JPH01316671A - Measuring instrument for loss amount of coaxial cable and loss compensation device for coaxial cable using this instrument - Google Patents

Abstract

PURPOSE:To accurately measure a loss amount for an optional frequency of a coaxial cable and to make capable to compensate by providing a pilot signal generating circuit, wave detecting circuit, arithmetic device, branching circuit, filter and variable gain circuit. CONSTITUTION:The instrument consists of the pilot signal generating circuit 2 to apply the pilot signals SP1, SP2 to the coaxial cable 1, wave detecting circuits 3, 4 to detect by separating the plural pilot signals applied from the circuit 2 and the arithmetic device 5. The loss amount of the cable 1 for a frequency (f) of the signal passing through the cable 1 is calculated by the device 5 based on the signals DP1, DP2 detected from the circuits 3, 4. The 1st branching circuit 6 to branch the signals SP1, SP2 and a main signal SM having a different frequency from the frequencies of the SP1, SP2, the 2nd branching circuit 7 to branch the receiving signals SP1, SP2, SM, a filter 8 by which the main receiving signal SM only is passed through and the variable gain circuit 9 are also provided. Then, the loss amount of the cable 1 for the main receiving signal SM is calculated by the device 5, and an amplitude of the main receiving signal SM is compensated by the circuit 9 in accordance with the loss amount.

Description

[Detailed Description of the Invention] [Summary] Regarding a device for measuring the amount of loss in a coaxial cable, the device is installed at one end of the coaxial cable, and is particularly aimed at accurately measuring the amount of loss in each coaxial cable. a pilot signal generation circuit that applies at least two pilot signals having different frequencies and equal amplitudes to the coaxial cable;
at least two detection circuits that are provided at the other end of the coaxial cable and separate and detect at least two pilot signals applied from the pilot signal generation circuit, and have different attenuation amounts depending on the frequency. The present invention is configured to include an arithmetic unit that calculates the loss amount of the coaxial cable with respect to the frequency of the signal passing through the coaxial cable based on at least two detection signals from the detection circuit.

[Industrial application field]

The present invention relates to an apparatus for accurately measuring loss in a coaxial cable, and an apparatus for compensating for the amount of loss.

INDUSTRIAL APPLICATION The apparatus of this invention is used for various apparatuses which communicate using a coaxial cable, for example, the earth station for satellite communications etc. which an indoor end station apparatus and an outdoor earth station apparatus are connected via a coaxial cable.

[Conventional technology]

As an example of a device that uses coaxial cables, we will take the case of a satellite communications earth station.

As the performance of communication satellites improves, it has become possible to communicate via artificial satellites using ultra-small earth stations with very small antennas with an aperture diameter of about 1.2 m, making it possible to connect earth stations directly to subscribers' premises. In such a communication system, it is desirable to make the earth station equipment as small as possible. In particular, the transmitter/receiver is attached to the back of the antenna, and the transmitter/receiver is connected indoors. A coaxial cable connects the earth station to the terminal equipment installed at the ground station, forming an earth station.Input and output intermediate frequency signals pass through the coaxial cable between the terminal equipment and the outdoor transmitting/receiving equipment. In addition to the intermediate frequency signal, signals for monitoring and controlling the transmitting/receiving device are also sent from the terminal device to the transmitting/receiving device.

The length of the coaxial cable between the outdoor transmitting/receiving device attached to the back of the antenna and the terminal equipment varies depending on these installation conditions. For this reason, the attenuation of the intermediate frequency signal varies depending on the length of the coaxial cable, which causes the transmission power level from the earth station to vary. On the other hand, the setting of the transmission power of the earth station is very strictly controlled, and it is necessary to eliminate variations in the transmission power due to the length of the coaxial cable.

A possible method for eliminating such fluctuations is to design the device using the longest possible coaxial cable and to wire the longest possible coaxial cable. If the distance between the transmitting/receiving device and the terminal equipment is short, roll up the excess cable. However, this method has cost problems associated with installing extra coaxial cables.

The next method is to use an amplifier or the like to compensate for the cable loss depending on the length of the coaxial cable. However, this method has a problem in that each installed coaxial cable must be accurately grasped and the correction amount must be determined accurately. Furthermore, at the installation site, it is necessary to open and scrape the waterproofed outdoor equipment, which poses operational problems.

Furthermore, a problem common to the above two methods is that it is virtually impossible to correct variations in temperature of the coaxial cable due to changes over time.

