JP2858975B2 - Loss measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loss measuring device for measuring a transmission loss of a signal cable.

[0002]

2. Description of the Related Art For example, as shown in FIG. 8A, a length D connecting a radio station 1 and an antenna device 2 is, for example, 50.
Measuring the transmission loss of a signal cable 3 of about m or a signal cable 3 connecting a plurality of communication bases in a factory is important in designing new communication equipment or in construction and maintenance of communication equipment. Matters. That is, when newly constructing communication equipment, it is necessary to set the output on the transmission side in consideration of the transmission loss. In the maintenance, when the transmission loss increases rapidly, it can be determined that some abnormality has occurred in the signal cable 3.

When measuring the loss of the signal cable 3 as described above, as shown in FIG. 8B, a transmitter 4 is connected to one end 3a of the signal cable 3, and a receiver 5 is connected to the other end 3b.
Connect. Then, a test signal having a constant signal level is applied from the transmitting device 4 to one end 3 a of the signal cable 3. This test signal is received by the receiving device 5 connected to the other end 3b. Then, the transmission signal level and the reception signal level are compared, and the number of decibels (dB) is measured.

In such a loss measuring device, in order to accurately measure the loss, the reception signal level of the reception device 5 is made to exactly match the transmission signal level of the transmission device 4 before performing the measurement. There is a need. That is, the input terminal of the receiving device 5 is connected to the output terminal of the transmitting device 4, and the signal levels of the devices 4 and 5 are calibrated.

[0005]

However, the above-described loss measuring apparatus has the following problems which must be solved.

That is, in order to perform the loss measurement, at least two operators are required to operate the devices 4 and 5 at both ends of the signal cable 3. Further, since it is necessary for each operator to perform measurement while communicating with each other, when the signal cable 3 to be measured is long, it is necessary to separately provide a dedicated telephone or prepare a portable radio. is there.

[0007] Further, since the loss measuring device is composed of the transmitting device 4 and the receiving device 5, the entire device becomes large and it is inconvenient to carry. Further, since it is necessary to separately provide components that can be used in common, manufacturing costs increase significantly.

Further, after performing the calibration work, each device 4,
5 needs to be moved to the positions of both ends 3a and 3b of the signal cable 3 and attached. As a result, the work efficiency of the loss measurement work is greatly reduced.

[0009] The present invention has been made in view of such circumstances, and by using a coupler and a short-circuit jig, the loss of a cable to be measured can be easily measured with a single device, and a loss measurement operation can be performed. It is an object of the present invention to provide a loss measuring device capable of greatly improving efficiency and greatly reducing construction and maintenance costs.

[0010]

In order to solve the above-mentioned problems, in a loss measuring apparatus according to the present invention, a transmitting section for outputting a test signal, a receiving section for receiving a test signal, and a transmitting section and a cable to be measured. A coupler inserted between one end and transmitting a test signal output from the transmission unit to the cable under test, and inputting a signal generated by reflection at the other end of the cable under test to the reception unit; A short-circuit jig that is detachably attached to the other end of the cable and short-circuits the other end of the cable to be measured, and is released from the test signal of the transmission unit and the test signal received by the reception unit with the short-circuit jig removed. Open-loss calculation means for calculating a loss, short-circuit loss calculation means for calculating a short-circuit loss from a test signal of a transmission unit and a test signal received by a reception unit with a short-circuit jig attached, open-circuit loss and short-circuit loss Measured cable from Cable loss is obtained a cable loss calculation means for calculating.

[0011]

According to the present invention, when the loss indicated by the difference (log ratio) of the reception test signal measured at the input terminal at the time of opening and the transmission test signal is La, and the loss at the time of short circuit is Lb, the signal The loss L for one way of the entire cable is given by equation (1). L = [(La / 2) + (Lb / 2)] / 2 (1)

Therefore, in the present invention, the test signal output from the transmission section is input to one end of the cable under test via the directional coupler. The test signal input to the cable under test is reflected at the other end, travels in the opposite direction, and is input to the receiving unit via the coupler. Therefore, each one-way loss La / 2, Lb at the time of opening and at the time of short circuit by removing or attaching the short-circuit jig attached to the other end of the cable to be measured.
/ 2 is measured. Thus, the loss L for one way of the entire signal cable is calculated according to the equation (1).

[0013]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is an external view of the loss measuring device according to the embodiment. An operation panel 11 on which a number of keys are arranged is provided on the front surface of the housing 10, and a display unit 12 formed of, for example, a CRT or EL is mounted adjacent to the operation panel 11. An output terminal 13 and an input terminal 14 for a test signal are mounted on the front surface.

