DE2203691C3 - Circuit arrangement for automatic station search in television receivers - Google Patents

Description

Circuits considerably.

An embodiment of the invention is shown in the drawing and will be described in more detail below The invention relates to a circuit arrangement 43 described. It shows

for an automatic station search system in Fernsehemp- Fig. 1 a circuit arrangement for obtaining

catching devices, in which with the help of an identification signal on a pulse,

dearly separated sync pulses an identifier si- F i g. 2 shows the voltage curve at points A.

gnal is obtained, which switches a discriminator tuned to the Bildträgerzwi- and B of the circuit arrangement in the absence of Koin Schen frequency, 45 zidenz and

the further increase of a to the vote of the F i g. 3 shows the voltage curve at points A.

Tuners serving sawtooth voltage and B at coincidence.

stops. In the circuit arrangement according to FIG. 1 become

In such circuit arrangements it is necessary to have a base with its emitter against ground, the sawtooth-shaped voltage rise of the 50 switched npn transistor 1 via an ohmic one With the coordination of the varactor diodes required voltage divider, which consists of resistors 2, 3 Then stop DC voltage when the tuning and which a capacitor 4 is connected upstream of Attention to a television station or approaching an impulse separation stage coming line synchronously is reached. pulses S supplied. These impulses are through

It is known that the network 2, 3, 4 differentiates for a station search, so that they can obtain the relevant stop signal from a discriminator tuned to the IF Tontra transistor 1 for only a fraction of the synchronism. Open this pulse duration. The collector of the transistor is method, however, has disadvantages. Since the sound carrier is connected to the cathode of a diode 6, the anode of which is only available in a sufficient size anode is connected to a switching point / 4, which is when the sound * and video carrier are approximately correct 60 via a resistor? is grounded and are in the passband of the IF curve, the arrival is β About one of capacitors, 9 existing calling time is short. The transmitter can therefore easily be overflowed from voltage divider line return refipulse 10 supplied. There is also a risk of being. When passing through the network ?, 8, 9 of an undesired response to the jammers are reaching the switching point A newspaper or for possible mixing products which lenrücklaufimpulse differentiated to a 85th Mismatch at switching point A can result, a possible sensor is also the anode of a further diode 11 other-sided audio carrier failure would also prevent the receiver, whose cathode with a catch of the video carrier. Capacitor 12 connected to ground connection '

punklÄ is connected. The connection point B is connected via a resistor 13 to the base of an npn transistor 15, which is connected to ground via a further resistor 14, the collector-emitter path of which is arranged between a discriminator 16 and ground.

The in F i g. 1 has the following effect: During the search, the line return pulses 10 reach the switching point A via the network ?, 8, 9. Since there are no synchronizing pulses previously, the transistor 1 remains blocked. 2 shows the voltage curve 17 associated with the switching point A. This pulse voltage is peaked through the diode 11 and the capacitor 12. This results in a voltage curve 18 at the connection point B. This voltage switches the transistor 15 through, so that the discriminator 16 matched to the IF picture carrier is switched ineffective. If the search now reaches a transmitter that is worthy of reception, a pulse separation stage supplies synchronizing pulses 5, which are differentiated via the network 2, 3, 4 and fed to the base of the transistor 1. If there is a coincidence of line return pulses and syncbron pulses, a voltage curve 19 is produced at switching point A and at switching point A, as shown in FIG

Switching points a voltage curve 29. This becomes the transistor 15 blocked and the disikrimitatoi 16 activated

The use of peak rectification results in a simple definition of the potential

i * the switching voltage, without the entire Koirradenzscufe having to be increased in terms of potential by complex measures. Another advantage is the short response time, since the capacitor 12 has a low sheet resistance of the diode 11

being charged. As a result, the coincidence is switched off immediately when the search is continued, thus avoiding stopping on the sound carrier .

In the event that you only have circuitry on transmitters with a bes ^f '.nmter. If the minimum field strength is to respond, it is very advantageous, for example, to remove the synchronizing pulses from a separate amplitude sieve that is dependent on the threshold value.

1 sheet of drawings

Claims (4)

It is also known that the stop signal required for a station search can be obtained from the sync pulses taken from a separation stage - H μ. Here- 1. Circuit arrangement for a station search with the ^^^ Ζ ^^ Άΐ automatic running in television receivers, at 5 level one looked up ^et ^ j ^ * f "f ** ^r with the help of the separated on an impulse sieve this «· / ^" ^ «J ™» « <** ^ ^ Qth sync impulses will also produce an identification signal that will interfere with the image. An integration circuit can switch a non-frequency-matched discriminator, between noise impulses, a disturbing noise, the further rise of a beat signal, which is created by sawtooth-shaped chip-desired mixing products not used by the tuner, and which stops the synchronization, characterized in that differentiate chronsignal. that the identification signal by means of a coincidence stage. The object of the invention is * "g ™ nde, Rx ₁ den is generated, deTdifferentiated Zeflenrücklauf in the electrical SucU emes television receiver pulse are fed and at the output of a 15 stop signal by means of a suitable circuit-rectifier arrangement (11, 12) is intended to establish order, giving way to the familiar which avoids a tip alignment of the parts. ...., output voltage takes place. This task is achieved according to the invention 2. Circuit arrangement according to claim 1, that solves that the identification signal by means of a coincidence characterized in that the identification signal ao stage is generated, the differentiated line return run Base of a switching transistor (15) are supplied pulses are supplied and at the output of a is, which is provided between the discriminator (16) and rectifier arrangement, via the one Mass is arranged. Peak rectification of the output voltage takes place. 3. Circuit arrangement according to claim 1 Another technical embodiment of the invention and 2, characterized in that the synonym consists in that the identification signal of the Bachron impulses (S) is supplied via a differentiating element (2, 3, sis of a switching transistor, which is between 4) are fed to the coincidence stage. the discriminator and ground is arranged. 4. Circuit arrangement according to claim 1, the advantages achieved by the invention exist to 3, dadi_ch characterized in that the synchronous in particular that the circuit arrangement pulses a separate, with a predetermined 30 is largely insensitive to interfering signals. A The amplitude stop signal provided with a threshold voltage occurs only when the frequency sieve is fulfilled are taken. and phase condition. In addition, the Noise and interference spectrum present on the amplitude filter only during the line return pulse 35 a signal is taken. This reduces the Duration of influence of the interference signals compared to known ones