In view of the above problems, it is conceivable to detect the amplitude of the transmitted intermediate frequency signal and directly control the level. However, this method uses SCPC (Single Channel
Although it is effective for continuous waves in communication systems such as Per Carrier), there is no signal in the case of periodic burst waves in TDMA communication systems used for satellite communication or isolated burst waves in packet communication systems. There is a problem that there is a period and the level cannot be simply controlled. That is, if level control is performed even during a period in which no signal is present, the level control will be performed based on a signal that does not exist, resulting in incorrect control.

In order to overcome this problem, the present applicant has proposed, for example, as disclosed in Japanese Patent Application Laid-Open No. 63-77226,
In an outdoor earth station device that receives a pilot signal from an indoor end station device via a coaxial cable, the variable equalizer is controlled based on the amount of attenuation of the detected output of the pilot signal, and the difference between the pilot signal and the main signal is controlled. We devised a communication system configured to further correct amplitude errors due to frequency differences. Here, amplitude error correction based on frequency difference is performed in addition to attenuation compensation based on the detected output of the pilot signal, since the loss in the coaxial cable is defined as a function of frequency, and the frequency of the pilot signal and the frequency of the main signal are different. Re-correction is being performed according to the frequency.

[Problem to be solved by the invention]

The above-mentioned frequency difference correction uses a loss obtained by interpolating the actual frequency and cable length based on a standardly obtained loss curve using frequency and cable length as parameters. Therefore, when coaxial cables with the same specifications are used, the correction content will be the same for all coaxial cables.

However, even if coaxial cables have the same specifications, the losses of individual coaxial cables vary depending on manufacturing lofts, installation conditions, and other factors, and are not exactly the same. Therefore, if standard loss data is used, there is a problem that accurate correction in accordance with the actual loss of each coaxial cable cannot be realized.

Furthermore, in this case, the actual cable length of each coaxial cable must be input as a parameter, requiring accurate measurement of the cable length. The coaxial cable may be replaced, which again requires accurate measurement and readjustment of the cable length.

Furthermore, the conventional method first performs amplitude correction based on the amplitude attenuation of the pilot signal, and then performs correction based on the frequency difference, and the correction principle is indirect, which is a factor that prevents accurate correction from being realized. is inherent.

In view of the above, an object of the present invention is first to provide a device that can accurately measure the loss of each coaxial cable, and second, to provide an apparatus that can accurately correct the loss based on the measured cable loss.

[Means for Solving the Problems and Effects] FIG. 1 shows a principle block diagram of a coaxial cable loss measuring device according to a first embodiment of the present invention. The coaxial cable loss measuring device is provided at one end A of the coaxial cable 1, and applies at least two pilot signals SP, SF3 having different frequencies f, f2 and equal amplitudes to the coaxial cable. a pilot signal generation circuit 2; and at least two detection circuits 3.4 provided at the other end B of the coaxial cable to separate and detect a plurality of pilot signals applied from the pilot signal generation circuit; It consists of an arithmetic unit 5.

The arithmetic unit 5 receives two detection signals DP from the detection circuit whose attenuation amounts differ depending on the frequency.

Based on DP, the loss amount LO3S of the coaxial cable with respect to the frequency f of the signal passing through the coaxial cable is calculated. That is, pilot signals having different frequencies and the same amplitude are passed through the coaxial cable 1, and from the amount of attenuation of the pilot signals, the amount of loss of the coaxial cable for the frequency f is calculated.

Further, a principle block diagram of a coaxial cable loss compensation device according to a second embodiment of the present invention is shown in FIG. 2, and the invention is applicable to the coaxial cable loss measurement device of the first embodiment,
In addition to the circuit shown in FIG. 1, the circuit is further provided at one end of the coaxial cable and receives pilot signals SPt and Sr1 from the pilot signal generation circuit, and a main signal SM having a frequency different from that of the pilot signal. a first branching circuit 6 for branching the received pilot signal and the received main signal; a second branching circuit 7 provided at the other end of the coaxial cable for branching the received pilot signal and the received main signal; It has a filter 8 which is provided after the branching circuit and allows only the received main signal to pass through, and a variable gain circuit (9) which is provided after the filter.

The detection circuit is connected to a second branching circuit to separate and detect only the received pilot signals, and the arithmetic unit calculates the amount of loss of the coaxial cable with respect to the received main signal and sends the result to the variable gain circuit. The variable gain circuit compensates the amplitude of the received main signal according to the applied coaxial cable loss amount.

Note that the branching circuits 6 and 7 are for branching the pilot signal and the main signal, respectively, but after measuring the loss amount of the coaxial cable in advance, it is possible to compensate for the loss amount for the main signal. It can be removed because it can be done.

