Archive for category: RF Radio circuits

Folded Dipole Antenna

RF Radio circuits | By: Diagram mania

Another common place one can see dipoles is as antennas for the FM band – these are folded dipoles. The tips of the antenna are folded back until they almost meet at the feedpoint, such that the antenna comprises one entire wavelength. The main advantage of this arrangement is an improved bandwidth over a standard […]

FM Radio Transmitter circuit

RF Radio circuits | By: Diagram mania

A simple fm radio transmitter circuit which covers frequencies from 88 to 108 MHz. It is built with 3 transistors: BC109, BFR91A and BFR96S. It is quite stable and the output power is around 200 mW. The first stage in a mic amplifier but if you connect this radio transmitter directly to an audio source […]

FM Radio Receiver Circuit

RF Radio circuits | By: Diagram mania

This simple fm radio receiver circuit consists of a regenerative rf stage, TR1, followed by a two of three-stage audio amplifier, TR2 to TR4. In some areas 3 stages of audio amplification may not be necessary, in which case TR3 and its associated components can be omitted and the free end of capacitor C5 connected […]

FM Radio Receiver Antenna Booster Circuit

RF Radio circuits | By: Diagram mania

This inexpensive FM radio receiver antenna booster uses the BF324 TO92 style pnp transistor in a grounded-base configuration. The circuit may be used as a signal booster with VHF receivers whose front end suffers from low sensitivity (such as many valved and army surplus types). The frequency range of the preamplifier is roughly from 75MHz […]

FM Power Amplifier BLY87A, BLY89A, KT920A, KT925B

RF Radio circuits | By: Diagram mania

A very simple fm power amplifier which can deliver 4W rf power with 12V power supply and BLY87A or KT920A and 20W with BLY89A or KT925B. If you use BLY87A or KT920A the input power must be 0.5W and 4W if you use BLY89A or KT925B. This fm power amplifier is designed to work on […]

FM Modulator Circuit

RF Radio circuits | By: Diagram mania

The FM modulator circuit (frequency modulation) is built with a Motorola MC1648P oscillator. Two varactors, Motorola MV-209 are used to frequency modulate the oscillator. The 5000 Ω potentiometer is used to bias the varactors for the best linearity. The output frequency of approximately 100 MHz can be adjusted by changing the value of the inductor. […]

FM Dipole Antenna

RF Radio circuits | By: Diagram mania

DIY FM dipole antenna or half wave antenna are the most used because is easy to build and cost a few bucks but has some drawbacks like little directionality, small gain. The rf dipole antenna is build generally like in the picture but it is symmetric and the coaxial cable is asymmetric, that’s why we […]

FM Bug Spy Transmitter Circuit

RF Radio circuits | By: Diagram mania

Take a look at this fm spy transmitter which can be used as a bug transmitter or as diy fm bug too. It uses a single IC 74F13, one coil, a capacitor, one trimmer, one resistor and ofcourse one electret mic. This spy bug is so easy to build and can give you a total […]

FM Antenna Booster Circuit

RF Radio circuits | By: Diagram mania

This is a low cost fm antenna booster that can be used to listen to programmes from distant FM stations clearly. The antenna fm booster circuit comprises a common-emitter tuned RF preamplifier wired around VHF/UHF transistor 2SC2570 (C2570). Assemble the circuit on a good-quality PCB (preferably, glass-epoxy). Adjust input/output trimmers (VC1/VC2) for maximum gain. Input […]

FM Antenna Amplifier Circuit

RF Radio circuits | By: Diagram mania

Use this fm antenna amplifier in areas where the signal reception of FM stations is too bad. This circuit is just the right thing to do it. It is designed in such a way that the supply current powering it flows through coaxial cable. With this technique, an extra cable to power the fm antenna […]