JPH0229034A - Receiver - Google Patents

Abstract

PURPOSE:To prevent a level of other reception signal from being exceeded due to the level reduction of a pilot signal by using a branch circuit so as to branch part of the reception signal outputted to a demodulator of the post- stage, applying level control to the branched output by a level control means and inputting the result. CONSTITUTION:A pilot level detector 5 is a narrow band detector in a receiver installed in the satellite communication earth station employing the SCPC system, only a pilot signal in an output signal of a variable attenuator 3 is detected and the detection output is digitized by an A/D converter 6 and inputted to a control circuit 7. The control circuit 7 compares the digital value with a reference value and since the attenuation of the variable attenuator 3 is controlled by an analog signal in a direction where the error is decrease, the level of the pilot signal given to a pilot frequency detector 4 is nearly kept constant. The control circuit 7 detects whether or not the error is within a prescribed range and if the error is deviated from the prescribed range, it is discriminated that the pilot signal reception is interrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a receiving device, and particularly to a receiving device for a satellite communication earth station that uses the FDMA system.

[Conventional technology]

Receiving equipment for satellite communication earth stations that use the FDMA method, especially SCPC (single channel per
A receiving device that receives a relatively narrow band signal such as in the carrier system uses the oscillation of a local oscillator of a frequency converter so that the pilot signal included in the received signal is frequency-converted into an intermediate frequency signal with a constant frequency. It is customary to control the frequency. The pilot signal is transmitted from the reference earth station with high frequency accuracy and relayed by the space station. Each received signal sent from each transmitting earth station and relayed by the space station is commonly frequency-converted by the above frequency converter, becomes an intermediate frequency signal of a predetermined frequency, and is output to the demodulator of each channel in the subsequent stage. be done. Through this frequency conversion, frequency errors in each received signal that occur during relay at the space station are also commonly corrected.

In order to detect the frequency of the pilot signal in the intermediate frequency band with a frequency detector and control the local oscillation frequency based on the detection result to keep the frequency of the pilot signal constant, the frequency detector must be able to accurately detect the frequency. It is necessary to keep the pilot input level constant.

Such a conventional receiving device uses a common variable attenuator to control the level of each received signal whose frequency has been commonly converted by a frequency converter, and performs variable attenuation so that the pilot signal in each level-controlled received signal is at a constant level. By controlling the frequency detector, the pilot level input to the frequency detector was kept constant.

[Problem to be solved by the invention]

In the conventional receiving device described above, the level of each received signal is controlled by a common variable attenuator before outputting it to the demodulator. If the received level of only the pilot signal decreases, the variable attenuator is controlled to compensate for this level drop, and the output level of the other received signals becomes excessive, causing the subsequent demodulator to malfunction. . Additionally, the local oscillator becomes free-running when the pilot signal is attenuated by rain, etc., and becomes a pilot signal receiving station, so if the frequency drift in the receiving station becomes large, it takes a long time to pull in the frequency when the reception is restored. There is.

An object of the present invention is to provide a receiving device that can prevent the output level of other received signals from becoming excessive due to a drop in the level of a pilot signal, and can keep the frequency drift of a local oscillator small even during a pilot signal reception station. It's about doing.

[Means to solve the problem]

The receiving device of the present invention includes a frequency converter that commonly converts the frequency of a plurality of received signals transmitted by a plurality of earth stations and relayed by a space station to an intermediate frequency band, and a branch circuit that branches the output signal of the frequency converter. a level control means for controlling the level of the branch output of the branch circuit based on a first control signal; a detection means for detecting the frequency and level of a pilot signal included in the output signal of the level control means; The first control signal is output based on the level detection result, and when the value of the first control signal is within a predetermined range, the second control signal is output based on the frequency detection result of the detection means, and the second control signal is output based on the frequency detection result of the detection means. control means for holding and outputting the immediately preceding value of the second control signal when the value of the first control signal deviates from the predetermined range; and a local oscillator that generates an oscillation signal and outputs it to the frequency converter.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. The embodiment shown in FIG. 1 is installed in a satellite communications earth station that uses the 5 CPC system. The pilot signal sent by the reference earth station and each signal sent by each transmitting earth station are relayed by the space station, received by the antenna of this earth station, and input to the embodiment shown in FIG. 1 via a low-noise amplifier. The output is branched and input to a demodulator for each subsequent channel.

