DK147120B - TELEVISION RECEIVER FOR MULTIPLE OPERATING FORMS - Google Patents

Description

147120 in o

The invention relates to a television receiver of the kind specified in the preamble of the claim.

Television receivers have found widespread use in entertainment, education, industry as well as in other 5 areas. In many places, besides the well-known state television stations, there are other stations whose primary task is to broadcast educational programs and information.

The television receivers used in these 10 special areas must preferably be able to reproduce these broadcast programs as well as pre-recorded programs in order to be universally adapted. Furthermore, certain educational facilities have camera equipment, whereby a lecture or other event can be broadcast locally on television and conducted 15 to a number of other places through a cable system. As can be seen, the signals that such a receiver must be able to respond to are fundamentally very different.

Basically, the biggest differences are the following. In the case of radio frequency broadcast, the video information is modulated on a carrier to be received, amplified, converted to an intermediate frequency signal, amplified and then detected. When using a tape recorder or camera, such a signal is a common video signal that is not superimposed on a carrier. During radio transmission, various interference can affect the signal prior to the demodulation of the desired video signal. Such influences are frequency- or phase-dependent, and consequently special care must be taken in the receiver construction to provide an optimal display. In the case of 30 color broadcasts, such disturbances are even more pronounced and consequently result in special design specifications for the color receiver. Many of these considerations include the optimization of medium frequency amplifiers, radio frequency amplifiers, special height raising and delay measures in the receiver's respective chrominance and luminance channels.

2

ISLAND

When a television signal is not modulated on a carrier, but constitutes the video signal itself, similar to what the receiver would normally achieve in the demodulation process, such a signal may conceivably be input directly into the first video amplifier stage or into the video amplifier chain. However, if the receiver is also to be capable of working with a radio frequency carrier signal, the introduction of such a signal cannot be obtained immediately without taking into account the difference between the "direct" signal and the video signal derived from the radio frequency signal. Such differences must be offset in a receiver compatible with a transmitted radio frequency signal and with video signals extracted directly from other sources, such as bands.

Accordingly, it is an object of the invention to provide the design of a television receiver of the kind specified in the preamble of the claim adapted to optimally receive radio frequency transmitted video signals as well as video signals provided from a tape recorder, a television camera or another suitable video signal source.

The stated object is achieved by a receiver which according to the invention is peculiar to the design and arrangement of the claim.

At the first position of the switch, the receiver is able to receive video signals that are not modulated on a carrier, ie. in the state they are output from VCRs or other video signal sources as discussed above. In this position of the switch, the 30 bias controlled second video amplifier which receives its non-modulated video signals with its output through its switch through the first sub-section of the switch is connected to the input of the usual video amplifier of the receiver which in this first position of the switch does not receive 35 some demodulated video signal from the signal processing and detection circuit as its power supply is interrupted

ISLAND

3 147120 of the third section of the switch. At the same time, the amplification of the other video amplifier is controlled by the DC amplifier whose input through the second sub-section of the switch is connected to the output of the AGC circuit, so that the "direct" video signal is also subjected to an automatic gain control or AGC function. By appropriate selection of parameters in the amplifiers included in the additional set of means, or by inserting appropriate transfer or filter circuits between them, the "direct" video signal may be affected separately in a manner suitable for receiving by the usual video amplifier of the receiver and to be processed by it to produce image signals similar to that obtained by receiving radio frequency transmitted video signals in the normal manner without further adjustment being required.

When the switch is in the second position, the receiver is substantially in the same state as before the modification according to the invention, and can thus receive radio frequency transmitted video signals in the normal manner.

The switch may be provided with additional positions and connected with appropriate circuits to establish the necessary internal connections for e.g. transmitting the video signal from a transmission 25 received on a radio frequency carrier to a VCR.

The invention will now be explained in more detail with reference to the exemplary embodiments of a television receiver according to the invention and parts thereof shown in the drawing, in which: FIG. 1 is a schematic block diagram of a remote vision receiver utilizing an amplifier controlled from the receiver's AGC circuit; FIG. 2 is a block diagram showing a color television receiver adapted to respond to both external video signals and video signals modulated on a radio frequency carrier; FIG. 3 is a detailed schematic diagram, partly in block form, of a color television receiver adapted to receive and record radio frequency transmitted signals and to work directly with external video signals; and FIG. 4 is a schematic diagram of a horizontal oscillator and phase detector which can be used in a receiver according to the invention.

