JP3101934B2 - Satellite signal receiving amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a satellite signal receiving amplifier capable of outputting at a certain appropriate level whether the level of a satellite signal is high or low by performing C amplification.

[0002]

2. Description of the Related Art As shown in FIG. 7, an AGC amplifier circuit 3f is provided between an input terminal 1f and an output terminal 2f, and the AGC amplifier circuit 3f has an AGC amplifier circuit 3f so that its output level becomes constant.
An AGC control circuit 4f for controlling the gain of the C amplifier circuit 3f is additionally provided, and a satellite signal receiving amplifier having a squelch circuit 20f connected between the AGC amplifier circuit 3f and the output terminal 2f is provided.

In such a satellite signal receiving amplifier, AG
Since the C control circuit 4f detects the level of the satellite signal and controls the gain of the AGC amplifier circuit 3f, the signal can be output at a constant appropriate level regardless of whether the level of the satellite signal is high or low. If the satellite signal stops or becomes weak, noise entering the input terminal 1f other than the satellite signal is greatly amplified by the AGC amplifier circuit 3f. In this case, the AGC control circuit 4f The squelch circuit 20f is operated to prevent the greatly amplified noise from being output from the output terminal 2f because the detection level of the satellite signal decreases due to the above.

[0004]

However, in the conventional satellite signal receiving amplifier, if the level of the input satellite signal is lower than the range in which the AGC can be amplified, for example, the noise level is low and the satellite signal is low. However, there is a problem that the output of the amplified satellite signal is stopped by activating the squelch circuit as described above, even if is available, that is, even if the necessary and sufficient CN ratio is obtained.

The present invention has been made to solve the above-mentioned problems (technical problems) of the prior art, and outputs a signal of a constant appropriate level regardless of whether the level of an input satellite signal is high or low. If the input signal is interrupted or the level is abnormally reduced, and only the noise is greatly amplified, the output of such noise can be cut off. It is an object of the present invention to provide a satellite signal receiving amplifier which can output and use the above-mentioned satellite signal when the satellite signal is available due to a low noise level even if the level is lowered. .

[0006]

In the satellite signal receiving amplifier according to the present invention, an AGC amplifier circuit is interposed between an input terminal and an output terminal, and the output level of the AGC amplifier circuit is constant. An AGC control circuit for controlling the gain of the AGC amplifier circuit is provided so that
In a satellite signal receiving amplifier in which a squelch circuit is connected between a GC amplifier circuit and an output terminal, the squelch circuit includes a switch means interposed between the AGC amplifier circuit and an output terminal; A noise extracting means for receiving an output signal of the amplifier circuit and extracting noise from the signal; and receiving the noise extracted by the noise extracting means, determining whether or not the level exceeds a predetermined level. Determining means for correspondingly opening and closing the switch means,
The noise extracting means includes an FM demodulator and a band-pass filter that passes noise of a band different from a band of a video or audio signal among output signals of the FM demodulator.

[0007]

When a satellite signal arrives, it is AGC-amplified and output at a predetermined output level. When the signal stops or the level becomes weak, the noise is greatly amplified. In this case, only the noise that has been greatly amplified is extracted by the noise extracting means, and the switch means is opened by the discriminating means that has received the extracted noise, so that the large amplified noise is prevented from going to the output terminal. If the noise level is low even when the signal level is low, the noise level extracted by the noise extraction unit is low, and the determination unit keeps the switch unit closed.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 shows a satellite signal receiving amplifier for one channel in a multi-channel satellite signal receiving amplifier.
In this figure, reference numeral 1 denotes an input terminal to which a converter in an antenna for receiving a satellite signal is connected, and from which a satellite signal, for example, a CS-IF signal is input. Reference numeral 2 denotes an output terminal, which is connected to a mixer for mixing with signals of other channels. 3 is an AGC amplifier circuit, 4 is a known AG
The C control circuit comprises an AGC detector 5, an AGC level adjuster 6, and a DC amplifier 7. Reference numeral 8 denotes a level fluctuation detection point, which is constituted by, for example, a branch. Next, 9 is a first mixer, 10 is a first local oscillator circuit, and these are C
This is for converting the S-IF signal into a second intermediate frequency signal. Reference numeral 11 denotes a band-pass filter for passing only one predetermined channel signal and excluding other channel signals. For example, a band-pass filter having a pass band of 386.5 to 413.5 MHz is used. Reference numeral 12 denotes a known intermediate frequency amplifier circuit. Reference numeral 13 denotes a second mixer, and reference numeral 14 denotes a second local oscillation circuit for returning the second intermediate frequency signal to a CS-IF signal again. Reference numeral 15 denotes a rear-stage amplifier circuit.