In the above, once the loss of the coaxial cable is measured after the coaxial cable is installed, there is no need to repeatedly measure the loss of the coaxial cable, so the loss of the coaxial cable is measured only immediately after the coaxial cable is installed. You can do it like this.

In this manner, the loss amount for the frequency of the main signal is directly calculated based on the actually measured loss amount, and the loss amount is directly compensated, so that accurate loss amount compensation is possible.

In the present invention, the main signal may be outputted continuously or intermittently.

〔Example〕

As an embodiment of the present invention, an apparatus for measuring the amount of loss in a coaxial cable and compensating for the amount of loss in the main signal based on the measured amount will be described with reference to FIG.

In FIG. 3, one end A of the coaxial cable l is provided with a distributor (hybrid) 6a and oscillators 21 and 22, each having an oscillation frequency f, , f. The main signal SM(
f) and pilot signals SP and Set from oscillators 21 and 22 are applied to the coaxial cable 1. FIG. 4 shows the relationship between pilot signals SP, SP2 and main signal SM. pilot signal s
The amplitudes of p, , sp, are assumed to be the same. Those frequencies f, , f have a relationship as shown by the solid line in the figure, or the main signal S
One of the frequencies f and I may be in a relationship as shown by a broken line so as to surround the frequency f of M.

At the other end B of the coaxial cable 1, a first detection circuit 3as consisting of a divider 7a, a filter 8a, a variable gain circuit 9as, a filter 31 and a detector 32, and a second detection circuit 4a consisting of a filter 41 and a detector 42 are connected. , and a 4-bit microprocessor (MPU) 5a are connected as shown. The distributor 7a separates the received main signal SM and pilot signals sp, , spa. Filter 8
a is a bandpass filter that passes the frequency (f) component of the main signal SM. The filter 31 receives the pilot signal S
This is a bandpass filter that passes only the frequency B(fl) component of P. The filter 41 receives the pilot signal Sl'
This is a bandpass filter that passes only the frequency (fz) component of t.

The pilot signals SPI, SP2, and main signal SM transmitted from one end A of the coaxial cable 1 to the coaxial cable 1 are attenuated based on their frequencies and the dimensions and length of the coaxial cable, respectively. The received pilot signal and main signal of
, 41 and 8a.

Here, the amount of loss in the coaxial cable has the characteristics shown in Figure 5. In other words, the frequency f of the signal passing through the coaxial cable and the amount of loss (attenuation) L (dB) are generally given by the following equation. It will be done.

1agL = alog f + b −
... (1) a, b: Variables Attenuation amount L 1 caused by pilot signals SPI and 5Pffi having the same amplitude passing through the same coaxial cable 1
．． L z (dB) is shown by the following formula.

The variables a and b are obtained from equation (2) and are expressed by the following equation.

a = (logL+ −]ogLz)
++ (3)α However, α=Iogf, -1agf.

Since f, , f2 are known, α and β are constants. L
l can be detected by the detector 32.1, and 1 can be detected by the detector 42.
The MPIJ 5a calculates a and b based on the outputs of these detectors 32 and 42. Furthermore, the MPtl 5a substitutes the calculated a and b into equation (1) to calculate the amount of loss L (dB) at the frequency f.

L=fxe"+e'・" (5)M
From this calculated loss amount L (dB), the PU 5a conversely calculates the gain to be compensated for by the variable gain circuit 9a: g = 1/
L is calculated and output to the variable gain circuit 9a.

The loss measure and gain g may be calculated once for the coaxial cable before passing the main signal. Therefore, these measurements and calculations may be more or less time consuming. Based on the gain g thus obtained, the amplitude of the main signal SM extracted from the filter 8a is compensated by the variable gain circuit 9a.

As is clear from the above, it is possible to accurately obtain the loss with respect to the frequency f for an actual coaxial cable, and furthermore, it is possible to accurately compensate for the loss based on the amount of loss.

FIG. 6 shows a more specific embodiment in which the present invention is applied to a small satellite earth station.

