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This short-wave converter, which doesn’t have a single coil requiring alignment, is intended to enable simple medium-wave receivers to be used to listen to short-wave signals. The converter transforms the 49-m short-wave band to the medium-wave frequency of 1.6 MHz. At the upper end of the medium-wave band, select an unoccupied frequency that you want to use for listening to the converted short-wave signals. Good reception performance can be obtained using a wire antenna with a length of one to two metres. Circuit diagram : Short-Wave Converter Circuit Diagram The converter contains a free-running oscillator with a frequency of around 4.4 MHz, which is tuned using two LEDs (which act as variable-capacitance diodes!) and a normal potentiometer. The frequency range is set by adjusting the emitter current using a 1-kΩ trimpot. The oscillator frequency depends strongly on the operating point. This is due to the combination of using an audio transistor and the extremely low supply volt...

Diagram for a Sine Wave Generator This is a circuit for generating a sine wave from a single operational amplifier. The feedback loop of the op amp in this circuit (741) consists of a twin-T filter connected between its output and its inverting input. Positive feedback for oscillation is provided by R2.    The twin-T filter (see Figure 2) is a passive notch filter composed of two T-networks, with maximum attenuation occurring at fn = 1/(2πRC) .  One of these T networks has one resistor and two capacitors, while the other has two resistors and one capacitor.    At the notch frequency fn of the twin-T filter, the total phase shift around the loop gain of this op amp circuit is zero, which satisfies the requirement for oscillation. This is why the circuit generates a sine wave with a frequency equal to fn = 1/(2πRC) .    Note that variable resistor R3 in the circuit needs to be adjusted (in relation to the chosen value for R) until oscillatio...

I have previously written quite a few articles on sinusoidal pulse width modulation (SPWM). I've discussed about how to generate the sine table, how to implement it, how to practically generate the SPWM signals (with example code) and also how to implement feedback with simple sine table manipulation with table pointer instead of complex PID control. All these methods have one thing in common regarding the implementation - use of the sine table and its control with the table pointer. Whether you use or implement feedback or not, the table pointer is used to access and retrieve values from the sine table. Before reading or going through this article, I suggest you go through these first: Tutorial (Click here to open tutorial): Generation and Implementation of Sine Wave Table   Article (Click here to open article): Smart Sine – Software to generate sine table Article (Click here to open article): Generation of sine wave using SPWM in PIC16F684 It took quite a while for me to unde...

Short-Wave Super regenerative Receiver Circuit diagram. Super regenerative receivers are characterized by their high sensitivity. The purpose of this experiment is to deter-mine whether they are also suitable for short-wave radio. Super regenerative receivers are relatively easy to build. You start by building a RF oscillator for the desired frequency. The only difference between a super regenerative receiver and an oscillator is in the base circuit. Instead of using a voltage divider, here we use a single, relatively high-resistance base resistor (100 kΩ to 1MΩ). Super regenerative oscillation occurs when the amplitude of the oscillation is sufficient to cause a strong negative charge to be applied repeatedly to the base. If the regeneration frequency is audible, adjust the values of the resistors and capacitors until it lies somewhere above 20 kHz. The optimum setting is when you hear a strong hissing sound. The subsequent audio amplifier should have a low upper cutoff frequency ...

This simple circuit is sure to have the police beating a path to your door- however, it has the added advantage of alerting you to their presence even before their footsteps fall on the doormat. Simple Radio Wave Alarm Circuit Diagram : Notes : The circuit transmits on Medium Wave (this is the small problem with the police). IC1a, together with a sensor (try a 20cm x 20cm sheet of tin foil) oscillates at just over 1MHz. This is modulated by an audio frequency (a continuous beep) produced by IC1b. When a hand or a foot approaches the sensor, the frequency of the transmitter (IC1a) drops appreciably. Suppose now that the circuit transmits at 1MHz. Suppose also that your radio is tuned to a frequency just below this. The 1MHz transmission will therefore not be heard by the radio. But bring a hand or a foot near to the sensor, and the transmitter's frequency will drop, and a beep will be heard from the radio. Attach the antenna to a multiplug adapter that is plugged into the mains, a...

This circuit voltage inverter was designed using common electronic components, it produces a negative voltage from a positive. It is very simple, its operation is reasonable and can be used in different utilities in electronics where one has to inverts tensions of a wave. Inverter Voltage Wave Circuit Diagram

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The proposed circuit generates accurately spaced PWM pulses which imitates a sine wave very closely and thus can be considered as good as its sine wave counter part design. Here we use  two stages for creating the required  PWM pulses, the stage comprising the ICs 741 and the other comprising the IC 555. Let’s learn the whole concept in details. How the Circuit Functions – The PWM Stage The circuit diagram can be understood with the following points: The two op amps are basically arranged to generate the required sample source voltages for the IC 555.  The couple of outputs from this stage is responsible for the generation of square waves and triangular waves. The second stage which is actually the heart of the circuit consists of the IC 555. Here the IC is wired in a monostable mode with the square waves from the op amp stage applied to its trigger pin #2 and the triangular waves applied to its control voltage pin # 5. The square wave input triggers the monostable to ge...

