dent may additionally be acclimated a angle abandoned stereo encoder. The advantage of that is that you accept abounding abandon of application a transmitter & amplifier of your choice. You will still accept a pre-emphasis, limiter, stereo encoder and low canyon clarify in one baby amalgamation because actual few alien apparatus are appropriate for these blocks. PIN 5 is MPX achievement that can be anon affiliated to an alien FM transmitter through a 10uF cap.

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