Regenerative Receiver with Dual Polarity

Overview

The circuit has been designed to function as amplifier-detector to produce high quality of audio output through the external earphone.

Terminology

• Receiver – an electronic device that converts incoming signals, in the form of microwave, electrical or radio, to a form that is perceivable by humans such as pictures, sound, light, navigational positions, digital data, measurement, and others
• AC126 – a small signal Germanium PNP transistor designed for use as a medium power amplifier
• 2N3904 – NPN device designed for general purpose low power amplifier and switch applications; extends to 100 mA as a switch and to 100 MHz as an amplifier

Circuit Explanation

Tuning the circuit to the appropriate frequency needs a sufficient amount of regeneration. This circuit is intended to operate on the AM broadcasting band with a frequency of 530 kHz to 1650 kHz. The output from the earphone can be fairly rated by different listeners. Tuning the circuit to preferred station will require the functionality of the 475pF variable capacitor while the regeneration of the receiver is smoothly controlled by the 200 pF variable capacitor. This capacitor is also known as the throttle capacitor where the variable reactance is shunting part of the feedback signal to ground for the control of overall regeneration.

It is significant that the inductors are properly in phase for the purpose of producing regeneration. Both are using Litz wire where inductor L1 has a value of 200 uH wound around the ferrite rod with 51 turns while inductor L2 has a value of 2.58 uH wound with 4 turns. L2 acts as the tickler coil where the anode of a vacuum tube is in series with the coil and coupled to the grid to provide feedback. The regeneration will increase the LC tank's signal level to accomplish efficient detection.

The detection is being handled by the 2N3904 transistor because of the non-linear characteristics of the base-emitter junction and is very useful above 10 MHz frequency as well as short wave frequencies having enough coils. The circuit has a very low power consumption wherein 60 uA from the 9 V source and 0.5 mA from the AC126, is being drained by the transistor 2N3904. This design can identify long distance source as far as 25 km from a medium powered local stations operating at 5 KW to 10 KW.

Since the audio transistor AC126 is a Germanium type, external biasing is not necessary because the build up of current amplifying factor can be achieved by the collector leakage current which has around 0.5 mA. With this, amplification will surely occur.

Application

Regenerative receivers have placed a vital role in the field of radio communication like in radio repair where the broadcast radio signals are monitored, as interference source identifier, in adjustment of oscillators, and in amateur radios.

There are several types of receivers that are used in various industries such as measuring receivers which are used in broadcast station to measure its signal strength; as communications receivers which is a part of a radio communication network; as specialized receiving scanners that can scan two or more discrete frequencies automatically; as satellite television scanners used in communication satellites for receiving television channels; as audio receivers used in home theater systems and home stereos; as telemetry receivers for reporting and remote measurement; and as crystal radio receivers powered by radio waves.