JPH06105974B2 - Polarizer control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a polarizer used in a satellite broadcast receiver that receives a plurality of television signals having different polarization planes transmitted from a satellite. .

2. Description of the Related Art Conventionally, satellite broadcasting (television signals) in the 4 GHz band (C band) such as the United States is composed of two types of signals whose polarization planes are vertical and horizontal. For example, when 24 channels (3.72 to 4.18 GHz) of TV signals are emitted from one satellite,
The odd channels are sent in vertical planes and the even channels are sent in horizontal planes of polarization. Each channel (there is also a satellite with the opposite polarization plane) has an occupied band of 40 MHz and CH space of 20 MHz, and it switches the polarization plane to prevent interference. Such satellite broadcasts
A polarizer provided at the focal point of the receiving antenna takes out a signal on either a vertical or horizontal plane of polarization and transmits it to a low noise converter (LNB) provided behind the polarizer.

FIG. 2 shows an example of the configuration of the conventional satellite broadcast receiver described above.

In FIG. 2, 1 is an antenna, 2 is a polarizer, and 3 is an LN.
B, 4a and 4b are provided with a signal cable, power to the polarizer 2, and a control signal transmission line 5 along the LNB 3 and the column 4b of the polarizer 2. Needless to say, 6 is a column of the antenna 1, and the elevation angle and direction of the antenna 1 (the eastward region is westward) can be changed. Reference numeral 7 is a satellite broadcast receiver, which is composed of the following components. Numeral 8 is a tuner also called a 2nd mixer, which uses LNN3 to tune 24 waves with a center frequency of 3.72 to 4.18 GHz to 970 to 14
Convert to 24 waves of 30MHz, and tune to one of them with tuner 8. The output of the tuner 8 has an IF frequency of 510 MHz and the band is, for example, 25 MHz. Reference numeral 9 is a video intermediate frequency amplifier circuit (hereinafter referred to as IF circuit), which is a band pass wave filter (BP
F) is included. 10 is a wideband FM detection circuit, for example P
LL detection is used. Reference numeral 11 is a voice detection circuit 11 for performing FM detection on the voice carrier being output from the FM detection circuit 10.
The output of the audio signal processing circuit 13 is converted into an appropriate level and frequency characteristic by the audio signal processing circuit 13 and output, and the output of the audio signal processing circuit 13 is supplied to the RF converter 14. On the other hand, the video signal processing circuit 12 removes the high frequency component of 4.2 MHz or more and the energy diffusion signal, outputs the signal at an appropriate level, and supplies the output of the video signal processing circuit 12 to the RF converter 14. 15 is an automatic polarization control circuit that changes the plane of polarization and stops it at the optimum point.

An example of the automatic polarization control circuit 15 is shown in FIG. First, the desired wave is set to N channel. Signal sent (N-1),
When considering the N, (N + 1) spectra in the IF band, they have the same level as shown in FIG. 4 (A). In this case, (N-
1) The center of the channel is 490MHz, and the center of the (N + 1) channel is 530MHz. When the plane of polarization of the polarizer 2 is approximately in the middle between the vertical and horizontal directions and the signal passes through the band pass wave filter as shown in FIG. 4 (B), the output of the IF circuit 9 is shown in FIG. 4 (C). It becomes like. If the N-channel signal is vertically polarized and the plane of polarization of the polarizer 2 is vertical, the adjacent-channel signal is about 15 as shown by the dotted line in FIG. 4 (A).
dB lower. (When the degree of separation of the polarizer 2 is set to 15 dB) Therefore, when passing through the band pass wave filter, a spectrum as shown in FIG. 4 (D) is obtained.

