Single circle
As a single circuit a simple type of radio and broadcasting -Empfängers referred to the single-circuit detection receiver . It only contains a single oscillating circuit . The resonant circuit is used for transmitter selection.
In addition to this technical clarification of terms, there is also a historically based usage of language that is largely based on publications from the post-war period. According to this, a single circle is always an audion , usually a feedback audion , with at least one electron tube as an active element. The term single-circuit was often used to distinguish it from the more complex multi-circuit receivers and the emergent superposition receivers and was typical language from the end of the Second World War to the beginning of the 1960s, when the tubes were replaced by the transistors.
From a technical point of view, for example, the detector receiver and the first transistor circuits that came into use with the development of the tip transistor after 1948 are single-circuit devices.
A single circle is the simplest member of the straight-ahead receiver family . Most people's receivers were single-circuit receivers and feedback audions, with an electron tube as the active element.
By switching off many high-performance radio transmitters in the medium wave range , fewer radio stations from Europe can be received today than 25 years ago.
Advantages and disadvantages
The main advantage of the single-circuit receiver over other types of receivers is its simple construction with a few components, which were often self-made at the time. Compared to superheterodyne receivers (superheterodyne) single circuit are replica secure items in electronics experiment kits and electronics hobbyists . Until about 1960 they were also often used by radio amateurs .
Because there is only one frequency-determining oscillating circuit in the single circuit, the selectivity is low, especially with the detector receiver and with rectification with bipolar transistors. The effective quality of the resonant circuit is significantly impaired because of the low-ohmic load caused by the headphones with regard to the loss resistance of the resonant circuit (a few kOhms were typical). The input resistance of a tube circuit is significantly higher (typically more than 500 kOhm). The feedback common in audion de-dampens the resonant circuit, which can lead to self-excitation and the associated interference with other receivers, but which can even reduce the reception bandwidth just below the oscillation point to such an extent that the reproduction of high audio frequencies is impaired. The approximate rectangular characteristic of a super typical for band filters is not achieved; the feedback in the single-circuit receiver with audio amplifier served practically to adjust the volume. The rectification and the feedback do not necessarily have to be in the same level with a single-circuit receiver, as a receiver from Loewe proves.
A single circuit with field effect transistor or electron tube practically does not have at least the problem of damping. With the Audion one avoids the attenuation through feedback and achieves an amplification and increase of the selectivity. Operation is complicated because both the reception frequency and the strength of the feedback have to be set. In addition, these devices generate radio waves themselves if operated incorrectly.
A circuit that does not have this disadvantage and still has good selectivity is described in the article detector receiver.
There were also single-circle handicraft instructions for FM radio reception. Since initially only one or a few transmitters existed, the principle of edge demodulation also enabled reception of these frequency-modulated transmitters. In the case of edge demodulation, the resonance frequency of the resonant circuit is slightly next to the receiving frequency, followed by amplitude demodulation (for example with a germanium tip diode ) and a low frequency amplifier. In this way, VHF could be received without having to use transistors (which were expensive at the time) for VHF frequencies.
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- ^ Conrad: Introduction to radio technology, Fachbuchverlag Leipzig, 1956, section "Straight-ahead receiver", p. 126 ff.
- ↑ The term single-circle only became established in common usage when audio circuits were already on the market as mass production. In the narrower sense, this almost always meant feedback audio receivers with an additional amplifier that enabled loudspeaker reception.
- ^ Meyers Lexicon Technology and Exact Natural Sciences 1969; Keyword "single-circuit receiver": receiving device (mostly audio receiver) with a single high-frequency (HF) oscillating circuit that can be tuned to the frequency to be received; the associated tube is mostly used for amplification and demodulation at the same time; E. are hardly common today.
- ↑ Loewe local receiver OE 333, a single-circuit with rectification in the second stage and without feedback ( page can no longer be accessed , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
