DE1238959B - Circuit arrangement for demodulating complex radio stereophonic signals - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

H04b

German class: 21 al- 16/03

Number: 1238 959

File number: Z11364 VIII a / 21 a2

Filing date: February 26, 1965

Open date: April 20, 1967

The invention relates to a circuit arrangement for demodulating complex radio stereo signals by using an auxiliary carrier (38 kHz) obtained from a pilot frequency (19 kHz) for electronic alternating switching of the complex stereo signal to the two speaker channels.

It is known to use a ring demodulator with diodes, one of which is diagonal Subcarrier (38 kHz) is fed and its other diagonal points the two speaker channels can be removed from ground. Feeding takes place at the point of symmetry of one diagonal of the mentioned stereo signal. In principle, ring demodulators with a large current flow angle and those known with a small current conduction angle. In the case of the former, there is a compensation for the system-related Cross-talk is necessary by supplying an anti-phase signal. Arrangements with With a small current conduction angle, compensation becomes superfluous.

In addition to stereophonic radio broadcasts, monophonic broadcasts should also be received. It is known to automatically switch from mono reception to stereo reception and vice versa Rectification of the subcarrier (38 kHz) obtained from the stereo signal with the one generated from it Make DC voltage by compensating a bias current. To do this, it is known at Mono operation to operate the diodes of a ring demodulator with a bias current in the forward direction, so that these diodes have a sufficiently low resistance in relation to the output load so that none Distortions for the low-frequency signal arise. The mentioned bias current is a special one for this purpose existing voltage divider taken from the supply voltage of the device. The resistor-capacitor combinations lying in two adjacent diode branches are dimensioned so that their time constant is large compared to the period of the subcarrier, so that the diode branches in the presence of the subcarrier frequency, i.e. in stereo operation, blocked and only in the voltage peaks of the subcarrier for the stereo signal are switched through. The stereo signal becomes usually a decoder input stage to be regarded as an impedance converter on one in the emitter or Collector branch removed working resistance and used for direct current separation an isolating capacitor is fed to the demodulator. The aforementioned separating capacitor represents the broadband stereo signal (30 Hz to 53 kHz)

Circuit arrangement for the demodulation of
complex radio stereophonic signals

Applicant:

Central laboratory for

Radio and television reception technology,

Dresden N15, Am Lagerplatz

(formerly Meschwitzstr.20SA)

Named as inventor:

Rudolf Irmler,

Dipl.-Ing. Rudolf Hannawald,

Dipl.-Ing. Dietrich Neske, Dresden

frequency-dependent resistance. To reduce

ao tion of frequency-dependent level and phase changes the capacitor must be dimensioned sufficiently large. In addition, he already provides called voltage divider for the diode bias current represents a high economic outlay, as additional Switching elements are required. The purpose of the invention is therefore to reduce the hitherto required circuit effort with simultaneous improvement of the stereophonic transmission.

The invention is based on the object of designing a circuit arrangement for demodulating complex radio stereo signals in such a way that the stereo signal reaches the demodulator with linear amplitude and phase and the supply of the bias current to the diodes is simplified.

This task is accomplished with a circuit arrangement for demodulating complex radio stereo signals by using an auxiliary carrier obtained from a pilot frequency for the electronic alternating switching of the complex stereo signal to the two loudspeaker channels by means of a ring demodulator, which has an automatic switchover via a bias current flowing through its diodes for mono and stereo operation and one diagonal with the secondary side one of the transformer coupling the subcarrier and its other diagonal with the symmetrical ones Loudspeaker channels is connected, solved according to the invention in that only two non-adjacent Branches of the ring demodulator each have an .RC element in Series connected to the diode of the branch and one between the i? C element and the diode Resistance dissipating the bias current to ground

