The modification of the DEGEN DE1103 radio receiver described below was done to provide the radio receiving in long and medium wave bands with an external antenna (or with the standard telescopic antenna), but not with the built-in ferrite rod antenna. Now while working on short waves too, the received signal from the standard telescopic or an external antenna is applied directly to the input of the first mixer, bypassing the Q1 transistor stage.
The schematic diagram of such a modification of the DEGEN DE1103 radio receiver is shown in Fig.1.
The received signal from the standard telescopic antenna or from the external antenna connector J1 “ANT” is applied to the input of the first mixer, made on transistors Q7 and Q8. Its path is through the wire jumper (shown in red in the schematic diagram), soldered between the pin 2 of J1 connector and the common point of the elements R111, D2 and D3, and then through the capacitor C1. While receiving strong signals the attenuator on resistors R106 and R105 can be turned on by the switch S1 “DX / LOCAL” between the capacitor C1 and the input of the first mixer. The electrical circuit with the diode D2 must be opened to prevent an unnecessary signal from the output of the transistor Q14 stage, agregated with the built-in ferrite rod antenna, from entering the input of the first mixer. Similarly, while receiving in the short wave band, the electrical circuit with the diode D3 must also be opened to prevent an unnecessary signal from the output of the transistor Q1 stage from entering the input of the first mixer. Both for the electrical circuit with diode D2 and for the electrical circuit with diode D3, the circuit opening points are shown in the schematic diagram with a red cross.
The maked modification is illustrated in the photos below. Fig.2 shows the soldered wire jumper (circled in red), and Fig.3 shows the locations of diodes D2 and D3, one of the pins of each of which can simply be unsoldered and slightly raised above the printed circuit board.
This modification may be necessary to connect an external active antenna to the receiver, such as, for example, the anti-noise ferrite rod antenna “Olusha-10-MW”.
ATTENTION! All modifications are made at your own risk. The author does not bear any responsibility for your actions with your radio receiver.
Copyright © Sergii Zadorozhnyi, 2012