In the state of the television receiver in which it is adapted to receive video information that is not modulated on a carrier, it is desirable to input the video signal directly into the receiver's video amplifier. Preferably, the magnitude of the input signal must be at a level approximately equal to the level that would exist at the input point when the receiver operates with a radio frequency transmitted signal. Eg. in a receiver using electron tubes, it will be desirable to input the signal at the grating or cathode of the first amplifier stage. The first video amplifier step used is the step or steps immediately following the video detector. The receiver's automatic gain control or AGC circuit, usually operated by this amplifier, will receive a signal similar to that sent to the AGC circuit by normal receiver operation. In normal receiver operation with a radio frequency transmit signal, the AGC circuit serves to set the gain of the tuner and the intermediate frequency to bring the level of the instant horizontal synchronization peak to a predetermined level regardless of the strength of the antenna signal. AGC is a common feature that can be provided by a typical television receiver to bring it to perform best on all channels and under all signal propagation conditions. When the receiver does not process an RF signal, the AGC control circuit is used in conjunction with other video sources such as tapes, television cameras, etc.

5 147120

ISLAND

In FIG. 1 shows an antenna 10 capable of receiving RF transmitted television signals and directing them to the input of a tuner, MF amplifier and video detector module 11. The radio frequency signal is amplified by the tuner, converted to a lower frequency MF signal and detected to provide a demodulated signal at the output of the video detector. Such features are extremely well known and embedded in the bottle of color and black and white receivers.

The output of the video detector is conventionally fed to a video amplifier chain 12, and is passed from there to an image tube 14. The image tube 14 is also connected to suitable circuits as a whole shown as a module 15.

The module 15 has an input terminal connected to the video amplifier 12. The module 15 provides deflection signals 15 and working potentials which enable the formation of a screen on the front of the picture tube 14.

Most receivers contain, as indicated, an ON / OFF controlled AGC circuit 16, the function of which is to create sufficient control of the tuner and MF gain 20 to bring the instant synchronization level to a predetermined value regardless of the antenna signal strength . The automatic gain control (AGC) is largely of the ON / OFF controlled nature and provides a control voltage proportional to the magnitude of the video signal at some point of the video amplifier chain. The control voltage is applied to the RF amplifiers or tuners and the MF amplifiers to increase their gain by decreasing antenna size signals or to decrease the gain of growing signals. In this way, the portion of the signal amplitude carrying the synchronization is kept relatively constant in the receiver and independent of the channel on which it is tuned, or of the normally expected signals of different size received at the antenna 10.

Accordingly, the AGC function of a receiver is relatively important to ensure optimal display over a wide range of signal amplitude variations.

ISLAND

6 U7120

FIG. 1 further shows a switch 20 having three contacts connected to a tape recorder 21, a television camera 22 and another video source 23. The arm 20 of the switch 20 is connected to a potentiometer 24.

5 The adjustable outlet of the potentiometer 24 is alternately connected through the capacitor 25 to the input of a DC coupled video amplifier 26 having an output terminal connected to the arm of an operating selector switch 27. A switch of the switch 27 is connected to an input of a video amplifier 12. other contact removes this connection. The input of the DC coupled amplifier 26 is also connected through a resistor 29 to the output of another DC amplifier 30, referred to as a polarity DC amplifier. The input of amplifier 15 30 is connected through another section 31 of the operating mode selector switch 27 to the output of the receiver ON / OFF controlled AGC circuit 16. An additional contact 32 of the operating start selector 27 removes the B + from the module 11 to insert the tuner contained therein , MF amplifier and video detector 20 out of function. FIG. 1 shows the contacts mentioned above with the operating start selector switch 27 set for video signal input setup. The switch 20 is connected to the output terminal of a tape recorder 21, the signal of which thus appears over the potentiometer 24. The potentiometer 25 24 acts to provide input level setting and is necessary for adaptation to the various expected levels of tape recorders, cameras and other video sources. With the one shown in FIG. 1, i.e. the operating selector switch 27 set in video signal input 30, the function of the receiver is as follows.

The tuner, MF amplifier and video detector module 11 is disabled by being switched off B + and consequently no signal due to RF broadcasts can be applied to the video amplifier 12. The tape machine 21 has e.g.

35 its output terminal connected to the input terminal of the DC coupled video amplifier 26. The video amplifier 26 η 147120 ο amplifies the playback signals of the tape machine to an appropriate level and passes them over the switch 27 to an early stage of the video amplifier 12. Video amplifier 12 or amplifier 12 26 5 is preferably the step of controlling the synchronization and AGC circuits. In this way, the receiver operates in the usual manner after the introduction of the tape recorder signal. However, the signal emanating from a tape, television camera or other video source may vary in amplitude by the peculiarities of the particular source. Correct adjustment of the potentiometer 24 is therefore important in order to obtain a correct display, as is the case with the RF transmission.

The ON / OFF controlled AGC circuit 16 is connected through the switch section 31 to the DC polarity amplifier 30 which through its resistor 29 has its output terminal connected to the input terminal of the amplifier 26. The control voltage of the AGC circuit 16 amplified by the polarity amplifier 30 used for biasing the input of the 20 DC coupled amplifier 26 through the resistor 29. The polarity of the applied signal provides for coupling of the amplifier 26, while the DC coupled amplifier 30 provides sufficient gain to bring the instantaneous horizontal synchronization peak level, as described above, 25 as to remain at the same predetermined value.

