JPS6114184Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an impedance transformer used, for example, in television reception equipment.

In Japan, 75Ω unbalanced impedance and 300Ω balanced impedance are used exclusively for television signal transmission. For example, the impedance of a television reception antenna is 300Ω balanced, and a 75Ω unbalanced coaxial cable is used for the transmission line to the television receiver. An impedance transformer is used as a device for converting and connecting components having different impedances, and conventionally, an impedance transformer having a configuration as shown in FIGS. 1 and 2 has been widely used. That is, terminals 1 and 1' are unbalanced terminals and are connected to a coaxial cable which is an unbalanced transmission line to a television receiver, and terminals 2 and 2' are balanced terminals and are connected to a television reception antenna. Such conventional impedance transformers not only require a special glasses-shaped core to form a closed magnetic circuit, but also require polyethylene-covered copper wires to be inserted through small holes drilled in the glasses-shaped core. However, the windings had to be applied one after another, making manufacturing difficult and lacking in mass productivity.

To solve this problem, a coil was constructed by winding a conductor wire around the outer circumference of a bobbin with a ground electrode on the inner surface, and a capacitor was connected between the unbalanced terminal and the balanced terminal. Impedance transformers have been devised (for example, the one shown in Japanese Utility Model Publication No. 53-27696). However, such a structure has the disadvantage that it is bulky because a bobbin is used for the coil, and the price is also high due to the cost of the bobbin parts.Furthermore, the coil may be subject to vibration when in use. Then, the connection between the coil winding and the unbalanced or balanced terminal is not only stressed due to the inertia due to the weight of the winding, but also due to the large inertia due to the large weight of the bobbin. A large amount of stress is also applied, which causes the connection between the conductor and the thin film electrode on the inner surface of the bobbin to become disconnected.

The present invention has been made to eliminate the above-mentioned drawbacks of the conventional methods, and aims to provide an impedance transformer that is small in bulk, can be provided at low cost, is durable, and has good electrical characteristics equivalent to the conventional ones. purpose.

The present invention will be explained below with reference to FIGS. 3 to 7. FIG. 3 shows the circuit configuration of the present invention, where 5 is an inductor, and a spiral coil is used. 6 is a capacitor, and a ceramic capacitor or a printed capacitor printed on a substrate is used as appropriate. FIG. 4 shows an example in which a coil 5a made of polyurethane copper wire is used for the inductor 5 and a ceramic capacitor 6a is used for the capacitor 6 in the above circuit configuration. , 1' are connected to a coaxial cable to a television receiver, and balanced terminals 2, 2' are connected to a television reception antenna.

In the above configuration, if the frequency band used is, for example, 470MHz to 770MHz, which is the UHF television broadcast band, the inductance of the coil 5 is several + nH.
Also, it is appropriate that the capacitance of the capacitor 6 is several PF.

The insertion loss characteristics of the above configuration are shown in Figure 5, and the VSWR characteristics are shown in Figure 6. According to the EIAJ (Electronic Industries Association of Japan) standards, the insertion loss is 1.5 dB or less and the VSWR is 2.5 or less for impedance transformers. If you apply this standard and look at the above characteristics, you will see that it shows good characteristics in the frequency range from 470MHz to 770MHz.

In FIGS. 5 and 6 above, between the unbalanced terminal 1 and the balanced terminals 2 and 2' in FIG.
The broken line shows the results of measuring the characteristics when a standard balun transformer for balanced/unbalanced conversion as shown in Figure 2 is connected, and the characteristics when the capacitor 6a is removed from the configuration shown in Figure 4. The two-dot chain line shows the results of measuring the characteristics when the coil 5a is removed and the terminals 2 and 2' are connected by a conductive wire instead. As is clear from this measurement result, in the case where the unbalanced terminal 1 and the balanced terminals 2, 2' are connected as described above by the coil 5a, capacitor 6a, etc., it complies with the EIAJ standard and meets the standard. Since good characteristics similar to those obtained when using a conversion transformer can be obtained, a device connected in this way has an unbalanced terminal 1, a balanced terminal 2,
It can be said that the unbalanced/balanced conversion is appropriately performed between 2' and 2'.

This characteristic was obtained by actually measuring an impedance transformer constructed using a polyurethane copper wire with a wire diameter of 0.6 mm, a coil 5a with a winding diameter of 3 mm, and a number of turns of 5, and a capacitance and a ceramic capacitor 6a of 1.5 PF. It is.

Next, FIG. 7 shows an embodiment with a different structure of the capacitor, in which the capacitor 6 in the circuit configuration of FIG. An example will be shown in which variations are eliminated and the effort of wiring is saved.

As described above, this invention has a configuration in which only the capacitor 6a and the coil 5a are interposed between the unbalanced terminals 1, 1' and the pair of balanced terminals 2, 2', so it is extremely difficult to use. It has the feature of being small in bulk. In particular, since the coil 5a is constructed of a self-supporting structure in which the conducting wire is simply spirally wound without a core, the coil 5a has the advantage of being significantly smaller in bulk than a conventional coil wound around a bobbin.

Moreover, since the coil 5a is composed of only one member consisting of only the wound conductive wire as described above, it has the advantage that it can be provided at an extremely low cost. In other words, there is no need for separate components such as the core or bobbin of conventional products in which the conductor is wound around a core or a bobbin with a ground electrode, and the cost is reduced by the cost of the components. It has the effect of making it possible.

Furthermore, the impedance transformer of the present invention may cause damage to the coil 5a due to shaking of the coaxial cable during use.
Even if vibration is applied to the coil 5a, as described above, which is just a conductor wound around the coil 5a, it is light and has low inertia, so only a small stress is applied to one end of the coil 5a and the connection between the other end and the terminal. This has the effect of preventing disconnection and extending the lifespan.

Moreover, the impedance transformer of the present invention has a structure that can exhibit the following three effects: (1) it is small in bulk, (2) it can be provided at low cost, and (3) it is durable and can be used for a long time. However, it has the great effect of exhibiting good electrical characteristics equivalent to those using a conventional core or a bobbin with a ground electrode.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional impedance transformer, Fig. 2 is a perspective view showing the configuration of the embodiment of Fig. 1, Fig. 3 is a circuit diagram of the present invention, and Fig. 4 is an impedance transformer of Fig. 3. 5 and 6 are characteristic diagrams of the embodiment shown in FIG. 4, and FIG. 7 is a perspective view showing a different embodiment from FIG. 3. 1... Center conductor of unbalanced terminal, 2, 2'... Balanced terminal, 5... Inductor, 6... Capacitor.

Claims (1)

[Scope of utility model registration request] It is equipped with an unbalanced terminal for connecting a coaxial cable for a television receiver and a pair of balanced terminals for connecting a television receiving antenna, one end of a capacitor is connected to the external conductor of the unbalanced terminal, and the other end of the capacitor is connected to the outer conductor of the unbalanced terminal. is connected to one of the pair of balanced terminals, and the center conductor of the unbalanced terminal and the other of the balanced terminals are connected to each other by a conductor, and a conductor is wound therein in a coreless spiral. 1. An impedance transformer characterized in that one end of a self-supporting coil is connected to the coil, and the other end of the coil is connected to one of the pair of balanced terminals.