FI67284C - OMVANDLARE FOER KABEL-TV - Google Patents

Description

R35FH M (11> ICUII.LUTUSJUL * A, SU (LH ORA

IJ UTLÄGGNINGSSKRIFT 0 / ZÖ4 C / ^ n Patent myCnneLly 11 02 1925 Patent neddolat ^ '' '(51) K »Jt / tat.CL3 h O' * N 7/16 FINLAND — FINLAND pi) 750683 (22) HriMrtpihi — AmBknh «DH 10.03.75 * '(23) AMtypihU — GlkH> ntK * H 10.03.75 (41) TdhK | trfklMk« l - Rihrk offantjlf 16.09.75

Patent and Registration Board * «-. £. **« * - (w> agg ^ aggoi 31., 0.84 (32) (33) (31) Pjry4 «ey muoOmn-8 · *** prtorfcst 15-03-71 »USA (US) 451490 (71) Oak Industries Inc., Crystal Lake, Illinois, USA (72) Ralph P. Harney, Wonder Lake, Illinois,

Stanley E. Guif, Madison, Wisconsin, USA (US) (7 ^) Oy Koister Ab

(54) Cable television converter - Omvandlare för kabel-TV

This invention relates to television code interpreting apparatus, and more particularly to a simply constructed, reliable cable television transducer having a plurality of input channels and one output channel and an oscillator for converting a cable TV signal into a usable signal for a TV receiver.

The features of the invention appear from the appended claims.

The invention is schematically illustrated in the accompanying drawings, in which: Figure 1 shows a block diagram of a cable television converter with means for determining an encoded signal; Figure 2 shows a block diagram of a modified decoder; Fig. 3 shows a schematic view of certain waveforms used in the encoding and decoding arrangement shown and described, and Fig. 4 shows a diagram of the waveform showing the distortion of the distortion wave during the vertical interval portion.

2 67284

The invention relates to a television decoder which can be used in pay-TV or pay-TV. The television signal is distorted at the upper end or at the transmitting station by means of a sine wave which is coupled as an additional modulation to the multi-part television signal. For example, a spurious wave with a frequency of about 15.75 kHz is connected directly to a television signal. The sine wave is phase locked to horizontal pacing pulses as shown in Figures 3A, 3B. Sine wave modulation has the effect of suppressing horizontal synchronization pulses and enhancing video between horizontal synchronization pulses because sine wave modulation is coupled to the entire TV signal and the distortion sine wave is present as amplitude modulation in the TV transmitter. The distortion sine wave can change the level of the television signal by about 6 dB. In U.S. Patent No. 3,081,376, Loughlin discloses a means for coupling such a distortion sine wave to a multipart television signal. In particular, the invention relates to a means for interpreting or explaining a multi-part television signal.

In Figure 1, a cable television converter of the general type described in U.S. Patent No. 3,333,198 to Mandell includes a cable inlet 10 connected to a first mixer 12 so that its output passes through a filter 16 and an amplifier 18 to a second filter 20. The filter 20 is connected to a second mixer 22 having an oscillator 24 and the output of the second mixer 22 connected to a filter 26. The parts described are conventional and are disclosed in said Mandell patent. Input terminal 20 receives a wide variety of cable channels; CATV systems typically use up to 13-26 channels. An adjustable oscillator 14 is used to monitor the selected channel, and the oscillator 24 converts the selected channel into a predetermined VHF channel that is not normally used as a public radio channel, but can be received by a standard TV receiver. Thus, all channels of the cable can be displayed on a specific channel of the TV that is not normally used, e.g. channel 3.

The output from the filter 26 is fed to an RF amplifier 28. Between the amplifier 28 and the filter 26 there is an interrupter 30 which normally removes the image signal from the next higher channel, e.g. channel 4. The attenuator 36 is connected to the amplifier 28 and the attenuator output is connected directly to the television. If the channel, 3 67284 selected using the oscillator 14, is a non-subscription channel, i. without the distortion being turned on, the TV signal is easily visible on the TV on channel 3.

The output of amplifier 28 also passes through channel 3 and filter 32 and the output of filter 32 passes to another RF amplifier 34. Automatic frequency control is provided by an AFC selector 38 connected to the output side of amplifier 34 and line 40 back to an adjustable oscillator 14.

The decoder part of the circuit includes a channel 3 audio carrier filter 42 connected to the output side of the amplifier 34, and the output side of the filter 42 is connected to an RF amplifier 44. A second channel 3 audio transmission filter 46 is connected to the AGC detector 48. The 15.74 kHz filter 50 is connected between the AGC detector 48 and the AGC amplifier 52.

In use, a TV signal varying in amplitude due to the switched sine wave is present on the input side of amplifier 28, assuming that oscillator 14 is tuned to the subscription channel. Filters 42 and 46 cause only the audio carrier frequency and associated sidebands to be present on the input side of the AGC detector 48. Since the distortion signal occurs as amplitude modulation in the sound carrier, a distortion signal occurs on the output side of the detector 48. In addition, there is a DC level that depends on the signal input level. The detector 48 output is switched via a filter 50 and an amplifier 52 an additional control signal to the amplifier 28. This additional control signal is in phase opposition with respect to changes in the sound carrier wave output level of the amplifier 28. Therefore changes in the sound carrier wave output level of the amplifier 28 will reduced as a factor equal to the loop gain of the amplifier 28 of the output side and the lisäohjaustuio side between. The audio carrier output from amplifier 28 thus contains only a small residual distortion signal. The video output from the amplifier 28 is simultaneously determined by the gain control signal and thus also contains only a small remaining distortion component. Although the remainder of the distortion signal remains in the final TV signal, but its level is low and permanent, there is virtually no detectable distortion.

