JP2002152290A - Modulation factor variable control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a modulation factor variable control system that can solve the problem of deteriorated carrier acquisition performance of a ground reception station, in the case of varying a data rate in the conventional rocket telemetry system. SOLUTION: An equalizer circuit 6 is provided at pre-stage of a pre- modulation filter 2, and thereby a modulation factor is automatically controlled to keep a difference between a carrier and a side lobe to be a constant value or over, even when the data rate is varied. Furthermore, since a pre-emphasis circuit 6' is employed for the equalizer circuit 6 to automatically control the modulation factor, no switching signal is required from the outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation degree variable control system, and more particularly to an improvement of a phase modulation circuit suitable for a transmitter mounted on a rocket.

[0002]

2. Description of the Related Art Communication using artificial satellites has been put to practical use for various purposes. Also, telemetry transmission and reception, in which various observation instruments are mounted on a rocket launched in the sky and the observation or measurement results of the observation instruments are transmitted to a receiving station on the ground, has become widespread. For communication with such a rocket-mounted telemetry transmitter or artificial satellite, communication accuracy is improved by using a phase-modulation digital communication, particularly a PSK (Phase Shift Keying) modulation method. .

FIG. 5 shows a conventional example of a phase modulation circuit of a telemetry transmitter mounted on a rocket. The conventional modulation circuit includes an input interface 1, a pre-modulation filter 2, an isolator 3, a phase modulator 4, and a high-frequency amplifier 5. The input interface 1 receives a modulation signal. A carrier signal is input to the isolator 3. The outputs of the premodulation filter 2 and the isolator 3 are input to the phase modulator 4. A modulated wave signal is output from the high frequency amplifier 5.

Here, the input interface 1 interfaces the modulated signal with a device on the other side. The pre-modulation filter 2 limits the occupied band of the modulation signal.
The isolator 3 isolates the phase modulator 4 from a carrier signal generator (not shown). The phase modulator 4 modulates the phase of the carrier with the modulation wave. The high-frequency amplifier 5 amplifies the carrier modulated by the phase modulator 4. The conventional modulation circuit has a fixed data rate, and is realized by mounting only one fixed pre-modulation filter 2 corresponding to the data rate. The premodulation filter 2 is provided for transmitting information with a minimum occupied frequency bandwidth from the viewpoint of effective use of frequency.

In the prior art, there is a modulation circuit having a pre-emphasis circuit, but the purpose of use is different.
One example of a conventional PSK modulation circuit system having a pre-emphasis circuit is disclosed in, for example, "Service Channel Modulation System" in Japanese Patent Application Laid-Open No. Sho 59-167166.
As disclosed in this patent publication, in this conventional PSK modulation circuit system, a pre-emphasis circuit is used for the purpose of improving a bit error rate.

[0006]

In a telemetry system mounted on a rocket, a fixed data rate limits the distance that a line can be established. Therefore, in order to secure a line over a long distance, a system has been constructed to secure a line margin by varying the data rate. However, in the case of such a system, there are the following problems if the conventional system described above is used as it is. That is, when the data rate is changed, the carrier capturing performance of the terrestrial receiving station deteriorates. The reason is that the carrier becomes smaller than the side lobe when the data rate is changed to a low rate because the cutoff frequency of the premodulation filter is fixed.

[0007] The receiving station on the ground tracks and captures the carrier of the transmitter, which adversely affects the capturing performance. This problem can be solved by mounting and switching a plurality of premodulation filters adapted to the variable data rate. However, such a solution is not optimal because it adds complexity and weight to the circuitry and requires an external switching signal.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a telemetry system capable of securing stable capture even if the data rate during rocket flight is varied. Another object of the present invention is to provide a system that can be constructed with a minimum number of additional circuits.

[0009]

A modulation degree variable control system according to the present invention comprises: an isolator to which a carrier signal is input;
A control system comprising: an input interface to which a modulation signal is input; a pre-modulation filter for limiting an occupied band of the modulation signal from the input interface; and a phase modulator for receiving the outputs of the pre-modulation filter and the isolator and performing phase modulation. An equalizer circuit is provided between the input interface and the pre-modulation filter, and the amplitude of the modulation signal is varied according to the data rate.

Further, according to a preferred embodiment of the modulation degree variable control system of the present invention, the equalizer circuit is constituted by passive elements such as resistors and capacitors. A pre-emphasis circuit is used as an equalizer circuit. The pre-emphasis circuit uses an active element. An operational amplifier is used as the active element, and an input impedance and a feedback impedance are connected to the operational amplifier.

[0011]

Next, the configuration and operation of a preferred embodiment of a modulation degree variable control circuit according to the present invention will be described in detail with reference to the accompanying drawings. For convenience of explanation, the same reference numerals are used for components corresponding to the above-described components of the related art.

FIG. 1 is a system diagram showing a configuration of a preferred embodiment of a modulation degree variable control system according to the present invention. This modulation degree variable control method includes an input interface 1 to which a modulation signal is input, an equalizer circuit 6, a premodulation filter 2, an isolator 3 to which a carrier signal is input, a phase modulator 4, and a high-frequency amplifier 5. Compared with the conventional modulation circuit described above with reference to FIG. 5, an equalizer circuit 6 is added between the input interface 1 and the pre-modulation filter 2.

Next, the function of each of the components 1 to 6 shown in FIG. The input interface 1 interfaces a modulated signal with a partner device.
The pre-modulation filter 2 limits an occupied band of a modulation signal input via the input interface 1. The isolator 3 isolates the phase modulator 4 from a carrier signal generator (not shown). The phase modulator 4 modulates the phase of the carrier with the modulation signal. The high-frequency amplifier 5 amplifies the carrier wave that has been phase-modulated by the phase modulator 4 and outputs a modulated wave signal. The equalizer circuit 6 varies the amplitude of the modulation signal according to the data rate.

