Showing posts with label wave. Show all posts
Showing posts with label wave. Show all posts
Thursday, December 26, 2013
Triangular Wave Oscillator
This design resulted from the need for a partial replacement of the well-known 8038 chip, which is no longer in production and there fore hardly obtainable.
An existing design for driving an LVDT sensor (Linear Variable Differential Transformer), where the 8038 was used as a variable sine wave oscillator, had to be modernised. It may have been possible to replace the 8038 with an Exar 2206, except that this chip couldn’t be used with the supply voltage used. For this reason we looked for a replacement using standard components, which should always be available.
Triangular Wave Oscillator Circuit diagram:
In this circuit two opamps from a TL074 (IC1.A and B) are used to generate a triangular wave, which can be set to a wide range of frequencies using P1. The following differential amplifier using T1 and T2 is configured in such a way that the triangular waveform is converted into a reasonably looking sinusoidal waveform. P2 is used to adjust the distortion to a minimum.
The third opamp (IC1.C) is configured as a difference amplifier, which presents the sine wave at its output. This signal is then buffered by the last opamp (IC1.D). Any offset at the output can be nulled using P3.
Author : Jac Hettema - Copyright : Elektor
Source : http://www.ecircuitslab.com/2012/06/triangular-wave-oscillator.html
Monday, September 2, 2013
Medium Wave Active Antenna
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 MOSFETs input and also by L2 and the varicaps at the MOSFETs 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 from TR2 and TR3. TR2 is operating in common emitter boosting voltage levels by just over 2, TR3 is operating in emitter follower giving the circuit a low output impedance.
Finally this active antenna can be used on other bands by changing the values of L1 and L2. To perform on multiple bands switches or relays can be used to change the value of L1 and L2.
Medium Wave Active Antenna Schematic
To drive low impedance (50 ohm) receivers, the medium output imepedance of the BF981 stage is enhanced by the composite amplifier made from TR2 and TR3. TR2 is operating in common emitter boosting voltage levels by just over 2, TR3 is operating in emitter follower giving the circuit a low output impedance.
Finally this active antenna can be used on other bands by changing the values of L1 and L2. To perform on multiple bands switches or relays can be used to change the value of L1 and L2.
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