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Category: RF Circuits / FM Transmitter Views: 211 Rank: 0 I have had requests to add a VHF FM transmitter, to the QRP collection. This project is a simple transmitter using only one crystal and will cover 145.00 to 146.00 MHz. The crystal is a 44.9333 MHz crystal for 145.500 receive, as used in the Trio (Kenwood) 2200, PYE, Motorolla, Tait equipment, to name but four. The frequency of the crystal is not critical as almost any other xtal for the 2-meter band will function. No provision has been made to tune the transmitter to different channels, as this transmitter was first used as a single channel `repeater box`, leaving my main rig free to be used on other channels. The circuit is given above and simply mixes the output of a (more or less) conventional receiver multiplier (x3) with the output of a 10.7MHz VFO that is modulated with true FM.Ordinary 1N4001 diodes will function well as varicap diodes, but if true varicap diodes (such as BA102 etc.) are used you will have to reduce the value of the 18pf capacitor coupling D1/D2 to L1. L1 may be a 10.7MHz IF transformer robbed from a domestic receiver, but remove the internal capacitor. Adjust L1 (10.2 - 11.2 MHz) to cover 145-146 MHz. The modulator is a simple circuit which I will post later. Two OP-Amps were used in the prototypes, the first was a MIC amplifier to bring the MIC AF OP up to 500mV RMS. Clamp the AF with a couple of back-to-back diodes (limiter) then the second OP-Amp amplifies the clipped AF to the correct level, (about 1.5v RMS) for 5KHz deviation. Adjust the gain of the first OP-AMP for MIC GAIN and adjust the gain of the second OP-AMP for deviation (with FULL AF). The output of the driver will supply about 10-20mW to the PA. I didn't use a PA because I lived so close to the repeater (path loss = -109dB). There are hundreds of VHF QRP PA's published in SPRAT, INTERNET, RSGB books, RadCom, and PACKET RADIO so I will leave that to your own ingenuity. A single transistor, such as the 2N3866 will be more than adequate to get up to 250mW, but an additional band-pass tuned circuit should be used between them. visit page.  Ordinary 1N4001 diodes will function well as varicap diodes, but if true varicap diodes (such as BA102 etc.) are used you will have to reduce the value of the 18pf capacitor coupling D1/D2 to L1. L1 may be a 10.7MHz IF transformer robbed from a domestic receiver, but remove the internal capacitor. Adjust L1 (10.2 - 11.2 MHz) to cover 145-146 MHz. The modulator is a simple circuit which I will post later. Two OP-Amps were used in the prototypes, the first was a MIC amplifier to bring the MIC AF OP up to 500mV RMS. Clamp the AF with a couple of back-to-back diodes (limiter) then the second OP-Amp amplifies the clipped AF to the correct level, (about 1.5v RMS) for 5KHz deviation. Adjust the gain of the first OP-AMP for MIC GAIN and adjust the gain of the second OP-AMP for deviation (with FULL AF). The output of the driver will supply about 10-20mW to the PA. I didn't use a PA because I lived so close to the repeater (path loss = -109dB). There are hundreds of VHF QRP PA's published in SPRAT, INTERNET, RSGB books, RadCom, and PACKET RADIO so I will leave that to your own ingenuity. A single transistor, such as the 2N3866 will be more than adequate to get up to 250mW, but an additional band-pass tuned circuit should be used between them. http://www.sm0vpo.com/tx/fm-tx1.htm
Related circuits A-one-transistor-fm-transmitter The 2N2222 circuitry is a three-element, phase-shift oscillator circuit, designed to yield a 1,000-Hz sine wave. The 1,000-Hz sine wave is then applied to the TCG-610 varactor diode, 6 pF at 4 V, which changes the tank capacitance, thus varying the rf oscillator frequency at a 1,000-Hz rate.... 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... This transmitter needs heatsink at 2N2219. With the C4 we regulate the frequency. With their C7, C8 we adapt the resistance of aerial (practically to them we regulate so that it is heard our voice in the radio as long as you become cleaner). 5W Chinese PLL FM Transmitter With LCD Printed Circuit Board (PCB) Here's PLL FM transmitter circuit from china. This circuit uses the familiar 2SC1971 for final power amplifier stage. The PLL controller of the FM transmitter use SAA1057 and PIC16F628 (download HEX file). 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... L1 is 0.112uH (this tunes to the middle of the FM band, 98 MHz, with VC1 at its centre value of 33pF). L1 is 5 turns of 22 swg enamelled copper wire close-wound on a 5mm (3/16") diameter former. Alternatively, you can have a fixed 33pF cap instead of VC1 and have L1 as an adjustable molded coil... RF transmitter uses AMI encoding Although alternate-mark-inversion (AMI) encoding is well-suited for direct-conversion FM transmission, designers often overlook the technique. AMI, a three-phase, synchronous-encoding technique, uses bipolar pulses to represent logic ones and no signal to represent logic zeros (Figure 1).... This transmitter has a range of up to 100 feet. It generates a complete multiplex stereo signal and is useful for cordless headphone applications in which an inexpensive socket stereo receiver can be used.
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Heres a easy VHF FM transmitter that could also be used to play audio files from an MP3 player or pc on an ordinary VHF FM radio. The circuit use no coils that have to be wound. This FM transmitter can be used to take heed ...
Heres a simple VHF FM transmitter that could be used to play audio files from an MP3 player or computer on a standard VHF FM radio. The circuit use no coils that have to be wound. This FM transmitter can be used to listen to ...
If you want to be independent of the local radio stations for testing VHF receivers, you need a frequency-modulated oscillator that covers the range of 89.5 to 108 MHz but building such an oscillator using discrete components is not that easy.
This FM transmitter circuit uses four radio frequency stages: a VHF oscillator built around transistor BF494 (T1), a preamplifier built around transistor BF200 (T2), a driver built around transistor 2N2219 (T3) and a power ...
... only one transistor for the receiver section and one IC for the audio section. This circuit is a self-quenching regenerative RF receiver also known as a ... ... vhf-fm-aircraft-transmitter-receiver. VHF FM Aircraft receiver: VHF FM Aircraft Receiver is a superregenative receiver developed for...
30W VHF FM Broadcast Amplifier. The 30 watt amplifier circuit shown below provides an appropriate power boost with an input of 4 watt up to 6 watts. The circuit is designed to cover 88-108MHz FM Broadcast Band. However ...
About Radio part 41 Quality Audio FM Transmitter
Radio Electronics: Frequency Modulation Basic Principles pt1-2 1964 US Army T...
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