As shown in FIG. 1, the receiver's AGC circuit 16 thus becomes part of the automatic bias loop when the receiver is set to receive a "direct" video signal. The advantages of this particular system are that the operating point of the amplifier 12 is the same as in normal operation, such as when receiving a transmitted RF signal. This causes slight luminance change in operating mode switching between the various external video signal sources and the RF transmission. Furthermore, in practice all critical operating conditions imposed on the video amplifier 12's working point can be disregarded, since the amplifier operates in substantially the same way as in the nominal mode of operation determined by the RF broadcast. Also, maintaining the synchronization peak at a fixed level due to the automatic gain control function provides effective DC voltage recovery of the signal transmitted to the image tube. This therefore gives the viewer an optimum clear picture.

In short, the receiver's own AGC circuit 16, 10, which normally operates on the tuner and the MF amplifiers, is advantageously used when the receiver is used to display "direct" video signals as described above. Therefore, the use of the ON / OFF controlled AGC circuit 16 in the manner described above serves to retain all of the advantages of the automatic gain control (AGC) needed when working with "direct" video signal sources, such as tape recorders, cameras, etc., while further ensuring that the television receiver operates as intended, without essential changes to the internal receiver parameters. This enables the receiver to function essentially as intended for RF broadcasts by simply switching it to FIG. 1, the operating mode selector switch 27 shown in the position indicated by dashed lines.

It should be noted that the use of the AGC circuit mentioned above can be utilized either in a black and white or color receiver.

In FIG. 2, there is shown a schematic block diagram of a color television receiver which can be adapted for receiving RF broadcast programs as well as for receiving "direct" 30 video signals originating from other sources, such as a television camera, a tape playback machine 21 or other video source 23 .

In short, in the embodiment of FIG. 2 the same AGC principle as described in connection with FIG. 1, and thus similar components performing the same functions have the same reference numerals. First

ISLAND

And, most importantly, the color receiver differs from the black and white receiver at the chrominance processing channel, which in the basic features comprises a chrominance amplifier 40. which consists of one or more steps of selective bandpass amplifiers, the transmission characteristic of which is centered within the chrominance subcarrier signal range. A burst signal separator 41 ON / OFF is controlled by a pulse taken from the horizontal synchronization circuits 15, which controls the separator 41 to conduct, at its output, to create an amplified version of the oscillating burst signal emitted during a color broadcast. The output of the burst signal separator 41 is connected to a chrominance oscillator 42, the output of which is phase synchronized with the burst signal and determines the chrominance subcarrier frequency 15 necessary to demodulate the chraninance sideband signals. Accordingly, one output of the chrominance oscillator 42 is connected to one input of the chrominance demodulator 43, and another input signal to the demodulator 43 is obtained from the chrominance amplifier 40. The output of the demodulator 43 is connected to appropriate electrodes in the color image tube 45 which may be a shadow mask tube. electron guns.

An automatic chrominance control and color extinguisher detector 46 has an input connected to oscillator 42 and largely serves to keep the amplitude of the burst signal at the output of chrominance amplifier 40 relatively constant despite variations in the signals supplied to the antenna. This effect is commonly referred to as automatic color regulation and, as such, serves as a supplement to the automatic gain control 30 (AGC) of the higher frequency chrominance components which are subject to selective attenuation due to changes in transmission path length and other. Another effect of the automatic chrominance control and color extinguisher detector 46 is switching off chrominance amplifier 35 40 during black and white broadcast to prevent false signals from deteriorating the image. The module described above is well known and is found in most conventional color receivers.

147120 In FIG. 2 is also shown a delay line 47 in the luminance channel. Such a delay line 47 is commonly referred to in the art as a luminance delay line and exists in a color receiver to compensate 5 for the delay to which the chrominance signals are subjected when processed by the narrow band chrominance amplifier, as opposed to the relatively small delay, they are amplified by the broadband amplifier 12. It is therefore the task of the delay line 10 to delay the luminance signals so that they arrive at the cathode of the image tube 45 at the same time as the associated chrominance signals arrive at the grids. When the receiver is operating in the video mode, such as mentioned with reference to FIG. 1, B + is removed from the MF amplifier 15 contained in module 11 through switch section 32.

The switch section 32 may be a suitable disk section or switch on the operating mode selector switch 27. The receiver can now process video signals that are input directly into the video amplifier.

However, the removal of the MF amplifier effect in the above-mentioned manner results in an interesting phenomenon, namely that the delay produced by the delay line 47 is now too long and that the chrominance signals with this delay when used in a conventional 25 receiver, therefore, will arrive at the image tube grids before the associated luminance signals arrive at the cathodes. Accordingly, it has been found that to use a conventional receiver both for signals transmitted through space on a carrier and for video signals received directly from a suitable source such as tapes or cameras, the delay produced by the luminance delay line must be reduced. to the video drive mode. The receiver therefore has a contact 48 mechanically connected to the operating mode selector switch 27, which short-circuits a portion of the delay line 46 when the receiver is used for displaying "direct" video signals from color image tapes or other sources.

