JPS59115627A - Device for preventing mixing of external radio wave - Google Patents

Abstract

PURPOSE:To prevent a signal due to an external radio wave mixed in a talking line from being mixed to an interface (IF) circuit by providing a shield member shielding primary and secondary windings of a coupling transformer to the said transformer between the IF circuit at a telephone exchange terminal and a talking line, and grounding the member. CONSTITUTION:The electrostatic shield members 5, 6 are provided between the primary and secondary windings of the transformers T1, T2. C5, C6, C7 and C8 are stray capacitances between the primary winding and the shield members 5, 6 and between the shield members 5, 6 and the secondary winding. It is supposed that a signal component due to an external radio wave appears on the talking lines 3, 4 and there is a difference between the components. In this case, the signal component due to the external radio wave flows to the talking line 4 through, e.g., the shield member 5, ground, the shield member 6 and the capacitance C8 from the line 3, but the signal does not flow to the IF circuits 1, 2. Thus, the component is never detected and the disturbing sound to be detected is not listened to by a telephone set. Further, the shield members 5, 6 give any hindrance to normal talking signal transmission.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an apparatus for preventing foreign radio wave contamination used in telephone exchanges.

Conventional Structure and Problems Generally, a plurality of interface circuits 1.2 are connected to each terminal of a telephone exchange, as shown in FIG.
．． 4, there are transformers T1 that connect both of them to each other.
, T2 are connected.

By the way, the telephone lines 3.4 are usually relatively long because they are connected to telephones or office lines, and if there is a radio transmitting station nearby, the telephone line 3.4 itself is connected to the radio transmitting station. There is a problem in that radio waves enter as external radio waves, are detected by non-linear elements such as transistors and diodes constituting the interface circuit 1.2, and are heard directly from the telephone, greatly interfering with normal telephone calls. That is, it is assumed that external radio waves from a radio transmitting station are incident on all communication lines 3 and 4, respectively.

In this case, of course, since the communication lines 3.4 are routed at different distances from the radio transmitting station, there will be a difference in the magnitude of the signals generated by the external radio waves on both communication lines 3.4. For example, the stray capacitance C2 between the primary winding and the secondary winding of the transformer T1 from the telephone line f#3, the interface circuit 1, the ground, the interface circuit 2,
Trance T! A current flows through the communication line 4 through the stray capacitance C4 between the primary winding and the secondary winding, and this is AM-detected by the non-linear elements such as transistors and diodes that constitute the interface circuit 1.2. The AM-detected signal will be directly transmitted from the telephone connected to .4, which will seriously impede normal communication.

Therefore, conventionally, as shown by the dotted line in Figure 1, the transformer 11. , IJI, the capacitors C1 and C3 are connected to the negative winding of IJI.
is connected, and the external radio wave signal input from the telephone line 3.4 is grounded by the capacitors C1 and C3.
There are also known configurations in which input is not input to the interface circuit 1.2, or in this type, the communication line 3 is
．． A normal voice signal transmitted through the 4-channel signal is also attenuated to a large extent in its high frequency range, resulting in a problem in that the frequency characteristics of the voice signal itself are significantly deteriorated.

Purpose of the Invention The present invention eliminates the above-mentioned drawbacks of the conventional technology, and is an excellent external device that has a simple configuration, does not affect the frequency characteristics of the call signal itself, and easily prevents the mixing of external radio waves. The purpose of this invention is to provide a device for preventing radio wave contamination.

Structure of the Invention The present invention provides a shield member between the primary and secondary windings of a transformer that mutually connects an interface circuit and a telephone line provided at each terminal of a telephone exchange to electrostatically shield them from each other. This shield member is grounded to prevent signals from external radio waves received through the communication line from entering the interface circuit.

DESCRIPTION OF THE EMBODIMENT FIG. 2 is an electrical wiring diagram of an embodiment of the foreign radio wave mixing prevention device of the present invention. In the figure, the same reference numerals as in FIG. It shows. and,
5.6 is an electrostatic shielding member provided between the primary and secondary windings of the transformers T1 and T2, respectively; for example, a metal plate, metal wire, etc. is placed between the primary and secondary windings. It is formed by winding. c5, c6, c7, c
8 indicates the stray capacitance formed between the secondary winding and the shield member 5.6 of the transformers T and 1T, and between the shield member 5.6 and the secondary winding, respectively.

In the above embodiment, it is assumed that signal components due to external radio waves appear at each of the communication ports '1IjI3.4, and a difference occurs in their values. In this case, the signal component due to the external radio wave flows from the communication line 3 to the communication port #i14 via the stray capacitance C, the electrostatic shield member 5, the ground, the electrostatic shield member 6, and the stray capacitance C8, but the interface circuit 1. 2, almost no flow will occur. Therefore, even if signal components due to external radio waves flow through the telephone line 3.4 itself,
This is rarely detected, and the detected interference is almost never heard by the telephone. and,
The static '1E nord section 5.6 is simply a stand provided for the static / - route.]・Lance '1゛1,'
This does not cause any problem in normal communication signal transmission between the primary and secondary windings of J2.

In addition to the effects of the invention, as is clear from the examples, the foreign radio wave mixing prevention device of the present invention is constructed by simply interposing a separate shield member between the primary and secondary windings of the transformer and grounding them. The structure is simple and extremely advantageous in practice. Particularly, the present invention has the advantage that it not only prevents the contamination of external radio waves, but also does not affect normal telephone call transmission in any way, so that normal telephone calls can be carried out effectively.

[Brief explanation of the drawing]

FIG. 1 is an electrical wiring diagram of a terminal section of a conventional telephone exchange, and FIG. 2 is a schematic electrical wiring diagram of an embodiment of the foreign radio wave mixing prevention device of the present invention. ■, 2...Interface circuit, 3.4...Telephone line, 5.6 - Shielding member, T1, T2...Transformer, Mountain ~ C8, Stray capacitance.

Claims (1)

[Claims] A shield member is provided between the primary winding and the secondary winding of a transformer that mutually connects the interface circuit provided at each terminal of the telephone exchange and the telephone line, and the shield member electrostatically shields them from each other.
By grounding this shield, you can prevent external radio waves received on the above telephone line.