DRM
In the radio bands, you can also receive stations using the new digital transmission method DRM
(Digital Radio Mondiale). You only hear a loud noise with the Audion. In order to decode, you will
need a very stable receiver, a PC and suitable decoder software. The stations can transmit their pro-
grams with quality similar to VHF, in this way, with additional text messages and, some, in stereo.
The receiver itself is not sufficiently stable, it can however be used with an external oscillator for DRM
reception.
There is still much more to discover with your shortwave radio. Further reception tests, tips and tricks
as well as enhancements for the receiver are described in the ELO online magazine, from the Franzis
Verlag (publishing house), at www.elo-web.de A suitable additional set for this radio, with components
and detailed instructions for DRM reception is available from Conrad Electronic SE (www.conrad.de),
order no. 19 22 43, price: Ä9.95. It can also be used with the medium wave radio from last year.
Notes to the Wiring Diagram
A simple detector straight receiver consists of a oscillating circuit and a rectifier diode. The reception
power is however limited, which means that only powerful stations can be received. The selectivity is
also low, because both the antenna and the rectifier diode dampen the oscillating circuit, resulting in
a large bandwidth. An Audion avoids these disadvantages and ensures very good sensitivity and
selectivity.
The Audion transistor T1 has three functions: Amplification, compensation of the oscillating circuit and
demodulation of the RF signal. The PNP transistor works as an emitter-follower. C2 and the internal
base-emitter-capacitance of approx. 5pF form a capacitive voltage divider. A Colpitts oscillator is formed
together with the oscillating circuit. The amplification can be chosen by suitably adjusting the emitter
current, so the oscillator does not yet oscillate. At this operating point, the transistor adjusts all losses
that occur in the oscillating circuit. The quality factor can be increased from about 50 to over 1,000. At a
reception frequency of 6 MHz, the bandwidth is approx. 6kHz, it is thus possible to separate channels,
which are close together.
The compensation also leads to an increase in signal amplitude. RF voltages of up to approx. 100
mV can occur at the base. The AM signals are demodulated to the input curve characteristic of the
transistor. The NF signal then appears at the emitter. R1 and C2 form a low pass filter, which
removes RF splits. T2 is an AF preamplifier for the integrated amplifier IC1. The AF stage also uses
a PNP transistor to prevent any confusion when installing.
A special feature of the Audion circuit is the direct coupling of the transistor to the oscillating circuit.
T1 operates with a collector emitter voltage of only approx. 0.6 v. In addition, the base emitter capac-
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Montage des éléments de commande
Le condensateur variable sert au réglage de la fréquence de réception souhaitée. Poser l’axe de pro-
longation sur le condensateur variable et serrer avec la vis de 2,5 mm de longueur. Éviter de serrer
l’axe trop fortement sur la butée et utiliser des pinces pour tenir l’axe. Le condensateur variable est
monté dans le boëtier ultérieurement à l’aide de deux petites vis et les rondelles assorties.
Monter le haut-parleur en l’introduisant dans la fente correspondante. Les bornes doivent être orien-
tées vers le bas pour permettre des liaisons courtes à la platine. Le haut-parleur est maintenu suffi-
samment bien dans la fente prévue à cet effet. Mais vous pouvez en plus utiliser une goutte de colle
ou de colle à chaud.
Le bouton de réglage du volume avec trois bornes comprend en outre l’interrupteur de marche/arrêt.
Quand l’axe est tourné complètement à gauche, l’interrupteur s’ouvre. Placer le bouton de réglage
du volume dans l’orifice de montage gauche. Une petite patte empêche une mise en place incorrec-
te. Fixez le bouton de réglage avec l’écrou à úil, ne pas oublier la rondelle. Monter le bouton de régla-
ge de rétroaction de la même manière dans la position centrale.
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Le condensateur variabl
Haut-parleur
