MXPA98002595A - Combination of visual and audible signals ntsc with signals - Google Patents

Abstract

The present invention relates to an apparatus and method for television signals transmitted on adjacent NTSC and DTV channels. The NTSC television signals for a first channel are selected from a frequency band that includes a plurality of channels and this first channel includes NTSC audible signals and NTSC visuals. A DTV television signal source is selected for a second channel in the same frequency band and the second channel is adjacent to the first channel. The NTSC visual signal and the DTV signal are combined to obtain a combined intermediate signal. The combined intermediate signal and the NTSC audible signal are then combined to obtain a combined output signal for application to antenna means for transmitting television signals.

Description

COMBINATION OF VISUAL AND AUDITABLE NTSC WITH DTV SIGNALS The present invention relates to the transmission of television signals, in particular to the combination of digital signals (DTV) with analog signals (NTSC). Television signals have traditionally been transmitted in an analog format known as NTSC. It is known that the Federal Communications Commission (FCC) will allow a new digital format known as DTV. It is expected that_ the digital format will be in operation before the year 2006. Each NTSC station present will carry out the simultaneous transmission of both NTSC signals and DTV signals. The NTSC signals may end as early as 2006. For an NTSC station to simultaneously transmit a DTV signal and an NTSC signal, it must have a second channel during the transient period. Until now, the FCC has typically allocated NTSC channels to a given geographical area by assigning only every second channel (ie, channels 2, 4, 6, 8, etc.), leaving unassigned intervening channels unassigned (ie, 1, 3, 5, etc.). This separation has contributed to maintaining non-interfering operation between the channels NTSC. It is believed that the FCC may now consider allocating non-allocated NTSC channels within a geographical area to DTV channels. This can lead to some difficulties in the interference of signals between channels. adjacent. All channels are 6 MHz wide, and unless special care is taken, these signals from adjacent channels can interfere with each other resulting in poor reception at the TV receivers. An object of the invention is to provide an apparatus and method by which television signals can be transmitted over adjacent NTSC and DTV channels. Television signals NTSC for a first channel are selected from a frequency band that includes a plurality of channels and where this first channel includes NTSC audible signals and NTSC visuals. A DTV television signal source is selected for a second channel in the same frequency band and where the second channel is adjacent to the first channel. The NTSC visual signal and the DTV signal combine to provide a combined intermediate signal. The combined intermediate signal and the NTSC audible signal are then combined to provide a combined output signal for - be applied to antenna means to transmit television signals. Advantageously, the television signals for the DTS channel are of a frequency band which is of higher frequencies than that of the NTSC channel. The NTSC channel can be called N and the DTV channel can be called N + l. The present invention includes an apparatus for transmitting television signals over adjacent NTSC and DTV channels including: a television signal source NTSC passes a first selected channel from a frequency band that includes a plurality of channels where said television signals NTSC include audible and visual signals; a source of DTV television signals of a second channel in said frequency band and where said second channel is adjacent to said first channel; first means for receiving and combining said NTSC visual signal and said DTV signal to obtain a combined intermediate signal; and second means for receiving and combining said combined intermediate signal with said NTSC audible signal and obtaining a combined output signal for application to transmitting means for transmitting television signals. The invention also includes a method of transmitting television signals over adjacent NTSC and DTC channels which includes the steps of: providing an NTSC channel, having both visual and audible NTSC signals, said NTSC channel being selected from a frequency band that includes a plurality of channels; providing a DTV channel having a DTV signal selected from said frequency band and wherein said DTV channel is adjacent to said NTSC channel; combining said NTSC visual signal with said DTV signal to obtain a combined intermediate signal; and combining said combined intermediate signal with said NTSC audible signal to obtain a combined output signal for application to transmitting means for transmitting television signals. The invention will now be described, by way of example, with reference to the accompanying drawings: Figure 1 is a graphic illustration of several frequency bands. Figure 2 is a graphic illustration of a low band VHF TV frequency band representing adjacent TV channels. Figure 3 is a graphic illustration of the amplitude with respect to the frequency, which represents the operation of adjacent NTSC and DTV channels, the DTV channel being "of higher frequencies, Figure 4 is a graphic illustration similar to that of the figure 3, but represents the NTSC channel as having higher frequencies Figure 5 is a block diagram illustrating an embodiment of the present invention Figure 6 is a graphic illustration representing a single input antenna of the type usable with the present invention and Figure 7 is an illustration in schematic block diagram similar to that of Figure 5, but in greater detail, Figure 1 illustrates several RF frequency bands that include a low band VHF TV frequency band, from approximately 54 MHz to 88 MHz. This is followed by an FM band from about 88 MHz to 108 MHz. The FM band is followed by a high band VHF TV band that extends from approximately 174 MHz to 216 MHz. The UHF TV band extends from approximately 470 MHz to 806 MHz. The VHF TV band and the UHF TV band are divided into TV * channels having a width of 6.0 MHz. Figure 2 illustrates the division of the low band VHF TV frequency band into channels 2-6. Each TV channel is 6 MHz wide and it is seen that the FCC has assigned these channels, starting at 54 MHz for channel -2 to 72 MHz for channel 4. Then there is a vacuum of 4 MHz and 76 MHz is assigned to 82 MHz to channel 5 that is followed by channel 6. It should be noted that channels 4 and 5 are not adjacent due to the empty area of 4 MHz in width.

