JPH0416537Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention arranges frequencies of low-frequency and high-frequency television signals via predetermined empty channels, and the video and audio carrier waves of the low-frequency television signals are The present invention relates to a frequency converter that receives a television signal known as a multi-distribution service network arranged inversely to a high frequency band and converts it into an intermediate frequency signal.

(Prior Art) A television network conventionally known as multi-distribution service (MDS) uses frequencies in the 2 to 3 GHz band and has been put into practical use as a service network to replace the CATV system.

Figure 3 shows the frequency allocation of the television signals used in this MDS. 1 and 2 channels are allocated from 2150 to 2162 MHz as the low-frequency television signal group, and a predetermined free space is allocated to this low-frequency television signal group. 2500~2886M via channel (2162~2500MHz)
31 channels are allocated as a group of high-frequency television signals between Hz.

By the way, the frequency arrangement of audio and video carrier waves in each channel of the high-frequency television signal group is as follows.
Video carrier wave in 6MHz band like VHF and UHF
1.25MHz, audio carrier 5.75MHz, but in each channel of the low-frequency TV signal group, the signal arrangement is reversed, with the video carrier 4.75MHz and the audio carrier 0.25MHz at 6MHz.

(Problem to be solved by the invention) However, when receiving such MDS television signals and converting them into predetermined intermediate frequency signals, the video and video signals in the low frequency television signal group and the high frequency television signal group must be Since the arrangement of audio carrier waves is in an inverse relationship, separate frequency converters must be provided for each of the low and high frequencies, and the circuits from the intermediate frequency circuit to the audio and video detection also have separate frequency converters for the low and high frequencies. However, there were problems in that a dedicated circuit had to be provided for the TV, making the receiving circuit complicated and making the television receiver expensive.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned problems in the prior art. The video carrier wave and audio carrier wave of the low frequency television signal group are arranged inversely to the high frequency television signal group, and the low frequency television signal group and the high frequency television signal group are converted into a predetermined intermediate frequency signal. In the frequency converter for converting, a local oscillator having a predetermined oscillation frequency higher than the upper limit frequency of the low frequency television signal group and lower than the lower limit frequency of the high frequency television signal group; A mixer that mixes the output of the local oscillator and an output circuit that outputs the difference signal or sum signal of the output of this mixer are provided, and the arrangement of carrier waves is reversed by setting a single local oscillation frequency. A certain low-frequency and high-frequency television signal group is frequency-converted, and the carrier wave arrangement of the low-frequency television signal group is inverted to match the carrier wave arrangement of the high frequency band.

(Embodiment) FIG. 1 is a circuit block diagram showing an embodiment of the present invention.

First, to explain the configuration, 1 is a mixed circuit,
A first input terminal 2 that inputs a received signal of a group of high-frequency television signals of one or more channels transmitted by MDS television broadcasting, and a second input terminal 3 that inputs a group of low-frequency television signals of one or more channels. has. A first input terminal 2 into which a group of high-frequency television signals is input is connected as an input to a bandpass filter 4, and this bandpass filter 4 passes television signals of, for example, 2500 to 2686MHz, which are the channel band of the high-frequency television signal group. It has a band characteristic that On the other hand, the second input terminal 3 into which the low frequency television signal group is input is connected to a bandpass filter 5, and the bandpass filter 5 serves as a channel band for the low frequency television signal group. For example, it has passband characteristics of a television signal of 2150 to 2162 MHz. The output of the band-pass filter 4 is connected to the amplifier 6 via a high-pass filter consisting of capacitors C1, C2 and an inductance L1, and the output of the band-pass filter 5 is connected via a low-pass filter consisting of inductances L2, L3 and a capacitor C3. Similarly, the input signal is connected to an amplifier 6, and an output is obtained from the amplifier 6, which is a combination of a high-frequency television signal group and a low-frequency television signal group. Amplifier 6
The output of the mixer 7 is inputted to one side of the mixer 7 which performs frequency conversion, and the oscillation output of the local oscillator 8 is given to the other side of the mixer 7.

Here, the oscillation frequency fo of the local oscillator 8 is determined as follows.

Figure 2 shows the setting of the local oscillation frequency fo for the low-frequency and high-frequency television signal groups in the embodiment shown in Figure 1. When the frequency is 2600MHz, the local oscillation frequency fo
is higher than the upper limit frequency of 2162MHz for the low frequency TV signal group, and the lower limit frequency of the high frequency TV signal group is 2600M
It is set to a predetermined value smaller than Hz. To explain in more detail, if the difference between the local oscillation frequency fo and the upper and lower limit frequencies of the low-frequency and high-frequency television signal groups is f1 and f2, the local oscillation frequency fo is determined so that f1<f2. , Therefore, f1=f2+Δf, and this Δf gives an empty channel to avoid interference between low and high frequencies when converting the frequency, and for example, Δf corresponding to two channels is set to 12 MHz.

According to such a local oscillation frequency fo, the local oscillation frequency fo is set to 2284 MHz, for example.

In order to obtain this local oscillation frequency fo = 2284 MHz, in the local oscillator 8 in Fig. 1, the crystal oscillator 9 first takes out the source oscillation output of 114.2 MHz, and the multiplier 1
0, the frequency is multiplied by 4 times by harmonic extraction and an oscillation output of 456.8MHz is taken out from the bandpass filter 11, and further multiplied by 5 times by the multiplier 12, and the local oscillation frequency fo=2284MHz is taken out from the bandpass filter 13. It is output to mixer 7.

Therefore, the mixer 7 mixes the local oscillation output of the frequency fo with the low-frequency and high-frequency television signals provided by the amplifier 6, and provides a frequency-converted signal by this mixing to the output circuit 14 at the next stage.

