JP4690435B2 - Broadcast relay method and broadcast relay apparatus - Google Patents

Description

  The present invention relates to a relay method for various broadcasts in television broadcast, for example, terrestrial digital broadcast, and a relay device used therefor.

  As shown in FIG. 3, a relay device in television broadcasting is one that adjusts the level of radio waves (multi-channel broadcast waves) received from a receiving station A and transmitted from a transmitting antenna B. Since the input level of the relay device varies depending on the radio wave environment in the atmosphere (space), an AGC circuit C is provided in the relay device to stabilize the output level, and the output level is adjusted for each channel by this AGC circuit. . Further, a squelch circuit (SQ) is provided for each channel so that noise is not sent to the space when the master station is stopped.

  3, the input signal (terrestrial digital broadcast wave) received by the receiving antenna A is amplified by the RF amplifiers 1 and 2 (FIG. 4), and a part of the input signal is branched by the branching device 3 (FIG. 4). The branch signal is detected by the detector (DET1). Since digital terrestrial broadcasting employs an OFDM (Orthogonal Frequency Division Multiplexing) system, the detection voltage at point A in FIG. 4 has an amplitude as shown in FIG. Therefore, in the relay device of FIG. 4, the detection voltage at point A is averaged through a low-pass filter (LPF: FIG. 4), and the averaged voltage (voltage at point B in FIG. 4) is amplified by the DC amplifier 4, and the voltage A gain controller (GC, for example, variable ATT) is controlled with reference to, and the output level of the broadcast wave signal is controlled to be constant with this GC. The voltage at point B in FIG. 4 is taken into a microcomputer, gate circuit, comparator, central processing circuit, etc. (these are collectively referred to as CPU), and when the voltage at point B is below a certain threshold, a squelch circuit (SQ) Is turned on (operates) and the output of the broadcast signal from the transmitting antenna is stopped. At this time, since the AGC is working, the apparatus gain is maximized (GC loss is minimized). When a broadcast signal is input during the operation of the squelch circuit (SQ) (when ON), the gain at the beginning is maximized, so that the voltage at point B in FIG. 4 becomes high but is converged by AGC and gradually becomes stable. The CPU monitors the point B voltage in FIG. 4 to determine the convergence of AGC, and when the point B voltage exceeds the threshold value, the squelch circuit (SQ) is turned off (operation stops) and a broadcast signal is transmitted. The signal is output from the antenna.

The conventional relay device has the following problems.
1. In digital terrestrial broadcasting, the SFN (Single Frequency Network) method is generally used from the viewpoint of effective frequency utilization. In SFN, since the channel (frequency) transmitted from the master station and input to the relay device is the same as the channel (frequency) output from the relay device, the radio wave output from the transmission antenna oscillates around the reception antenna and oscillates. There is a case. As an example of the countermeasure, the distance between the receiving antenna and the transmitting antenna is increased, or an expensive canceller is used for each channel. The former measure requires a large site, and the latter measure increases costs.
2. Since the AGC function makes the output level constant, the lower the input level from the master station, the higher the gain of the relay device, and the more easily affected by the wraparound between the antennas.
3. When the master station stops, the device gain is maximized by the AGC function, and oscillation occurs when the device gain exceeds the wraparound amount (FIG. 7). If oscillation occurs before the squelch function is executed, the oscillation continues, and the spectrum of the detection signal at point A in FIG. 4 is as shown in FIG.
4). At the time of the stoppage, radio waves (FIG. 7) other than the OFDM modulation wave are radiated from the relay device, but this radiation is not preferable in the radio wave law.
5. Since the CPU monitors the voltage after averaging the OFDM voltage through a low-pass filter (LPF: FIG. 4), the control of the squelch circuit by the CPU is slow, and the response of the squelch circuit is also slow.

Prior to the development of the present invention, the present inventors conducted experiments on the broadcast relay apparatus to confirm the following in order to solve the above-described problems of the conventional broadcast relay apparatus.
1. Since there is an AGC function, if the fluctuation of the input level is within the control range of the variable attenuator (variable ATT), oscillation does not occur even if the amount of sneak between the antennas fluctuates.
2. Even when the amount of sneak between the receiving antenna and the transmitting antenna is the same as the apparatus gain, no video deterioration is observed.
3. The detection waveform is different between the detection voltage when the normal terrestrial digital broadcast signal is output (FIG. 5) and the detection voltage during oscillation (FIG. 6). The modulated signal of the terrestrial digital broadcast wave has a voltage fluctuating with time (FIG. 5), but at the time of oscillation, there is no time fluctuation like CW (continue wave: unmodulated wave) and is constant (FIG. 6). .

  The broadcast relay method and the broadcast relay apparatus of the present invention use the waveform difference to turn on the squelch circuit (SQ) when the detection voltage becomes constant (no fluctuation), and the output signal is transmitted to the transmission antenna. From being transmitted or the squelch function is implemented before oscillation.