The FCC has assigned every second channel to an NTSC station leaving the intermediate channels unassigned. This is true both in the low frequency and high frequency VHF bands as well as in the UHF TV band. With the advent of high definition television there will be some pressure for the FCC to allocate some DTV channels to the spaces represented by the non-assigned NTSC channels in some geographical areas. Problems arise when adjacent channels are assigned, assigning a channel to an NTSC station and assigning the adjacent channel to a DTV station. The problems differ somewhat depending on whether the DTV station is the highest number channel (highest frequency) or is the lowest frequency channel. The tendency has been to refer to the assignments of adjacent channels, where the upper channel is a DTV assignment as an N + l Channel Assignment (N referring to the lower channel which is an NTSC station and referring "+1" to the DTV station). of upper channel). An N + l channel allocation situation is illustrated in figure 3 and a channel assignment Nl (where the DTV assignment is the lower frequency) is illustrated in figure 4.- figure 3 illustrates the radiation configuration that takes place in an N + l Assignment where the lower channel is an NTSC channel and the upper channel is a DTV channel. As illustrated in Figure 3, the lower channel is channel 23 and extends from 524 MHz to 530 MHz. The upper DTV channel is channel 24 and extends from 530 MHz to 536 MHz. The NTSC signal includes a visual portion 10 and an audible portion 12 '. It is known that an NTSC source will often provide two outputs that include a visual output corresponding to the visual portion 10 and an audible output corresponding to the audible portion 12. These two sources provide a waveform as depicted in Figure 3. where the visual portion 10 and the audible portion 12 have been combined. Figure 3 represents that the maximum value of the visual portion 10 occurs at approximately 525 MHz within the limits defined by the channel 23. However, the audible portion 12 is at the upper end of the frequency band of the channel 23 and the maximum values at about 528 MHz. Accordingly, the audible portion 12 is quite close to the lower frequency end of the DTV frequency signal of the channel 24. The assignment of these two channels adjacent to each other in an N + 1 configuration presents the problem of combining an NTSC signal with the DTV signal, where the audio portion 12 of the NTSC signal and the lower frequency end of the DTV signal may interfere with each other. This has to be compared with the operation N1 to be described below with reference to FIG. 4. In FIG. 4 the DTV signal is assigned to channel 22 which extends from 518 MHz to 524 MHz and the NTSC signal is assigned to channel 24. which extends from 524 MHz to 530 MHz. In this configuration Nl, there is a frequency range 20 between the right edge 22 of the DTV signal and the visual signal NTSC 10. Consequently, in a Nl assembly it is easier to combine a signal DTV with an NTSC signal (having both a visual portion 10 and an audible portion 12) because of the interval 20 that exists between the two frequency ranges. In order to avoid the interference presented by an assembly N + l, as illustrated in FIG. 3, the present invention contemplates that, for an N + l assembly (which can also be used in a Nl assembly), the interference can be minimized by combining first the portion of the visual signal NTSC 10 (which does not include the portion of the audible signal 12) with the DTV signal to obtain a combined intermediate signal which is then combined with the audible signal NTSC to obtain a combined output signal for application to an antenna to transmit television signals. The foregoing can be better understood with reference to Figures 5-7. Figure 5 illustrates an embodiment of the present invention. The illustrated NTSC 100 signal source provides visual signals 102 as well as audible signals 104. In addition, the illustrated DTV source 110 provides DTV signals 112. The NTSC 102 visual signals may correspond to the visual signal portion NTSC 10 in the waveforms of FIGS. 3 and 4. Likewise, the NTSC 104 audible signals may correspond to the of audible signal 12 in Figures 3 and 4. The DTV source 110 provides DTV signals such as the higher signals of channel 24 in Figure 3 or lower frequency signals such as channel 22 (Nl) in Figure 4. The maximum advantage of the invention is implemented, however, by an Assignment N + 1, in which the higher frequency signals (N + 1) are the DTV signals 112. Thus, according to the invention, the 'visual signals NTSC together with the DTV signals are combined in a channel combiner 120. The output of the channel combiner 120 is a combined intermediate signal 122 which is combined with the audible signal 104 in a combiner 124. The combiner 124 provides an output signal co mbinada 126 which is then applied to a common antenna 128 to transmit television signals. This method of combining - three signals can be called "triplexion". The combiner 