11 147-120 o In FIG. 3 is a partial schematic diagram of a typical commercially available color television receiver which can be used with both RF transmitted signals and "direct" video signals from other 5 sources.

An antenna 49 is connected to the input of a radio frequency tuner 50 which at its output provides a signal which is fed to the MF amplifier 51. The MF amplifier 51 has an output terminal connected to the input terminal of 10 a video detector 52 and to the audio portion 54 of a television receiver. The output of the video detector 52 is usually directly connected to the input of a suitable video amplifier.

In this particular case, the video amplifier contains a first amplifier step 56 containing a pentode.

The anode of the pentode is connected to the lattice in an amplifier trio 57 having anode and cathode loads to operate synchronization and AGC circuits and luminance channel, respectively.

The anode of the triode 57 is connected to an input of the synchronizer separator 61 and to the input electrode of an ON / OFF controlled AGC pentode 60 through a resistor 62.

The pentode 60 ON / OFF is controlled by a positive impulse supplied through the capacitor 63, which is connected between the anode of the pentode 60 and the deflection drive and output circuit module 64. The ON / OFF controlled pentode 60 produces at its anode control voltage proportional to the magnitude of the synchronization peak level of the signal supplied to the grid. The anode load contains appropriate RC filter networks for filtering the control voltage before passing it to the RF and MF amplifiers. The deflection drive and output circuit module 64 includes the vertical and horizontal output circuits comprising the return transformer and the various high voltage circuits normally found in a conventional receiver.

Accordingly, two output lines from module 64, designated X and Y, are shown to provide horizontal and vertical deflection waveforms for use with the yoke 66 associated with the image tube 67, which may be a shadow mask tube with three electron guns.

The drive signals for the deflection circuits are extracted from the horizontal oscillator 68 and the vertical oscillator 69 synchronized by the synchronizer separator 61. Generally, in such a chrominance processing circuitry, the and the color extinguisher of the first video amplifier 56, whose anode is AC coupled to the processed circuit 70 by a capacitor 71. The chrominance processing circuit outputs are connected to the chrominance demodulator circuit 72 to provide color difference signals suitable for use in image through the chrominance drive circuits 73. The output of the video amplifier triode is during normal receiver operation through switch switch 74, delay line 20 and then switch 20 75 connected to the input of a further luminance delay line 76. The cutter line 76 has an output terminal connected to the input terminal of a video amplifier 77. Amplifier 77 drives through a suitable network 78 the cathodes of image tube 77 with the relatively broadband 25 luminance signals. The delay lines 120 and 76 are selected to ensure that the luminance signals, when amplified by the broadband amplifier, arrive at the cathodes of the image tube 67 approximately simultaneously with the arrival of the corresponding chrominance signals to the image tube grids. It is noted that the receiver, with the exception of the switch contacts 74 and 76 and the split delay lines 120 and 76 briefly discussed above, is of a conventional nature.

The additional circuitry contained in this receiver which adapts it to work with "direct" video signals, such as those emitted by a tape recorder or camera, will now be described in more detail.

0 147120 13

The aforementioned switch contacts 74 and 75 are switches on the same switch which control other contacts, such as 80, 81, 82, 83 and 84. Each of the contacts listed above is designed as single-pole correspondence switches, although other suitable switching devices may be used. In FIG. 3, a switching function is shown schematically showing that the receiver responds conventionally to an RF transmission when the switching contacts 74, 75 and 80 to 84 are placed in the position shown by the dotted line or upwards. When the switch switches are positioned in the position shown in the figure, the receiver responds to a "direct" video signal supplied from a source as indicated above.

For the purposes of FIG. 3, the above contact is placed in the position corresponding to the use of the receiver with "direct" video signals as shown. A video signal source is connected to a connector 86 having a terminal connected to a potentiometer 87. The potentiometer 87 enables an input level setting to enable the user to set the size of the signal 20 fed to the receiver. The adjustable output of the potentiometer 87 is connected through a capacitor 88 to the base of an amplifier transistor 89. The transistor 89 is connected in an emitter follower array and its collector is connected through a current limiting resistor 90 25 to a working voltage source designated as + V. The collector is decoupled for AC signals by a capacitor 91. A biasing network for transistor 89 contains resistors 92 and 93 which are connected between the + Vcc supply and the transistor base.

The emitter of transistor 89 is connected to the reference potential point through a load resistor 94 and is connected through a self-induction 95 to the base of an amplifier transistor 96.

147120 14 0

The transistor 96 is arranged in an emitter grounded arrangement and has a collector load consisting of a resistor 99 in series with a shunt height uplift 100 connected between the + V supply and the collector.

