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Showing posts with label receiver. Show all posts

Monday, September 2, 2013

AM Receiver Schematic

This is a compact three transistor, regenerative receiver with fixed feedback. It is similar in principle to the ZN414 radio IC which is now no longer available. The design is simple and sensitivity and selectivity of the receiver are good.

AM Receiver Schematic

Notes:
All general purpose transistors should work in this circuit, I used three BC109C transistors in my prototype.The tuned circuit is designed for medium wave. I used a ferrite rod and tuning capacitor from an old radio which tuned from approximately 550 - 1600kHz. Q1 and Q2 form a compund transistor pair featuring high gain and very high input impedance. This is necessary so as not to unduly load the tank circuit.

The 120k resistor provides regenerative feedback,between Q2 output and the tank circuit input and its value affects the overall performance of the whole circuit. Too much feedback and the circuit will become unstable producing a "howling sound". Insufficient feedback and the receiver becomes "deaf". If the circuit oscillates,then R1s value may be decreased; try 68k. If there is a lack of sensitivity, then try increasing R1 to around 150k. R1 could also be replaced by a fixed resisor say 33k and a preset resistor of 100k. This will give adjustment of sensitivity and selectivity of the receiver.

Transistor Q3 has a dual purpose; it performs demodulation of the RF carrier whilst at the same time, amplifying the audio signal. Audio level varies on the strength of the received station but I had typically 10-40 mV. This will directly drive high impedance headphones or can be fed into a suitable amplifier.

Construction:
All connections should be short, a veroboard or tagstrip layout are suitable. The tuning capacitor has fixed and moving plates. The moving plates should be connected to the "cold" end of the tank circuit, this is the base of Q1, and the fixed plates to the "hot end" of the coil, the juction of R1 and C1. If connections on the capacitor are reversed, then moving your hand near the capacitor will cause unwanted stability and oscillation.

Finally here are some voltagee checks from my breadboard prototype.This should help in determining a working circuit:

All measurements made with a fresh 9volt battery and three BC109C transistors with respect to the battery negative terminal.

Q1 (b) 1.31V
Q2 (b) 0.71V
Q2 (c) 1.34V
Q3 (b) 0.62V
Q3 (c) 3.87V

Saturday, April 13, 2013

Tuned Radio Frequency TRF Receiver

Super heterodyne receivers have been heavily produced due to the fact round 1924, but for reasons of value did not become a hit except the Nineteen Thirties. Before the 2d world war different, more practical receiver technologies any suchs the TRF receiver and the regenerative receiver were nonetheless popular.

Circuit diagram :

$\"Tuned$

Tuned Radio Frequency (TRF) Receiver Circuit Diagram

The circuit described here is in accordance with the old technology, however brought updated a The most vital part of the circuit is the input stage, the place certain comments is used to reach good sensitivity and selectivity. The first stage is adjusted in order that it isn't moderately on the level of oscillation. This will increase the gain and the selectivity, giving a slender bandwidth. To do so, the potentiometer connected to the drain of the FET need to be adjusted very carefully: top-quality efficiency of the receiver depends on its environment. In best prerequisites a couple of strong stations must be out there right through the day the use of a 50 cm antenna. At night time, several times this number should be available.

The frequency range of the receiver runs from 6 MHz to 8 MHz. This vary quilts the forty nine m and the forty one m shortwave bands during which many European stations broad-cast. Not bad for one of these easy circuit! The circuit appoints six transistors. The first stage is a selective amplifier, followed via a transistor detector. Two low-frequency amplifier degrees full the circuit. The last stage is a push-pull arrangement for most effective force of the low-impedance loud-speaker. This circuit association is some-times referred to as a ‘1V2 receiver’ (one preamplifier, one detector and two audio frequency ranges).

Setting-up is easy. Adjust P1 unless the purpose is reached the place the circuit starts to oscillate: a whistle might be heard from the loudspeaker. Now back off the potentiometer except the whistle stops. The receiver can now be tuned to a broad-caster. Occasional further adjustment of the potentiometer is also required after the station is tuned in. The receiver functions from a provide volt-age of between 5 V and 12 V and makes use of little or no current. A 9 V PP3 (6F22) battery will have to give an extraordinarily long life.

http://www.ecircuitslab.com/2012/02/tuned-radio-frequency-trf-receiver.html