124, as will be described in more detail below with reference to FIG. 7, includes deviating hybrids attached with phase control to reduce the amount of audible power lost. The output of the combiner 124 is applied to a single power antenna 128 by means of a single output 130. The output 130 and the antenna 128 are described in greater detail in Figure 6. Figure 6 represents the power line driver. output 130 which takes the form of a coaxial cable having a central conductor 132 and an external conductor 134. This coaxial cable is connected to a single power input antenna, such as a slotted antenna, a panel antenna or the like. In the embodiment illustrated in FIG. 6, a compartment of a multi-compartment slotted antenna is shown. This antenna includes a cylindrical mast 200 of cylindrical cross section and made of electrically conductive material, such as steel or aluminum. The mast 200 coaxially surrounds an internal conductor 202 that extends the entire length of the mast. The conductor 202 may take the form of an elongated metal rod. or tube. Each compartment (only one compartment is shown in figure 6) includes a vertical slot 204. With each slot is associated a coupling probe 206 which is suitably fixed, for example by welding, to one side of the slot in its essentially middle portion . The probe is normally located inside the mast's inner side. Such a coupling probe contributes to coupling the energy within the mast so that the radiating field appears through the slot in which a coupling probe is associated. The slotted antenna is energized by the coaxial cable where the central conductor 132 is connected to the internal conductor 202 of the slotted antenna and the external conductor 134 of the cable is electrically connected to the mast 200. Although only one slot 204 is shown on the mast 200, the antenna will have several slots spaced apart from each other preferably a distance of the order of one wavelength at the operating frequency. The vertical length of each slot is of the order of 1/2 wavelength. The slots are optimized in size and slot spacing for a particular channel, such as channel 23 or 24 and so on. A change in the operating frequency requires a change in the slot length and the spacing between the vertically oriented slots. Figure 7 illustrates in more detail the circuitry of Figure 5. The channel combiner 120 of Figure 6 is illustrated in Figure 7 and includes a 90 ° input hybrid 300 having an input to receive the visual signal NTSC 102 of the NTSC 100 source and a second input that is connected to ground by means of a resistor 302. The outputs of the hybrid 300 are applied through bandpass filters 304 and 305 to a pair of inputs of a second hybrid of 90 ° 306. The DTV signal 112 of the DTV source 110 is also supplied to an input of the hybrid 306. The output of this hybrid supplies a combined intermediate signal 122 to a combiner 124 to be described later. The intermediate signal of the combiner can be considered as a signal I that satisfies the following equation: 1 = v + DTV Equation 1 where V is equal to the visual signal 102 and DTV is equal to the DTV signal 112. The combined intermediate signal 122 is supplied to the combiner 124 which includes back-shifting hybrids HYl and HY2. The output of hybrid HYl at point 320 satisfies the following equation: Equation 2 where V is equal to V + DTV and A is equal to the audible signal 104. - The output at 320 of the hyl hybrid is supplied to an input of a 90 ° hybrid 330. The output 322 of the HYl hybrid circuit is supplied to the phase compensation line 324. The output of HYl hybrid circuit at point 322 is according to the following equation: - V '+ ^ A 3 3 Equation 3 The hybrid 330 is provided with a pair of adjustable bypass cavity resonators 332 and 334 that can be used to adjust the phase of the signals to minimize the loss of audible power. The output of the hybrid 330 is supplied to a HY2 hybrid input. The second input to the hybrid is obtained from the phase and time compensation line 324. Another input is connected by means of a resistor 340 to ground. The output of hybrid HY2 is equal to V '+ A or V + DTV + A and is supplied as output signal 126. This signal is applied via the coaxial cable to the single input antenna having a bandwidth of two channels, enough to transmit the adjacent channels both NTSC and DTV. Apparatus and method for television signals transmitted by adjacent NTSC and DTV channels. The NTSC television signals for a first channel are selected from a frequency band that includes a plurality of channels and this first channel includes NTSC audible signals and NTSC visuals. A DTV television signal source is selected for a second channel in the same frequency band and the second channel is adjacent to the first channel. The NTSC visual signal and the DTV signal are combined to obtain a combined intermediate signal. The combined intermediate signal and the NTSC audible signal are then combined to obtain a combined output signal for application to antenna means for transmitting television signals.

