JPH0357338A - Tap connection system - Google Patents

Abstract

PURPOSE:To improve a return loss of a trunk line without too tight requirements on the performance of a tap itself by connecting taps at an interval of an odd number multiple of 1/4 wavelength in a coaxial cable with respect to a frequency of a transmission signal. CONSTITUTION:Marks 101a, 101b are provided to a coaxial cable 101. The mark 101a is marked onto an outer sheath at an interval of 1/4 wavelength lambdag in a coaxial cable 101 with respect to a data speed of 10Mbps and modulation frequency is 20MHz. Moreover, the mark 101b is marked onto an outer sheath at an interval of 1/4 wavelength lambdag' in a coaxial cable 101 with respect to a data speed of 5Mbps and modulation frequency is 10MHz. Then taps T1, T2,... are connected at an interval of an odd number multiple of 1/4 wavelength in the coaxial cable with respect to the higher frequency of the fundamental wave component of a transmission signal, while checking the marks 101a, 101b. Thus, the return loss of a trunk line is improved without too tight requirements on the performance of the taps themselves and the workability of the tap connection work is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a LAN that performs code conversion or modulation of data signals to perform communication on a non-directional bus-type coaxial network.
(Local Area Network) tap connection method.

[Prior Art] In recent years, robots, automatic machines, etc. have been introduced due to the automation of production in factories. When controlling these machines in an integrated manner, a LAN using a computer is often used. As one type of LAN, a bus-type coaxial cable network has been standardized (IEEE 802.4), in which a large number of non-directional taps for branching transmission signals are connected in series to a single coaxial cable.

An example of the configuration of this bus type coaxial cable network is shown in FIG. The coaxial cable 300 constituting the main line has a higher frequency of the fundamental wave of the coded or modulated transmission signal (for example, 5 Mbps in the case of a data rate of 5 Mbps).
MHz, or 10 MHz in the case of FSK modulation to 10 MHz).
Taps 301a. 30l
b, 301c... are connected in series. Further, at both ends of the coaxial cable 300, terminating resistors 302a. 3G
2b is connected with a resistance value equal to the characteristic impedance of the coaxial cable 300. This terminating resistor 302a.
302b is for eliminating reflection of the transmitted signal.

Tap 301a. 30lb, 301c, . . . are connected to the coaxial cable 300 side constituting the main line and the information equipment 304 side, for example.
a, 304b. 3 0 4 Branch line 3 connecting to c-...
03a. 303b, 303c, etc., the branch coupling attenuation amount is 20 dB. This tap 301a. The return loss (return loss) on the main line side of 30lb, 301c... is tab 301a
．． 30lb. Since 301c... is constituted by a transformer for branching and coupling, it does not have an ideal characteristic impedance, and is, for example, about 30 to 35 dB with respect to the transmission signal.

Figure 4 shows the phase coherence (phase continuity) of the transmitted signal.
Data speed in FSK modulation method: 5Mbps, 10Mbps
FIG. 2 is a diagram showing the relationship between modulation frequency and waveform corresponding to data 1.0 of s. For example, if the data rate is 5 MbpsL, the higher modulation frequency is 10 MHz.

Now, assuming that the speed of light is C, the frequency is f, and the shortening rate is A, the wavelength λg within the coaxial cable is determined by C λg - TxA (1). Here, if C-3X108m, A=0.86, it becomes λg - 25.8m, and λg/2 - 1
Tap connections will be made except for 2.9m.

Under these conditions, 12 taps 301a. 30lb, 301
c = - on the coaxial cable 300, respectively, 1.5 m
, 1.5 m, 4 m, 1.5 m, 1.5 m,
4m, 1.5 rn, 1.5 m, 5m, 1.
Figure 5 shows the results of simulating the return loss of the main line as seen from the l end when 11 lines of 5 m and 1.5 m are connected in series to form a main line. In FIG. 5, the solid line indicates the return loss, and the dotted line indicates the amount of attenuation at the other end.