FIG. 2 shows a specific example of the equalizer circuit 6.
The equalizer circuit 6 shown in FIG. 2 includes a resistor 7 and a capacitor 8 connected in parallel between an input terminal 10 and an output terminal 11, and a resistor 9 connected between the output terminal 11 and ground.

Next, the change in the waveform of the modulation signal in FIG. 1 will be described. In FIG. 1, when a modulation signal is input to an input interface 1, the input interface 1 converts the modulation signal into a modulation voltage waveform. The equalizer circuit 6 varies the amplitude of the modulation voltage waveform according to the frequency component of the modulation voltage waveform. The pre-modulation filter 2 limits the band of the modulated voltage waveform whose amplitude has been varied by the equalizer circuit 6. The phase modulator 4 applies a phase modulation to a carrier using a modulation voltage waveform band-limited by the pre-modulation filter 2.

FIG. 4 shows the characteristics of the equalizer circuit 6, that is, the relationship between the data rate and the output voltage of the equalizer circuit 6. The horizontal axis represents the data rate, and the vertical axis represents the output of the equalizer circuit 6. As shown in FIG. 4, the equalizer circuit 6
Operates according to the frequency component of the modulation voltage waveform,
No external control signal is required. The type of the equalizer circuit 6 depends on the type of the premodulation filter 2. Furthermore, in this embodiment, various premodulation filters 2 can be supported by selecting the type of the equalizer circuit 6. In this way, when the data rate is varied, the difference between the carrier and the side lobe of the modulation spectrum is kept at a certain value or more.

A second embodiment of the modulation degree variable control system according to the present invention will be described. Its basic configuration is as described above, but the equalizer circuit 6 is changed to a pre-emphasis circuit. FIG. 3 shows a specific example of the pre-emphasis circuit. The pre-emphasis circuit 6 'in FIG. 3 is a variable gain amplifier using an operational amplifier (operational amplifier) 20 as an active element. The pre-emphasis circuit 6 ′ includes an operational amplifier 20, an input impedance connected between the inverting input terminal (−) of the operational amplifier 20 and the input terminal 21, and a feedback connected between the inverting input terminal of the operational amplifier 20 and the output terminal 22. It is constituted by a resistor 26. The input impedance is constituted by a resistor 23 and a series circuit of a resistor 24 and a capacitor 25 connected in parallel to the resistor. The non-inverting input terminal (+) of the operational amplifier 20 is applied with a reference voltage by a voltage dividing circuit including resistors 27 and 28 connected in series. This pre-emphasis circuit 6 '
According to the above, it is possible to perform variable control of the modulation degree more finely than the equalizer circuit 6.

The configuration and operation of the preferred embodiment of the modulation degree variable control system according to the present invention have been described above in detail. However, it should be noted that such an embodiment is merely an example of the present invention and does not limit the present invention in any way. It will be readily apparent to those skilled in the art that various modifications can be made in accordance with the particular application without departing from the spirit of the invention.

[0019]

As will be understood from the above description, the modulation degree variable control system according to the present invention has the following remarkable practical effects. First, stable carrier capture performance can be maintained when the data rate is variable. The reason is that the modulation voltage waveform is variably controlled by the equalizer circuit (pre-emphasis circuit). Second, the circuit is simple. The reason is that the premodulation filter can be realized by one filter having a cutoff frequency corresponding to the maximum data rate. Third, a system can be constructed with the transmitter alone. The reason is that the switching signal becomes unnecessary because the equalizer circuit controls the amplitude of the modulation voltage waveform according to the frequency component.

[Brief description of the drawings]

FIG. 1 is a block diagram of a preferred embodiment of a modulation degree variable control system according to the present invention.

FIG. 2 is a circuit diagram of a specific example of the equalizer circuit shown in FIG.

FIG. 3 is a circuit diagram of a specific example of a pre-emphasis circuit used as the equalizer circuit shown in FIG.

FIG. 4 is a graph showing a data rate of the equalizer circuit shown in FIG. 2 versus an output characteristic of the equalizer circuit;

FIG. 5 is a block diagram of a conventional modulation degree variable control method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input interface 2 Premodulation filter 3 Isolator 4 Phase modulator 5 High frequency amplifier 6 Equalizer circuit 6 'Preemphasis circuit 20 Operational amplifier

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Naoya Tsuda 3-18-21 Shibaura, Minato-ku, Tokyo NEC Engineering Co., Ltd. F-term (reference) 5K004 AA01 AA03 BA02 DD04 5K066 AA05 BB04 CC02 DD02 DD34 GG07 GG17 HH01 JJ02

Claims (5)

[Claims] An isolator to which a carrier signal is input;
A modulation system comprising: an input interface to which a modulation signal is input; a pre-modulation filter for limiting an occupied band of the modulation signal from the input interface; and a phase modulator for receiving the output of the pre-modulation filter and the isolator and performing phase modulation. A modulation degree variable control method, wherein an equalizer circuit is provided between the input interface and the pre-modulation filter, and an amplitude of the modulation signal is changed according to a data rate. 2. The modulation degree variable control system according to claim 1, wherein said equalizer circuit is constituted by passive elements such as resistors and capacitors. 3. The modulation degree variable control system according to claim 1, wherein a pre-emphasis circuit is used as said equalizer circuit. 4. The modulation degree variable control method according to claim 3, wherein said pre-emphasis circuit uses an active element. 5. The modulation degree variable control method according to claim 4, wherein an operational amplifier is used as said active element, and an input impedance and a feedback impedance are connected to said operational amplifier.