RF Transmitters

The transmitting system consists of two tuned circuits such that the one containing the spark-gap is a persistent oscillator; the other, containing the aerial structure, is a free radiator maintained in oscillation by being coupled to the first. The transmitting system consists of two electrically coupled circuits, one of which, containing the air-gap, is a powerful but not persistent oscillator, being provided with a device for quenching the spark so soon as it has imparted sufficient energy to the other circuit containing the aerial structure, this second circuit then independently radiating the train of slightly damped waves at its own period.

For a fixed frequency transmitter one commonly used method is to use a resonant quartz crystal in a Crystal oscillator to fix the frequency. Where the frequency has to be variable, several options can be used.

For VHF transmitters, it is often not possible to operate the oscillator at the final output frequency.

In such cases, for reasons including frequency stability, it is better to multiply the frequency of the free running oscillator up to the final, required frequency. The task of many transmitters is to transmit some form of information using a radio signal (carrier wave) which has been modulated to carry the intelligence.

A few rare types of transmitter do not carry information: the RF generator in a microwave oven, electrosurgery, and induction heating. RF transmitters that do not carry information are required by law to operate in an ISM band. In many cases the carrier wave is mixed with another electrical signal to impose information upon it. This occurs in Amplitude modulation (AM). Amplitude Modulation: In Amplitude modulation the instantaneous change in the amplitude of the carrier Frequency with respect to the amplitude of the modulating or Base band signal.

Beacon-transmitter

This transmitter can be used for transmitter hunts, for remote key finding, or for radio telemetry in model rockets. It can be tuned to the two meter band or other VHF bands by charging Cl and Ll. 11 is four turns of #20 enameled wire airwound, 0.25 inch in diameter (use a drill bit), 0.2 inch long, centertapped. The antenna can be 18 inches of any type of wire. IC2 functions as an audio oscillator that is turned on and off by IC1 about once per second. ..

Atv Jr Transmitter 440Mhz Circuit

This low-power video transmitter is useful for R/C applications, surveillance, or amateur radio applications. Seven transistors are used in a crystal oscillator-multiplier RF power amplifier chain, and a high-level video modulator. A 9- to 14-Vdc supply is required. ..

49Mhz Fm Transmitter Circuit

This 49-MHz FM transmitter consists of an audio amplifier, a low-pass filter, three RF stages, and a regulated-dc power supply. The output is about 16 mW into a 50- load. This transmitter can be used in many 49-MHz applications, such as in a baby monitor, cordless telephone,..

Plate Touch Sensor Circuit

This system operates on the principle that capacitance loading of an oscillator will lower its frequency. When a foreign body comes into contact with touch plate, the frequency of Ul is lowered...

10M Dsb Qrp Transmitter With Vfo Circuit

The three schematics represent three building blocks for a 10-meter SSB transmitter. Or these blocks can be used separately as circuit modules for other transmitters. The VFO board uses an FET transmittal oscillator, the VFO signal is mixed in an NE602 mixer and is amplified by Q2 to a level sufficient to drive an SBL-1 mixer in the transmit mixer stage (+7 to +10 dBm). In the balance mixer/modulator board, an 11-MHz crystal oscillator drives a diode balanced mixer...

40M-cw-transceiver

The unit consists of a direct conversion receiver and 1-W transmitter. The direct conversion receiver VFO is tuned just off frequency from the incoming signal. This difference in frequency produces a clean, strong, and solid audio tone signal. Detect the resonant frequency of the transmitter VFO by using the GDO as a field-strength meter. Because of the large capacitance in the Colpitts VFO, the tuning coil will have fewer turns than the mixer coil. Use the capacitance.....

Amateur Television Transmitter

Although the unit was designed for 2 W operation, Q6 and Q7 stages and associated components can be omitted ..

902Mhz-cw-transmitter

The oscillator, Q1, is a standard overtone circuit. A fifth-overtone crystal, 80.545 MHz, is operated on the seventh overtone, 112.763 MHz. C6 couples the output of the oscillator to Q2, which operates as a doubler to 225.5 MHz. A double-tuned circuit using C7, L2, L3, C10 is used in the collector of Q2 to reduce the level of the 112-MHz dscillator signal. The output of Q2 is capacitivelJ: coupled at C11 to the base of Q3. ..

