JPH0422397B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a satellite broadcast receiver that receives a plurality of television signals having different planes of polarization transmitted from a satellite.

BACKGROUND ART Conventionally, satellite broadcasting (television signals) in the 4 GHz band (C band) in the United States and elsewhere has consisted of two types of signals with vertical and horizontal polarization planes. For example, when 24 channels (3.74 to 4.18 GHz) of television signals are emitted from one satellite, the odd channels are sent vertically and the even channels are sent horizontally.
(There are also satellites with opposite polarization planes.) Each channel has an occupied band of 40MHz, and the CH space is 20MHz, and the polarization plane is switched to prevent interference. In this type of satellite broadcasting, a polarizer installed at the focal point of the receiving antenna extracts signals with either vertical or horizontal polarization and sends them to a low-noise converter (LNB) installed behind the polarizer. It is structured to convey the message. FIG. 3 shows an example of the configuration of the above-mentioned conventional satellite broadcasting receiver. In Figure 3, 1 is an antenna, 2 is a polarizer, 3 is an LNB, and 4a and 4b are
LNB 3, along the pillar 4b with the polarizer 2 pillar,
A signal cable, power to the polarizer 2, and a control signal transmission line 5 are installed. 6 is the support of antenna 1, and the elevation angle and direction of antenna 1 (eastward or westward)
Needless to say, it can change. 7 is a satellite broadcasting receiver, which consists of the following components.
8 is a tuner also called a 2nd mixer.
24 waves with center frequency of 3.72~4.18GHz with LNB3
Convert to 24 waves from 970 to 1430MHz, tuner 8,
Attune to one of those waves. The output of tuner 8 is
For example, the IF frequency is 510MHz and the band is 25MHz. 9 is a video intermediate frequency amplification circuit (hereinafter referred to as an IF circuit), which includes a band pass filter (BPF). 10 is a wideband FM detection circuit, such as a PLL
detection is used. Reference numeral 11 denotes an audio detection circuit 11 that performs FM detection on the audio carrier wave being output from the FM detection circuit 10.
The output of the audio detection circuit 11 is converted into an appropriate level and frequency characteristic by the audio signal processing circuit 13 and outputted, and the output of the audio signal processing circuit 13 is also supplied to the RF converter 14. On the other hand, the video signal processing circuit 12 removes high-frequency components of 4.2 MHz or higher 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, let the desired wave be the N channel. The spectra of the transmitted signals (N-1), N, and (N+1) are
When considering the IF band, the levels are assumed to be equal, as shown in Figure 5A. In this case, the center of the (N-1) channel is 490MHz, and the center of the (N+1) channel is 490MHz.
It shall be 530MHz. The polarization plane of polarizer 2 is
When the signal is approximately halfway between vertical and horizontal, the signal is as shown in Figure 5B.
The output of the IF circuit 9 becomes as shown in FIG. 5C. Assuming that the N-channel signal is vertically polarized, when the plane of polarization of the polarizer 2 becomes vertical, the signal of the adjacent channel drops by about 15 dB, as shown by the dotted line in FIG. 5A. (The degree of separation of polarizer 2 is
15 dB) Therefore, when it passes through a bandpass waver, the spectrum will be as shown in Fig. 5D.

In the above explanation, the spectrum is illustrated assuming that the FM frequency shift of a normal television signal is about 10 MHz on average. The same applies to each of 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. 7A. 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 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.
In other words, the polarization plane of polarizer 2 (probe in the case of a polar rotor) is -45 degrees or more in the horizontal direction from the reference point 0 degrees.
From the point where is turned, that is, ST in Figure 7, change the polarization plane to horizontal (-45 degrees), 0 degrees, and vertical (+45 degrees).
Assuming that one sweep of the polarization plane ends at a point further beyond the vertical direction, that is, at END in FIG. 7, under an ideal operating condition, the polarization plane changes as shown by the solid line in FIG. 7A. Similarly, the relationship between the angle of the plane of polarization and the output of the AGC detection circuit 16 when receiving a horizontally polarized signal is shown by the dotted line in FIG. 7A.