CG

The self-induction 95, connected between the emitter of transistor 89 and base of transistor 96, is series resonant with capacitor 101. Capacitor 101 is connected in series with a Q attenuation resistor 102 between base of transistor 96 and ground. The self-induction 95, capacitor 10 101 and resistor 102 form a bresonance circuit with small Q, and act as a medium frequency amplifier simulator circuit for the chrominance subcarrier signal components. The collector of transistor 96 is connected to the base of amplifier transistor 105 having its emitter connected to the 15 + Vcc supply through series resistors 106 and 107. A decoupling capacitor 108 is connected between the junction of resistors 106 and 107 and a point of reference potential.

The collector of the amplifier transistor 105 is connected through a resistor 109 at a point with the reference potential and directly connected to the arm of the switch 83, as shown in the "direct" video position. The switch 83 couples the collector of transistor 105 to the cathode of the first video amplifier, the pentode 56. This coupling 25 sets the video signal amplified by the former. said step, capable of being inserted directly into the cathode of the first video amplifier 56. It is also noted that in the "direct" video position, the switch 80 serves to remove the B + from the MF amplifier 51. This sets the front circuit of the receiver out of function, thereby preventing any radio frequency signal from being processed under the "direct" video mode. The pentode 56 amplifies the inserted cathode signal to produce at its anode the amplified video signals which would normally have been produced thereon by an RF transmission. The effect of the aforementioned self-induction 95 in conjunction with capacitor 101 further serves to act on the video signal supplied from the external source to intentionally affect this signal as it would have been affected if it were produced by demodulation. of a 5 MF signal.

To achieve this, the resonant peak of the serial network 95, 101 with small Q is selected around 3.08 MHz or slightly lower. This allows the chrominance sideband frequencies to be amplified on the inclined portion of the circuit band pass. In essence, if the radio frequency signal were transmitted, the chrominance sideband frequencies would be amplified by the MF amplifier at the same location with relatively the same slope on the MF amplifier's bandpass curve.

Therefore, the intention of the series resonant circuit 95, 101 with the small Q is intentionally to distort an optimal NTSC signal, in which the amplitudes of the chrominance and luminance components of the signal are relatively uniform and have not undergone any distortion due to propagation or due to the MF. and RF amplification.

Many of the circuits in a receiver are specially adapted to the radio frequency propagating signals. Examples of such circuit adaptations are RF and MF stage bandpass characteristics, etc. Considering these factors, the optimum NTSC signal must be distorted prior to insertion into the receiver's video amplifier to enable the receiver to respond in a conventional manner.

The amplified signal on the anode of pentode 56 is now routed in the usual way to the chrominance processing circuit 70 through capacitor 71 and thus to the remainder 30 of the chrominance circuit shown, to provide the image tube 67 with proper color drive signals. It is seen that as far as the chrominance processing channel is concerned, there is no difference between these "direct" signals and the signals it would receive if an RF broadcast occurred. The Chrominans-35 elevation networks conventionally found in such a receiver still serve to elevate the chrominance signal prior to insertion into the demodulator to anticipate

ISLAND

The decay of the chrominance components as a result of the MF frequency, etc. The chrominance elevation network networks do not need to be altered or affected because the video signals are intentionally distorted by the effect of self-induction 95 and capacitor 101 as described above.

The amplified video signal on the anode of the pentode 56 is fed to the grid of the amplifier trio 57. The amplified signal occurring at the anode of the trio 57 is, of course, still connected to the ON / OFF controlled AGC circuit paddle 60 through the resistor 62 and with synchronizing separator circuit 61. In this way, horizontal and vertical oscillator circuits 68 and 69 and deflection drive and output circuits 64 receive the same signals that would be received during normal broadcasting, and thus serve to provide the necessary potentials and deflection waveforms to produce raster. However, the AGC circuit, which is normally connected to the tuner and the MF amplifier, does not operate these modules as they are disabled due to the removal of B +, e.g. from the 20 MF amplifier 51.

However, the anode in the pentode 60 is connected through the resistors 108, 109 and 110 to the cathode of a diode 111, the anode of which is connected to the base of an amplifier transistor 112. The transistor 112 has its emitter connected to ground and the collector connected to the junction between the resistors 92 and 93 forming part of the base biasing network of transistor 89. The cathode of diode 111 and base of transistor 112 are also connected through a resistor 114 to switch 84 which, during the "direct" video mode, imposes a voltage referred to as + V1, through resistor 116, thereby biasing transistor 112 and diode 111 in the conducting direction. In this way, with the diode 111 biased in the conductor direction, the AGC variations occurring across the resistor 110 in the anode 35 circuit of the pentode 60 serve to modulate or vary the bias of the transistor 112. Transistor 112, depending on its line, serves to vary the current through transistor 89 by affecting the base current. Accordingly, changes in the collector current through transistor 89 serve to change the operating voltage at the base of transistor 96. Transistor 5 112 also serves to reverse the polarity of the variations applied to its base to ensure that the automatic biasing effect is in the proper phase in relative to the number of steps used to amplify the "direct" video signal.