In the above description, the spectrum is illustrated assuming that the frequency shift of FM of a normal television signal is about 10 MHz on average.
The same applies to the following figures. On the other hand, the relationship between the polarization plane of the polarizer 2 and the output of the AGC detection circuit 16 is shown by the solid line in FIG. The AGC detection circuit 16 generates a DC voltage proportional to the output of the IF circuit 9, controls the gain of the IF circuit 9 of the tuner 8, and keeps the input and output of the IF circuit 9 constant. That is,
AGC is not applied to the IF circuit 9. Therefore, when the plane of polarization becomes vertical and the signal amplitude becomes maximum, the output of the AGC detection circuit 16 becomes maximum. That is, from the reference point 0 degree, in the horizontal direction −
The polarization plane is changed from the point where the polarization plane of the polarizer 2 (probe in the case of a polar rotor) is rotated by 45 degrees or more, that is, from ST in FIG. Change)
Assuming that one sweep of the plane of polarization is completed at a point beyond the vertical, that is, at END in FIG. 6, the line changes in the ideal operating state as shown by the solid line in FIG. 6 (A). Similarly, when the horizontal polarization signal is received, the angle of the polarization plane and the AGC detection circuit 16
The output relationship is shown by the dotted line in FIG.

It is in an ideal state that the relationship of the dotted line or the solid line of FIG. 6 (A) is obtained, and the operation at this time will be described together with FIG. 3 and FIG. 6 (A). If the desired wave is N channel,
When the channel N is designated, the output of the 3-input NOR gate 21 becomes low level, and the flip-flop 20 is set.
The Q output becomes high level, and the sweep voltage generation circuit
From 19, a sawtooth voltage or a triangular wave is generated. on the other hand,
The output of the 3-input NOR gate 21 is transmitted to the peak hold circuit 17, and the held voltage is discharged. The polarization plane of the polarizer 2 changes as the output voltage of the sweep voltage generating circuit 19 changes. When a type called a ferro-feed is used as the polarizer 2, a sweep voltage is amplified and used. Since the rotation angle of the plane of polarization is determined in comparison with the pulse width in the type called polara, the sweep voltage is converted into a pulse width by the pulse generator 22 and supplied to the polarizer 2. Here we consider a polarota. In FIG. 6 (A)
Changing the polarization from the ST, at + 45 degrees, the AGC voltage and reaches the maximum value, the peak-hold the peak voltage P _V peak-hold circuit 17. When the sweep voltage reaches END, it changes from ST again. At this time, the level comparator 18 outputs the output of the AGC detection circuit 16 and the peak hold circuit 1
The outputs of 7 are compared, and when they match, a negative pulse is output and the flip-flop 20 is reset. Flip flop 20
Q output becomes low level and sweep voltage generation circuit 19
The sweep voltage is not generated, and the DC power that rotates the rotor of the polarizer 2 is not supplied from the DC voltage supply circuit 23. (The DC voltage supply circuit 23 supplies DC power to the polarizer 2 only while Q of the flip-flop 20 is at a high level)
Therefore, the polarization plane of the polar rotor stops at +45 degrees, which is the optimum position.

Next, consider a case where the desired wave is 4 to 5 dB weaker than the adjacent CH. (In reality, such a situation occurs in the United States.) When the plane of polarization of the polarizer 2 is in the middle between horizontal and vertical,
Alternatively, when there is no polarizer 2, the output side of the tuner 8
The spectrum is as shown in FIG. At this time, assuming that the polarization plane in the previous state is horizontal and this time it is vertical, when the polarization plane of the polarizer 2 does not start changing, the output of the tuner 8 is
The spectrum is as shown in FIG. 5A, and the spectrum is as shown in FIG. 5D even after passing through the band pass wave filter. In such a state, when the plane of polarization starts to be changed from ST, FIG. 6 (B)
_'Become a peak, P _V' P _H as a dashed line or higher than, be higher than the P V _'of it is P _H', it is there to become a peak in front of the regular P _V. At this time, the output of the tuner 8 is as shown in FIG. When the influence of an adjacent wave is small, the solid or broken line in FIG. 6B results and the optimum plane of polarization is determined as in the case of FIG. 6A. Even when the power is turned on or when the sweep start is manually instructed,
It operates as described above.

