Posted on Wednesday, February 1, 2012 • Category: FM Transmitters
Here's a long range 300mW FM Transmitter for the 88MHz to 108MHz band. This particular TX is of special interest to those wishing to build low power Power Amplifiers for the VHF bands since it used impedance matching, power amplifier and antenna filtering, all of which should be used by radio constructors, whether it be for amateur radio or any other form of radio. The features of this project are: Higher output power - 150mW min (at 9v) and 300mW+ (at 12.5v). Very pure output signal due to careful design and filtering. VARICAP modulation - possibility to add a synthesizer. Single sided Printed Circuit Board, only 40mm x 72mm. Covers the domestic FM band - 88MHz to 108MHz. Easy to build, but coil winding experience IS required
Posted on Tuesday, January 24, 2012 • Category: LED
Here is a circuit for simulating breathing / pulsing LED with the 555 timer chip. It became very popular and i received many comments and emails with people that made this circuit and worked fine, as well as comments with people that had troubles converting it to operate at 12 volts supply. It was designed to operate with 5 volts, because i plan to use it for a future PC mod. Since the PC power supply has 5 volts output, and since the LEDs that i plan to use require 3.8 volts to operate, choosing 5 volts for supply was the best choice to minimize power dissipation on the transistor.
Posted on Tuesday, January 17, 2012 • Category: FM Transmitters
The objective of this 1.5V FM Broadcast Transmitter design is to provide a simple low-power transmitter solution for broadcasting audio from various audio sources. This transmitter accepts stereo input via two 470K resistors. Since there is no audio level control on the input, the audio level out from the source needs to be adjusted. Or, you can just add a 10k as an input level control. Transmitter's frequency, as built is tunable via spreading or compressing the coil to the desired frequency, and the coil can be glued down. If you want to make one that's tunable, it might be easiest to reduce the 18 pf capacitor and put a small trimmer capacitor in parallel with the inductor (across the reduced value capacitor). Voltage variable capacitors would be an nice alternative to a mechanical variable capacitor but they don't offer much tuning range with only a 1.5V power supply.
Posted on Sunday, January 8, 2012 • Category: FM Transmitters
This FM Broadcast Transmitter 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. Oscillator frequency is set by a 5 turn tapped inductor and 13 pF capacitor.
Posted on Wednesday, January 4, 2012 • Category: TV Transmitters
This is a small TV transmitter circuit which transmits in VHF band, negative sound modulation and PAL video modulation. It is suitable in countries where the B and G system is used.
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