It can be seen from FIG. 5 that the return loss worsens when the frequency is low. For example, in the case of phase coherent FSX modulation with a data rate of 5 Mbps, the band used is:
The frequency is 2 to 15 MHz. Therefore, when a return loss of 22 dB or more is required, it is necessary to further improve the return loss of a single tap.

[Problem to be solved by the invention] However, since the tap is composed of a transformer, it is necessary to improve the return loss over a wide band and to accommodate various combinations of tap connection lengths. It requires difficult technical elements such as optimizing the number of turns, reducing distributed capacitance, selecting a core material, and correcting impedance, resulting in high costs.

Further, when performing connection work using a coaxial cable, measurement is required to exclude the 172 wavelength within the coaxial cable, which makes the work difficult.

The present invention was made in view of the above points, and it is possible to improve the return loss characteristics of the main line without requiring undue performance of the tap alone, and to improve the workability of tap connection work. The purpose is to provide a tap connection method.

[Means and effects for solving the problem] The present invention provides a non-directional bus type coaxial network,
A good trunk system is achieved by connecting taps at odd multiples of 1/4 of the coaxial cable's internal wavelength at the higher frequency of the fundamental wave component of the transmitted signal and canceling the reflected waves from each tap. At the same time, various marks are provided for each of the 174 wavelengths in the coaxial cable corresponding to the frequency to be transmitted in advance on the outer sheath of the coaxial cable constituting the main line, thereby facilitating tap connection work.

[Example] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an example of connection of a trunk coaxial cable used in the tap connection method of the present invention. As shown in FIG. 2A, this coaxial cable 101 is provided with a mark 101a and a mark 1.0lb.

The mark iota is the wavelength λg in the coaxial cable 101 at a data rate of 10 Mbps and a variable frequency of 20 MHz.
Two types of marks, Δ・IOJ and r▲・IOJ, are alternately marked on the outer skin at 174 intervals. On the other hand, the mark ioib indicates the wavelength λg in the coaxial cable 101 at a data rate of 5 Mbps and a modulation frequency of 10} IHz. ' at 1/4 intervals of '
・5'' and ``▼・5'' are alternately marked on the outer skin.

A data rate of 10 Mbps using a coaxial cable 10L provided with such a mark iota, 10lb
Taps TI, T2, T3, etc. to configure the main line for use
An example in which ・ is connected is shown in FIG. This tab Tl,
T2, T3, . . . are connected at mark A positions of the coaxial cable 101 at odd multiples of λg/4, respectively.

That is, between tab Tl and 72, λg/4, tap T2
-T3 is connected as 3λg/4. Here, if the transmission wave from tap TI is 10MHz, then from equation (1), λg/4-3.225 m, 3λg
/ 4 = 9.675 m of coaxial cable length.

The phase relationship between the transmitted signal and the reflected wave within the coaxial cable lot is shown in FIG. 4(e). In the diagram (C), 103a is a transmitted signal, 103b is a reflected wave at tap T2, l03c is a reflected wave at tap T3, LO3d is a reflected wave at tap T4, l03e is a reflected wave at tap T5, and 103f is a reflected wave at tap T5. This is the reflected wave at tap T6. Each reflected wave 103b-1031' reflected back to the tap Tl is 0° or 1
80' (the amount of phase shift is shown in the range of O'' to 360', for example, 450''-90'). Therefore, the phase difference of 180@ between the reflected waves causes a canceling effect, and good main line return loss characteristics are obtained.

Next, tap T when the data rate is 5 Mbps.
l', T2'. The connection example of T3'... is shown in the same figure (d
). Taps TI' and T2' are connected by λg'/4, and taps T2' and T3' are connected by 3λg'/4.

Since the frequency of the transmitted signal is 10 MIlz, λg'/4=6.45 m, 3λg' as in the previous case.
/4=19.35 m.