Figure 2 uses the same interpretation principle without a conventional CATV converter. In this case, the plurality of switches 54 and 56 couple the cable to either the input side directly to the receiver described in Example 57 to 4 67 284 or cable decoder. The decoder may include a bandpass filter 58 that bypasses the channel selected as the subscription channel. The output side of filter 58 is connected to amplifier 60 and then to second filter 62. Mixer 64 receives one input from filter 62 and another input from oscillator 66. If e.g. the subscription channel is a letter channel, e.g. channel C, then the oscillator is adjusted so that the output from the mixer is a normally unused channel On TV, e.g., channel 3, as described above. In this context, it is obvious that the invention is not limited to channel 3, but this is a commonly used CATV output channel. The output from mixer 64 goes to filter 68. Filter 68 is connected to RF amplifier 28 and other parts of the decoder are similar to those described in connection with dry 1.

In use, the circuit of Figure 2 operates in the same way as the circuit of Figure 1 with respect to decoding a sine wave distorted TV signal. The main difference is that there is no conversion of all the channels in the cable to a specific selected channel that is not normally used in the receiver. Thus, only the subscription channel is converted to this channel and the other channels of the cable are routed directly to the receiver.

Figure 3 shows the signal distorting sine wave at the top of the figure and directly below it are the horizontal synchronization pulses of the television signal. The sine wave distortion signal has the same frequency as the horizontal sync pulses of the TV signal and the phase ratio shown in Fig. 3. The described distortion results in suppression of the horizontal synchronization pulse and amplification of the video signal, which is intended to result in the loss of correct horizontal synchronization in the television set.

As described above, the TV signal output by the decoder is distorted. Experiments have shown that a residual distortion of about 5% does not interfere with the operation of the horizontal synchronization circuits in the TV. However, such residual distortion causes a slight darkening in the video signal in the middle of the horizontal synchronization pulses.

However, residual distortion may interfere with the operation of the TV's vertical sync and AGC circuits. During part of the vertical interval, pacing pulses occur at a frequency twice the frequency of normal horizontal pacing. This occurs during equalization pulse intervals and notched (vertical synchronization) pulse intervals. See. Figure 3C.

5 67284 The effect of residual distortion on the vertical interval is that it produces a higher peak level than occurs at any other time in the TV picture. Because both pacing and AGC circuits are used in the TV at peak signal levels, this change in peak level that occurs during a small portion of the picture can interfere with pacing and AGC circuits. The residual distortion effect can be eliminated at the upper end by suppressing the distortion signal during at least the nine line intervals shown in Fig. 3C.

Figure 4 shows the envelope of a distortion signal suitably suppressed during a portion of the vertical interval. It should be noted that the suppression has a gradual effect and is gradually removed and used only during part of the vertical interval, although in some applications it could be used throughout the cycle. The operation preferably takes place only during the part of the vertical interval during which the equalization pulses and the vertical synchronization pulses are transmitted.

The invention should not be limited to any particular frequency or sine wave signal switching means. It is preferred that the distortion signal be coupled to a multi-part television signal at the central station as the signal travels out of the cable.

Although the preferred embodiment of the invention has been presented and shown above, it will be apparent that many modifications, changes and modifications may be made therein.

Claims (5)

6 67284 A cable television converter having a plurality of input channels (10) and one output channel (36) and an oscillator (14) for converting a cable TV signal into a usable signal for a TV receiver, and means for decoding a TV signal distorted into a substantially constant frequency horizontal line frequency. characterized in that when the distorting sine wave is suppressed for at least part of the vertical interval of the TV signal, said means comprise an RF amplifier (28) having an input for a distorted TV signal, a second input for a substantially constant frequency clearing wave and an output for a sine wave residual TV a detector (48) connected to the output of the amplifier (2C) for detecting a residual sine wave, filter means (42) connected between the RF amplifier (28) and the detector (48), an amplifier (52) connected to the detector for raising the level of the residual sine wave detected, the output of the amplifier (52) being connected to an RF amplifier (28 ) to generate a clearing wave, and an AFC circuit (38) connected between the output of the RF amplifier (28) and the oscillator (14). Cable television converter according to claim 1, characterized in that the RF amplifier (28) comprises two separate RF amplifiers (28, 34) separated by a bandpass filter (32) capable of removing all but one of the TV channels. Cable television converter according to claim 1, characterized in that it comprises single-channel audio carrier filtering means (42, 46) connected between the detector (48) and the output of the RF amplifier (28). Cable television converter according to claim 3, characterized in that the sound carrier filtering means comprise two separate sound carrier filters (42, 46) separated by an amplifier (44). Cable television converter according to Claim 1, characterized in that the output of the converter is taken from the output of the RF amplifier (28).