JPH09139688A - Receiver and audio transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply inexpensively make up the receiver of the audio transmitter. SOLUTION: The receiver uses an RF amplifier 502 to amplify a transmission signal at a 900MHz band from a transmitter side and received by an antenna 501, the amplified signal is fed to a mixer 504 via a band pass filter 503 and the signal is converted into an intermediate frequency signal whose carrier frequency is 10.7MHz. In this case, a local oscillating frequency is set to be an upper side of the transmission frequency and the operating band of the frequency of the transmission signal is selected to a band where a production ratio of image disturbance is lower when the local oscillation frequency is set to an upper side of the transmission frequency. An intermediate frequency signal from the mixer 504 is amplified by an intermediate frequency amplifier 509 and the amplified signal is fed to an FM detection circuit 510 to obtain a stereo modulation signal, and the stereo modulation signal is processed by a stereo demodulation circuit 511 to obtain voice signals AL, AR. Since the single conversion system by the mixer 504 is adopted, the receiver is simply inexpensively made up.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver and an audio transmission device. More specifically, the present invention relates to a receiver and an audio transmission device that can be configured easily and inexpensively by converting the frequency of a transmission signal by a single frequency conversion means to obtain an intermediate frequency signal.

[0002]

2. Description of the Related Art Conventionally, on the transmitter side, an output audio signal of a television receiver, an audio system or the like is FM-modulated to form a transmission signal, and this transmission signal is transmitted from a transmission antenna, while on the receiver side, An audio transmission device has been proposed in which the transmission signal received by a reception antenna is processed to obtain an audio signal.

FIG. 4 shows a transmitter 100 that constitutes an audio transmission device. The transmitter 100 has an input terminal 10 to which a left channel audio signal AL and a right channel audio signal AR output from a television receiver, for example, are respectively supplied.
1L, 101R and buffer amplifiers 102L, 102R
And pre-emphasis circuits 103L and 103R for enhancing high frequencies of the audio signals AL and AR. The buffer amplifiers 102L and 102R include input terminals 101L and 101R and a pre-emphasis circuit 103L, respectively.
It is inserted between 103R.

Further, the transmitter 100 has a voice signal A which is high-frequency emphasized by the pre-emphasis circuits 103L and 103R.
It has a stereo modulation circuit 104 for obtaining a pilot tone stereo modulation signal using L and AR. In this case, the subcarrier frequency is set to 3fh in order to prevent the beat signal due to the horizontal frequency (fh) component of the video signal included in the audio signals AL and AR from being generated in the audible frequency band.

Further, the transmitter 100 includes an adder 105 for adding a bias voltage to the stereo modulation signal output from the stereo modulation circuit 104, and a variable resistor 106 for supplying the bias voltage to the adder 105. have. One end of the variable resistor 106 is connected to the power supply terminal (Vcc) and the other end is grounded. The voltage obtained at the mover of the variable resistor 106 is supplied as a bias voltage to the adder 105 via the resistor 107.

Further, the transmitter 100 has an FM modulation circuit 108 for performing FM (frequency modulation) modulation processing on the stereo modulation signal added with the bias voltage output from the adder 105. This FM modulation circuit 1
Reference numeral 08 denotes a voltage controlled oscillator, and the stereo modulated signal to which the bias voltage is added is supplied as a control signal so that a transmission signal (FM modulation signal) having a carrier frequency of 900 MHz band can be obtained. There is.

Further, the transmitter 100 includes an FM modulation circuit 10
RF (radio freqency) amplifier 1 that amplifies the transmission signal output from 8 to a level that can be transmitted from the transmission antenna
09 and a transmission antenna 110 for transmitting the transmission signal amplified by the RF amplifier 109 to the receiving side.

In the above structure, the input terminals 101L,
The audio signals AL and AR supplied to the 101R are supplied to the pre-emphasis circuits 103L and 103R via the buffer amplifiers 102L and 102R, respectively, are subjected to high-frequency emphasis, and then are supplied to the stereo modulation circuit 104, which are of the pilot tone type. A stereo modulated signal is formed. Then, a bias voltage is added to the stereo modulated signal by the adder 105 and then supplied to the FM modulation circuit 108 to generate F
M-modulation processing is performed to form a transmission signal (FM modulation signal) having a carrier frequency of 900 MHz band. Here, by moving the mover position of the variable resistor 106 to adjust the bias voltage, the carrier frequency and hence the transmission frequency can be adjusted. Then, the F output from the FM modulation circuit 108
The M-modulated signal is amplified by the RF amplifier 109 and then supplied to the transmission antenna 110 and transmitted to the reception side.