Next, reference numeral 20 denotes a squelch circuit. Reference numeral 21 denotes switch means in the circuit, which is constituted by, for example, a relay. 22 is a noise extraction means for extracting only noise from the output signal of the intermediate frequency amplification circuit 12,
It comprises an FM demodulator 23 and a band pass filter 24. As is well known, the FM demodulator 23 has an input side CN.
Ratio is proportional to the S / N ratio on the output side, and the CN ratio on the input side is
When the ratio falls below the threshold level, the S / N ratio on the output side sharply decreases, and the output signal level does not change even if the input signal level changes.
The band-pass filter 24 is designed to pass only the noise band out of the output signal of the FM demodulator 23, and has a pass band of 10.2 to 11.2 MHz, for example. The pass band of the band-pass filter 24 may be a pass band that passes another frequency band as long as it passes a frequency band in which noise and video and audio signals do not exist. Next, reference numeral 25 denotes a determination means for receiving the noise extracted by the noise extraction means 22, determining whether the level of the noise exceeds a predetermined level, and opening and closing the switch means 21 correspondingly. is there. 26 indicates a detector in the means, 27 indicates a DC amplifier, and 28 indicates a comparator.

Next, the operation of the receiving amplifier having the above configuration will be described with reference to FIG.
A description will be given based on FIGS. 2 (A) to 2 (D) show the states of the signals at the points indicated by A to D in FIG. In these figures, solid lines indicate satellite signals intended for reception, and broken lines indicate noise.

First, a normal level range, that is, AGC
A case where a satellite signal in a range (for example, 68 to 87 dBμ) that can be handled by the above-described method is received will be described with reference to FIG. The input terminal 1 receives, for example, a signal as shown in FIG. This signal is amplified by the AGC amplifier circuit 3, converted into a second intermediate frequency signal by the mixer 9, passed through the band-pass filter 11, and then amplified by the intermediate frequency amplifier circuit 12. In this case, the output signal of the AGC amplifying circuit 3 becomes a predetermined level by controlling the gain of the AGC amplifying circuit 3 by the AGC control circuit 4. As a result, at the level change detection point 8, the level of the second intermediate frequency signal is changed as shown in FIG. As shown in (B), the level becomes a predetermined level, for example, 89 dBμ. Next, the signal is converted into a CS-IF signal again in the second mixer 13 and amplified in the post-amplifier circuit 15.

On the other hand, the output signal of the intermediate frequency amplifier circuit 12 is demodulated by the FM demodulator 23 to become a signal as shown in FIG. The bandpass filter 24 extracts, for example, noise in a band indicated by hatching from these signals. The noise extracted by the band-pass filter 24 is detected by the detector 26, amplified by the DC amplifier 27, and reaches the comparator 28 as a signal of the voltage value V2 in FIG. In this case, as is clear from FIG. 6, the voltage value V2 is set to a predetermined constant level V in the comparator 28.
0 (for example, a voltage corresponding to a CN ratio of 4 dB, for example, 2.6
V) and V1 (for example, 2.0 V at a voltage corresponding to a CN ratio of 2 dB), the comparator 28 outputs a signal to make the switch means 21 conductive. as a result,
The switch means 21 is kept closed as shown in FIG. Since the switch means 21 is in the closed state as described above, the CS-IF signal amplified by the latter-stage amplifier circuit 15 is shown in FIG.
Is output from the output terminal 2 as shown in FIG.

In the above case, even if the level of the satellite signal entering the input terminal 1 is low as shown by the two-dot chain line in FIG. 2A, it is included in the normal range. The satellite signal is amplified to a predetermined level by the AGC amplifier circuit 3 and output from the output terminal 2 at the same level as in the above case.

Next, the case where the satellite signal coming into the input terminal 1 stops will be described. In this case, the state of the signal at each point A to D in the circuit of FIG. 1 is as shown in FIGS. 3A to 3D. That is, since only noise enters the input terminal 1, the AGC amplifier circuit 3 amplifies only the noise to a predetermined level, and at the point B in FIG. 1, only the amplified noise as shown in FIG. Exists. Then, the output of the FM demodulator 23 is also only high-level noise as shown in FIG. As a result, the signal supplied to the comparator 28 becomes as low as V3 (for example, 1.4 V) in FIG. 6, and the comparator 28 outputs a signal for turning off the switch means 21. When the switch means 21 is opened by this signal, the amplified noise does not reach the output terminal 2 even if the noise of FIG. Does not output only noise. Therefore, even if the adjacent channel transmission is performed on the stage subsequent to the amplifier, there is no adverse effect of noise on the adjacent channel transmission.

