DE1266815B - Circuit arrangement for the automatic switchover of the receiver from mono to stereo when receiving stereo broadcasts based on the pilot tone method - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

H 04b

German class: 21 a2 - 1.6 / 03

Number: 1266 815

File number: G 43914 VIII a / 21 a2

Filing date: June 19, 1965

Display day; April 25, 1968

The patent application G41889 Villa / 21a ² (German Auslegeschrift 1253 318) relates to a circuit arrangement for the automatic switching of the receiver from "mono" to "stereo" when receiving stereo programs broadcast using the pilot tone method, in which a voltage generated in the stereo decoder and one in its The voltage dependent on the RF level can control a relay which effects the switchover from mono to stereo in such a way that the switchover only takes place when both voltages are present. The characteristic feature of the circuit arrangement according to the main patent application is its structure in the manner of a Schmitt trigger, the input stage of which is supplemented by a second input stage and the voltage generated in the stereo decoder is fed to one input stage and the voltage, which is dependent on the RF level in terms of its size, is fed to the other. This circuit can only tip over when both input stages are blocked, but as a flip-flop circuit it has a sudden characteristic that avoids creeping transitions, ie it provides clear operating states.

With this circuit, however, it is actually necessary to set the control to be relatively insensitive. Namely, if the recipient is between two senders during the vote, the Pilot tone generates enough power from the noise to be able to effect a switchover. is also the level setting but at a relatively small RF level, this path is also free under certain circumstances, since the interference level then becomes a capable of supplying sufficient voltage for the switchover. So there would be a switch on Stereo, although satisfactory stereo reception is not possible.

In order to avoid an uncontrolled switchover to stereo depending on the interference level, a would have to be Time constant element can be inserted into the circuit, which integrates the dependent on the RF level DC voltage makes. In order to suppress interference pulses effectively, its time constant must however, chosen to be relatively large. Under these circumstances it can happen that the recipient remains in the stereo position when tuning from one stereo station to an adjacent one Transmitter with a monaural program is skipped. The result is that over the difference channel the reception is severely disturbed.

In order to avoid these difficulties, it is proposed according to the invention that the control electrode circuit arrangement for automatic
Switching the receiver from mono to
Stereo when receiving stereo broadcasts broadcast using the pilot tone method

Addition to registration: G 41889 VIII a / 21 a2 - Auslegeschrift 1 253 318

Applicant:

GRUNDIG E. M. V.

Electro-mechanical research institute,

Owner Max Grundig,

8510 Fürth, Kurgartenstr. 37

Named as inventor:

Uwe Ciaassen, 8502 Zirndorf

the output stage of the Schmitt trigger is bridged by a capacitor to ground, in such a way that that the decisive stage for controlling the changeover relay when charging a large and when Discharge is given a small time constant. So you can do the necessary integration of the RF level supplied DC voltage without the receiver when changing from a stereo transmitter would remain on a different type of transmitter in the "Stereo" position; because as long as both input stages are blocked, the capacitor causes one slow change in the voltage applied to the control electrode. On the other hand, it becomes one of the inputs open, the capacitor is quickly discharged via one or the other input stage.

An embodiment of the invention and further details thereof are given below explained in more detail with reference to the drawing, in which the same reference numerals are chosen for the same parts as in the main patent application.

In the drawing, T ₁ , T ₂ again denote the transistors of the input _{stages, which} are controlled by a voltage U _stl supplied by the stereo decoder or a voltage U si2 that is dependent on the HF level in terms of its magnitude. T ₃ is the tran-

809 540/304

sistor of the output stage, in the collector circuit of which the relay R switching from mono to stereo is located.

According to the invention, the base of the transistor T ₃ is bridged by a capacitor C with a capacitance of 25 μΡ to ground. As long as the transistors T ₁ and T _{2 are} blocked, this capacitor causes a slow change in the base voltage of the transistor T ₃ ; its charging time constant is therefore large, so that the necessary integration of the direct voltage supplied by the HF level can take place. If, on the other hand, one of the transistors T ₁ or T _{2 is} opened, the capacitor is rapidly discharged via the transistor T ₁ or the transistor T ₂ . The discharge time constant of the capacitor is small in this case, so that if the RF level or the pilot tone fails, the receiver will quickly switch to mono operation.

Claims (1)

Claim: Circuit arrangement for the automatic switchover of the receiver from "mono" to »Stereo« when receiving stereo programs broadcast according to the pilot tone process that are after Type of a Schmitt trigger is constructed, the input stage of which is through a second input stage is supplemented and the one input stage the voltage generated in the stereo coder and the other the voltage, which is dependent in its size on the RF level, is supplied, according to patent application G 41889 Villa / 21 a2 (German patent specification 1253318), characterized in that the control electrode of the output stage of the Schmitt trigger is followed by a capacitor Ground is bridged in such a way that the decisive stage for controlling the changeover relay a large time constant is given when charging and a small time constant when discharging. 1 sheet of drawings 809 540/304 4.68 © Bundesdruckerei Berlin