JPH0526843Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a diversity receiving device, and particularly to a diversity receiving device that is optimal for use in demodulating telemetry signals for space communications.

[Conventional technology]

Conventionally, diversity receiving devices have been used in communications such as telemetry reception from artificial satellites.

An example of a conventional diversity receiving device is shown in FIG. 5 and will be described.

This diversity receiving device includes mixers 1a and 1b and first gain control amplifiers 2a and 2.
b, first band wavers 3a and 3b,
AGC loop waveformers 4a and 4b, AGC waveform detectors 5a and 5b, voltage controlled oscillators 6a and 6b, X1 amplifier 7, X(-1) amplifier 8,
Phase detector 9, second gain control amplifiers 10a and 10b, combiner 11, and video detector 12
It is equipped with

In addition, is the input terminal to which the A channel (Ach) input signal is applied, and is the B channel (Bch).
The input terminal to which the input signal is applied is the output terminal from which the output signal is obtained.

Mixers 1a and 1b mix the input signal of the A channel (Ach) and the input signal of the B channel (Bch) with the outputs from the voltage controlled oscillators 6a and 6b, respectively, and convert them into an intermediate frequency; A phase detector 9 that outputs a voltage according to the phase difference between the input signal of the channel (Ach) and the input signal of the B channel (Bch) forms a phase tracking loop, and keeps the signal level from the mixers 1a and 1b constant. Detect the levels of the input signals of the first gain control amplifiers 2a and 2b, the input signal of the A channel (Ach), and the input signal of the B channel (Bch), respectively.
AGC detectors 5a, 5b and this AGC detector 5a,
AGC that inputs the output of 5b and extracts the AGC voltage
The loop wavers 4a, 4b form an AGC loop, and the first gain control amplifiers 2a, 2b
A second gain control amplifier 10 whose input is the output of
a, 10b, and this second gain control amplifier 10
A combiner 11 that combines the outputs of outputs a and 10b forms a combining circuit.

Also, a mixer 1a and a first gain control amplifier 2
a, the first band wave detector 3a, and the phase detector 9
The first closed loop is formed by the 9, the X(-1) amplifier 8 and the voltage controlled oscillator 6b.
A closed loop is formed. Here, the phase detector 9 is shared by the first closed loop and the second closed loop.

Next, the operation of the diversity receiving apparatus shown in FIG. 5 will be explained.

First, the input signal of the A channel (Ach) applied to the input terminal is mixed with the output from the voltage controlled oscillator 6a in the mixer 1a, converted into an intermediate frequency signal, and then the signal level is kept constant in the first gain control amplifier 2a. The signal is band-limited by the first bandpass filter 3a and then input to the phase detector 9. In addition, the input signal of the B channel (Bch) applied to the input terminal is mixed with the output from the voltage controlled oscillator 6a in the mixer 1b, and after being converted into an intermediate frequency signal, the signal level is kept constant in the first gain control amplifier 2b. and the phase detector 9 after band limiting in the first band wave detector 3b.
Enter. This phase detector 9 outputs a voltage corresponding to the phase difference between the input signal of the A channel (Ach) and the input signal of the B channel (Bch), and the phase of the voltage controlled oscillator 6a is detected through the X1 amplifier 7 for Ach. Control. In addition, the voltage controlled oscillator 6 is connected to the X(-1) amplifier 8 for Bch.
Control the phase of b.

The phases of the voltage controlled oscillator 6a and the voltage controlled oscillator 6b are controlled to be opposite to each other. Therefore, it works so that the output voltage of the phase detector 9 is always zero (0). In other words, the Ach input signal and the Bch input signal of the phase detector 9 are in phase, and accordingly, the Ach input signal of the synthesizer 11 and the Bch input signal are in phase.
Bch input signals are in phase and combined.

Next, the control of the signal combination ratio in this combiner 11 is performed by detecting the Ach signal level with the AGC detector 5a and then passing the Ach signal level through the AGC loop waver 4a.
After detecting the AGC voltage and the Bch signal level with the AGC detector 5b, the Bch is passed through the AGC loop waver 4b.
Compare the AGC voltage of the second gain control amplifier 1
0a and the second gain control amplifier 10b, the signal combining ratio is controlled. In other words, the intermediate frequency signal of the channel with the strong signal level is
On the other hand, the intermediate frequency signal of the weak signal level channel is passed through the input signal level ratio 1/K of 2.
This is achieved by combining through a circuit with a multiplier gain.

[Problem that the invention attempts to solve]

In the conventional diversity receiving device described above,
The detection characteristics of AGC detector 5a and AGC detector 5b are
Curve b is similar to curve a of the ideal characteristic in Figure 2, which is a diagram showing the AGC characteristics.As the C/N of the input signal deteriorates, detection is performed at C+N, so the AGC voltage becomes a constant voltage near the threshold. becomes. Therefore, the second gain control amplifier 10a and the second gain control amplifier 1 that determine the combining ratio
Since the control voltage 0b does not produce an output corresponding to the original signal input level difference, there is a problem in that the input signal of the channel with a weak signal level adversely affects the input signal C/N of the channel with the signal level.

For example, as shown in FIG. 3, which is a diagram showing the diversity synthesis characteristic, when both channels have the same input level, the S/N characteristic when inputting a single channel is as shown by curve c.
However, when the signal input level of one channel is constant and the signal input level of the other channel decreases to near the threshold, the output S/N of the video detector 12 is theoretically improved by 3 dB compared to N. Originally, the curve f is curve e
As a result, a deterioration phenomenon occurs. In FIG. 3, curve d shows the S/N ratio when both channels have the same input level.