A coupler 15 formed of, for example, a bridge circuit is connected between the output terminal 13 and the input terminal 14. A short-circuit jig 16 is detachably provided at the measurement-side terminal 15 a of the coupler 15. Further, one end 17a of the cable under measurement 17 to which the BNC connector is attached is located close to the short-circuit jig 16. A short-circuit jig 18 is detachably provided at the other end 17b of the cable 17 to be measured.

The coupler 15 is configured, for example, as shown in FIG. That is, the signal input from the output terminal 13 to the coupler 15 is applied to the signal applying transformer 15c.
Applied to the primary winding. The signal extracted from the secondary winding of the signal applying transformer 15c is output to the measuring terminal 15a via the impedance elements 15d, 15e, and 15f having the same impedance as the characteristic impedance of the cable 17 to be measured. . Also, the measurement side terminal 15
The primary winding of the signal pickup transformer 15g is connected between the terminal a and the connection point of the impedance elements 15e and 15f. Then, the signal g is extracted from the secondary winding of the signal pickup transformer 15g.

Therefore, the coupler 15 has a function of transmitting the signal input from the output terminal 13 to the measuring terminal 15a as it is and transmitting the signal input from the measuring terminal 15a to the receiving terminal 14 as it is. doing.

Each of the short-circuit jigs 16 and 18 is, for example, shown in FIG.
It is configured as shown in FIG. FIG. 4A shows a state where the short-circuit jig 18 is removed from the other end 17b of the cable 17 to be measured. That is, the cable under test 17 to which a high-frequency signal of, for example, 1 MHz to several GHz is transmitted includes a core wire 19 and a ground wire 20 woven around the core wire 19. Then, for example, the BNC connector 21 is connected. Therefore, when the short-circuit jig 18 is removed, the core wire 19 and the ground wire 20 are open.

On the other hand, FIG. 4B shows a state in which a short-circuit jig 18 is attached to the other end 17b of the cable 17 to which the BNC connector 21 is attached. An annular short-circuit plate 18a is incorporated in the short-circuit jig 18, and when the short-circuit jig 18 is attached, the core wire 19 and the ground wire 20 are short-circuited. FIG. 1 is a block diagram showing a schematic configuration of the loss measuring device.

This loss measuring device is roughly divided into a transmitting unit 22 for outputting a test signal, a receiving unit 23 for receiving a test signal, and a microcomputer for calculating and displaying a cable loss L using the received signal. And an operation display unit 24 formed of

In the transmission section 22, the reference signal a having the fixed frequency f _S output from the oscillator 25 is input to the transmission mixer circuit 26. On the other hand, the local oscillation circuit 27 is constituted by a kind of voltage controlled oscillator (VCO), and outputs a local oscillation signal c having a frequency f _L proportional to the signal level of the sawtooth signal d input from the sweep signal generation circuit 28. Output. This local oscillation signal c is input to the transmission mixer circuit 26. The transmission mixer circuit 26 combines the reference signal “a” and the local oscillation signal “c” to generate a difference frequency f _D (f _C −f _L ).
Is transmitted from the output terminal 13 to the coupler 15. The test signal e is input to a detector 29 for monitoring.

The test signal e input to the coupler 15 is applied from the measuring terminal 15a to one end 17a of the cable 17 to be measured. The test signal e is the other end 17 of the cable 17 to be measured.
The signal b is reflected from the measurement side terminal 15a of the coupler 15 and is input to the receiver 23 via the input terminal 14 as a test signal g.

The test signal g having the frequency f _D inputted to the receiving section 23 is inputted to the receiving mixer circuit 30. The local oscillator 2 shared with the transmission unit 22 is provided in the reception mixer circuit 30.
7, a local oscillation signal c having a frequency f _L is input.
The reception mixer circuit 30 outputs a signal having a fixed frequency f _S obtained by adding the frequency f _L of the local oscillation signal c to the frequency f _D of the test signal g to the next detector 31. The DC detection signal h output from the detector 31 is sent to the calculation display unit 24. The DC detection signal i output from the detector 29 is also input to the calculation display unit 24.

