JPH057348A - Automatic input switching device - Google Patents

Abstract

PURPOSE:To automatically switch an input switching means by the presence or the absence of an input signal. CONSTITUTION:A first television signal S1 is converted into the frequency of the dead channel of television by a frequency conversion circuit 30. The frequency-converted first television signal S1 and a second television signal S2 for broadcasting are supplied to the input switching means 22. The video carrier of the first television signal S1 is detected by a carrier detection circuit 36, and carrier detection output Sa is obtained. The first television signal S1 is supplied to a video detection circuit 44 as well, and video output is detected. When both video detection output Sb and the carrier detection output Sa are obtained at a time, the input switching means 22 is switched automatically to a first television signal S1 side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television signal automatic input switching apparatus suitable for application to a video wireless transmission / reception system or the like.

[0002]

Video wireless transceiver systems are known. This video wireless transmission / reception system is an indoor transmission / reception system that is prevalent in the United States and the like. For example, a video signal (for convenience, referred to as a first television signal S1) captured by the video camera 12 as shown in FIG. When viewed with the television receiver 26, the cable connecting the video camera 12 and the television receiver 26 is generally short, such as 1 to 2 m. Therefore, the video camera 12 must be operated by approaching the television receiver 26. I won't.

In order to solve such inconvenience, a video wireless transmission / reception system 10 has been developed so that the video camera 12 can be operated from a place apart from the television receiver 26 to some extent. Is.

The outline thereof is as shown in FIG. 2. For example, the first television signal S1 output from the video camera 12 is transmitted by using the video wireless transmitter 14. 16 is a transmitting antenna (rod antenna or the like). In the United States, the current frequency band of TV channels (8
Since the frequency band higher than 3 channels is addressed as a civic band, the transmission frequency is video wireless frequency (902-928MH) in this civic band.
z).

A receiving antenna (rod antenna or the like) 18 is attached to the receiver 20 installed indoors, and the first television signal S1 received by the receiving antenna 18 is transmitted in the receiver 20 to a television channel. After being frequency-converted into a television signal of an empty channel (for example, 3 channels or 4 channels of VHF band), it is supplied to an antenna input terminal (not shown) of the television receiver 26 via the input switching means 22. It

The input switching means 22 includes an outdoor antenna 2
A television signal for broadcasting (referred to as a second television signal S2) received at 4 or the like is supplied, and one of them is manually selected. The input switching means 22 is usually built in the receiver 20. Input sources for the transmitter 14 include a stationary video deck (VCR), a cable TV, and the like in addition to the video camera 12, and the input sources are not particularly limited.

[0007]

As described above, in the video wireless transmission / reception system 10 used indoors or the like, the switching between the first and second television signals S1 and S2 is performed manually. The switching and confirmation of the switching state are very troublesome. In particular, since the receiver 20 is often installed close to the television receiver 26, the switching state of the input switching means 22 must be confirmed each time the first television signal S1 is viewed. It will not happen.

Therefore, the present invention has solved such a conventional problem, and provides an automatic input switching apparatus suitable for application to a video wireless transmission / reception system or the like capable of automatically switching a television signal. It is a proposal.

[0009]

In order to solve the above-mentioned problems, according to the present invention, an input for switching between a first television signal and a second television signal to be supplied to a television receiver is provided. In the switching device, the input switching means has the input switching means, and the input switching means is provided on the first television signal side only when the video signal of the received first television signal and the video signal are simultaneously detected. It is characterized in that it is adapted to be automatically switched to select.

[0010]

In FIG. 1, the receiving antenna 18 makes the first
When the television signal S1 of 1 is received, the carrier detection circuit 36 detects the video carrier in the first television signal S1, so that the carrier detection output Sa is obtained.

Similarly, when the first television signal S1 is properly received, the video signal thereof is detected by the video detection circuit 44.
In this case, the image detection output Sb is also obtained. These are carrier detection output Sa and image detection output S
Input switching means 22 by AND output when b is obtained
Are automatically switched to the first television signal S1 side. Otherwise, the second television signal S2
It is assumed that the input switching means 22 is controlled so that can be selected.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a case where an example of the automatic input switching device according to the present invention is applied to the above-mentioned video wireless transmission / reception system will be described in detail with reference to the drawings.