Next, the level of the satellite signal coming into the input terminal 1 is lower than the normal range, and the level of the noise coming into the input terminal 1 is even lower, so that a predetermined C signal is set between the input terminal 1 and the satellite signal.
A case where an N ratio of, for example, 14 dB is obtained will be described. In this case, the signals at points A to D in FIG.
(D). That is, the AGC amplifier circuit 3
FIG. 1 amplifies the signal entering the input terminal 1 with the maximum gain.
The signal at point B is in a state as shown in FIG.
Then, the signal is demodulated by the FM demodulator 23 to become a signal as shown in FIG. In this case, the signal input to the comparator 28 is V4 in FIG.
V), the comparator 28 outputs a signal to make the switch means 21 conductive. As a result, a signal as shown in FIG.

Next, when the NF characteristic of the satellite antenna (converter) is degraded, or when the level of a signal reaching the satellite antenna decreases due to rainy weather, the level of noise entering the input terminal 1 is extremely high. A case will be described, for example, in the case of the same degree as the satellite signal coming there. In this case, FIG.
The signals at points A to D are in the states shown in FIGS. 5A to 5D. That is, since the satellite signal and the noise are at the same level at the input terminal 1, the point B in FIG.
Is in a state as shown in FIG. When this signal is demodulated by the FM demodulator 23, a large noise appears at its output. as a result,
The signal input to the comparator 28 is V5 (for example, 1.5 V) in FIG.
And outputs a signal for shutting off. As a result, output terminal 2
Does not output any signal as shown in FIG.

[0017]

As described above, according to the present invention, when a satellite signal enters the input terminal 1, even if the signal level is high or low, the signal level is amplified by AGC and adjusted to an appropriate level. Of course you can output,

If the satellite signal stops or its level becomes weak, noise entering the input terminal 1 other than the satellite signal is greatly amplified by the AGC amplifier circuit 3. In this case, The noise extraction means 22 extracts only the noise that has been greatly amplified, and the switch means 21 is opened by the determination means 25 that has received the extracted noise, so that the noise that has been greatly amplified goes to the output terminal 2. It can be cut off, and there is an effect that the adverse effect of noise on the subsequent stage can be prevented.

Further, according to the present invention, even if the level of the incoming satellite signal falls below the range that can be handled by AGC, if the noise level is relatively lower than the level of the satellite signal, That is, when the satellite signal is available, the level of the noise extracted by the noise extraction unit 22 is low, and the determination unit 25 keeps the switch unit 21 closed. It is effective in solving the above-mentioned conventional technical problems, such as being able to pass through and enabling its use.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a receiving amplifier.

FIGS. 2A to 2D are diagrams showing signal states at corresponding points A to D in FIG. 1 when the level of an input satellite signal is in a normal range.

FIGS. 3A to 3D are diagrams showing states of signals at corresponding points A to D in FIG. 1 when an input satellite signal stops.

FIGS. 4A to 4D are diagrams showing states of signals at corresponding points A to D in FIG. 1 when the level of an input satellite signal is lower than a normal range and noise is also lower.

5 (A) to 5 (D) show high levels of input noise and C
The figure which shows the state of the signal of each corresponding point AD of FIG. 1 when N ratio is bad.

FIG. 6 is a diagram illustrating characteristics of a comparator in a determination unit.

FIG. 7 is a block circuit diagram of a conventional receiving amplifier.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input end 2 Output end 3 AGC amplifier circuit 4 AGC control circuit 20 Squelch circuit 21 Switch means 22 Noise extraction means 25 Judgment means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-160229 (JP, A) JP-A-1-93820 (JP, U) JP-A-54-38819 (JP, Y2) (58) Investigation Field (Int.Cl. ⁷ , DB name) H03G 3/20-3/34

Claims (1)

(57) [Claims] An AGC amplifier circuit is provided between an input terminal and an output terminal, and the AGC amplifier circuit controls the gain of the AGC amplifier circuit so that its output level becomes a constant value. An AGC control circuit is provided, and the AGC
In a satellite signal receiving amplifier in which a squelch circuit is connected between an amplifier circuit and an output terminal, the squelch circuit includes switch means interposed between the AGC amplifier circuit and an output terminal; A noise extracting means for receiving an output signal of the circuit and extracting noise from the signal; and receiving the noise extracted by the noise extracting means, determining whether or not the level exceeds a predetermined level. and a discrimination means for corresponding closing means, on
The noise extracting means includes an FM demodulator and an output of the FM demodulator.
Of the input signals, a band different from the band of the video or audio signal
An amplifier for receiving a satellite signal, comprising: a band-pass filter that passes noise .