One broadcast relay method of the present invention, by branching a portion of the broadcast wave signal received by receiving antenna, controls the gain of the gain controller on the basis of a detection signal obtained by detecting the branch signals, In the broadcast wave relay method, the AGC function for controlling the received broadcast wave signal for each channel to control the output signal level is provided, and the signal transmission is stopped by the squelch function when the broadcast wave signal is cut off. In this method, the presence / absence of the signal amplitude is judged and the squelch circuit is turned on to stop the output of the broadcast wave signal when the signal becomes none, and the squelch circuit is turned off and the broadcast wave signal is outputted when the signal becomes yes.

Other methods of broadcast relay method of the present invention, as claimed in claim 1, branches a part of the received broadcast wave signal by the receiving antenna, on the basis of a detection signal obtained by detecting the branch signal gain controller By controlling the gain of the AGC, it has an AGC function to control the output signal level by controlling the received broadcast wave signal for each channel, and when the broadcast wave signal is cut off, the squelch function stops signal transmission In the broadcast wave relay method, the AC component in the detection signal is extracted and detected, and when the detected AC component is compared with the threshold value and becomes equal to or lower than the threshold value, the squelch circuit is turned on to stop the output of the broadcast signal, This is a method of turning off the squelch circuit and outputting a broadcast signal when the threshold value is exceeded.

One broadcast relay device of the present invention, channels and branching unit branches a part of the broadcast wave signal received by receiving antenna, a detector for detecting a branch signal, an input signal based on the detection signal In a broadcast relay apparatus comprising a gain controller that controls each time, a squelch circuit that operates when a broadcast wave signal is interrupted to stop signal transmission from a transmission antenna, and a controller that controls ON / OFF of the squelch circuit And a capture path (10 in FIG. 1) for capturing the detection signal into the controller, and the controller determines the presence or absence of the amplitude of the detection signal and turns the squelch circuit ON when the detection signal becomes zero. Is stopped, and when it is present, the squelch circuit is turned off to output a broadcast wave signal.

Other devices broadcast relay device of the present invention, as claimed in claim 2, wherein a branching device for branching a part of the received broadcast wave signal by the receiving antenna, a detector for detecting a branch signal, detection A gain controller that controls the input signal for each channel based on the signal, a squelch circuit that operates when the broadcast wave signal is interrupted to stop signal transmission from the transmission antenna, and a controller that controls ON / OFF of the squelch circuit In the broadcast relay apparatus comprising: an AC extraction circuit (20 in FIG. 2) for extracting an AC component in the detection signal; and an AC detection circuit (21 in FIG. 2) for detecting the AC component extracted by the AC extraction circuit 20 The controller compares the detection signal detected by the AC detection circuit 21 with a threshold value, and when the threshold signal is below the threshold value, turns on the squelch circuit to stop the output of the broadcast signal. The Ruchi circuit is a device for outputting the broadcast signal to OFF.

The present invention has the following effects.
1. An oscillation countermeasure function can be realized at low cost with a simple configuration of the input path 10, the AC extraction circuit 20, and the detection circuit 21 in an existing relay device.
2. Since the waveform immediately after detection is detected, it is possible to detect the disconnection of the input signal instantaneously, and when the fluctuating detection voltage disappears (when the broadcast wave signal is disconnected), the squelch circuit (SQ) turns on and before oscillation Since the squelch function is executed, oscillation can be reliably prevented.
3. When the amount of sneak between the receiving antenna and the transmitting antenna is large, in the AGC method with a constant output, oscillation occurs when the master station stops. However, in the present invention, oscillation or oscillation starts by detecting the waveform immediately after detection. Since the transmission output can be turned off by detecting this, the wraparound loop is cut and oscillation stops, the squelch function works, and when the master station returns, it starts without causing oscillation by normal operation.

(Embodiment 1 of broadcast relay apparatus)
An embodiment of the broadcast relay device of the present invention will be described below with reference to FIG. 1 includes an RF amplifier 1, a gain controller (GC), an RF amplifier 2, a detector (DET1), a low-pass filter (LPF), a DC amplifier 3, a squelch circuit (SQ), a microcomputer or a gate circuit (CPU). And a capture path 10 is provided for capturing the output of the detector (DET1) into the CPU.

(Embodiment 1 of broadcast relay method)
In the broadcast relay apparatus of FIG. 1, an input signal (broadcast wave) received by a receiving antenna is amplified by an RF amplifier 1, gain controlled by a gain controller (GC), amplified by an RF amplifier 2, and a squelch circuit ( SQ) is transmitted from the transmitting antenna. During this time, a part of the input signal is branched by the branching device 3 and detected by the DET1. The detection voltage at point A in FIG. 1 has an amplitude as shown in FIG. 5 when normal, but when this detection voltage falls below a certain threshold value (abnormality occurs), the squelch circuit (SQ) is turned on. (In operation), the output of the broadcast signal from the transmitting antenna is stopped. At this time, since the AGC is working, the apparatus gain is maximum (the GC loss is minimum). Therefore, when a broadcast wave signal is input while the squelch circuit (SQ) is ON, the detection is initially performed because the gain is maximum. Although the voltage increases, the AGC gradually converges and stabilizes as shown in FIG. In FIG. 1, the detection voltage (point A voltage in FIG. 1) is monitored by the CPU to determine the convergence of AGC, and when the detection voltage exceeds a threshold value, the squelch circuit (SQ) is turned off and the transmission antenna Broadcast signal is output.