Each of the detection signals i and h input to the operation display unit 24 is converted into a digital value by an A / D converter (not shown) at regular intervals determined by the resolution of the frequency f _D. And the short-circuit loss calculating means 33. Open loss calculation means 32 and short circuit loss calculation means 3
3 is a test signal e. Using the values of the input digital detection signals i and h. g of each open loss L at each frequency f _D
a, Calculate each short-circuit loss Lb. Cable loss calculation unit 34 calculates a loss L at each frequency f _D with the foregoing equation (1). L = [(La / 2) + (Lb / 2)] / 2 (1) In the actual calculation processing, the loss La and Lb are logarithmically converted from the ratio of the signal level of each test signal and g. Expressed in decibels (dB). The calculated loss L at each frequency f _D is graphically displayed on the next display unit 12 with the frequency f _D as a horizontal axis. The measurement procedure in the loss measuring device thus configured will be described step by step.

(1) First, the loss of the loss measuring device itself and the loss of the coupler 15 are measured in advance. In this case, a state not connected to the measurement cable 17 to the measurement terminal 15a of the coupler 15, and without connecting the short-circuit jig 16, calculates the open loss Lac at each frequency f _D. Next, in a state of attaching the short fixture 16 to the measurement terminal 15a, to calculate the short-circuit loss Lbc at each frequency f _D. Then, to calculate the calibration loss Lc at each frequency f _D. Lc = Note [(Lac / 2) + ( Lbc / 2)] / 2 ... (2), this calibration loss loss Lc at each frequency f _D is stored as a calibration value in the storage unit in the arithmetic display unit 24.

(2) When the calibration work is completed, the coupler 1
Then, the short-circuit jig 16 of the measurement-side terminal 15a is removed, and one end 17a of the cable 17 to be measured is connected via the above-described BNC connector. First, while maintaining the other end 17b of the cable under test 17 in an open state, each frequency f
The open loss Lam at _D is measured. Next, short-circuit jig 1
In a state attached 6 the measurement terminal 15a, the frequency f _D
The short circuit loss Lbm at is measured. And each frequency f
The measured loss Lm at _D is calculated. Lm = [(Lam / 2) + (Lbm / 2)] / 2 (3)

[0027] (3) When the measuring loss Lm is calculated, by correcting the measured loss Lm with the calibration loss loss Lc stored in the storage unit obtains the correct loss L at each frequency f _D. L = Lm-Lc (4)

FIG. 5 shows the constants of the sweep signal generation circuit 28 and the local oscillator 27 when the frequency f _D of the test signal e is 1M.
Hz to 1.6 GHz, and each frequency f _D (= 1) of the cable under test 17 having a length D = 50 m.
FIG. 9 is a graph showing measured loss characteristics at 16001600 MHz. FIG. 6 is an enlarged view of the vertical axis of the loss characteristic diagram of FIG.

In the figure, the characteristic A is the loss characteristic measured with the apparatus of the embodiment, and the characteristic B is the loss characteristic measured with the conventional apparatus shown in FIG. As shown in the figure, it can be understood that both characteristics A and B are well matched when the cable loss L is within a certain range, for example, 12 dB or less.

The inconsistency of the cable loss L beyond a certain limit is due to the separation characteristic of the coupler 15. That is, when the level difference between the signal level of the test signal e input from the output terminal 13 to the coupler 15 and the signal level of the test signal g input to the coupler 15 from the cable under test 17 is too large. Contains the test signal e
Leaks to the input terminal 14 side. Therefore, the signal level of the test signal g input to the receiving unit 23 becomes higher than the actual value, and a correct signal level cannot be measured.

However, if the length D of the cable under test 17 is not so long, the cable loss L in a normal case does not exceed the above-mentioned predetermined limit, so that a practically sufficiently accurate measured value can be obtained.

Note that if only the frequency characteristic is to be looked at instead of obtaining the exact loss amount for the input test signal e at each frequency f _D , the above-described calibration processing of (1) is omitted and (3) Only the measured loss Lm represented by the equation may be displayed in a graph. FIG. 7 is a diagram illustrating a connection state in a case where the mismatch attenuation (VSWR) of the antenna is measured using the loss measuring device according to the embodiment.

The mismatch attenuation (VSWR) is the impedance matching between the signal cable 40 and the antenna 41,
This is an attenuation amount indicating the degree of mismatch. If the antenna 41 and the signal cable 40 are completely matched, no reflected wave is generated at this connection.