Incidentally, so-called ground wave interference, 500 MHz, if in the vicinity of 520 MHz, P _H of Figure 6 from its effects _12, AGC in terms other than P _V
The voltage becomes maximum and the optimum polarization plane cannot be set.

Problems to be Solved by the Invention However, the above-described configuration has a problem that the following malfunctions often occur due to the strength and weakness of radio waves, interfering waves, and the like.

(1) Malfunction due to the influence of adjacent channel signals.

(2) Malfunction due to input difference between adjacent channel and desired wave signal.

(3) Malfunction due to ground wave interference.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a satellite broadcast receiver that does not cause the above malfunctions.

Means for Solving the Problems The present invention is to solve the above-mentioned problems, and a band pass wave detector (hereinafter referred to as BPE) having a bandwidth different from the IF band is provided on the input side of the AGC detection circuit, and The passband width of the BPF is of a switching type.

Action The IF band BPF of the present invention has a characteristic for improving the transmission characteristics of the video signal (for example, the width of the −3 dB point is 24 MHz). The second BPF with the characteristics of is provided to prevent the AGC voltage from malfunctioning due to interference of adjacent waves or terrestrial waves.
The band characteristic of is further narrowed to avoid the malfunction of the setting of the polarizer.

Example Hereinafter, a control device for a polarizer according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the main part of this embodiment. The same parts as those in the conventional example are designated by the same reference numerals. IF
When the BPF characteristic of the circuit 9 is the solid line in FIG. 7 (A) and the polarization plane is set horizontally, if the N channel sent by vertical polarization is specified, the tuner 8 tunes to the N channel. However, the frequency spectrum of the output is as shown in FIG. 7 (C). However, the desired wave is 5 dB weaker than the adjacent wave, and the vertical and horizontal separation of the polarizer 2 is 15 dB. When no pulse is applied to the polar rotor from the pulse generator 22, the desired wave P ₁ is 20 dB lower than the carrier levels P ₀ and P ₂ of the adjacent waves, as shown in FIG. 7 (C). Therefore, even if it passes through the BPF of the IF circuit 9, P ₁ of the desired wave is 5 dB lower than P ₀ and P ₁ of the adjacent waves. Even if the polarization plane of the polarizer is rotated and set correctly vertically, P ₁ is only 10 dB higher than P ₀ and P ₁ . Therefore, the setting of the polarization plane has a high probability of including an error. Therefore, on the input side of the AGC detector 16, BPF31
(Characterized by the broken line in FIG. 7A) and BPF32 (characterized by the one-dot chain line in FIG. 7) are inserted. When N channel is specified, the flip-flop 20 is set, the Q output becomes high level, and DC power is supplied from the DC power supply circuit 23 to the polarizer 2 and the relay 24L, as in the conventional example.
The switch 24S has a short circuit between terminals a and c. Therefore, IF
The BPF characteristic from the input of the circuit 9 to the input of the AGC detector 16 is shown by the broken line in Fig. 7 (B) and is ± 10MH from the center of the desired wave.
Attenuation of 15 dB at a point away from z, 50 dB or more at a point of ± 20 MHz, P ₁ becomes 30 dB or more higher than P ₀ and P ₂ at the input of AGC detector 16 immediately after channel switching, and sweep starts. Then, if the plane of polarization is shifted from the horizontal optimum point, the difference between P ₁ and P ₀ , P ₂ at the input of the AGC detector 16 becomes 30 dB or more. If the levels of the desired wave and the adjacent wave are the same, the difference between P ₁ and P ₀ , P ₂ at the input of the AGC detector 16 is 35 dB or more. Therefore, if the sweep is started from FIG. 6 ST, the pulse width corresponding to the voltage is generated by the pulse generator 22 and the polarizer 2 is controlled, the relationship between the polarization plane and the AGC voltage is shown in FIG. 6 (A). The solid line of is obtained. That is, the AGC voltage at the peak point P _V is held in the peak hold circuit 17, and the sweep from ST is performed again.
The level comparison circuit 18 compares the voltage of the AGC detector 16 with the voltage stored in the peak hold circuit 17. The point of coincidence between them is the vertical polarization plane and is set correctly. When the setting is completed, the flip-flop 20 is reset by the output of the level comparator 18, the DC power of the DC voltage supply circuit 23 is not output, and the current stops flowing through the relay 24L, and the switch 24S is connected to the terminal b.
A short circuit occurs between -c. Therefore, from the input of IF circuit 9 to AGC
The BPF pass band up to the input of the detector 16 is the solid line in FIG. 7 (B). The adjacent wave after polarization matching is 35dB of the filter
And, it becomes lower than the level of the desired wave by 50 dB, which is obtained by adding 15 dB of polarization plane separation of the polarizer 2. Also, attenuation of 520,500MHz is 5d
B Yes Reduces malfunction due to ground wave interference. Further, even if the desired wave is weaker than the adjacent wave by about 5 dB, the above-mentioned 50 dB attenuation deteriorates to 45 dB, and the influence of the adjacent wave does not appear on the AGC voltage. Also, by making the BPF for AGC detection wider than when setting the polarization plane, an accurate AGC voltage can be obtained even for signals with large frequency shifts, and the operation up to the detection output of video signals becomes stable and accurate. . In the above description, it was considered that the plane of polarization was horizontal when the N channel was designated, but if the plane of polarization was vertical from the beginning, the output of the tuner 8 would be as shown in FIG. 4 (C). If the voltage of the sweep voltage generating circuit 19 is swept from ST, the output of the tuner 8 also appears in the case of FIG. 7 (C). Also, may be considered as the same even when the desired wave is horizontal / polarization, FIG. 6 (A) voltage of the polarization plane relationship broken line obtained, P _H is the peak-hold in the peak hold circuit 17 . The output of the AGC detector 16 is added to the tuner 8 to control the gain of the IF circuit 9.
Therefore, a detection circuit for controlling the plane of polarization is unnecessary.

