JPS5923679A - Antenna switching circuit of vtr - Google Patents

Abstract

PURPOSE:To obtain stable input matching characteristics and good noise factor characteristics, by providing a by-pass circuit in parallel to a halving circuit of an antenna switching circuit and thereby eliminating the use of unstable halving circuit in a VTR mode. CONSTITUTION:Input signal from a TV antenna is halved by an halving circuit 1. A signal outputted from an output terminal 3 is inputted to a built-in tuner 5 of VTR, stored in the tape of VTR, and an output signal from a terminal 4 is added to the terminal 9 of a switching circuit 7. A signal from the terminal 9 and a signal from an RF modulater 11 are switched and selected electronically by the circuit 7, and inputted to a TV receiver from a terminal 8. A by-pass circuit 13 is provided in parallel to the halving circuit 1, and a switch 17 linked with the switch 16 of the circuit 7 is provided in the circuit 13. When the switch 16 is made to VTR mode, the halving circuit 1 is by-passed by the switch 17 and unstable halving circuit 1 is not used. Thus, input matching characteristics and noise factor characteristics are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna switching circuit for a VTR, and more particularly to an antenna switching circuit with excellent input matching characteristics and tuner noise figure characteristics.

A conventional block diagram of an antenna switching circuit for a video tape recorder (VTR) is shown in FIG. 1, and its operation will be explained below. The signal inputted to the television antenna 20 in FIG. 1 is inputted to the input terminal 2 of the 2-way distribution circuit 10,
The signal is divided into two by the two-way distribution circuit 1 and outputted from the terminal 3.4. The signal output from terminal 3 is input to input terminal 6 of tuner 50 built in vTn (not shown).
VTit selects the desired received signal and selects 171. A good signal is recorded on the vl''R tape by a subsequent circuit (not shown).

Another output signal from the two-way distribution circuit 1 is inputted from the terminal 4 to the terminal 9 of the switching circuit 7.

This switching circuit 7 is output from the RF modulator 11,
The signals inputted to the terminal 10 and the signals inputted from the terminal 9 are usually electronically switched and sorted and outputted from the terminal 8, and the terminal is connected to a general television receiver.

Here, the switch of the switching circuit 7 is the terminal 9111! When connected to terminal VC (hereinafter referred to as TV mode), the television receiver connected to terminal 8 is connected to 2 distribution circuit 1.
Either the tuner 5 with built-in VTnK is receiving the other signal and the IA program is being recorded), or the VTnK is not used and the TV program is being recorded. The receiver is being used alone. At this time, the two-way distribution circuit 1 performs the operation of dividing the Kigo signal into two, but when the switch of the switching circuit 7 is connected to the terminal 10 side (hereinafter abbreviated as I/TR 7-mode), The output terminal 4 of the 2-way divider 1 is in an open state, and the terminals 3 and 4 are connected to each other.
Since the load conditions of t are different, it becomes difficult to operate as a stable two-way divider, and there is a defect that the constant input matching characteristic on the side of the two-way divider circuit 1 from the terminal 2 is disturbed.

An object of the present invention is to provide a VTR with improved noise figure characteristics including good input matching characteristics and a two-antenna distribution circuit for the tuner.
An object of the present invention is to provide an antenna switching circuit.

In order to achieve the above object, in the present invention, when the switch of the switching circuit is connected to the RF module and connected to the terminal side, the operation of the two-way distribution circuit is not necessary.
A circuit is provided that bypasses all input signals directly to the antenna built-in tuner without passing through the distribution circuit, thereby improving the input matching characteristics and eliminating the one-way distribution loss to improve the noise figure characteristics.

Hereinafter, the implementation configuration of the present invention will be explained with reference to FIG. Second
The same reference numerals as in FIG. 1 are designated by 1i1- in FIG. 1. The 411 difference from FIG. 1 is that a bypass circuit block 13 is added, and this bypass circuit block 13 has a similar function to the switching circuit 7.

When the switch 16 of the switching circuit 7 is connected to the terminal 9 side (in TV mode), in conjunction with this switch 16, the first and third edges of the bypass circuit 13 are connected to the ground 18 side, and the bypass The operation of the circuit 13 is in the off state, and the first
Figure and I? The 10 functions of the two-way distribution circuit are operated in the same manner as 11.

Next, when the switch 16 of the switching circuit 7 is connected to the terminal 10 side (in VT11 mode), the bypass circuit g1130) operates in conjunction with this switch 16.7. Switch 17 is connected to terminal 151111I. In this state, the 2-distribution circuit 1 is short-circuited to the bypass circuit 13, and the antenna input Nozuki B is not divided into 2 by the 2-distribution circuit 1, but is directly routed to the tuner 50 input terminal via the 13 bypass circuits. is input.

This is because the antenna input signal does not suffer from the distribution loss that occurs in the two-way distribution circuit 1, and does not pass through the two-way distribution circuit 1, which is unstable during conventional operation.

Stable input matching characteristics and good noise figure characteristics should be obtained.

1. In order to operate correctly, the connection point 19 between the antenna input terminal's input point 2 of the 2-way distribution circuit 10 and the bypass circuit 13 must be disconnected from the connection point 19 and the 2-way distribution circuit input terminal 2 when in VTR mode. Although it should be made into a state, V
The impedance of the bypass circuit 13 in TR mode is 2.
Since the input impedance is very low compared to the input impedance of the distribution circuit 1, the bypass circuit 13 operates without adding a new complicated switch circuit to this connection point.

As explained above, according to the present invention, the switching circuit
Mo? Since an unstable two-way distribution circuit is not used when the input terminal is connected to the terminal connected to the generator (VTR mode), stable input matching characteristics and good noise figure characteristics can be obtained.

Normally, the distribution loss of this two-way distribution circuit is about 4 dB, so the noise figure characteristic can be improved by 4rlF+.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional VTII antenna I switching circuit, and FIG. 2 is a block diagram of a vTn antenna switching circuit according to the present invention. 1...2 distribution circuit, 5...VTR built-in'f-use, 7, °, switching circuit, 11...RF modulator, 1
3...Bypass circuit. Representative Patent Attorney Usui J Jtl Office”-,1,,,. r (!゛・1

Claims (1)

[Claims] VTn consisting of 2 distribution circuit 1, switching circuit 7 and tuner 5
In the antenna input circuit, there is a bypass circuit 13 for directly inputting the input signal received by the antenna to the tuner 5 without passing it through the 2-way distribution circuit 1 in the VTR mode.
1. An antenna switching circuit for a VTR, characterized in that the antenna switching circuit is switchably provided in parallel with a distribution circuit 1.