[0034] As the measurement procedure, in a state in which not at all connect the antenna 41 to the signal cable 40, the procedure described above to determine the cable loss L at each frequency f _D of the signal cable 40. Next, the short-circuit jig 18 of the signal cable 40 is removed, and the antenna 41 is connected. Then, to measure one way losses Ld at each frequency f _D in this state. The mismatch attenuation (VSWR) is expressed by equation (5). VSWR = (Ld−L) (5) As described above, by using the loss measuring device of the embodiment, the mismatch attenuation (VSWR) of the antenna 41 with respect to the signal cable 40 can be easily measured.

According to the loss measuring apparatus thus configured, the transmitting section 22 for outputting the test signal e applied to the cable under test 17 and the receiving section for receiving the test signal g transmitted reciprocally through the cable under test 17. 23 are housed in the same housing 11. Therefore, many circuit members such as the local oscillator 27 can be used in common, so that the entire device can be made smaller and lighter than the conventional device composed of two devices, a transmitting device and a receiving device, and can be manufactured. Costs can be significantly reduced.

Since the transmission mixer circuit 26 and the reception mixer circuit 30 are driven and controlled by a set of the sweep signal generation circuit 28 and the local oscillation circuit 27, the detection signal h of the received test signal g and the transmitted test signal h Synchronization between the signal e and the detection signal i is completely established, and the same frequency f _D
Each loss is calculated based on the detected signals i and h,
Measurement accuracy is improved.

Further, the cable loss L can be measured only by connecting one measuring device to one end 17a of the cable under test 17 and attaching the short-circuit jig 18 to the other end 17b of the cable under test 17. Calibration work is also performed on the cable under test 17.
Can be carried out only on the one end 17a side. Therefore, the work efficiency of the measurement can be greatly improved.

The present invention is not limited to the embodiment described above. Although the bridge circuit shown in FIG. 3 is used as the coupler 15 in the embodiment, a directional coupler for separating and extracting the traveling wave and the reflected wave may be used.

[0039]

As described above, according to the loss measuring apparatus of the present invention, the test signal output from the transmitting section is applied to the cable under test, and the signal generated by the reflection at the other end in the cable under test is transmitted. There is provided a coupler for guiding to the receiving section, and a short-circuit jig for short-circuiting the other end of the cable under test. Therefore, by comparing each input / output test signal,
The loss of the cable to be measured can be measured with one device. Therefore, the efficiency of the loss measurement operation can be greatly improved, and the entire apparatus can be formed small and lightweight, and the manufacturing cost can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a loss measuring device according to one embodiment of the present invention;

FIG. 2 is a diagram showing a connection state between the apparatus of the embodiment and a cable under test;

FIG. 3 is a circuit diagram showing a coupler in the apparatus according to the embodiment;

FIG. 4 is a sectional view showing a connection state between a cable under test and a short-circuit jig;

FIG. 5 is a loss characteristic diagram measured by the apparatus of the embodiment,

FIG. 6 is an enlarged view showing a main part of the loss characteristic diagram of FIG. 5;

FIG. 7 is a connection diagram when the mismatch attenuation of the antenna is measured using the apparatus of the embodiment;

FIG. 8 is a schematic diagram showing loss measurement using a conventional device.

[Explanation of symbols]

12 ... display unit, 13 ... output terminal, 14 ... input terminal, 15
... Coupling device, 16, 18 ... Short jig, 17 ... Cable to be measured, 21 ... BNC connector, 22 ... Transmission unit, 23 ... Reception unit, 24 ... Calculation display unit, 25 ... Oscillator, 26 ... Transmission mixer circuit, 27 ... local oscillation circuit, 28 ... sweep signal generation circuit, 29, 31 ... detector, 30 ... reception mixer circuit. 32
... Open loss calculating means, 33 ... Short circuit loss calculating means, 34 ...
Cable loss calculating means, 40: signal cable, 41: antenna.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01R 27/04 G01R 27/26

Claims (1)

(57) [Claims] A transmitter for outputting a test signal; a receiver for receiving a test signal; and a transmitter interposed between the transmitter and one end of a cable under test; A coupler (15) for transmitting a test signal output from a transmission unit to the cable under test, and inputting a signal generated by reflection at the other end of the cable under test to the reception unit; and A short-circuit jig (18) that is detachably provided at the other end and short-circuits the other end of the cable to be measured, and a test signal of the transmission unit and a test signal received by the reception unit with the short-circuit jig removed. Open loss calculation means (32) for calculating open loss from
Short-circuit loss calculating means (33) for calculating a short-circuit loss from a test signal of a transmitting unit and a test signal received by a receiving unit with the short-circuit jig attached; A loss measuring device comprising: a cable loss calculating means (34) for calculating a cable loss of a measurement cable.