In view of the above points, the present invention was devised to solve the above problems, and its purpose is to improve the AGC voltage characteristics relative to the signal input level near the threshold in a diversity combiner. An object of the present invention is to provide a receiving device that can realize a good diversity effect.

[Means for solving problems]

In order to achieve the above object, the diversity receiver of the present invention detects the noise level of each of the two input signals to be received, and based on the detected outputs, the diversity receiver of each AGC detector making up the AGC loop.
By subtracting the increase in the AGC voltage due to noise from the AGC voltage, the control signal of the gain control amplifier, which determines the signal synthesis ratio depending on the magnitude of the noise level, is corrected.

[Effect]

In this invention, the noise level of the input signal is detected and the diversity combining ratio is controlled.
Subtract processing to AGC voltage. In the diversity combiner, even if the signal input level of a channel with a weak signal level decreases and approaches the threshold point, the C/N ratio after combining will be worse than the C/N of a channel with a strong signal level. It works to prevent it from happening.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing an embodiment of a diversity receiver according to the present invention.

In FIG. 1, the same reference numerals as in FIG. It constitutes a circuit that detects the noise level of the B channel (Bch) input signal. 15a and 15b are subtracters, which are provided in the control signal system of the second gain control amplifiers 10a and 10b. Then, the output of the circuit for detecting the noise level is converted to the subtracter 15a, 1.
5b, and the control signals of the second gain control amplifiers 10a, 10b are corrected depending on the magnitude of the noise level.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

First, since the operations of the components having the same reference numerals as those in FIG. 5 are the same as those described above, their explanations will be omitted here.

Next, the second band wave generator 13a inputs the intermediate frequency signal after AGC from the first gain control amplifier 2a. At that time, this second band wave device 1
The intermediate frequency 3a is set at a point where there is no signal spectrum. Therefore, only the noise component is outputted from the output of the second bandpass filter 13a.

The amplitude detector 14a detects the amplitude of the noise component output from the second bandpass detector 13a.

This detection characteristic is shown in FIG. Curve g in FIG. 4, which shows the noise level detection characteristic, is the voltage output characteristic corresponding to the signal input level versus noise amplitude.
It increases as the signal input level decreases. and,
In this output characteristic, the curve h is compared with the reference voltage corresponding to the point where the AGC characteristic deviates from the ideal curve in Figure 2, which is a diagram showing the AGC characteristic.
is applied to the subtracter 15a to improve the AGC characteristics near the threshold.

The operation of this subtracter 15a is to detect the noise level of the input signal and subtract the increase in AGC voltage due to noise from the AGC voltage, thereby improving the signal input level versus AGC voltage characteristic near the threshold. I can do it.

This characteristic improvement applies to the circuit consisting of the second band wave detector 13b, the amplitude detector 14b, and the subtracter 15b, and operates in the same manner.

Therefore, even if the signal input level of one channel is constant and the signal input level of the other channel drops to near the threshold,
The output S/N of the video detector 12 after synthesis does not cause any deterioration phenomenon, and the S/N of the video output is determined by the C/N of the strong signal channel.

[Effect of idea]

As explained above, according to the present invention, the AGC characteristics near the threshold are improved by detecting the noise level of the input signal and subtracting it from the AGC voltage that controls the diversity combining ratio.
Since a good diversity effect can be achieved, the practical effect is extremely large. In particular, it can be an effective means in the field of space communications where the signal input levels of both channels alternately fluctuate or where it is necessary to acquire data down to a low signal input level.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an embodiment of the diversity receiver according to the present invention, Figure 2 is a diagram showing AGC characteristics, Figure 3 is a diagram showing diversity combining characteristics, and Figure 4 is a diagram showing noise level detection. FIG. 5 is a block diagram showing an example of a conventional diversity receiving device. 1a, 1b...mixer, 2a, 2b...first gain control amplifier, 3a, 3b...first band waver, 4a, 4b...AGC loop waver, 5a,
5b...AGC detector, 6a, 6b...Voltage controlled oscillator, 9...Phase detector, 10a, 10b...
Second gain control amplifier, 11... combiner, 13
a, 13b...second band wave generator, 14a, 14
b...Amplitude detector, 15a, 15b...Subtractor.

Claims (1)

[Claims for Utility Model Registration] A mixer for converting two input signals to be received into an intermediate frequency signal and a voltage controlled oscillator, respectively, and the intermediate frequency signal output from these mixers is a phase tracking loop that is input to a phase detector and configured to control each of the voltage controlled oscillators according to the phase difference between the two signals so that the phases of the two signals become in-phase; The intermediate frequency signal output from each mixer is inputted to the first gain control amplifier and detected by the AGC detector, and the detected output is used as the AGC voltage to be applied to the AGC.
first and second AGC loops configured to supply the first gain control amplifier through a waveform generator to maintain a constant output signal level in the first gain control amplifier; a second gain control amplifier for determining the signal combination ratio by inputting the output signals of each of the first gain control amplifiers in the second AGC loop, and inputting the AGC voltages of each of the AGC detectors together;
a gain control amplifier, and a combining circuit configured from a combiner that combines the respective output signals of these second gain control amplifiers, the diversity receiving device comprising: a circuit for detecting the noise level of each of the two input signals; and a subtracter inserted in a signal path for supplying the AGC voltage obtained from each of the AGC detectors to each of the second gain control amplifiers, and these subtractors are connected to each of the circuits for detecting the noise level. Input each output, and based on the output, calculate the AGC voltage of each AGC detector due to noise.
A diversity receiving device characterized by subtracting an increase in AGC voltage.