JPH03210882A - Mixer for head end - Google Patents

Abstract

PURPOSE:To improve carrier to noise ratio by mixing a television broadcast signal at a 1st mixer means, eliminating a noise at the outside of the pass band in a band pass filter using each frequency band as its pass band and mixing the result at a 2nd mixing means. CONSTITUTION:Output signals from mixers 21-28 are fed to a mixer 8 via signal transmission circuits 61-68. The signal transmission circuit 61 sends a signal of a frequency in a 1st split band, the signal transmission circuit 62 sends a signal of a frequency in a 2nd split band,... the signal transmission circuit 68 sends a signal of a frequency in a 8th split band. The output signals of the signal transmission lines 61-68 are mixed by a mixer 8. The output signal from the mixer 8 is amplified as required by a broad band amplifier 30, the level is adjusted by a level adjustment device 32 and fed to an output terminal 34. Then the signal is fed to a trunk line from the output terminal 34.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mixing device used in a head end for sending a plurality of television broadcast signals and the like to a main line in a communal viewing and viewing system.

[Prior Art] Conventionally, in the above-mentioned head-ent, for example, television broadcast signals, which are output signals from a plurality of frequency converters, may be mixed by one mixer. In order to provide versatility, these frequency converters are configured so that the frequency of the local oscillator is variable so that the frequency of the output signal can be set to any desired frequency. Therefore, the amplifier provided at the output stage of each frequency converter has a wide band so that it can amplify the output signal of any frequency.

[Problems to be Solved by the Invention] However, since a broadband amplifier is used in the output stage of each frequency converter, the output signal of this amplifier contains a lot of noise.

Since these are mixed by the mixer, the output signal of the mixer contains a lot of noise, which degrades the C/N ratio at the output side of the mixer.In an attempt to prevent this, Each frequency converter is a dedicated frequency converter for frequency converting a television broadcast signal of a specific frequency to a television broadcast signal of another specific frequency, and the output stage amplifier of each frequency converter is a narrow band amplifier. However, this creates a new problem in that each frequency converter must be custom-built and dedicated, which increases costs.

[Means for solving the problem] In order to achieve the above object, the present invention divides the entire frequency band of a plurality of television broadcast signals of different frequencies into n divided bands, each of which is a pass band. n
n signal transmission means including n bandpass filters; selection means provided in each of these signal transmission means for selecting which of the n bandpass filters to energize; and n signal transmission means including n bandpass filters; n pieces of said television broadcasting signals, each of which is provided upstream of said transmission means and whose frequency is within the passband of a band-pass filter selected in said corresponding signal transmission means, are mixed and supplied to said corresponding signal transmission means; and a second mixing means for mixing the outputs of the respective signal transmission means.

[Operation] In the present invention, the bandpass filters of each signal transmission means are selected by each selection means so that when the passbands of the bandpass filters energized in each signal transmission means are combined, the entire band of each television broadcast signal is obtained. When a filter is selected, each television broadcast signal mixed by each first mixing means passes through a band pass filter whose own frequency is within the pass band in the subsequent signal transmission means, and then passes through a band pass filter whose own frequency is within the pass band. are mixed and output.

[Example] This example describes 4
This is a mixing device that mixes and outputs a total of 60 television broadcast signals in the frequency band of 0011Hz, and as shown in FIG. , 100M1lz to 1
50M1i, second band...400118. The system is divided into a total of eight subbands including an eighth subband of 45G11Hz, and for each subband, television broadcast signals having frequencies within the subband are mixed, and these are further mixed.

That is, in this embodiment, as shown in FIG.
The mixer 21 has a total of eight mixers (6), and the mixer 21 is supplied with eight waves of television broadcast signals having frequencies within the first subband through eight input terminals 4°. □
The mixer 27 is supplied with eight television broadcast signals having frequencies within the second subband through eight input terminals 4□, and the mixer 27 is supplied with eight television broadcast signals having frequencies within the second subband. six waves of television broadcast signals having frequencies within the eighth sub-band are supplied to the mixer 2 through six input terminals 47 (not shown); Signals are provided via six input terminals 46. These mixers 21 to 2 are 5011H2 to 4
It has a wide band that can mix television broadcast signals in the 5011 tlz band.

The output signals of these mixers 21 to 28 are supplied to the mixer 8 via signal transmission circuits 61 to 66. The signal transmission circuit 6 transmits a signal with a frequency within the first divided band, and the signal transmission circuit 6□ transmits a signal with a frequency within the second divided band. The circuit 66 is the eighth
A signal of a frequency within the divided band is transmitted.

Each of the signal transmission circuits 61 to 68 is specifically configured as shown in FIG. That is, the signal transmission circuit 6m is
It has eight band pass filters 91 to 98 whose pass bands are the first to eighth divided bands. These band-pass filters 91 to 96 are single-current type, and the anodes of PIN diodes 10□ to 106 are connected to their input sides, and these PIN diodes 101 to 10
．． The cathodes of mixer 2. is connected to the output side of the high frequency blocking coil 14 and the resistor 16.
is grounded through. In addition, the band pass filter 91
On the output side of 96, there are PIN diodes 1B and 1B.
8a are connected, and their cathodes are connected to each other, and the interconnection point is connected to the input side of the mixer 8 via a DC blocking capacitor 20 and to the input side of the mixer 8 via a high frequency blocking coil 22 and a resistor 24. and grounded.

Furthermore, each bandpass filter 9. The output sides of 9a to 9a are connected to the selection circuit 28 via high frequency blocking coils 261 to 268.
Connected to 1. This selection circuit 28m is
The high frequency blocking coil 26. which is connected to the band pass filter to be used among the band pass filters 9I to 98, in this example 9I. A current is passed through. As a result, current flows through the PIN diode 18I, the high frequency blocking coil 22, and the resistor 24, and the high frequency resistance value of the PIN diode IL decreases. In addition, the current is passed through a bandpass filter 9. ,
It also flows through the PIN diode lO1, the high frequency blocking coil 14, and the resistor 16, and the high frequency resistance value of the PIN diode 10t also decreases.

Therefore, the eight waves of television broadcast signals of the first subband mixed by the mixer 21 are filtered through the band pass filter 9. is supplied to Here, even if the output of the mixer 2□ contains noise outside the first divided band, the pass band of the band pass filter 9 is the first divided band, so the output of the band pass filter 9I The other signal transmission circuits 62 to 66, which do not include these noises, are similarly configured.

The reason why each of the signal transmission circuits 61 to 6a is provided with bandpass filters 91 to 96, respectively, is as follows. In the above example, the mixer 2 receives the television broadcast signal within the first subband, the mixer 22 receives the television broadcast signal within the second subband, and the mixer 28 receives the television broadcast signal within the eighth subband. This is just one example, and depending on the situation, it may be different from the above, for example, mixer 2. A television broadcast signal within the I81 subband may be supplied to the mixer 22 within the second subband. Therefore, the television broadcast signal in which subband is transmitted to which mixer 21
This is to make it possible to deal with the situation even if it is supplied to the

Each signal transmission circuit6. The output signals from 6 to 6 are mixed by mixer 8. This mixer 8 is a wideband mixer capable of mixing television broadcast signals in a band of 50 MH to 450 MH. The output signal of this mixer 8 is amplified by a wideband amplifier 30 as necessary, and after its level is adjusted by a level adjuster 32,
The signal is supplied to the output terminal 34. And this output terminal 34
is supplied to the main line.

4(I) shows the output signal of the signal transmission circuit 61, (n) shows the output signal of the signal transmission circuit 62, etc. ([) shows the output signal of the signal transmission circuit 66. A to H represent the level of the television broadcast signal, and a to H represent the noise level. The outputs of the mixers 21 to 26 each contain noise in the entire band as shown by the phantom lines, but the outputs of the signal transmission circuits 6I to 66 contain noise that passes through the band pass filter selected in each. The television broadcast signal and noise within the band are included, but the noise in other bands is not included. Therefore, the output of the mixer 8 is a mixture of the output signals of these signal transmission circuits 6□ to 6a. Since the signal is equivalent to one full-band noise as shown in (■), the C/N ratio can be greatly improved. If the output of mixers 2□ to 2a is used as is, mixer 8
When mixing with As a result, the C/N ratio deteriorates.

This will be explained using a mathematical formula. When the mixer 8 is supplied with a television broadcast signal from one of the signal transmission circuits 61 to 66, the carrier-to-noise ratio (C/N) s of the mixer 8
is set to 65dB. This is done in consideration of the noise generated inside the mixer 8 and the signal source (equivalent internal resistance of the signal transmission circuit). Then, the carrier-to-noise ratio (C/N) s of the input television broadcast signal itself is 70d.
Let it be B. Carrier-to-noise ratio (C/N) at the output of mixer 8 at this time. is (C/N)O= 1°”g(1
/Xs ) + (1/Xs ), however, Xl is (
(:/N) The true value of IC, X2 is the true value of (c/N) i. Here, each signal transmission circuit 61 to 6. When a signal is supplied from
1og 7), and converting this to x2, we get (C/
N). When calculated, (C/N). is approximately 59.9 dB.

On the other hand, (C/N) when the signals from each mixer 2 to 26 are directly supplied to mixer 8. is calculated in the same manner as above and is approximately 52.1 dB. In other words, this example has a C/N of about 7.6 dB. is improved.

In the above embodiment, the frequency band of the television broadcast signal to be transmitted was set to 5011 MHz to 450 MHz, but this frequency band can be changed depending on the situation. However, this number of divisions can also be changed depending on the situation.

[Effects of the Invention] As described above, according to the present invention, in each of a plurality of bands,
Television broadcast signals are mixed by the first mixing means, noise outside the passband is removed by a bandpass filter in the signal transmission circuit that uses the respective frequency bands as the passbands of these mixed outputs, and then the second mixer is mixed. Since the mixing is carried out by the mixing means of , the carrier wave-to-noise ratio can be improved. Moreover, each signal transmission circuit includes a plurality of bandpass filters having each divided band as a passband, and the output of the first mixing means corresponding to the bandpass filter selected by the selection means is supplied. With this configuration, it is possible to deal with whichever band the television broadcast signal is supplied to which of the first mixing means.

[Brief explanation of drawings]

FIG. 1 is a detailed block diagram of one embodiment of the mixing device according to the present invention, FIG. 2 is a schematic block diagram of the same embodiment, FIG. 3 is a diagram showing band division in the same embodiment, and FIG. 4 is the same. FIG. 3 is an explanatory diagram of the operation of the embodiment. 2m to 26...Mixer (first mixing means), 6m
68... Signal transmission circuit, 8... Mixer (second mixing means), 9. 96 to 96 band pass filters, 28 to 286 selection circuits (selection means).

Claims (1)

[Claims] (1) n signal transmission means including n bandpass filters whose passbands are n divided bands obtained by dividing the entire frequency band of a plurality of television broadcast signals of different frequencies, and each of these signal transmission means a selection means provided in each of the transmission means for selecting which of the n bandpass filters to be energized; and a selection means provided in each preceding stage of the n signal transmission means and selected in the corresponding signal transmission means; mixing the outputs of each of the signal transmission means with n first mixing means for mixing the plurality of said television broadcast signals having frequencies within the pass band of the band pass filter and supplying the mixture to the corresponding said signal transmission means; a second mixing means;
Mixing device for head end with.