This automatic input switching device is used in a state where it is built in the receiver 20 of the video wireless transmission / reception system 10, and is the first television received by the receiving antenna 18 as shown in FIG. John signal S1
Is converted into a frequency band of an empty channel (for example, 3/4 channel) of the television channel in the frequency conversion circuit 30 as described above. For the frequency conversion, the frequency conversion circuit 30 is provided with a local oscillation circuit 32.

The frequency-converted first television signal S1 is supplied to the input switching means 22. The second television signal S2 is also supplied to this, and any one of them is selected and supplied to the television receiver 26 (FIG. 2). The input switching means 22 is automatically controlled by the output described below.

The frequency-converted first television signal S1 is supplied to the bandpass filter 34 and band-limited so as to pass only the band of the video carrier of the designated empty channel (3 or 4 channels). The first television signal S1 that has passed through the bandpass filter 34 is supplied to the next carrier detection circuit 36 to detect a video carrier. The detected image carrier is supplied to the comparator 38 having a hysteresis function, and the image carrier having a predetermined level or higher is detected. The detection output is set as the carrier detection output Sa.

The reason why the comparator 38 is provided with a hysteresis function is to prevent erroneous detection that the image carrier is present even when the image carrier is generated instantaneously.

The first television signal S1 that has passed through the band pass filter 34 is further supplied to the AM detection circuit 40, and the video signal of the first television signal S1 is AM-detected. As for the AM detection output, the high-pass part of the video signal is output by the bandpass filter 42, and this is supplied to the video detection circuit 44. In the case of a television signal accompanied by a video, a predetermined video detection output is obtained from the video detection circuit 44, and this is further compared in level by a comparator 46 having a hysteresis function.

Therefore, when the video output is equal to or higher than a predetermined level, the video detection output Sb is obtained, and the AND circuit 48 logically sums this with the above-mentioned carrier detection output Sa. This logical sum output is supplied to the input switching means 22 as a switching control signal, and the input switching means 22 is switched to the first television signal S1 side only when both the carrier detection output Sa and the video detection output Sb are obtained. ..

As described above, the input switching means 22 is switched only when the carrier detection output Sa and the video detection output Sb are obtained at the same time in order to avoid a malfunction. By doing so, the input switching means 2 is provided only when the first television signal S1 is received.
2 can be automatically switched.

In the normal mode, that is, when the television signal for broadcasting is viewed, since the first television signal S1 is not present, the input switching means 22 remains in the switching state shown by the broken line.

In FIG. 1, when a voltage control type oscillator (VCO, VCXO, etc.) is used as the local oscillator 32, and if the bandpass filter 34 is a tuning type bandpass filter configuration, a bandpass filter is used for the voltage control signal. The frequency can be set to an appropriate value.

For example, if the first television signal S1 is 3
Based on the voltage control signal obtained from the variable resistor 50, the local oscillation frequency of the local oscillator 32 and the band pass of the band pass filter 34 are converted depending on whether the frequency is converted into the frequency of the channel or the frequency of the four channels. The frequency can be changed synchronously. By doing so, the selectivity of the bandpass filter 34 is increased, and the carrier detection accuracy is improved accordingly.

Although the present invention has been applied to the video wireless transmission / reception system in the above description, it can also be applied to a television signal input switching device in a multi-source type television receiver.

[0024]

As described above, in the automatic input switching device according to the present invention, the first television signal side is selected only when the video signal of the first television signal and the video signal are simultaneously detected. As described above, the input switching means is automatically controlled.

According to this, since the television signal can be automatically selected depending on the presence or absence of the input, it is not necessary to manually switch the input. Therefore, it is very convenient to use, and it does not cause input switching mistakes.
Therefore, the present invention is extremely suitable when applied to the video wireless transmission / reception system described above.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of an automatic input switching device according to the present invention.

FIG. 2 is a system diagram showing an example of a video wireless transmission / reception system.

[Explanation of symbols]

 10 transmission / reception system 12 video camera 14 transmitter 20 receiver 22 input switching means 26 television receiver 30 frequency conversion circuit 36 carrier detection circuit 44 video detection circuit Sa carrier detection output Sb video detection output

Claims (1)

Claim: What is claimed is: 1. An input switching device for switching between a first television signal and a second television signal and supplying the television signal to a television receiver. The input switching means is automatically switched to select the first television signal side only when the video signals of the received first television signal and the video signal are simultaneously detected. An automatic input switching device characterized by being made.