709 550/229

Claims (3)

i 238 959 is provided and that between the center tap the secondary side of the transformer and an emitter or collector side working resistor of the decoder input stage one in addition to the stereo signal also at the same time via the dissipating resistors outflowing bias current to the ring demodulator there is a conductive galvanic connection. This design of the ring demodulator makes it possible to feed the stereo signal into the Make ring demodulator according to the invention by galvanic connection. If so far a separating capacitor was required, it is possible through the solution described in the task The requirement mentioned that the stereo signal be fed to the demodulator with linear amplitude and phase, To ideally fulfill without dimensioning difficulties and at the same time the supply of the preliminary current to simplify as much as possible. The invention is explained in more detail using an exemplary embodiment. To this end, one is according to the invention possible circuit arrangement shown in the drawing. The ring demodulator shown consists of diodes 1, 2, 3, 4, two of which are not adjacent 1 and 3 in their bridge branch in series with one each of a resistor 5 and a charging capacitor 6 existing parallel connection are connected. From the junctions of the diodes 1 or 3 with the associated i? C element, leakage resistors 7 and 8 are connected to ground, which off Must be the same size for reasons of symmetry. The connection points 9 and 10 of the diodes 2 and 4 with the AC members are one with the secondary side Connected transformer 11, via which the regenerated subcarrier arrives at the ring demodulator. The connection points 12 and 13 of the diodes 1 with 4 resp. 2 with 3 represent the taps for the balanced speaker channels 14 and 15. A center tap 16 is galvanic to the emitter-side working resistor 17 of a decoder input stage 18 tied together. With mono reception, the subcarrier is at the diagonal points 9 and 10 of the ring demodulator not available. The bias current is at the symmetry point 16 of the transformer 11 is fed and flows through the diodes 2 and 3, the bleeder resistor 8 and through the Diodes 4 and 1 and the bleeder resistor 7 to ground. The low-resistance due to the bias current Diodes connect the symmetry point 16, into which the audio signal is also fed, to the two Speaker channels. The bias current is generated by the working resistor 17 and for the Maintain the required voltage at the operating point of the input stage. With stereo reception, is through the pilot frequency contained in the stereo signal via a carrier recovery stage at the diagonal points 9 and 10 an auxiliary carrier frequency alternating voltage effective, the one blocking the diodes Direct voltage on the capacitors 6 can arise. Depending on the current polarity of the Carrier voltage in the voltage peaks the diodes 2 and 3 or the diodes 4 and 1 are conductive for the speaker channels. Both channels are thereby due to the strictly symmetrical circuit arrangement rated equally. In addition to the better transmission of the stereo signal to the ring demodulator, this circuit arrangement has the advantage of saving an isolating capacitor at the same time. aside from that is now by that the bias current the diodes 2 and 3 as well as 4 and 1 with the stereo signal is fed directly, a special circuit for generating this bias current with series resistors and filter capacitor superfluous, so that the circuit arrangement according to the invention also in this Respect leads to a saving. List of the reference symbols used 1 diode, 2 diode, 3 diode,
4 diode, 5 resistance, 6 charging capacitor, 7 leakage resistance, 8 leakage resistance,
9 connection point, 10 connection point, 11 transformers, 12 liaison office, 13 liaison office,
14 speaker channel, 15 speaker channel, 16 center tap, 17 working resistance, 18 decoder input stage. Claim: Circuit arrangement for demodulating complex radio stereo signals through use an auxiliary carrier (38 kHz) obtained from a pilot frequency (19 kHz) for the electronic Alternating switching of the complex stereo signal to the two speaker channels by means of a ring demodulator which, via a bias current flowing through its diodes, with a Automatic switchover for mono and stereo operation works together and its one diagonal with the secondary side of a transformer coupling the subcarrier and its other diagonal is connected to the balanced speaker channels, characterized that only in two non-adjacent branches of the ring demodulator one ÄC element (5, 6) in series connected to the diode (1 or 3) of the branch and between the i? C element (5, 6) and the diode (1 or 3) each has a resistor (7 or 8) that dissipates the bias current to ground and that between the center tap (16) of the secondary side of the transformer (11) and one emitter or collector side working resistance (17) of the decoder input stage (18) one next the stereo signal is also the same as the one flowing off via the dissipating resistors (7 or 8) There is a conductive galvanic connection to the ring demodulator. Considered publications:
German Auslegeschrift No. 1149 396;
U.S. Patent No. 3,070,662;
Magazine "radio mentor", issue 12/1963, p. 1018 6 _S to 1021; "Funk-Technik" magazine, 13/1964, pp. 464,465. 1 sheet of drawings 709 550/229 4.67 © Bundesdruckerei Berlin