JPS6410144B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic monitoring device for direct current resistance, which is one of the maintenance monitoring items for antenna/feed line systems for television broadcasting, etc.

If the contact between the power supply line connection deteriorates, it may lead to a burnout accident. Since contact deterioration manifests itself as an increase in contact resistance, monitoring of DC resistance is of great importance.

In conventional operating conditions, high-frequency waves are fed to the antenna through the feed line, making it impossible to directly observe DC resistance. Therefore, during periodic inspections performed when radio waves were stopped at night, part of the power supply system was disassembled and the DC resistance on the antenna side was measured from there. With this type of measurement, DC resistance cannot be constantly monitored and changes in DC resistance cannot be observed continuously, so it is difficult to say that it is 100% useful in predicting and preventing accidents.

The present invention has been made with these points in mind, and an object of the present invention is to provide an automatic DC resistance monitoring device that can constantly monitor the DC resistance on the antenna side. The configuration of the present invention that achieves the above object is a coupler connected between the output side of the transmitter and the feed line to the antenna, the coupler being connected to each other by 1/4
A helical transmission line with a high characteristic impedance that has a transmitter side inner conductor and a feeder side inner conductor that are wavelength-coaxially coupled, and is branch-connected to one end of the feeder side inner conductor, and this helical transmission line is grounded at appropriate intervals. The coupler has a coupled line that reduces leakage of high-frequency signals due to a capacitance of The present invention is characterized by comprising a low-frequency oscillator for flowing a low-frequency current, and a monitoring device for monitoring the DC resistance of the antenna feed line system based on the voltage generated by the low-frequency current.

The present invention will be explained below based on the embodiment shown in FIG.

In this embodiment, a coupler 4, which will be described later, is connected between the output side of the transmitter 1 and the antenna 2 and the feeder line 3, and a low-frequency current is applied to the feeder line 3 and the antenna 2 via the coupler 4. is applied, and the DC resistance is monitored based on the voltage generated by that current. Since high frequency waves are supplied from the transmitter 1 to the feeder line and the antenna, various measures have been taken to prevent the coupler 4 from becoming a hindrance. The transmitter 1 is connected to the input terminal 4a of the coupler 4, and the feeder line 3 is connected to the output terminal 4b. The coupler 4 mainly includes a transmitter side inner conductor 5, a feeder side inner conductor 6,
It consists of an outer conductor 7 provided on the outside of these and a coupled line 8 connected to one end of the inner conductor 6 on the feeder side. The transmitter side inner conductor 5 is attached to the inner side of the power supply line side inner conductor 6 via an insulator 9 such as Teflon or polyethylene. This transmitter side inner conductor 5
The length of insertion into the feeder side inner conductor 6 is such that the dielectric of the insulator 9 remains insulated in terms of direct current, but the transmitter 1 side and the feeder side inner conductor 6 are connected in terms of high frequency. In consideration of the wavelength, it is effectively set to 1/4 wavelength.
If the outer conductor 7 is also considered, the coupler 4 forms a triple coax. Furthermore, the coupler 4 has a coupled line 8 in which the inner conductor 8a is connected to one end of the feed line side inner conductor 6.
is provided. The coupled line 8 is for passing a low-frequency current in order to measure the resistance of the feeder line 3 and the antenna 2, and is used to affect the transmission of high-frequency energy from the transmitter 1 to the antenna 2 via the feeder line 3. It is configured to prevent high frequencies from leaking to the observation terminal 4c of the coupler 4. Therefore, the inner conductor 8a of the coupled line 8 is a helical conductor with high characteristic impedance, and capacitances 8c are effectively loaded in parallel with the outer conductor 8b at 1/4 wavelength intervals. That is, the helical conductor 8
A and the capacitance 8c constitute a low-pass filter to prevent high frequencies from leaking to the observation terminal 4c of the coupled line 8.

A low frequency current I for resistance monitoring is passed from this observation terminal 4c. Therefore, the low frequency oscillator 10
The output of amplifier 11, resistor 12 and low pass filter 1
3. Due to this current I, a voltage V becomes V=I・r due to the resistance r looking at the antenna side.
occurs. By observing this, the DC resistance r can be monitored. In this embodiment, the voltage V is amplified by an amplifier 14 with high input impedance and displayed by an indicator 15 for indication or recording. Further, the output of the amplifier 14 is compared with a separately prepared reference voltage 16 by a comparator 17, and when it exceeds the reference voltage, an alarm 18 issues an alarm.