In the figure, an indoor terminal station device 100 and an outdoor small earth station device 200 are connected by a coaxial cable 300. Cable loss occurs in this coaxial cable. The terminal device 100 includes a baseband processor 101, a demodulator 102, a modulator 103, a control signal modulator 104, a supervisory signal modulator 105, and a duplexer 106 connected to the terminal. The earth station device 200 includes a duplexer 2.
01, down converter 202, low noise amplifier 203,
polarization splitter 204, antenna 205, power amplifier 206,
The basic operation of 0 or more in which the up converter 207, the supervisory signal modulator 208, and the control signal demodulator 209 are provided is the modulator 103 and the duplexer 1 of the terminal device 100.
The intermediate frequency signal IF to be transmitted is output to the coaxial cable 300 via the coaxial cable 300. This intermediate frequency signal IF is received via the duplexer 201 of the earth station device 200, and is converted from the intermediate frequency to a high frequency by the up converter 207.
The signal is amplified by a power amplifier 206 and radiated from an antenna 205 via a polarization splitter 204. On the other hand, the antenna 205
The high frequency signal received is introduced into the low noise amplifier 203 via the polarization splitter 204 and output from the down converter 202 to the terminal device 100 via the coaxial cable 300. This received signal is input to the baseband processor 101 via a branching filter 106 and a demodulator 102.

In order for the end station bag W100 to monitor the earth station device 200, a control signal modulator 104, a supervisory signal modulator 105, a supervisory signal modulator 208, and a control signal demodulator 209 are provided, respectively. Due to these, in addition to the intermediate frequency signal IF,
The control signal 5CNT is transmitted and received.

The intermediate frequency signal is continuous in the case of a continuous wave, but is intermittent in the case of a periodic burst wave or an isolated burst wave. However, the control signal is continuously transmitted and received regardless of the presence or absence of the intermediate frequency signal.

The terminal equipment 100 is provided with oscillators 108 and 109 that generate pilot signals sp, , sp, and the duplexer 10
Connect to 6. The earth station device 200 includes a loss calculation and compensation circuit 250, a duplexer 201, and an upconverter 2.
Provided between 07 and 07. The loss calculation and compensation circuit 250 is configured similarly to the filter 8as variable gain circuit 9a% detection circuits 3a, 4a and MPU 5a in FIG. A variable attenuator using a bin diode can be used as the variable gain circuit.

By configuring as described above, the loss of the coaxial cable can be accurately measured even in a small satellite earth station, and the loss can be accurately compensated.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to accurately measure the amount of loss of a coaxial cable at any frequency. Furthermore, the present invention can accurately compensate for the amount of loss of a signal at a specific frequency based on the amount of loss measured in this manner.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the principle of the coaxial cable loss measuring device of the present invention, Fig. 2 is a block diagram of the principle of the coaxial cable loss compensation device of the present invention, and Fig. 3 is a coaxial cable loss measuring device according to an embodiment of the present invention. FIG. 4 is a diagram showing the relationship between the signals in FIG. 3, FIG. 5 is a diagram showing the relationship between frequency and cable loss, and FIG. 6 is a coaxial diagram of another embodiment of the present invention. FIG. 2 is a configuration diagram of a cable loss measurement and compensation device. (Explanation of symbols) 1... Coaxial cable, 2... Pilot signal generation circuit, 3.4... Detection circuit, 5... Arithmetic device, 6.7
...Distributor, 8...Filter, 9...Variable gain circuit.

Claims (1)

[Claims] 1. At least two pilot signals (SP_1, SP_2) having different frequencies (f_1, f_2) and equal amplitudes are provided at one end (A) of the coaxial cable (1).
2) to the coaxial cable; and a pilot signal generation circuit (2) provided at the other end (B) of the coaxial cable to separate at least two pilot signals applied from the pilot signal generation circuit. Based on at least two detection circuits (3, 4) that perform detection based on the frequency and at least two detection signals (DP_1, DP_2) from the detection circuits that have different attenuation amounts depending on the frequency,
A coaxial cable loss measuring device, comprising: an arithmetic device (5) that calculates a coaxial cable loss (LOSS) with respect to a frequency (f) of a signal passing through the coaxial cable. 2. Provided at one end of the coaxial cable to generate a pilot signal (SP_1) from the pilot signal generation circuit.
, SP_2) and a main signal (SM) having a frequency different from the frequency of the pilot signal.
), and a second branching circuit (7) that is provided at the other end of the coaxial cable and separates the received pilot signal and the received main signal.
), a filter (8) provided after the second branching circuit and passing only the received main signal, and a variable gain circuit (9) provided after the filter, The detection circuit is connected to a second branching circuit and separates and detects only the received pilot signals, and the arithmetic unit calculates the amount of loss of the coaxial cable with respect to the received main signal and outputs it to the variable gain circuit. 2. The coaxial cable loss compensation device according to claim 1, wherein the variable gain circuit is configured to compensate the amplitude of the received main signal according to the applied coaxial cable loss amount.