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DDR all-transistor radio

Sternchen (little star) was the first civil radio made in the former DDR (East-Germany), that was fully built with transistors. It was developed in 1958, and was manufactured from 1959 onwards by VEB Sternradio in Sonneberg (DDR), and from 1961 onwards also in Berlin. It is suitable for the reception of the Medium Wave band (MW) from 510 to 1620 kHz, and is powered by a 9V battery.
The radio measures 14.5 x 9 x 3.5 cm, weights 320 grams, and was available in a wide variety of colours. It is housed in a plastic enclosure with a metal grid over the internal speaker. At the right side it has a 3.5 mm socket for the connection of an earpiece, which was available separately.

It was the first radio in the DDR that was fully transistorised and that was powered by a (then) relatively new 9V block battery. Sternchen soon became a popular consumer item in the former Eastern Block state. It was often carried around in a leader carrying case with velvet lining.
Sternchen portable all-transistor DDR radio

Sternchen was not only used by consumers however, but also by international spies and agents working in the DDR. Such agents were commonly DDR citizens that were working for one of the Western intelligence services, such as the West-German BND, the British MI6 or the American CIA.
For the reception of instructions from the free West, the agent needed an unobtrusive radio, and Sternchen was a good candidate for this. The coded instructions were sent by a Numbers Station operating in the Short Wave band (SW), for which Sternchen was unsuitable. Posession of an SW radio was considered illegal in the DDR.

To overcome this restriction, Western agencies started distributing so-called BND converters, that converted Sternchen into a short-wave radio that could receive two crystal-based channels on which the BND transmitted its coded messages.
BND SW Converter with crystal installed

The BND Converter was actually a mixer, or down converter, that produced an output signal at 1500 kHz in the MW-band. The posession of a BND Converter was extremely dangerous in the DDR, and it had to be concealed properly in order to hide it from the authorities during an un­expected search. Furthermore, the device's crystal oscillator produced such a strong signal, that it could easily be picked up outside the building, making it liable to radio direction finding.
Sternchen portable all-transistor DDR radio Front view Upper right corner with carrying strap eye, on/off volume knob and earphone socket Logo Earphone Sternchen with earphone Sternchen in leather carrying case - seen from the rear Sternchen in leather carrying case

Sternchen radios were available in plastic cases with the following colours [2]:
  • White
  • Yellow
  • Blue
  • Red
  • Orange
  • Violet
  • Green
  • Turcoise
Getting access to the interior of the Sternchen is pretty straightforward and does not require any tools. The rear panel of the plastic body can be separated by inserting a small coin or a finger nail in the small gap at the top, and pulling-off the panel, after which the interior will be visible.

The interior of the radio resembles a portable Japanese radio from the 1960s and 70s, and consists of a pertinax printed circuit board (PCB) with the electronic components. Clearly visible are the ferrite antenna, the tuning capacitor, the loudspeaker, and various types of transistors.
Sternchen open

Opening the rear lid Sternchen open Interior Battery compartment Ferrite antenna Tuning capacitor VALVO transistor

Circuit diagram
The image below shows the original circuit diagram of the first Sternchen that was released in 1959. Its model number is 57/69 TT. Click the image to view it in a better resolution. The radio was built with parts from Eastern Block manufacturers, but also with Western parts, such as the OC44 and OC45 transistors that were sourced from Valvo (later: Philips) in West-Germany [3].

Sternchen 57/69 TT - original circuit diagram - click to enlarge

In a later variant, a diode was added to the circuit in order to improve the Automatic Gain Control (AGC) of the radio. Furthermore the transistor types were changed a number of times, as and when newer and better versions became available. The improved version is shown below [3].

Sternchen - improved circuit diagram - click to enlarge

  1. Original Sternchen leaflet
    Si 752/59 50 V-17-17 2012. 1959. 2 pages.

  1. Wikipedia, Sternchen (Radio)
    Retrieved March 2017.

  2. Ditmars Radioseiten, Sternradio Sonneberg
    Retrieved March 2017.

  3. Wumpus Welt der Radios, Sternchen circuit diagrams
    Retrieved march 2017.

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Crypto Museum. Created: Wednesday 15 March 2017. Last changed: Wednesday, 15 March 2017 - 20:55 CET.
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