In an ideal situation, the relationship shown by the dotted line or solid line in Figure 7A is obtained, but the operation at this time is shown in Figure 4.
This will be described in conjunction with Figure 7A. If the desired wave is N channels, specifying channel N requires 3 inputs.
The output of NOR gate 21 goes low, setting flip-flop 20, and its Q output goes high, causing sweep voltage generation circuit 19 to generate a sawtooth voltage or triangular wave. On the other hand, the output of the three-input NOR gate 21 is transmitted to the peak hold circuit 17 to discharge the held voltage. As the output voltage of the sweep voltage generation circuit 19 changes, the plane of polarization of the polarizer 2 changes.
When a polarizer 2 of a type called a ferrofield is used, the sweep voltage is amplified and used. In a type called a polar rotor, the rotation angle of the plane of polarization is determined by comparison with the pulse width, so the sweep voltage is converted into a pulse width by the pulse generator 22 and supplied to the polarizer 2. Here we consider Polarota. By changing the polarization plane from ST in Figure 7A,
Assuming that the AGC voltage reaches its maximum value at +45 degrees,
This peak voltage P _V is held at its peak by a peak hold circuit 17 . When the sweep voltage reaches END, it makes the same change again from ST. At this time, the level comparator 18 compares the output of the AGC detection circuit 16 and the output of the peak hold circuit 17, and when they match, outputs a negative pulse and outputs a negative pulse to the flip-flop 20.
Reset. When the Q output of the flip-flop 20 becomes low level, the sweep voltage generation circuit 19
The sweep voltage is no longer generated, and the DC power for rotating the rotor of the polarizer 2 is no longer supplied from the DC voltage supply circuit 23. (DC voltage supply circuit 2
3 supplies DC power to the polarizer 2 only while the Q of the flip-flop 20 is at a high level) Therefore, the polarization plane of the polar rotor stops at the optimum position of +45 degrees. Next, consider a case where the desired wave is 4 to 5 dB weaker than the adjacent CH. (Such a situation actually occurs in America.) The plane of polarization of polarizer 2 is horizontal,
At the vertical midpoint, or when there is no polarizer 2, the output side of the tuner 8 has a spectrum as shown in FIG. 6D. At this time, the polarization plane in the previous state is horizontal,
Assuming that it is vertical this time, when the polarization plane of the polarizer 2 does not start to change, the output of the tuner 8 will be as shown in Fig. 6A.
Even after passing through the band-pass filter, the spectrum is as shown in FIG. 6D. In such a state, if you start changing the polarization plane from ST, the 7th
As shown by the dashed line in Figure B, P′ _H becomes a peak, and P′ _V
Even if P′ _V is higher than P′ _H ,
The peak may occur before the regular _PV . At this time, the output of the tuner 8 becomes as shown in FIG. 6C. When the influence of adjacent waves is small, the optimum plane of polarization is determined by the solid line or broken line in FIG. 7B in the same way as in the case of FIG. 7A. It operates as described above when the power is turned on and when a sweep start is manually instructed.

In addition, so-called terrestrial interference is 500MHz, 520M
If it is around Hz, the influence will cause P _H in Figure 7,
The AGC voltage becomes maximum at points other than P _V , making it impossible to set the optimal polarization plane.

Problems to be Solved by the Invention However, the above-mentioned configuration has the problem that the following malfunctions often occur due to the strength of radio waves, interference waves, etc.

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

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

(3) Malfunction due to terrestrial interference.

In view of the above-mentioned problems, the present invention aims to provide a satellite broadcasting receiver that does not cause the above-mentioned malfunctions.

Means for Solving the Problems The present invention solves the above-mentioned problems, and includes a polarization plane control circuit that sets a polarizer that selects a polarization plane to an optimal state, and a polarization plane control circuit that sets a polarization plane control circuit in a comfortable state. A polarization state discriminating circuit for supplying a control signal indicating a certain condition is provided, and a band pass waver narrower than the transmission bandwidth of the video signal is provided on the input side of the state discriminating circuit.

Effects The present invention narrows the bandwidth, sufficiently attenuates signal components of adjacent channels, and
Even if the plane of polarization matches the adjacent channel, the circuit is configured so that an AGC voltage exceeding the level of the desired wave is not generated, thereby eliminating the influence of the adjacent channel.

Embodiment FIG. 1 shows the configuration of a satellite broadcasting receiver in an embodiment of the present invention.

In Fig. 1, 2 is a polarizer, 9F is a bandpass filter (hereinafter referred to as BPF), which is obtained by extracting the bandpass filter from the conventional IF circuit 9, and 9A is an intermediate forming the other amplifier section. Frequency amplification circuit (IF
circuit), 10 is an FM detection circuit, and the same parts as in Fig. 4 are given the same numbers.