(Embodiment 2 of broadcast relay device)
A second embodiment of the broadcast relay device of the present invention will be described below with reference to FIG. 2 includes an RF amplifier 1, a gain controller (GC), an RF amplifier 2, a first detector (DET1), a low-pass filter (LPF), a DC amplifier 3, a squelch circuit (SQ), a microcomputer or A gate circuit (CPU), an AC extraction circuit 20 using capacitors C1 and C2 and an AC amplifier, and a second AC detection circuit (DET2: 21 in FIG. 2) for detecting an AC component extracted by the AC extraction circuit 20. I have.

(Embodiment 2 of broadcast relay method)
2, the input signal (broadcast wave) received by the receiving antenna is amplified by the RF amplifier 1, gain controlled by the gain controller (GC), amplified by the RF amplifier 2, and squelch circuit ( SQ) is transmitted from the transmitting antenna. During this time, a part of the input signal is branched by the branching device 5 and detected by the DET1. The detection voltage at point A in FIG. 1 has an amplitude as shown in FIG. In FIG. 2, the detection voltage at point A is averaged by a low-pass filter (LPF), and the gain of the gain controller (GC) is controlled based on the voltage at point B in FIG. The

  In FIG. 2, the AC component in the signal detected by the detector (DET1) is extracted by the capacitor C1, amplified by the AC amplifier, the AC component in the output signal of the AC amplifier is extracted by the capacitor C2, and the detector (DET2) is extracted. ) Is detected. The output voltage of DET2 (the voltage at point C in FIG. 1) is generated when an OFDM signal (broadcast wave) is input (present: 1 V, for example), and is zero (or almost 0 V) when oscillating or stopped. The CPU captures the voltage at point C, and when it becomes 0 V, the squelch circuit (SQ) is turned on and the output of the broadcast signal from the transmission antenna 2 is stopped. At this time, since the AGC is working, the apparatus gain is maximum (the GC loss is minimum). Therefore, when a broadcast signal is input during the operation of the squelch circuit (SQ), the gain is initially maximum, and the point B in FIG. However, the voltage is gradually converged by AGC and stabilized to a substantially constant amplitude as shown in FIG. At this time, the voltage at point B in FIG. 2 is monitored by the CPU to determine the convergence of AGC. Further, the voltage at point C in FIG. 1 is present (for example, 1 V), and the control signal from the CPU to the squelch circuit (SQ) turns off the squelch circuit (SQ) and the broadcast signal is output from the transmission antenna 2.

The circuit diagram which shows an example of embodiment of the AGC circuit and squelch circuit control circuit in the broadcast relay apparatus of this invention. The circuit diagram which shows the other example of embodiment of the AGC circuit and squelch circuit control circuit in the broadcast relay apparatus of this invention. Schematic diagram of a conventional broadcast relay device. FIG. 4 is an explanatory diagram of an AGC circuit and a squelch circuit control circuit in the broadcast relay device of FIG. 3. Waveform explanatory drawing of the detection voltage of the terrestrial digital broadcast wave in the A point of the broadcast relay apparatus of FIG. Waveform explanatory drawing of the detection voltage at the time of the oscillation in the point A of the broadcast relay apparatus of FIG. Waveform explanatory drawing of the detection voltage before and behind the oscillation generation | occurrence | production in the A point of the broadcast relay apparatus of FIG. FIG. 3 is an explanatory diagram of an example of an oscillation spectrum at point A of the broadcast relay device of FIG. 1.

1, 2 RF amplifier 3 Branching device 10 Take-in route 20 AC take-out circuit 21 AC detection circuit

Claims (2)

  A part of the broadcast wave signal received by the receiving antenna is branched, and the gain of the gain controller is controlled based on the detection signal obtained by detecting the branch signal, thereby controlling the received broadcast wave signal for each channel. In the broadcast wave relay method having an AGC function for controlling the output signal level and stopping the signal transmission by the squelch function when the broadcast wave signal is interrupted, the AC component in the detection signal is extracted and detected and detected. The AC component and the threshold value are compared, and when the value falls below the threshold value, the squelch circuit is turned on to stop the output of the broadcast signal. Relay method.   A branching device that branches a part of the broadcast wave signal received by the receiving antenna, a detector that detects the branch signal, a gain controller that controls the input signal for each channel based on the detection signal, and a broadcast wave signal AC extraction circuit that extracts an AC component in the detection signal in a broadcast relay device that includes a squelch circuit that operates when it is disconnected and stops signal transmission from the transmission antenna, and a controller that controls ON / OFF of the squelch circuit And an AC detection circuit for detecting the AC component extracted by the AC extraction circuit, and a controller. The controller compares the detection signal detected by the AC detection circuit with the threshold value and turns on the squelch circuit when the threshold value is below the threshold value. The broadcast relay apparatus is characterized in that the output of the broadcast signal is stopped and the squelch circuit is turned off to output the broadcast signal when the threshold value is exceeded.

Images