Many radio amateurs "who are over 40" began his career with the transistor radio on the midrange. If your area has a reception in the medium or long waves, Receiver under this scheme will be a good occasion to recall school years.
The figure shows a simple diagram of a receiver in a range of MW or LW (depending on the number of turns of the coil L1) powered from the mains via the power supply from the faulty television game console "Kanga" and "Dandy".
Antenna – magnetic, based ferrite rod. But if one is not enough, always possible to the top (under the scheme) plate of the variable capacitor C2 via the capacitor 10-100 pF attach long antenna. Then it will be possible to make even remote radio stations. But of course, Only if there is no strong local, – otherwise she will score, receiver then direct amplification.
The signal from the antenna circuit L1-C2 supplied through a coupling capacitor C1 to the RF amplifier-detector input transistor VT1. Cascade covered by positive feedback via the outlet to the emitter coil contour VT1. PIC depth is controlled by the variable resistor R9. It can help you quickly in tune in the station to adjust the sensitivity and selectivity of the receiver. At the far right position on the scheme R9 PIC missing. Thus the minimum receiver sensitivity, but bandwidth is the widest. It is suitable for receiving a local radio station powerful. R9 left turning can be increased according to the scheme PIC. This increases the sensitivity and bandwidth narrows, it is better to receive distant stations.
But infinitely increase the PIC will not work, – It is advanced in the generation mode, A self-excited the greatest sensitivity and selectivity will be somewhere on the very threshold of self-excitation.
The transistor collector junction operates as amplitude detector VT1. This contributes to the capacitor C3.
Transistor VT2 is preliminary ULF. The signal supplied to its collector through a regulator R2 volume on a completely standard ULF transistors VT3-VT5. Amplifier with direct coupling between the stages. Cascade preamplification configured transistor VT3. The output stage is built on the push-pull circuit in raznostrukturnyh transistor VT4 and VT5.
Optimal mode ULF DC set the selection of the resistor R3 so, that at the emitters of transistors VT3 and VT4 voltage was equal to half the voltage across the capacitor C9.
Speaker V1 – speaker of the handheld radio. It fits almost any broadband from 4 to 20 ohm.
For L1 coil winding need a ferrite core diameter 8 mm and a length of at least 100 mm. It is necessary to glue the paper tube, which will frame and wind the coil is not it. For receiving in the range SV (MW) We need to be wound around 80-90 any turns of the winding wire diameter 0,3-1 mm. Withdrawal from the 8th round of. For the long wave range is increased to the number of turns 260-280, Well, thinner wire – 0,1-0,2 mm. Withdrawal from the 25th round of. In the first case, the winding turn to turn, second – vnaval, but broken down by 5 sections.
Variable capacitor C1 can and other container, but not less than the specified. BC549 transistors can be replaced by KT3102, and BC559 – of KT3107 (or KT315 and KT361, respectively).
Mounting receiver formed on a piece of foil Steklotekstolit.
Mounting configured volumetrically, for a common zero accepted foil foil fiberglass.
Author: Snegirev I.
A source: Radiokonstruktor №4 / 2018