24 is a narrowband filter whose response characteristics are shown in Figure 2B.
25 dB, and the passband width is about 12 MHz, which is half of about 24 MHz in FIG. 5B. Figure 2 A is
The input spectrum of BPF9F is shown, and N of the desired wave is shown.
If the channel is vertical and the channel before it is receiving a horizontally polarized signal, polarizer 2
When not controlling, the input of BPF9F is as shown in Figure 2 A.
The spectrum will look like this. BPF9F and IF circuit 9
The output of A becomes C in Figure 6, and the peak of the desired wave is P ₁
, the peaks P ₀ and P ₁ of adjacent CHs are at the same level. If the desired wave is 5dB weaker, the BPF is 9F.
The output of the IF circuit 9A is as shown in FIG. 6D. If such a state exists, it is difficult to set the plane of polarization of the polarizer 2 at the correct position. If the characteristics of the narrow band filter 24 are attenuated by 25 dB at the adjacent carrier position as shown in Figure 2B, BPF 9F is eliminated and the IF circuit 9A is
Even if the output of the narrowband filter 24 is as shown in Figure 2A, the output of the narrowband filter 24 will be the solid line in Figure 2C, and the peak P ₁ of the desired wave will be at a level 10 dB higher than the carrier peaks P ₀ and P ₁ of the adjacent channels. becomes. what if,
Even if the desired wave is 5 dB weaker than the adjacent channel, the output of the narrowband filter 24 becomes the dashed line in FIG. 2C, and P ₁ is 5 dB higher than P ₀ and P ₂ . In addition, BPF
When 9F BPF characteristics are overlapped, P ₀ and P ₂ are further increased by 15 dB.
It is attenuated and becomes a 20dB lower level. Therefore, if the plane of polarization is set vertically, the desired wave will be
Even if it is 5 dB weaker, if the separation degree of polarizer 2 is 15 dB,
The difference between P ₁ and P ₀ and P ₂ is 35 dB. In this way, the desired wave signal is independent of the polarization plane setting of polarizer 2.
If it is 20 dB or more stronger than the adjacent channel, the relationship between the polarization plane of the polarizer 2 and the AGC voltage (output of the AGC detection circuit 16) becomes the solid line or dotted line in FIG. 7A,
The optimum point of the plane of polarization can be easily set. Note that if a narrowband filter 24 with the same characteristics as BPF9F is used, the carrier attenuation of the adjacent channel will be degraded by 10 dB, so when the plane of polarization is reversed, _P1 of the desired wave in Fig. 2 will be ₀ , _P2 will be attenuated by 15 dB, and if the desired wave is 5 dB weaker than the adjacent channel, the difference between P ₁ and P ₀ , P ₂ will be about 10 dB, and although the influence will appear slightly, it will be almost the same as the curve shown in Figure 7 A. is obtained. Also, when terrestrial interference is at 520M and 500MHz, the amount of attenuation can be obtained by using the narrow band filter 24 (characteristics shown in Figure 2B) to obtain 10dB, but if BPF9F with the characteristics shown in Figure 6B is used, Does not attenuate even if stacked. The AGC detector 16 is a circuit that detects the output amplitude of the IF circuit 9A, and it goes without saying that if the output is applied to the IF amplification stage of the tuner 8, AGC can be applied.

In the above explanation, we have described the case where the polarization plane of the polarizer 2 starts from a state opposite to that of the desired wave, but when the polarization plane of the polarizer 2 and the polarization plane of the desired wave match, that is, the output of the tuner 8. Even if the spectrum starts out as shown in FIG. 5C, if the plane of polarization of the polarizer 2 is changed, a state as shown in FIG. 2A will occur. but,
In either case, due to the filter characteristics shown in Figure 2B, the level of the desired wave is sufficiently higher than the level of the adjacent wave on the input side of AGC detection, so the relationship shown by the solid line or broken line in Figure 7A is obtained, and the polarization The plane of polarization of wave device 2 matches the plane of polarization of the desired wave.

Effects of the Invention As described above, the present invention can produce the following excellent effects.

(1) The signal of the adjacent channel is 5 to 6 dB lower than the desired signal.
Even if it is strong, it will not malfunction.

(2) Malfunctions caused by terrestrial interference can be reduced.

(3) Since the band of the video signal system is not affected, the video detection output can maintain good characteristics.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the main parts of a satellite broadcasting receiver according to an embodiment of the present invention, Fig. 2 is a characteristic diagram of the same narrow band filter, and Fig. 3 is a block diagram of a conventional satellite broadcasting receiver. FIG. 4 is a block diagram of the polarizer control circuit, FIGS. 5 and 6 are characteristic diagrams for explaining the operation, and FIG. 7 is a characteristic diagram showing the relationship between the AGC voltage and the plane of polarization. 2...Polarizer, 9F...Band pass waver, 9A
...Intermediate frequency amplifier circuit, 10...FM detection circuit,
16...AGC detection circuit, 17...Peak hold circuit, 18...Level comparator, 19...Sweep voltage generation circuit, 20...Flip-flop, 2
1...3-input NOR gate, 22...pulse generator, 23...DC voltage supply circuit, 24...narrow band filter.

Claims (1)

[Claims] 1. A polarization control circuit configured to receive a plurality of television signals having different polarization planes transmitted from a satellite, and setting a polarizer that selects the polarization plane to an optimum state; and a polarization plane state determination circuit that supplies a control signal indicating that the polarization plane of the polarizer is in the optimum state, and a band-pass transducer narrower than the transmission bandwidth of the video signal is provided on the input side of the state determination circuit. A satellite broadcasting receiver characterized by: