JPH0477489B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a signal transmission method, and more specifically, the present invention relates to a signal transmission method, and more specifically, the present invention includes a receiving station and a transmitting station connected by a relay transmission path, and receives broadcast waves at the receiving station. The present invention relates to a signal transmission method in which a signal is sent to a transmitting station via a relay transmission path, and a broadcast wave is transmitted from the transmitting station upon receiving the signal sent from the receiving station.

[Prior Art] Television relay stations and cable television broadcasting facilities sometimes adopt a system in which the receiving station and transmitting station are separated due to reception conditions.

In other words, when transmitting television signals from a receiving station to a transmitting station via a relay transmission line composed of optical fiber cables, etc., the received broadcast waves are not converted into intermediate frequency signals or baseband signals, but are transmitted as they are. There are two methods: a method of transmitting a signal, and a method of converting a received broadcast wave into an intermediate frequency signal, a baseband signal, etc., and transmitting the converted signal.

However, with the method of directly transmitting received broadcast waves without converting them into intermediate frequency signals or baseband signals, if the receiving station and transmitting station are relatively far apart and the relay transmission line is relatively long, the relay transmission line Since the transmission loss becomes large, it is necessary to add a repeater or the like in the middle of the relay transmission path, resulting in deterioration of signal quality and increase in system cost.

Therefore, in order to reduce transmission loss on relay transmission lines and to improve economic efficiency, received broadcast waves are generally converted into intermediate frequency signals, baseband signals, etc., and then transmitted. A method is used in which intermediate frequency signals, baseband signals, etc. sent out from a receiving station are converted back into broadcast waves.

In this case, from the viewpoint of effective frequency utilization, it is desirable that the transmitting station converts the intermediate frequency signal, baseband signal, etc. sent from the receiving station into a broadcast wave having the same carrier frequency as the received broadcast wave.

[Problems to be Solved by the Invention] However, as described above, the receiving station converts the received broadcast waves into intermediate frequency signals, baseband signals, etc., sends them to the transmitting station via an intermediate transmission path, and receives them at the transmitting station. When converting an intermediate frequency signal, baseband signal, etc. sent from a station to a broadcast wave with the same carrier frequency as the received broadcast wave, a local oscillator consisting of a crystal oscillator is installed at each receiving station and transmitting station for frequency conversion. If provided, the frequency of the broadcast wave obtained at the transmitting station, which becomes the rebroadcast wave, will deviate slightly from the frequency of the received broadcast wave, which is the original transmission wave, due to the deviation of each oscillation frequency within the allowable range, and the receiver will If there is direct wave interference on the side, this frequency difference becomes a beat and causes a deterioration in image quality.

For this reason, conventionally, the transmitting station generally transmits intermediate frequency signals, baseband signals, etc. sent out from the receiving station to broadcast waves with a carrier frequency different from that of the received broadcast wave, for example, if the received broadcast wave is a VHF channel, the transmitting station transmits the intermediate frequency signal, baseband signal, etc. VHF with small channel and potential electric field
This is converted into broadcast waves from vacant channels, etc., which is an unfavorable result from the standpoint of effective use of radio frequencies.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and when a signal transmitted from a receiving station is converted back into a broadcast wave having the same carrier frequency as the received broadcast wave at a transmitting station, a retransmitted wave is generated. An object of the present invention is to provide a signal transmission method in which the frequency of a broadcast wave obtained at a transmitting station does not deviate from the frequency of a received broadcast wave, which is an original transmission wave, and the radio wave frequency can be used effectively.

[Means for Solving the Problems] In order to achieve the above-mentioned object, a signal transmission method according to the present invention includes a receiving station and a transmitting station connected through a relay transmission path, and receives broadcast waves at the receiving station. In a signal transmission method in which a signal is sent to a transmitting station via a relay transmission path, the signal sent from the receiving station is received, and a broadcast wave is transmitted from the transmitting station.
At the receiving station, the received broadcast wave is converted into a signal of a lower frequency using a local oscillation signal, and the low frequency signal and the local oscillation signal are transmitted to the transmitting station via the same or different relay transmission path. The transmitting station synchronizes with the receiving station using the local signal sent from the receiving station, and transmits the low frequency signal sent from the receiving station to the receiving broadcast again. It is characterized in that it is configured to convert into broadcast waves having the same carrier frequency as the waves.

[Operation] In the signal transmission method according to the present invention, the broadcast wave obtained at the transmitting station as the retransmission wave is synchronized with the received broadcast wave, which is the original transmission wave, and has the completely same frequency.

[Example] Hereinafter, an example of the present invention will be described in detail using the drawings.

Using optical fiber cable for relay transmission line,
In the diagram showing an embodiment of the present invention, a received broadcast wave, which is an original transmission wave received by a receiving antenna, etc., is supplied to an input terminal 10a of a receiving station system 10, and this received broadcast wave is amplified by a high frequency amplifier 11. and supplied to the mixer 12.

The receiving station system 10 is also provided with an oscillator 15, and a signal of a predetermined frequency obtained from the oscillator 15 is divided into two signals by a divider 16, one of which is multiplied by a multiplier 17. It is supplied to the mixer 12 as a local oscillation signal.

In the mixer 12, the received broadcast wave amplified by the high frequency amplifier 11 is frequency-converted into an intermediate frequency signal by the local oscillation signal supplied from the multiplier 17, and the intermediate frequency signal is amplified by the intermediate frequency amplifier 13 and demultiplexed. 14.

Further, the other signal obtained from the oscillator 15 and divided into two types of signals by the distributor 16 is supplied to the duplexer 14 as a synchronizing signal.

Then, in the demultiplexer 14, the intermediate frequency signal amplified by the intermediate frequency amplifier 13 and the synchronization signal supplied from the distributor 16 are combined, and the combined signal is converted into an optical signal by the optical transmitter 18, The optical signal is sent out to an optical fiber cable 30 as a relay transmission path and transmitted to the transmitting station system 20.

Therefore, the intermediate frequency signal and the synchronization signal are simultaneously sent from the receiving station system 10 to the transmitting station system 20 side through the optical fiber cable 30.

Now, in the transmitting station system 20, the optical signal sent from the receiving station system 10 through the optical fiber cable 30 is converted into an electrical signal by the optical receiver 21, that is, an intermediate frequency signal and a synchronization signal are sent from the optical receiver 21. A synthesized electrical signal is obtained, and the synthesized electrical signal is again divided into an intermediate frequency signal and a synchronization signal by the splitter 22.

The intermediate frequency signals divided in this way are amplified by the intermediate frequency amplifier 23 and supplied to the mixer 24, and the divided synchronization signals are multiplied by the multiplier 26 and supplied to the mixer 24 as a local oscillation signal. .

Then, in the mixer 24, the intermediate frequency signal amplified by the intermediate frequency amplifier 23 is transferred to a multiplier 26.
The frequency of the broadcast wave is again converted into a broadcast wave having the same carrier frequency as the received broadcast wave by the local oscillator signal supplied from the receiver, and the broadcast wave is amplified by the high frequency amplifier 25 and output to the output terminal 20a.

The broadcast wave guided to the output terminal 20a is transmitted as a retransmission wave. In this case, the broadcast wave that becomes the retransmission wave obtained at the output terminal 20a is synchronized with the received broadcast wave that is the original transmission wave, and has the completely same carrier frequency.

Note that the signal transmission method according to the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist thereof.

For example, at the receiving station, a baseband signal may be obtained from the intermediate frequency signal by video detection, and the baseband signal may be sent to the transmitting station together with the local signal.

Of course, in this case, at the transmitting station, the baseband signal sent from the receiving station is image-modulated to obtain an intermediate frequency signal, and the intermediate frequency signal is frequency-converted into a broadcast wave as described above.

Further, the local oscillator signal may be sent to the transmitting station through a relay transmission path different from the relay transmission path through which television signals such as intermediate frequency signals and baseband signals are sent.

Furthermore, it goes without saying that the information signal according to the present invention can be applied not only to television signals but also to other types of signals in the same manner as described above.

[Effects of the Invention] As described above, according to the present invention, when a signal transmitted from a receiving station is converted at a transmitting station into a broadcast wave having the same carrier frequency as the received broadcast wave, the transmitting station becomes a retransmitted wave. Since the frequency of the broadcast waves obtained at the time does not deviate from the frequency of the received broadcast waves, which are the original transmitted waves, it is possible to use the frequency effectively, and it is possible to improve the frequency of the broadcast waves received by television receivers and cable television subscribers. brings convenience to

[Brief explanation of the drawing]

The figure is a system diagram showing an example in which the signal transmission method according to the present invention is applied to an example in which an optical fiber cable is used as a relay transmission path. 10... Receiving station system (receiving station), 10a... Input terminal, 11, 25... High frequency amplifier, 12, 24
... Mixer, 13, 23 ... Intermediate frequency amplifier, 1
4, 22... splitter, 15... oscillator, 16...
Distributor, 17, 26... Multiplier, 18... Optical transmitter, 20... Transmitting station system (transmitting station), 21... Optical receiver, 30... Optical fiber cable.

Claims (1)

[Scope of Claims] 1. A system comprising a receiving station and a transmitting station connected by a relay transmission line, receiving broadcast waves at the receiving station, transmitting signals to the transmitting station via the relay transmission line, and transmitting signals from the receiving station. In a signal transmission method of receiving a signal and transmitting a broadcast wave from a transmitting station, the receiving station converts the received broadcast wave into a signal of a lower frequency using a local signal, and also converts the received broadcast wave to a signal of a lower frequency. and the above local signal are sent to the above transmitting station through the same or different relay transmission path, and the above transmitting station is synchronized with the above receiving station using the local signal sent from the above receiving station. , converting the low frequency signal sent from the receiving station back into a broadcast wave having the same carrier frequency as the received broadcast wave.