AM receiver circuit john April - 8 - 2009 14Share 14 Share Description.
Here is a low cost AM receiver circuit that can be tuned from around 550 to 1100 KHz. Three transistors are used in this project. The transistors Q1 and Q2 are wired as a compound transistor pair in which Q1 is an emitter follower and Q2 is a common emitter amplifier. The emitter follower prevents the loading of tank circuit, while the common emitter amplifier necessary voltage gain. The L1 and C2 forms the tank circuit.The L1 also does the job of antenna.The series combination of R6 and R7 gives a regenerative feedback between output of the Q2 and tank circuit. The transistor Q3 performs the demodulation of the carrier signal. It also provides amplification the demodulated signal. The audio output is coupled out from the collector of Q3 via the capacitor C3.Capacitor C6 provides some noise filtering. Circuit diagram.
Notes.
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The circuit can be assembled on a general purpose PCB. Use a 9V PP3 battery for powering the circuit. R7 can be used to adjust the sensitivity and selectivity of the circuit. A high impedance head phone can be used for listening the radio. For L1 make 60 turns of 26 SWG enameled copper wire on a 3/8 inch diameter, 3inch long ferrite rod. The moving plates of C2 must be connected to the base of Q1 and fixed plates must be connected to the junction of C3 and R6.Reversing the connection may decrease the stability.
Some voltage values at different points on the working circuit .
Q1 (b) 1.31V Q2 (b) 0.71V Q2 (c) 1.34V Q3 (b) 0.62V L1 wound on the ferrite rod is the antenna. the ferrite rod will receive the magnetic flux available in the atmosphere. L1 & C2 are the tuned circuit will tune to the required frequency and resonate. if you want to connect any external antenna you can connect it through a 10PF capacitor to L1 which connected o Q1 base.
AM Transmitter circuit admin April - 6 - 2008 22Share
Simple AM Transmitter Description
Here is the circuit diagram of a simple AM transmitter circuit that can transmit your audios to your backyard.This circuit is designed with limited power output to match the FCC regulations and still produces enough amplitude modulation of voice in the medium wave band to satisfy your personal needs.You will love this!. The circuit has two parts , an audio amplifier and a radio frequency oscillator. The oscillator is built around Q1 (BC109) and related components. The tank circuit with inductance L1 and capacitance VC1 is tunable in the range of 500kHz to 1600KHz. These components can be easily obtained from your old medium wave radio. Q1 is provided with regenerative feedback by connecting the base and collector of Q1 to opposite ends of the tank circuit. C2 ,the 1nF capacitance , couples signals from the base to the top of L1, and C4 the 100pF capacitance ensures that the oscillation is transfered from collector, to the emitter, and through the internal base emitter resistance of the transistor Q2 (BC 109) , back to the base again. The resistor R7 has a vital part in this circuit. It ensures that the oscillation will not be shunted to ground trough the very low value internal emitter resistance, re of Q1(BC 109), and also increases the input impedance such that the modulation signal will not be shunted to ground. Q2 is wired as a common emitter RF amplifier, C5 decouples the emitter resistance and unleashes full gain of this stage. The microphone can be electret condenser microphone and the amount of AM modulation can be adjusted by the 4.7 K variable resistanceR5.
Am Transmitter Circuit Diagram with Parts List.
Am Transmitter Circuit Diagram
Notes . • • • •
The transmission frequency can be adjusted using the variable capacitance C3. Use a 200uH inductor for the L1 in the tank circuit. Power the circuit using a 9V battery for noise free operation. Use a 30 cm long insulated Copper wire as the antenna.
Instead of bc109c transistor other transistor options are BC107, BC548,BC148, 2N2222 The approximate inductance of a single-layer air-core coil may be calculated from the simplified formula: L = (d²n²)/(18d+40l) where: L = inductance in uH, d = coil diameter in inches, l = coil length in inches, and n = number of turns. This formula is a close approximation for coils having a length equal to or greater than 0.4 d.
Long range AM transmitter. john February - 23 - 2009 4Share Description.
Here is the circuit diagram of an easy to build long range AM transmitter circuit based on three transistors.With correct tuning and a matching antenna, the transmitter can deliver signals up to a distance of 2 kilometers. The audio signal to be transmitted is given to the base of the transistor Q1 via the audio driver transformer T1.The modulated signal is developed at the collector of transistor Q1.The frequency of the transmitted signal can be tuned adjusting the gang condenser C7.The required amplification of the modulated signal is done by the two transistors Q2 and Q3.The two transistor amplifier stages are connected in parallel for obtaining maximum power. The signal to be transmitted is coupled to the antenna via the capacitor C4. Circuit diagram with Parts list.
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The inductor L1 can be made by making 56 turns of 365 WG enameled copper wire on a 1 cm former. The transformer T1 can be a general purpose audio driver transformer seen in transistor radios. Inductor L2 can be a 10 mH general purpose radio frequency choke. Use a 1 meter insulated copper wire as antenna. The circuit can be powered from a 9V PP3 battery. Adjust the value of C7 for maximum range. Also, you can experiment with the length of antenna for maximum range. The resonator F1 used here is a two terminal type without a ground pin. If you are using a three terminal one, the ground pin must be connected to the circuit’s ground.
How to make an Air-Core Inductor john March - 4 - 2010 3Share Sometimes
you may be unable to find a particular inductor the market. This is actually a problem faced by most of the electronic hobbyists and the problem becomes more serious if your project is RF related. The inductors required for RF circuits (antenna, tuner, amplifier etc) are almost impossible to find in the market and the only solution is nothing other than home-brewing them.
With a little practice and patience you can construct almost all air cored inductors at home. The inductance of an air cored inductor can be represented using the simplified formula shown below and to calculate the inductance of an air-core inductor, the same equation may be used. L = [d2 n2] / [18d + 40l] • •
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Where’ L ‘ is the inductance in Micro Henries [µH] ‘d’ is the diameter of the coil from one wire centre to another wire centre. It should be specifies in inches. ‘l’ is the length of the coil specified in inches. ‘n’ is the number of turns.
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The length of the coil used in the inductor should be equal to or 0.4 times the diameter of the coil. As shown in the equation, inductance of the air-core inductor varies as the square of the number of turns. Thus the value ‘l’ is multiplied four times if the value of ‘n’ is doubled. The value of ‘l’ is multiplied by two if the value of ‘n’ is increased up to 40%.
Winding the coil. •
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The coil must be first wounded on a plastic former of the adequate diameter (equal to the required core diameter). The winding must be tight and adjacent turns must be as close as possible. After the winding is complete, slowly withdraw the core without disturbing the coil. Now apply a thin layer of epoxy over the coil surface for mechanical support. Remove the insulation from the coil ends.
Example
Suppose you want to make an inductor which produces an inductance of 10 μH. The diameter of the coil is 1 inch and the coil length is given by 1.25 inches. You will have to find the number of turns of the coil. Thus substituting the values in the above equation t L = 10 inches d = 1inch l = 1.25 inches n = √{L [18d * 40l]} / d = 26 Thus, the number of turns of the coil will be 26. Number of turns/inch = 20.8
Hi Fady you mean 200 to 500uH (micro henrys) use tha above formula. it cannot be variable but either 200 or 500uH can be made. L = [d2 n2] / [18d + 40l]
•Where’ L ‘ is the inductance in Micro Henries [µH] •‘d’ is the diameter of the coil from one wire centre to another wire centre. It should be specifies in inches. •‘l’ is the length of the coil specified in inches. •‘n’ is the number of turns.
