JP2629559B2 - In-vehicle television device and in-vehicle FM transmitter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-vehicle FM transmitter capable of transmitting an audio signal of a television receiver as an FM signal, and a vehicular television having the FM transmitter.

[0002]

2. Description of the Related Art A conventional FM transmitter converts not only television sound but also sound signals of various devices into FM broadcast waves, and its transmission frequency has a disturbing relationship with FM broadcast stations in various parts of Japan. In many cases, the frequency is selected from 76 MHz to 79 MHz where the number of stations is small so that the number of stations is not changed, and a switching method of two or more waves is used so as to avoid interference depending on the area.

For example, 77.7 MHz and 78.2 MHz,
Or 77.5 MHz and 77.9 MHz.

[0004]

SUMMARY OF THE INVENTION A conventional FM transmitter converts television sound into an FM broadcast wave, and
In the case of reception by the M receiving device, as the interference that the FM transmitter device gives to the television device, there is a harmonic interference of the transmission frequency, but the television VHF high band is one.
Since it is 70 MHz to 222 MHz, it can be avoided if the FM transmitter transmission frequency is set to 76 MHz to 85 MHz, and there is almost no problem with the conventional FM transmitter device.

[0005] Next, as the interference that the FM receiver gives to the television device, there is harmonic interference of the local oscillation frequency of the FM receiver.

[0006] This interference is caused by the fact that the transmission frequency of the FM transmitter is 77.7 MHz, 78.
Assuming that the frequency is 2 MHz, the FM receiver sets this transmission frequency to 1
In order to convert to an intermediate frequency of 0.7 MHz, oscillations of 67.0 MHz and 67.5 MHz are performed as local oscillation frequencies.

At this time, harmonics of the local oscillation frequency are generated,
201.0 MHz and 202.5 MHz of the third harmonic are radiated from the main body of the FM receiver as unnecessary radiation and from the antenna of the FM receiver as antenna terminal voltages, and penetrate from the antenna of the television, and enter the television. When received on channel 9, it is mixed into the band of the video signal as interference,
Each becomes a luminance beat disturbance and a color beat disturbance.

This interference is not a problem if the antennas of the FM receiver and the television receiver are sufficiently separated, but the transmission output of the FM transmitter is regulated to 54 dBμv / m or less according to the 3m method regulated by the Radio Law. Since the practical reach is about 3 m to 5 m, there is a problem when used indoors or in a car. In particular, in-vehicle television devices have a problem that they are susceptible to interference since the distance between the FM transmitter device and the antenna is very short.

The present invention has been made for the purpose of avoiding this interfering relationship.

[0010]

According to a first aspect of the present invention, there is provided a television receiver, and an audio signal of the television receiver is transmitted as an FM signal having a specific frequency in an FM broadcast band. In the in-vehicle television device having an FM transmitter device for allowing a signal to be received by an FM receiving device capable of receiving an FM signal of an FM broadcast band, the specific frequency is such that a second harmonic of the frequency is a television VH.
F is lower than the high band, and the F
A third harmonic of a local oscillation frequency of the FM receiving apparatus that has received the M signal has a value that is 1.25 MHz lower than a video carrier frequency of a television VHF high band channel. The invention according to claim 2 is the vehicle-mounted television device according to claim 1, wherein a plurality of frequencies can be selectively set as the specific frequency, and one of the plurality of frequencies is set to 76. The frequency is 7 MHz or 78.7 MHz.

According to a third aspect of the present invention, an audio signal of a television receiver can be transmitted as an FM signal of a specific frequency in an FM broadcast band, and the FM signal can be received in an FM broadcast band. In the on-vehicle FM transmitter to be received by the FM receiver, the specific frequency is such that the second harmonic of the frequency is lower than the television VHF high band, and the FM receiving the FM signal of this frequency. The third harmonic of the local oscillation frequency of the receiving device is a value which is lower than the video carrier frequency of the television VHF high band channel by 1.25 MHz, and the invention according to claim 4 is characterized in that: 4. The on-vehicle FM transmitter according to claim 3, wherein a plurality of frequencies can be selectively set as the specific frequency. One of the frequency, 76.7
MHz or 78.7 MHz.

[0012]

FIG. 1 shows a television sound F according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of an M transmitter device. This is an example of application to a small in-vehicle television with a built-in FM transmitter.
The transmission frequency of the FM transmitter is a two-wave switching system of 76.7 MHz or 78.7 MHz.

A small vehicle-mounted television (10) with a built-in FM transmitter is provided with a broadcast wave VHF channels 1 to 12 and a UHF channel 1 by a vehicle-mounted television antenna (101).
3 to 62, and the audio signal is transmitted to the FM transmitter (102) at a frequency of 76.7 MHz or 78.7 MHz.
It is converted into a broadcast wave and radiated by a built-in transmitting antenna (103).