The function is as follows: If the DC level of the signal at the base of the transistor 89 becomes too positive, then the DC level of the signal input at the cathode of the first video amplifier stage 56 is also too positive, and consequently the amplified DC level at the anode of the pentode 56 is positive. Thus, the AGC control pentode 60 receives at the grid a video signal with a DC level which does not allow conduction. Therefore, in this mode of operation, transistor 112 conducts more powerfully. Thus, the increased conduit of transistor 112 reduces the DC voltage applied to the base of transistor 89. In this way, the DC level of the signal fed to the transistor 96 decreases, as does the DC level of the signal appearing at the transistor 105's collector, which is fed to the cathode of the pentode 56. Thus, the effect decreases the DC voltage level at the anode of pentode 56. This, therefore, serves to keep the video signal level at the anode of pentode 56 approximately equal to the level that would occur thereon upon receiving a normal RF transmission, thus enabling the AGC circuit to conduct and maintain the video amplifier bias and operating points. relatively constant and under AGC controlled operation.

The trio 57 serves through its cathode to drive the luminance delay line 76 through the switches 74 and 75, if two identical contacts are connected to each other.

It is noted that the other contacts of switches 74 and 75 are connected to each other through a delay line portion 120 when the switch, when moving the switch arms,

ISLAND

18 147Ϊ20 is up in the RF broadcast operating position. Therefore, as previously mentioned, the delay line 120 and the delay line 76 are arranged one after the other to obtain a longer delay for the luminance channel during the RF broadcast than the delay in processing the "direct" video signal. If the same delay was used for the RF appearance as for the "direct" video mode, the luminance signals would arrive at the cathode of the picture frame after the corresponding chrominance signals had arrived at the respective grids under the "direct" video mode. of this delay control is due to the fact that the MF amplifiers and RF amplifiers are removed from the circuit and consequently cannot serve to delay the chrominance components of the composite signal 15 differently than the luminance components of this signal, therefore the chrominance components, upon receiving a normal RF transmission, when occurring at the anode of pentode 56, substantially a further delay over the luminance components due to the receiver processing circuits before being fed to the chrominance processing circuit 70. This additional delay does not necessarily occur when signals from other sources are used.

The switch 81 creates another useful function that is used when working with tape signals or other "direct" video signals. The switch 81 supplies the accompanying audio portion of the "direct" signal which may be recorded on a separate tape track or may be emitted from a suitable audio amplifier circuit from a preamplifier.

121, which has an output terminal connected to switch 30g thus through the switch 81's am with the audio portion 54 of the television receiver. Such a connection can be formed through the receiver's strength and tone control. The audio signal applied is bypassed by the audio demodulators as the external audio signal in conjunction with the external video signal 35 appears in its original form. In this way, the video signal can be displayed on the picture tube while passing the audio signal through the receiver's speaker system to give the viewer a normal view.

ISLAND

147120 19

A further contact 82 is shown having an arm connected to ground and the two contacts connected to the arm connected to the horizontal oscillator module 68.

A resistor 123 is shown in series with the switch in switch 5 82 in the receiver's RF broadcast working position. The other contacts corresponding to the external video position are shown to be largely connected directly to the oscillator 68.

Essentially, the function of the switch 62 is followed. During normal receiver operation, the horizontal oscillator 10 68 is synchronized by the synchronization pulses extracted from the synchronizer separator 61. A phase detector acts to induce a control voltage in accordance with the phase difference of the synchronization pulse control pulse 15 and the phase difference. the horizontal oscillator 68 to make sure it locks to the correct phase. The output of the phase detector is pre-filtered to prevent noise and other components from incorrectly affecting the control voltage and pulling the oscillator 68 out of frequency. A normal receiver operating mode requires a narrow bandpass filter for the control voltage before it is applied to the oscillator circuit. This is necessary due to the expected lower signal / noise levels in the receiver when working with an RF transmission.

However, it results in problems when maintaining "direct" video signal sources as described above, especially from bands, this degree of filtering is maintained prior to the application of the control voltage to the oscillator. A typical form of tape recorder which can be adapted to record and reproduce video signals containing composite signals needed for color broadcasting can use a helical scan for recording and playing video information using a number of magnet heads, usually two.

In the typical case, two heads are 180 ° 35 apart on a main drum. As one head leaves the belt, the other head slides into the belt to complete

ISLAND

147120 20 reproduction or recording of video information. Due to mechanical tolerances in the recorder and alignment of the heads, etc., the width of the horizontal synchronization pulses can be affected. The problem arises in that a head entering the band may begin to reproduce the horizontal synchronization pulse in a different phase than the head just leaving the band. The ELitration network provided for the phase detector during an RF broadcast is arranged in accordance with an expected noise level 10 in connection with the incoming video signal. Therefore, the filtration network will undesirably slow down the reaction rate of the phase detector output more than is desirable and necessary for adaptation to the phase disturbances present in a playback signal.