If you insist on using a valve radio and listening to medium-wave stations, you have a problem: the existing broadcasters have only a limited number of records. Here there’s only one remedy, which is to build your own medium-wave transmitter. After that, you can play your own CDs via the radio. The transmitter frequency is stabilised using a 976-kHz ceramic resonator taken from a TV remote control unit. Fine tuning is provided by the trimmer capacitor. If there’s another station in the background, which will probably be weak, you can tune it to a heterodyne null, such as 981 kHz. As an operator of a medium-wave transmitter, that’s your obligation with respect to the frequency allocations. And that’s despite the fact that the range of the transmitter is quite modest. The small ferrite coil in the transmitter couples directly into the ferrite rod antenna in the radio. Medium-Wave Modulator Circuit Diagram The modulator is designed as an emitter follower that modulates the supply voltage ...

The circuit presented here illustrates the fact that in spite of all kinds of new component and technology, it is still possible to design useful, and interesting, circuits. The circuit is based on two well-established transistors, a Type BF256C and a BF494. In conjunction with the requisite resistors and capacitors, these form a well-working antenna amplifier. Note that they are direct coupled. Transistor T1 is the input amplifier cum buffer, while the BF494, in a common-ground configuration, provides the necessary amplification. The amplifier is designed for operation at frequencies between 10 MHz and 30 MHz, which is the larger part of the short-wave range, and has a gain of 20 dB. Inductor L1 is wound on an Amidon core Type T-37-6. The primary consists of 2 turns, and the secondary of 12 turns 0.3 mm dia. enameled copper wire. The number of turns may be experimented with for other frequency ranges. The input circuit is tuned to the wanted station with capacitor C1. The response of ...

Frequency Modulation Another means of encoding a wave of information is by producing a complex wave whose frequency is varied in proportion to the instantaneous amplitude of the information wave. Such an encoding is frequency modulation. The result of this encoding or modulation process is a complex modulated wave whose instantaneous frequency is a function of the amplitude of the modulating wave and differs from the frequency of the carrier from instant to instant as the amplitude of the modulating wave varies. The following equation provides the equivalent formula for FM: v(t) Asin( t M sin( t)) c f i = w + w where, v(t) is the instantaneous voltage A is the peak value of the carrier wc is the carrier angular velocity Mf is the modulation index wi is the modulating signal angular velocity The FM formula is really complex. In figure 1 is the waveform of a FM signal. To solve for the frequency components of an FM wave requires the use of the Bessel functions. They show that frequency-m...

The proposed circuit generates accurately spaced PWM pulses which imitates a sine wave very closely and thus can be considered as good as its sine wave counter part design. Here we use two stages for creating the required PWM pulses, the stage comprising the ICs 741 and the other comprising the IC 555. Let’s learn the whole concept in details. How the Circuit Functions – The PWM Stage The circuit diagram of the proposed pure sine wave inverter can be understood with the following points: The two op amps are basically arranged to generate the required sample source voltages for the IC 555. The couple of outputs from this stage is responsible for the generation of square waves and triangular waves. The second stage which is actually the heart of the circuit consists of the IC 555. Here the IC is wired in a monostable mode with the square waves from the op amp stage applied to its trigger pin #2 and the triangular waves applied to its control voltage pin # 5. The square ...

This circuit is designed to amplify the input from a telescopic whip antenna. The preamplifier is designed to cover the medium waveband from about 550Khz to 1650Khz. The tuning voltage required is 1 to 12 volts and can be obtained from a 10k potentiometer connected to the 12 Volt power supply. Medium Wave Active Antenna Schematic RV1 is the gain control allowing weak signals to be amplified or strong signals to be attenuated. The control voltage is applied to gate 2 of TR1, a dual-gate MOSFET, the signal voltage applied via gate 1; the input signal being tuned via L1 and the two varicap diodes at the MOSFET's input and also by L2 and the varicaps at the MOSFET's drain terminal. Both tuned circuits provide high selectivity across the entire tuning range. To aid stability the MOSFET stage is fed from a stabilized supply consisting of ZD1 and R6. To drive low impedance (50 ohm) receivers, the medium output imepedance of the BF981 stage is enhanced by the composite amplifier made f...

This circuit is a sine wave oscillator which uses operational amplifiers working in oscillation back (positive feedback), or the oscillation output to the input. This oscillator is called Wien bridge circuit is often used. The oscillator Sine wave oscillator is difficult to be done due to the distortion of the oscillation signal, different oscillator square wave, triangle wave oscillator (sawtooth). Oscillator Sine wave Circuit Diagram In the case of C1 = C2 = C, R = R1 = R2, giving the frequency of oscillation and can be calculated using the following formula. Formula Sine Wave Oscillator The example of the circuit was made this time is shown below. f = 1 / (2 x 3.14 x 10 -6 0.01 x 10 x 15 x 3) f = 1 / (0.942 x 10 -3) f = 1.062 x 10 3 f = 1062 Hz The actual frequency of the circuit was 900 Hz.