The operation of the above embodiment will be described below. A coupler 4 is connected between the transmitter 1 and the feed line 3, but as mentioned above, the coupler 4 is connected to high frequencies, and the characteristic impedance of the coupling line 8 is high. , the high frequency energy from the transmitter 1 is transmitted to the feeder line 3 and antenna 2 without any hindrance.

On the other hand, the low frequency current from the low frequency oscillator 10 passes through the amplifier 11, the resistor 12 and the low pass filter 13,
The inner conductor 8a of the coupled line 8 leads to the coupler 4. The inner conductor 8a of the coupled line 8 is connected to the feed line inner conductor 6 of the coupler 4 and is insulated from the transmitter side inner conductor 5, so the low frequency current I enters the inner conductor of the feed line 3. Further, it reaches the antenna 2, turns back at the feeding part of the antenna 2, takes the opposite route through the outer conductor, and returns to the low frequency oscillator 10. Therefore, a voltage of V=I·r is generated between the inner and outer conductors of the low-frequency oscillator 10 side terminal of the low-pass filter 13, where r is the DC resistance when looking from this terminal toward the antenna. However, the frequency of the low frequency oscillator 10 is sufficiently low, and the resistance thereto is assumed to be equal to the DC resistance.
Since the resistances of the low-pass filter 13 and the coupler 4 are sufficiently low, the DC resistance r mentioned above is approximately equal to the DC resistance of the feed line and the antenna system. The value R of resistor 12 is R≫
If r is set, the current I will be constant regardless of the change in r, so if the above V is observed, the feed line
Changes in the DC resistance of the antenna system can be observed.

Since the low frequency current I can be caused to flow regardless of whether radio waves are emitted or stopped, the direct current resistance r of the antenna feed line can be continuously monitored at all times.

Normally, the DC resistance of the antenna/feed line system of a television broadcasting core station is 20 to 30 mΩ, so if the output current I of the low frequency oscillator is selected to be 100 mA, for example,
V=2 to 3 mV. Increased deterioration of DC resistance 5
If the voltage V
The observation range is V = 2 to 150 mV. Taking a slight margin, even if it is 1 to 200 mV, this value is within the range that can be detected accurately, and the S/N is over 20 dB.
is obtained.

Next, regarding the coupler 4, the voltage generated within the coupler,
We will discuss the power capacity of the coupler in the main line section, the power capacity of the coupler in the coupled line section, and VSWR.

(1) Voltage generated within the coupler; Of the voltages generated within the coupler 4, the voltage that requires the most attention is the voltage generated in the gap between the transmitter side inner conductor 5 and the feeder side inner conductor 6. This voltage is maximum at the tip (open end) of the transmitter side inner conductor 5. This maximum voltage sets the characteristic impedance of the main line to Z ₀ , both inner conductors 5,
When the characteristic impedance of the gap 6 is Z _G and the transmission power of the main line is P, it is given by the following equation (1).

For example, if the inner diameter of the feeder side inner conductor 6 is 50 mm, the gap is 5 mm, and this gap is filled with polyethylene with a dielectric constant of 2.3, then Z _G =8.83Ω,
Now, if Z _O = 50Ω and P = 50KW, then V _Gnax =
Although the voltage is 279V, the maximum electric field generated is 56V/mm, so there is no problem in terms of withstand voltage.

(2) Power capacity of the coupler in the main line section; for this, it is necessary to take into account the heat loss of the coaxial section constituted by both inner conductors 5 and 6. The current distribution in this coaxial section is zero at the open end, that is, at the tip of the transmitter side inner conductor 5, and is a sine distribution such that it becomes equal to the main line current at the input end. Therefore, the average heat loss in the coaxial section is equal to the amount of heat generated in the same length of the main line conductor. Therefore, in the main line, it is thought that the heat loss in both inner conductors 5 and 6 will be twice the normal amount, so if the dimensions of each inner conductor 5 and 6 are raised one rank higher than the dimensions of the feeder line 3. good.