The on-vehicle FM radio (11) receives a normal FM broadcast wave by the on-vehicle FM antenna (111), and receives the FM broadcast wave radiated from the FM transmitter transmitting antenna when the on-vehicle television is used.

At this time, the local oscillation frequency of the FM radio is 6
It is 6.0 MHz or 68.0 MHz, and its fundamental wave and harmonics are radiated from the FM radio body as unnecessary radiation and from the on-vehicle antenna as antenna terminal voltage. FIG.
(A) is a frequency relation diagram at a transmission wave number of 76.7 MHz. FIG. 2B is a frequency relationship diagram when the number of transmitted waves is 78.7 MHz.

The television VHF high band (20) is a band of 170 MHz to 222 MHz, and is a fundamental (21) harmonic (211) of an FM transmitter transmission frequency.
(212), the fundamental wave of the local oscillation frequency of FM radio (2
2) and harmonics (221) and (222).

FIG. 3 is a frequency relation diagram in the vicinity of the television VHF high band channel 9.

Channel 9 has a video carrier (30) in which a video signal is -1.25 MH in a vestigial sideband system as in (31)
Modulated from z to +4.2 MHz.

The chrominance signal is carrier-suppressed double-balanced modulated to the chrominance subcarrier (32) and has a bandwidth of about ± 500 KHZ.

The audio signal is FM-modulated at ± 25 KHZ to an audio carrier (33) approximately 6 db lower than the video carrier.

Here, the third harmonic of the local oscillation frequency of the FM radio is 198.0 MHz and 204 MHz, which are located at the boundary between channels 8 and 9 and channels 9 and 10, that is, 1.25 MHz lower than the video carrier.

FIG. 4 is a graph showing the selectivity characteristics of the intermediate frequency circuit of the television. ing.

Further, the lower channel audio carrier (44) and the upper channel video carrier (45) are trapped and
db or more.

Therefore, it can be seen that at a frequency (46) 1.25 MHz lower than the video carrier, the interference is suppressed by attenuating by about 30 to 40 db.

[0025]

As described above, according to the present invention, in a vehicle-mounted television device and a vehicle-mounted FM transmitter device, for a specific frequency transmitted from the FM transmitter device, the second harmonic of the frequency is set to the television. It is lower than the VHF high band, and the third harmonic of the local oscillation frequency of the FM receiving apparatus receiving the FM signal of this frequency is 1.25MH _Z lower than the video carrier frequency of the channel of the television VHF high-band With this value, the transmission frequency of the FM transmitter device can be improved by suppressing the interference given to the television receiver to a minimum, and the interference given from the FM receiver to the television receiver can be minimized. Can be suppressed. Therefore, there is an effect that frequency interference can be suppressed to a minimum even though the FM transmitter device or the FM receiver device that is close to or built in the television receiver is used in a narrow space.

[Brief description of the drawings]

FIG. 1 is a block diagram of an FM transmitter for television sound according to an embodiment of the present invention.

FIG. 2A is a frequency relation diagram at a transmission frequency of 76.7 MHz. (B) is a frequency relation diagram at a transmission frequency of 78.7 MHz.

FIG. 3 is a frequency relation diagram around a television VHF high band channel 9;

FIG. 4 is a diagram showing television intermediate frequency circuit selectivity characteristics.

Claims (4)

(57) [Claims] 1. A television receiver, and an FM receiver capable of transmitting an audio signal of the television receiver as an FM signal of a specific frequency in an FM broadcast band and receiving the FM signal in an FM broadcast band. An in-vehicle television device having an FM transmitter device to be received by the device,
The specific frequency is such that the second harmonic of the frequency is lower than the television VHF high band, and the third harmonic of the local oscillation frequency of the FM receiver that has received the FM signal of this frequency is the television. An in-vehicle television device characterized in that the value is 1.25 MHz lower than the video carrier frequency of the John VHF high band channel. 2. The method according to claim 1, wherein a plurality of frequencies can be selectively set as the specific frequency, and one of the plurality of frequencies is 76.7 MHz or 78.7 MHz. 2. The on-vehicle television device according to 1. 3. An audio signal of a television receiver is FM
It is transmitted as an FM signal of a specific frequency in the broadcast band,
In the in-vehicle FM transmitter device which causes the FM signal to be received by the FM receiver capable of receiving the FM signal in the FM broadcast band, the specific frequency is such that the second harmonic of the frequency is lower than the television VHF high band, In addition, the third harmonic of the local oscillation frequency of the FM receiver that has received the FM signal of this frequency is 1.25 M higher than the video carrier frequency of the television VHF high band channel.
A vehicle-mounted FM transmitter characterized in that the frequency is lowered by Hz. 4. The specific frequency, wherein a plurality of frequencies can be selectively set, and one of the plurality of frequencies is 76.7 MHz or 78.7 MHz. 4. The on-vehicle FM transmitter device according to 3.