1750M Transverter Circuit

This circuit was described in a recent edition of an amateur radio magazine. It allows operation in the 160- to 190-kHz band with up to 1 W (license free) in any mode (CW/SSB/FM, etc.) It consists of a receiving converter for 5 kHz to 450 kHz and a transmitting converter to convert the 3.66- to 3.69-MHz (80 meter) range to 160 to 190 kHz. ..

1-2Mhz broadcast transmitter

T1 is a low impedance output transformer..

Low-frequency-transmitter

The crystal oscillator, which uses two sections of IC1, a 4001 quad 2-input NOR gate, is a standard and reliable design. The oscillator"s 1.85-MHz, square-wave output feeds IC2, a 4017 divide-by-10 counter. The count enable and reset terminals, pins 13 and 15, are normally held high by resistor R3, and the counter is activated by bringing those pins low by closing telegraph key S1-an arrangement that guarantees that the final state of IC2 pin 12 is always high. ..

Simple Fm Transmitter Circuit

Running from a 9-V battery, this transmitter can be used as a wireless microphone with an ordinary 88- to 108-MHz FM broadcast receiver. Keep the antenna length under 12 inches to comply with FCC limits. LI is 6 turns of #24 wire wound around a pencil or a 14 form, with turns spaced 1 wire diameter...

80M-amateur-radio-transmitter

This transmitter consists of a keyed crystal oscillator/driver and a high efficiency final, each with a TMOS Power FET as the active element. The total parts cost less than $20, and no special construction skills or circuit boards are required. The Pierce oscillator is unique because the high 4ss of the final amplifier power FET, 700 -1200 pF, is used as part of the capacitive feedback network. In fact, the oscillator will not work without Q2 installed. ..

27Mhz and 49Mhz rf oscillator-transmitter

The modulator and oscillator consist of two NPN transistors. The base of the modulator transistor is driven by a bidirectional current source with the voltage range for the high condition limited by a saturating PNP collector to the pin 4 Vreg voltage and low condition limited by a saturating NPN collector in series with a diode to ground. The crystal oscillator/transmitter transistor is configured to oscillate in a class C mode..

Low-cost-half-duplex-information-transmission-link

In a half-duplex system, information can flow in both directions, but only one direction at any given time. The conventional method of building a half-duplex link requires a separate emitter and detector, connected with directional couplers, at each end of the fiber. The GFOE1A series of infrared emitting diodes are highly efficient, long-lived emitters, which are also sensitive to the 940 nm infrared they produce. ..

1W-cwtransmitter

This is a little transmitter that could be put into a plastic Easter egg. It delivers approximately 1 W of measured rf output into a 50-0 dummy load, and creates no heating problems with the circuit. The crystal is a series fundamental type, and the power source provides 9 V with a 2-A supply. The transmitter can operate at another frequency, but C1 and C2 might have to be changed for the circuit to work properly. ..

10M Dsb Transmitter Circuit

A DSB transmitter is much cheaper to build than an SSB transmitter because no filter or phasing networks are required. This circuit produces up to 1-W output on the 10-meter band. The frequency 28.322 MHz is used, which is a commonly available clock frequency crystal. CW operation is also provided. ..

Vacuum Tube 80-40M Transmitter Circuit

Using a 6BW6 vacuum tube, the above transmitter delivers about 5 W output. CI is adjusted for cleanest CW note. C8 and C9 are 365 pF and dual-365 pF (paralleled) tuning capacitors. LI is 35 turns of #24 enamelled wire on a 1 plastic tube. FT-243 crystals for 3.5 or 7 MHz are used. ..

Hf Low-Power Cw Transmitter

Suitable for amateur use, this 1.5-W transmitter runs on a 12-V supply. Ql is an oscillator using a surplus FT2..

27.125Mhz Nbfm Transmitter Circuit

Using a Motorola MC2833 one-chip FM transmitter, a few support components, and an MPF6660 FET RF amp, this transmitter delivers about 3 W into a 50- load...

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