This is a design circuit for receiver circuit that have better sensitivity due to the inclusion of one extra stage of amplification and the use of a higher rail voltage. This is the figure of the circuit;
The higher rail voltage gives some stages a higher gain due to the higher amplitude of the signal. But some of the gain has been lost in the diode pump as this type of pump requires more energy to charge the 10u than a 0.47u. The use of a center-tapped voltage source saves two transistors in the bridge network but necessitates the use of a double-pole switch to disconnect both halves of the supply. The use of a PNP transistor for Q1has simply turned the circuit up-side-down however the antenna is still connected to the collector and the parallel tuned circuit is also on the collector. The circuit is turned on by the 33k on the base and the 47n keeps it rigid and turns the stage into a common base configuration. The parallel resonant circuit made up of the 8-turn inductor and 15p, starts the circuit oscillating and the 39p between collector and emitter provides feedback for the transistor to supply pulses of energy to the tuned circuit to keep it oscillating. The 220R and 39p are the emitter biasing components, as well as the 390R, 10n and 47n. The 100R and 47u are stage-separating components to remove low-frequency noise from the power rails and the 22n across the first stage tightens up the power rails as far as the high frequency is concerned and allows the low-frequency component to appear across the 3k3. The signal across this resistor is picked off via the 10k/39n combination and passed to two stages of amplification.
The 10k and 4n7 form a filter to remove high frequency pulses. A high frequency pulse will try to charge the 4n7 and most of the amplitude of the pulse will be lost (attenuated) in the 10k resistor. Exactly how this works is as follows: The high-frequency pulse will rise and fall before the 4n7 has time to charge. But a low-frequency will charge the 4n7 and enter the 39n for amplification by the rest of the circuit. Going back to the first stage, we have already mentioned that it is oscillating at 27MHz and the MOST ACTIVE lead of the circuit is the collector and this is where the antenna is connected. The waveform produced by the circuit is passed to the antenna and radiated to the surroundings.
The higher rail voltage gives some stages a higher gain due to the higher amplitude of the signal. But some of the gain has been lost in the diode pump as this type of pump requires more energy to charge the 10u than a 0.47u. The use of a center-tapped voltage source saves two transistors in the bridge network but necessitates the use of a double-pole switch to disconnect both halves of the supply. The use of a PNP transistor for Q1has simply turned the circuit up-side-down however the antenna is still connected to the collector and the parallel tuned circuit is also on the collector. The circuit is turned on by the 33k on the base and the 47n keeps it rigid and turns the stage into a common base configuration. The parallel resonant circuit made up of the 8-turn inductor and 15p, starts the circuit oscillating and the 39p between collector and emitter provides feedback for the transistor to supply pulses of energy to the tuned circuit to keep it oscillating. The 220R and 39p are the emitter biasing components, as well as the 390R, 10n and 47n. The 100R and 47u are stage-separating components to remove low-frequency noise from the power rails and the 22n across the first stage tightens up the power rails as far as the high frequency is concerned and allows the low-frequency component to appear across the 3k3. The signal across this resistor is picked off via the 10k/39n combination and passed to two stages of amplification.
The 10k and 4n7 form a filter to remove high frequency pulses. A high frequency pulse will try to charge the 4n7 and most of the amplitude of the pulse will be lost (attenuated) in the 10k resistor. Exactly how this works is as follows: The high-frequency pulse will rise and fall before the 4n7 has time to charge. But a low-frequency will charge the 4n7 and enter the 39n for amplification by the rest of the circuit. Going back to the first stage, we have already mentioned that it is oscillating at 27MHz and the MOST ACTIVE lead of the circuit is the collector and this is where the antenna is connected. The waveform produced by the circuit is passed to the antenna and radiated to the surroundings.
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