Thus, the degree of filtration must be decreased after the phase detector.

Accordingly, the switch 82 serves to decrease the degree of effective filtering under the "direct" video signal mode to allow the phase detector associated with the horizontal oscillator 68 to respond 20 to the variations that may occur in the phase of the horizontal synchronization pulse during a band display. Increasing the filter band pass thereby enables the receiver in the video operation position to follow such transitions more quickly, and consequently maintain the phase synchronization of the horizontal oscillator 68 despite distortions following the horizontal synchronization pulses.

By summarizing the above description, it can be seen how the receiver must be changed to adapt the various signal sources to create the optimum display, independent of the means for producing the video signal.

In such a universally acting receiver, there is another feature which enables the user to record programs received by the receiver when it operates with radio frequency transmitted signals on tape. As . above, when a radio frequency broadcast is desired to be received, the switches 74, 75, and 80-84 in the position shown by the dashed line or move its arms upward.

In FIG. 3, it is seen that cathode in trio 57 is connected 5 to the input or base of amplifier transistor 125.

Connected between the cathode of the trio 57 and a point of reference potential is a selective network comprising a resistor 126 in series with the cathode of the trio 57 and the base of the transistor 125. A resistor 127 in series with a self-induction 128 is connected between the base of transistor 125 and a point of reference potential and serves as a voltage divider for supplying bias to transistor 125. A high frequency compensation selective network consists of a capacitor 124 in series with a resistors 130 and 15 are parallel to resistor 127 and capacitor 132. Self-induction 128 is parallel to capacitor 131 and resonates therewith at the end of the composite signals having the highest frequency or near the frequency range being recorded. of the chrominance subcarrier-20 components.

The resonant circuit described above comprises, in the basic features, an elevation network to elevate the chrominance sub-wave components of the composite signal occurring at the cathode of the trio 57, so as to compensate for the attenuation such components are subjected to during processing by the MF and RF amplifiers. .

In this way, the amplitude distribution in the signal that is based on the transistor 125 approaches substantially the conventional NTSC signal. Transistor 125 is positioned 30 in an emitter ground array with a collector load resistor 135 and an emitter coupling resistor 136. A delay line 138 is connected between the collector of transistor 125 and base of transistor 139. The function of delay line 138 is to provide a differential delay of approx. 0.2 microseconds between the luminance and chrominance components.

0

It is recalled that in describing the playback circuit, a second delay in the luminance channel was required at the "direct" video drive. This was due to the omission of the RF and MF amplifiers, which also caused a differential delay of approx. 0.2 microseconds between the chrominance and luminance components as opposed to the delay between the components when processed through the RF and MF steps. Accordingly, in order to provide a recorder with signals to be recorded on tape, the differential delay of 0.2 microseconds between the chrominance and luminance components caused by the video detector by the effect of the RF and MF stages must be offset. This is the purpose of delay line 138 so that the signal recorded on the tape again corresponds to the conventional NTSC signal in which there is no significant differential delay between the luminance and chrominance components.

Amplifier transistor 139 serves to amplify the composite signal passed to its base, and carries the amplified signal to base in a subsequent amplifier transistor 140 which is also located in an emitter grounded array. Furthermore, transistor 140 acts to amplify the composite signal to a level appropriate for supply to the input terminal of a buffer amplifier stage with a transistor 145. Buffer transistor 145 25 has its collector connected to ground through a load resistor 146 and has its emitter connected to + V supply through a counterconnection resistor 147. The composite video signal is connected through a large capacitor 148 to a video recording output socket 150. The output socket 30 150 may be connected to the video terminal of a tape recorder by means of a video cable or other conventional means for recording the video signal. recording medium.

The receiver with the additional circuit described above can be used to record, by means of a tape recorder, transmitted radio frequency signals duly demodulated to video signals by ordinary reception function.

23 14712α ο

It is noted that the audio receiver portion of the television is connected through the switch 81 in the position shown by the dotted line, after demodulation by means of the receiver's audio demulator, to pass the audio signal to the output amplifier transistor 155. Transistor 155 is placed in an emitter follower array and its emitter is through a capacitor 156 connected to a suitable output socket 157 designated as audio recording output. This enables the user to record the audio portion together with the video portion of a suitable recording and playback apparatus, such as a screwdriver.

In FIG. 4 shows a horizontal oscillator circuit.

The horizontal oscillator circuit contains a triode 150, the lattice of which is connected to a horizontal phase detector-15 circuit containing two diodes 151 and 152. The horizontal synchronization pulse from synchronizer separator 61 is passed through capacitor 153 to the junction of diodes 151 and 152. The horizontal oscillator signal is passed through a capacitor 180 to the anode 20 of the diode 151. A capacitor 181 serves to divide the signal amplitude to achieve a proper level. The diodes at their output provide an AC voltage proportional to the phase difference between the horizontal synchronization pulses and the oscillator signal.