Claims (9)

1. CLAIMS 1. Apparatus for transmitting television signals over adjacent NTSC and DTV channels including: a source of NTSC television signals for a first selected channel from a frequency band including a plurality of channels where said NTSC television signals include audible and visual signals; a source of DTV television signals of a second channel in said frequency band and where said second channel is adjacent to said first channel; first means for receiving and combining said NTSC visual signal and said DTV signal to obtain a combined intermediate signal; and second means for receiving and combining said combined intermediate signal with said NTSC audible signal and obtaining a combined output signal for application to transmitting means for transmitting television signals. Apparatus as claimed in claim 1, wherein said second means includes a hybrid input coupler and a hybrid output coupler and an intermediate hybrid coupler located between said first and second couplers, and preferably said intermediate hybrid coupler includes resonance means of cavity in derivation. Apparatus as claimed in claim 2, wherein said shunt cavity resonator means include first and second adjustable shunt resonators, and which also include a phase shifter coupled between said hybrid input and output couplings. 4. Apparatus as claimed in any of claims 1 to 3, wherein said DTV signals are at higher frequencies than said NTSC signals. Apparatus as claimed in any one of claims 1 to 4 including said transmitting means having a common single input antenna having a bandwidth of two channels for transmitting said NTSC and DTV signals. Apparatus as claimed in claim 2, wherein said second means includes a hybrid input coupler and a hybrid output coupler and an intermediate hybrid coupler located between said first and second couplers. Apparatus as claimed in claim 6, wherein said intermediate hybrid coupler includes bypass cavity resonator means, and preferably said bypass resonator means includes first and second adjustable bypass resonators. A method of transmitting television signals over adjacent NTSC and DTC channels which includes the steps of: providing an NTSC channel, having visual and audible NTSC signals, said NTSC channel being selected from a frequency band that includes a plurality of channels; providing a DTV channel having a DTV signal selected from said frequency band and wherein said DTV channel is adjacent to said NTSC channel; combining said NTSC visual signal with said DTV signal to obtain a combined intermediate signal; and combining said combined intermediate signal with said NTSC audible signal to obtain a combined output signal for application to transmitting means for transmitting television signals. 9. A method as claimed in claim 8, wherein said step of providing a DTV channel includes selecting a DTV signal of higher frequency than that of said visual and audible NTSC signals.