The output circuit 14 includes a bandpass filter 16, amplifiers 17 and 18, and a capacitor C for cutting DC.
4, and a frequency-converted signal is taken out from an output terminal 19. In this output circuit 14, a bandpass filter 16 has a passband characteristic for extracting a difference signal from the mixed output of the mixer 7,
When the local oscillation frequency is fo=2284MHz,
The passband characteristics are set from 122 to 402MHz.

Next, the frequency conversion according to the embodiment of FIG.
This will be explained with reference to the signal frequency allocation diagram shown in the figure.

First, 31 channels of high-frequency television signals having a channel band of 2600 to 2686 MHz are input to the first input terminal 2, and only the high-frequency television signal group is input by the bandpass filter 4 and the next high-pass filter. is extracted. Also, the second input terminal 3
A low frequency television signal group having a channel frequency band of 2150 to 2162 MHz is input, and only the low frequency television signal group is extracted by the bandpass filter 5 and the low pass filter. These high frequency television signal groups and low frequency television signal groups are summed and amplified by an amplifier 6 and input to a mixer 7. Since the mixer 7 is given a local oscillation output with a local oscillation frequency fo = 2284MHz from the local oscillator 8, the local oscillation frequency fo
The sum and difference signals of the low-frequency and high-frequency television signals are obtained as frequency conversion outputs. Of the frequency converted output of the mixer 7, the bandpass filter 16 of the output circuit 14 converts the passband characteristic of the difference signal.
Since it has a frequency of 122 to 402 MHz, only the difference signal among the outputs of the mixer 7 is output from the output terminal 19.

As is clear from FIG. 2, the frequency-converted difference signal at the output terminal 19 has a channel arrangement in which the low-frequency television signal group before frequency conversion is folded back around the local oscillation frequency fo, and the channel positions are reversed. . Therefore, the video and audio carrier waves in each channel of the low frequency television signal group are
As shown in Figure 3, even if the channel position of the low-frequency television signal group is reversed to the high-frequency television signal group, the channel position of the low-frequency television signal group is swapped due to frequency conversion, so that the video and audio carriers are exactly the same as those of the high-frequency television signal group. frequency arrangement. Therefore, the circuit section after the output terminal 19 can be shared by the low frequency television signal group and the high frequency television signal group.

Of course, the frequency converter that converts the low frequency TV signal group and the high frequency TV signal group to a predetermined intermediate frequency requires only one local oscillator, and there is no need to perform frequency conversion separately for low frequency and high frequency bands. .

Although the above embodiment takes the television signal used in MDS as an example, the present invention is not limited to this. It is possible to directly apply frequency conversion in the reception and playback of appropriate television broadcasts that have the frequency allocation of a low-frequency television signal group and a low-frequency television signal group, and the video and audio carrier waves of one television signal group are reversely allocated to the other television signal group. Can be applied. Further, if the bandpass filter 16 of the output circuit 14 has a passband characteristic of the sum signal, only the sum signal can be output.

(Effects of the invention) As explained above, according to the invention, the low-frequency television signal group and the high-frequency television signal group of one or more channels are arranged in frequency with a predetermined empty channel width, and the low-frequency television signal group the video carrier wave and the audio carrier wave of the group are reversely arranged with respect to the group of high frequency television signals;
In a frequency converter that converts a low-frequency television signal group and a high-frequency television signal group into a predetermined intermediate frequency signal, a predetermined oscillation frequency higher than the upper limit frequency of the low-frequency television signal group and lower than the lower limit frequency of the high-frequency television signal group. , a mixer that mixes the output of the local oscillator with the low-frequency television signal group or the high-frequency television signal group, and an output circuit that outputs the difference or sum signal of the mixer output. ,
Even if the frequency arrangement of the video and carrier waves of the low-frequency television signal group is reversed to that of the high-frequency television signal group, the difference signal obtained by frequency conversion using a local oscillation frequency that is intermediate between the two can be output. By reversing the channel arrangement of the low-frequency TV signal group, it is possible to match the video and audio frequency arrangement of the low-frequency TV signal group with the high-frequency TV signal group, and by this reverse swapping, it is possible to match the frequency arrangement of the video and audio of the low-frequency TV signal group to the high-frequency TV signal group. It is possible to convert high-frequency and low-frequency television signals into intermediate frequency signals with a single frequency converter, and the receiving circuit after the frequency converter can be shared for high and low frequencies.
Compared to the case where frequency conversion is performed separately for low and high frequencies, the circuit configuration can be significantly simplified, and the cost of the television receiver itself can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing an embodiment of the present invention, FIG. 2 is a frequency allocation diagram showing frequency conversion according to the invention, and FIG. 3 is a channel frequency allocation diagram in MDS. 1...Mixing circuit, 2...First input terminal, 3...
...Second input terminal, 4, 5, 11, 13, 16...
... Band pass filter, 6, 17, 18 ... Amplifier, 7 ... Mixer, 8 ... Local oscillator, 9 ... Crystal oscillator, 10, 12 ... Multiplier, 19 ... Output terminal.

Claims (1)

[Claims for Utility Model Registration] One or more channels of low-frequency television signal group and high-frequency television signal group are arranged in frequency with a predetermined empty channel width, and the video carrier wave and audio carrier wave of the low-frequency television signal group are a frequency converter arranged inversely to the high frequency television signal group and converting the low frequency television signal group and the high frequency television signal group into a predetermined intermediate frequency signal, the frequency being higher than the upper limit frequency of the low frequency television signal group; a local oscillator having a predetermined oscillation frequency lower than the lower limit frequency of the high-frequency television signal group; a mixer for mixing the low-frequency television signal group and the high-frequency television signal group with the output of the local oscillator; 1. A frequency converter, comprising: an output circuit that outputs a difference or sum signal of the outputs of the frequency converter.