The control voltage is passed through the resistor 157 to the grid of the trio 150. Filtering is provided at the grid of the trio 150 by means of a capacitor 158 which is connected between the grid and the point of reference potential and the selective RC network consisting of a capacitor 160 of series with a resistor 161 connected in parallel with capacitor 158. The amplified control voltage occurring between the anode and cathode of the trio 150 is applied through a potentiometer 163 in series with a resistor 164 of the horizontal oscillator circuit containing the triode 165. The resistors 163 and 164 are connected between the cathode of the trio 150 and the lattice of the trio 165. The triode 147120 24 0 165 is contained in the horizontal oscillator portion, which serves to provide feedback between the anode and lattice of the triode through a self-inducting 168 and a capacitor 170. The control voltage applied to the lattice through the potentiometer 163 serves to synchronize the horizontal oscillator in phase with the horizontal synchronization pulses.

A tuned circuit comprising a self-induction 127 in parallel with a capacitor 178 is disposed between the cathode 10 of the oscillator trio 165 and ground. The tuned circuit's function is to allow normal receiver function to provide a sinusoidal voltage with the horizontal oscillator frequency, which again limits the oscillator's control range and helps to maintain the horizontal frequency within narrow tolerances by providing a relatively narrow bandpass for the RF. broadcast operating mode.

When the receiver operates in the "direct" or external video operating position as described in connection with FIG. 3, the contact 82 in the embodiment of FIG. 4 and serves to remove the resistor 133 in series with the resistor 161, which again serves to reduce the filter effect and allow faster changes in the control voltage to be applied to the grid of the trio 150. At the same time, the switch 82 in the shown position serves to bypass the tuned circuit consisting of self-induction 177 and capacitor 178 by connecting the cathode of oscillator 155 to ground.

This in turn widens the effective band pass of the oscillator, and enables the oscillator to be controlled over wider control voltage ranges with steeper or faster changes from one control level to another. Therefore, in the "direct" video position, the oscillator can change phase and frequency much more rapidly with incoming control information from the phase detector to enable it to follow the relatively rapid interference that may occur during a band playback in the phase of the horizontal synchronization pulses.

O When the switch 82 is in the RF broadcast position, the resistor 123 acts in parallel with the resistor 161 and thus serves to lower the resistance of the combination and to provide a stronger attenuation of the control signal for higher frequencies at the grid of the trio 150. In this mode of operation, the parallel resonant circuit connected to the cathode of the trio 165 is also contained within the circuit and serves to narrow the control range of the horizontal qscillator.

As an example, below is a table of coraponent-10 values for use in the FIG. 3. Data on components not included in the table are given in the figure.

Resistance 87 3500 ohms 90 10 ohms 15 92 5600 ohms 93 5600 ohms 94 3300 ohms 99 1500 ohms 102 330 ohms 20 106 82 ohms 107 18 ohms 109 220 ohms 126 750 ohms 127 270 ohms 25 130 180 ohms 135 820 ohms 136 330 ohms 146 82 ohm 147 39 ohm 30 Capacitor 88 25 µΕ 91 0.01 µΡ

101 39 pF

108 2200 pF

124 560 pF

35 1 3 1 4 7 0 pF

132 330 pF

148 500 µF

147120 26 0

Self-reduction (variable) 95 For resonance with capacitor 101 at approx.

2.5-3.1 MHz.

100 120 μΚ 5 128 For resonance with capacitor 131 at approx.

(variable) 4-4.5 MHz

Transistor 89 2N3694 96 2N3694 105 2N3644 10 112 2N3694 125 2N3694 139 2N3644 140 2N3694 145 2N3644 15 155 2N3694

Diode 111 Silicon diode such as FD222

Claims (1)

147120 0 PATENT REQUIREMENTS. A television receiver for several modes of operation and of the kind comprising a) means (10) for receiving a radio frequency carrier modulated with a first video signal and directing it to a processing and detection circuit (11) in which the video signal is extracted from the thus modulated (b) a first video amplifier (12) adapted to receive the first video signal thus extracted, process it and transmit it to a display means (14), and (c) an automatic gain control circuit or AGC circuit (16); adapted to depend, in dependence 15 on the amplitude of the extracted first video signal, on the gain in the processing and detection circuit (11), characterized by, d) a further set of means adapted to receive a second unrelated video signal to any radio frequency carrier, which further set of means comprises dl) a bias controlled second video amplifier (26) arranged at its input for receiving said second video signal, and which at its output through a first sub-section (27) of a switch (27,31,32) is connected to an input of the first video amplifier (12), d2) a DC voltage amplifier (30) whose input through a 30 portion sub-section (31) of the switch (27,31,32) is connected to an output of the AGC circuit (16) and whose output is thus connected to an input of the bias controlled second video amplifier (26), that its control bias and thus its gain may be changed depending on the output voltage of the DC amplifier (30), and at