The embodiment shown in FIG. 1 includes a frequency converter 1 that commonly converts the frequency of each received signal into an intermediate frequency band, and a branch circuit 2 that outputs the output signal of the frequency converter 1 to a demodulator and branches a part of it. , a variable attenuator 3 that controls the level of the branch output of the branch circuit 2, a pilot frequency detector 4 and a pilot level detector 5 that detect the frequency and level of the pilot signal included in the output signal of the variable attenuator 3, and a pilot An A/D converter 6 that converts each detection signal of the frequency detector 4 and pilot level detector 5 into digital values;
A control circuit 7 that outputs two digital values based on the two output values of the D converter 6, and a control circuit 7 that converts one output value of the control circuit 7 into an analog signal and uses this analog signal to output the variable attenuator 3.
A D/A converter 8 that controls the amount of attenuation of the control circuit 7, a D/A converter 9 that converts the other output value of the control circuit 7 into an analog signal, and a frequency based on the analog signal outputted by the D/A converter 9. and a local oscillator 10 that generates a local oscillation signal and outputs it to the frequency converter 1.

The pilot level detector 5 is a narrow band detector, and detects only the pilot signal in the output signal of the variable attenuator 3.
．． and output it. This detected output is digitized by the A7/'D converter 6 and input to the control circuit 7. The control circuit 7 compares this input digital value with a reference value and outputs an error value. This error value is converted into an analog signal by the D/A converter 8, and this analog signal controls the attenuation amount of the variable attenuator 3 in a direction that reduces the error value, so that the pilot input to the pilot frequency detector 4 The signal level remains approximately constant. The control circuit 7 also detects whether the error value is within a certain range, and determines that the pilot signal has been cut off when the error value deviates from this certain range.

The pilot frequency detector 5 is a phase comparator that compares the phases of the input pilot signal and the reference frequency signal,
The frequency of the pilot signal is detected in the form of a phase error of the pilot signal with respect to a reference frequency signal. The phase error output from the pilot frequency detector 4 is digitized by the A/D converter 6 and input to the control circuit 7, and the contents of the phase error register in the control circuit 7 are updated. The contents of this phase error register are converted into an analog signal by the D/A converter 9, and the oscillation frequency of the local oscillator 10 is controlled by this analog signal to reduce the phase error, so that the frequency converter 1 outputs . Including the Bairot signal,
The frequencies of the received signals in the intermediate frequency band are each maintained at a predetermined frequency.

When the control circuit 7 determines from the value of the error value output to the D/A converter 8 that the pilot signal is not received, it stops updating the contents of the phase error register.

Therefore, while the reception of the pilot signal is interrupted, the phase error register retains the value immediately before the reception is interrupted, and the local oscillator 1
Since the output signal of the 00 frequency frequency converter (D/A converter 9) is also maintained at the value immediately before the reception of the pilot signal is interrupted, the frequency drift of the local oscillator 10 during reception interruption is small.

The operation of the embodiment shown in FIG. 1 has been described above.

Note that a variable gain amplifier can also be used as the level control means. Further, the present invention can be applied to the case where the frequency of the pilot signal is detected by a frequency discriminator, and the same effect as in the above embodiment can be obtained.

〔Effect of the invention〕

As explained above, the present invention branches a part of the received signal to be output to the demodulator at the subsequent stage using a branch circuit, controls the level of the branched output using the level control means, and inputs the level to the detection means. This has the effect of preventing the level of other received signals from becoming excessive due to the level drop, which causes the subsequent demodulator to malfunction, and also prevents the pilot signal from being received while the reception is interrupted or by the second control signal just before the reception is interrupted. By holding this in the control means, it is possible to keep the frequency drift of the local oscillator small during this period and to speed up the frequency pull-in of the local oscillator when the reception of the pilot signal is recovered.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. 1... Frequency converter, 2... Branch circuit, 3... Variable attenuator, 4... Pilot frequency detector, 5...・Pilot level detector, 6...A/D converter, 7...Control circuit, 8, 9...D/A converter, 10...
...Local oscillator. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] a frequency converter that commonly converts the frequency of multiple received signals transmitted by multiple earth stations and relayed by the space station to an intermediate frequency band;
A branch circuit that branches the output signal of this frequency converter, level control means that level-controls the branch output of this branch circuit based on a first control signal, and detection means for detecting a level; and outputting the first control signal based on the level detection result of the detection means, and detecting the frequency of the detection means when the value of the first control signal is within a predetermined range. A second control signal is output based on the result and the first control signal is output.
control means for holding and outputting the immediately preceding value of the second control signal when the value of the control signal deviates from the predetermined range; and a local oscillation signal having a frequency based on the second control signal. a local oscillator that generates and outputs the generated signal to the frequency converter.