(3) Power capacity of the coupler in the coupled line; consider how thick the helical conductor 8a in the coupled line 8 should be. In this case, since the helical conductor 8a is grounded by a large capacitance 8c at a point effectively 1/4 wavelength away from the input end (main line side), the power capacity can be approximated by direct grounding. By this approximation, the equivalent circuit of the coupled line 8 is as shown in FIG. Now, if voltage V _H is generated in the inner conductor of power supply line 3 and current I _H is flowing, V _H =√ _O・...Equation (3) is obtained. However, P is the transmission power and Z _O is the characteristic impedance of the main line. On the other hand, helical conductor 8
Since the effective length of a is 1/4 wavelength, the current I _h flowing through it is maximum at the grounded end, and is given by I _h = V _H /Z _h . . . equation (4). However, Z _h is the characteristic impedance of the coupled line 8. From the above formulas (2), (3), and (4), I _h = Z _p /Z _h · I _H ... Formula (5). Therefore, if the helical conductor 8a and the inner conductor of the feeder line 3 are made of the same material, the thickness of the helical conductor 8a should be approximately Z _p /Z _h times the thickness of the inner conductor of the feeder line 3. It turns out.

(4) VSWR: Coupler 4 is designed to have no reflection at the design center frequency, but let's consider the frequency characteristics. FIG. 3 shows an equivalent circuit of the coupler 4. Series reactance jx in Figure 3
is the input reactance of the open-ended coaxial line composed of the transmitter-side inner conductor 5 and the feeder-side inner conductor 6, and is given as jx=-jZ _G ·cotθ...Equation (6). However, θ is the electrical length of the open-ended coaxial line. On the other hand, the parallel successor jB is
The input susceptance when looking at the coupled line 8 from the main line side is, if the parallel capacitance 8c of the helical conductor 8a is large, the second and subsequent stages can be ignored, so it can be considered using the equivalent circuit in Figure 4, jB =−jcosθ+1/ωcZ _h sinθ/Z _h sinθ−1/ωcc
osθ...Equation (7) is obtained. However, it is assumed that the electrical length per section of the helical conductor 8a is also θ. ω is the angular frequency and C is the capacitance value. Therefore, when the output terminal 4b is terminated with the characteristic impedance Z _p in the equivalent circuit of Fig. 3, the reflection coefficient seen from the input terminal 4a is is given by

Now, C = 50PF, Z _G = 8.83Ω, Z _h = 250Ω, Z _p =
50Ω, and considering the Haiti channel of television broadcasting, under the condition that θ = 90° at 195MHz.
Calculate |Γ| in the range of 170~220MHz to calculate VSWR
When calculated, it is less than 1.03. Next, considering the roach channel, calculate |Γ| in the range of 90 to 108 MHz under the condition that θ = 90° at 99 MHz.
When calculating the VSWR, it is below 1.09. Therefore, it is possible to maintain a sufficiently small VSWR.

As explained above, according to the device of the present invention, it is possible to constantly monitor the resistance of the feeder line/antenna system, and it is possible to detect deterioration of contact at the connection part of the feeder line in advance, thereby preventing a burnout accident. This has the effect of being able to prevent this from happening.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIGS. 2 to 4 are equivalent circuit diagrams for explanation. 1 is a transmitter, 2 is an antenna, 3 is a feed line, 4 is a coupler, 5 is a transmitter side inner conductor, 6 is a feed line side inner conductor, 8 is a coupling line, 10 is a low frequency oscillator, 12 is a resistor, 13 is a low-pass filter, 14 is an amplifier, 16 is a reference voltage, 17 is a comparator, and 18 is an alarm.

Claims (1)

[Claims] 1 A coupler connected between the transmitter output side and the feeder line to the antenna, which has an inner conductor on the transmitter side and an inner conductor on the feeder side that are coaxially coupled to each other by 1/4 wavelength. The coupler has a helical transmission line with high characteristic impedance that is branch-connected to one end of the inner conductor on the wire side, and a coupling line that reduces leakage of high-frequency signals and is formed by capacitance that grounds the helical transmission line at appropriate intervals. , a low-frequency oscillator for flowing a low-frequency current from the coupling line of the coupler to the inner conductor of the feeder through a low-pass filter for reducing a high-frequency signal, and a voltage generated by the low-frequency current. 1. An automatic direct current resistance monitoring device for an antenna feed line system, comprising: a monitoring device for monitoring the direct current resistance of the antenna feed line system based on the above information.