The phase relationship between the transmitted signal and the reflected wave in this case is shown in FIG. 4(e). In figure (e), l05a is the coaxial cable 1 when the transmission signal is sent out at 10MHz from tap TI'.
105b shows the phase relationship of the reflected wave at tap T2', and 105c shows the phase relationship of the reflected wave at tap T3'. In this case, as in the case of 10 Mbps, reflected waves 105b. The reflected waves cancel each other out between the 105e and good return loss characteristics of the main line can be obtained.

FIG. 2 shows the characteristic surface of the result of simulating the return loss of a main line used for data at 5 Mbps according to the method of the present invention. Here, we assume that the performance of a single tap is the same as before,
As a coaxial cable connecting 12 taps, each 6.45 m. 6.45 m. 19.35m, 6
．． 45m, 19J5m. 6.45 m. 6.45
m. 6.45 m. 6.45m, 19.35
m. The case where 11 cables with a length of 6.45 m are used is shown.

It can be seen that the return loss of the main line has improved to 22 dB or more within the used band of 2 to 15 MHz with a data rate of 5 Mbps. Note that the dotted line in the figure indicates the amount of attenuation at the last tap.

From the above, the tap connection length p is 4. Here, λg is the wavelength within the coaxial cable at the higher modulation frequency of the transmitted signal.

For example, if the wavelength in the coaxial cable is chosen to be lower than the modulation frequency, the return loss at twice the frequency will worsen as a result of the phase matching between the reflected waves, as shown in S in Figure 2. I will do it. Therefore, it is better to select the wavelength λg for a higher frequency.

The above is a case where the return port of the main line is good for 10 MHz. It is possible that the problem will be worse for 20 MHz, so in order to make it better for 20 MHz, it is necessary to add 174 m, which is the wavelength of the coaxial cable circle for 20 MHz, in the middle of the main line, or 3.225 m from equation (1).
It is also effective to provide Moreover, from the configuration shown in FIG. 1, when the connection length of the tap is long, reflected waves within the coaxial cable are also attenuated. In such a case, it is also effective to add taps at intervals of 1/4 of the wavelength within the coaxial cable in order to effectively cancel out the reflected waves.

In addition, tap connection conditions are improved by providing a large number of 2FJ type marks indicating odd/even numbers on the outer sheath of the coaxial cable used, at 1/4 of the wavelength within the coaxial cable, corresponding to the frequency used. can be easily dealt with.

[Effects of the Invention] As described above, according to the present invention, when constructing a bus-type coaxial cable network, taps are connected at odd multiples of 1/4 of the wavelength in the coaxial cable relative to the frequency of the signal to be transmitted. As a result, the return loss of the main line can be improved without requiring the performance of the tap unit to be more than necessary, so that the cost of the tap unit can be reduced. Furthermore, by providing marks on the outer sheath of the coaxial cable for every 1/4 of the wavelength, taps can be easily connected, so that a high-quality trunk line can be constructed at low cost.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining a tap connection method according to an embodiment of the present invention, Fig. 2 is a characteristic diagram of return loss in the same embodiment, and Fig. 3 shows the configuration of a conventional bus type coaxial network. FIG. 4 is a block diagram showing the relationship between modulation frequency and waveform with respect to data rate used in a conventional bus-type coaxial network, and FIG. 5 is a characteristic diagram of a return rotor using a conventional tap connection. 101a, 10lb-7-ku, T1-T6, Tl'
~T3' --- Tap, l O 3 a-- Transmitted signal, 103b-103f... Reflected wave, 105a-
...Transmission signal, 105bS105c...Reflected wave.

Claims (1)

[Claims] In a bus type coaxial network consisting of non-directional taps connected in series on a coaxial cable, 1/4 of the wavelength within the coaxial cable at the higher frequency of the fundamental wave component of the transmitted signal.
A tap connection method characterized in that marks are provided on the coaxial cable at intervals, and the taps are connected at intervals of odd multiples of the 1/4 wavelength according to the marks.