Showing posts with label transmitter. Show all posts
Showing posts with label transmitter. Show all posts
Friday, December 27, 2013
Long Range FM Transmitter
The power output of many transmitter circuits are very low because no power amplifier stages are 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.
Long Range FM Transmitter Circuit diagram :
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 signal 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 license is illegal in India.
WARNING: Transmitting on the UK Commercial FM band is also illegal in the UK, please see the general disclaimer. This circuit is shown for educational purposes only.
Source : www.ecircuitslab.com
Friday, December 20, 2013
Two Transistor AM Transmitter
There are not many AM transmitters that are easier to build than this one because the inductor is not tapped and has a single winding. There is no need to wind the inductor as it is a readily available RF choke (eg, Jaycar Cat LF-1536). To make the circuit as small as possible, the conventional tuning capacitor has been dispensed with and fixed 220pF capacitors used instead.
Circuit diagram:
Simple AM Transmitter Circuit Diagram
To tune it to a particular frequency, reduce one or both of the 220pF capacitors to raise the frequency or add capacitance in parallel to lower the frequency. Q1 is biased with a 1MO resistor to give a high input impedance and this allows the use of a crystal ear piece as a low cost microphone.
Read the rest entry[...]
Circuit diagram:
Simple AM Transmitter Circuit Diagram
To tune it to a particular frequency, reduce one or both of the 220pF capacitors to raise the frequency or add capacitance in parallel to lower the frequency. Q1 is biased with a 1MO resistor to give a high input impedance and this allows the use of a crystal ear piece as a low cost microphone.
Author: Peter Goodwin
Tuesday, April 9, 2013
Medium Power FM Transmitter Circuit Using Transistor
This is a design circuit diagram of a moderate power FM transmitter circuit. This circuit is built operation by two transistors. This is a figure of complete circuit.
Operation of this circuit is explain as the voice signals picked by the microphone will be amplified by the transistor Q1.The second transistor is wired as an oscillator operating in the FM band. The output of T1 is given to the base of T2.T2 performs the modulation also. The tank circuit comprising of components L1 and C6 determines the frequency of the signal, and can be varied by adjusting C6.The capacitor C7 couples the FM signal to the antenna. The inductor L1 can be made by making 6 turns of 0.8mm enameled copper wire on a 5.5mm diameter/4.5mm length plastic former.
With a matching antenna and proper tuning this transmitter can have range up to 100 meter. The Antenna A1 can be a 1M long wire. The circuit can be powered from a9V PP3 battery.
Operation of this circuit is explain as the voice signals picked by the microphone will be amplified by the transistor Q1.The second transistor is wired as an oscillator operating in the FM band. The output of T1 is given to the base of T2.T2 performs the modulation also. The tank circuit comprising of components L1 and C6 determines the frequency of the signal, and can be varied by adjusting C6.The capacitor C7 couples the FM signal to the antenna. The inductor L1 can be made by making 6 turns of 0.8mm enameled copper wire on a 5.5mm diameter/4.5mm length plastic former.
With a matching antenna and proper tuning this transmitter can have range up to 100 meter. The Antenna A1 can be a 1M long wire. The circuit can be powered from a9V PP3 battery.
Subscribe to:
Posts (Atom)