EFFECTS OF THE INVENTION As described above, according to the present invention, (1) the interference of adjacent waves and ground waves can be eliminated.

(2) Since the input band of AGC detection is narrowed only while setting the polarization plane, AGC operation is not affected and the detection output performance is good.

That is, it is possible to exert an excellent effect.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of a control device for a polarizer according to an embodiment of the present invention, FIG. 2 is a block diagram of a receiving system of a satellite broadcast receiver, and FIG. 3 is a peak of AGC voltage of a conventional example. Block diagrams of the hold circuit, FIGS. 4 and 5 are spectrum diagrams of tuner output and BPF output, FIG. 6 is a characteristic diagram showing the relationship between the AGC voltage and the angle of the polarization plane, and FIG. 7 is the AGC of the present invention. FIG. 6 is a spectrum diagram of the input of the circuit. 2 …… Polarizer, 16 …… AGC detector, 17 …… Peak voltage hold circuit, 18 …… Level comparison circuit, 19 …… Sweep voltage generation circuit, 20 …… Flip float, 22 …… Pulse generator, 23 ...... DC power supply circuit, 24 …… Relay, 31,32
…… BPF.

Claims (1)

[Claims] 1. A polarizer for selecting a polarization plane of a television signal having a vertical or horizontal polarization plane transmitted from a satellite, a low noise converter installed immediately after the polarizer, and the converter. A tuner for inputting an output, an intermediate frequency amplifier for inputting an output of the tuner, an FM detection circuit for inputting an output of the intermediate frequency amplifier, and a polarization control circuit for controlling a polarization plane of the polarizer. A first band pass filter for inputting an output of the intermediate frequency amplifier and passing only a signal of a tuning channel; and a second band pass filter for inputting an output of the first band pass filter. And a switching means for switching and outputting the signal from the first or second band pass filter, and an AGC detection circuit for inputting the output of the switching means. By changing the wavefront, the peak value of the output of the AGC detection circuit and the value stored in the peak hold circuit are compared by the comparison means, and the signal from the second bandpass filter is only until the two coincide. A control device for a polarizer, characterized in that it is switched to.