Next, FIG. 5 shows a receiver 200 which constitutes an audio transmission apparatus. The receiver 200 includes a receiving antenna 2 that receives a transmission signal sent from the transmitting side.
01, an RF amplifier 202 for amplifying a transmission signal received by the receiving antenna 201, and a first intermediate frequency in which the carrier frequency is lower than the 900 MHz band by converting the frequency of the transmission signal amplified by the RF amplifier 202. A frequency conversion circuit 203 for obtaining a frequency signal, a tuning circuit 204 for selecting a target frequency signal from the output signal of the frequency conversion circuit 203, and a frequency of the frequency signal selected by the tuning circuit 204. Mixer 205 for obtaining a second intermediate frequency signal whose carrier frequency is lower than the first intermediate frequency signal, a local oscillator circuit 206 for supplying a local oscillation signal to this mixer 205, and a variable for obtaining a tuning voltage. And a resistor 207.

The tuning circuit 204 has a double tuning configuration. That is, the output side of the frequency conversion circuit 203 is grounded via the coil 301, and is also grounded via the series circuit of the variable capacitance diode (varicap) 302 and the capacitor 303. Further, the input side of the mixer 204 is a coil 304 electromagnetically coupled to the coil 301 described above.
And the variable capacitance diode 305
And is grounded via the series circuit of the capacitor 306.

Further, one end of the variable resistor 207 is connected to the power supply terminal (Vcc), the other end is grounded, and the mover thereof is grounded via the capacitor 208. Then, the tuning voltage obtained at the mover of the variable resistor 207 is
The voltage is applied to the connection point between the variable capacitance diode 302 and the capacitor 303 via the resistor 209, and is applied to the connection point between the variable capacitance diode 305 and the capacitor 306 via the resistor 210.

A variable capacitance diode 211 is connected to the local oscillator circuit 206. This variable capacitance diode 211
The tuning voltage obtained in the mover of the variable resistor 207 is applied to the anode of the above-mentioned via the resistor 212. In this case, by moving the mover position of the variable resistor 207 to adjust the tuning voltage, the frequency of the local oscillation signal output from the local oscillation circuit 206 can be adjusted, which enables the tuning operation. In addition,
As described above, since the tuning voltage is also supplied to the tuning circuit 204 to adjust the capacitances of the variable capacitance diodes 302 and 305, the tuning frequency of the tuning circuit 204 changes in synchronization with the frequency change of the local oscillation signal due to the tuning operation. Will be done.

The receiver 200 also includes an intermediate frequency amplifier 213 for amplifying the second intermediate frequency signal output from the mixer 205, and a second intermediate frequency amplifier 213 for amplifying the second intermediate frequency signal.
An FM detection circuit 214 for performing FM detection processing on the intermediate frequency signal to obtain a stereo modulation signal as a baseband signal, and stereo demodulation processing for the stereo modulation signal output from the FM detection circuit 214. And a stereo demodulation circuit 215 for obtaining a left channel audio signal AL and a right channel audio signal AR.
5, de-emphasis circuits 216L and 216R for performing high-frequency attenuation processing on the audio signals AL and AR to restore flat frequency characteristics, and audio signals output from the de-emphasis circuits 216L and 216R. AL, A
Output terminals 217L and 217 for deriving R respectively
R.

In the above structure, the receiving antenna 201
The 900 MHz band transmission signal received from the transmitting side is amplified by the RF amplifier 202, frequency-converted by the frequency conversion circuit 203 into a first intermediate frequency signal, and then selected by the tuning circuit 204 and selected by the mixer 205. And converted into a second intermediate frequency signal. And mixer 2
The second intermediate frequency signal output from 05 is amplified by the intermediate frequency amplifier 213 and then FM detected by the FM detection circuit 214 to obtain a pilot tone stereo modulation signal. Then, this stereo modulated signal is supplied to the stereo demodulation circuit 215 and subjected to stereo demodulation processing to obtain audio signals AL and AR, and these audio signals AL and AR are output terminals 217L and 216L via de-emphasis circuits 216L and 216R, respectively. 217R. Therefore, by connecting, for example, a headphone to the output terminals 217L and 217R, it is possible to obtain a stereo audio output by the audio signals AL and AR.

[0015]

By the way, in the receiver 200 in the above-mentioned audio transmission device, the frequency conversion circuit 203 frequency-converts the 900 MHz band transmission signal transmitted from the transmission side to generate the first intermediate frequency signal. In addition to obtaining the signal, the mixer 205 is frequency-converted by the mixer 205 to obtain the second intermediate frequency signal. In addition, a tuning circuit 204 having a double tuning configuration is provided in front of the mixer 205.
Is configured to be inserted. Therefore, there is a problem that the configuration is complicated and expensive.

Therefore, an object of the present invention is to provide a receiver and an audio transmission device which can be constructed simply and inexpensively.

[0017]

SUMMARY OF THE INVENTION A receiver according to the present invention comprises a receiving antenna for receiving a transmitting signal and a single frequency for converting the frequency of the transmitting signal received by the receiving antenna to obtain an intermediate frequency signal. The frequency conversion means includes a conversion means and a detection means for detecting the intermediate frequency signal output from the frequency conversion means to obtain a baseband signal. The frequency conversion means reduces the frequency of the transmission signal to 1/30 or less to generate the intermediate frequency signal. I will get it.

The frequency of the transmission signal received by the receiving antenna is converted to a frequency of 1/30 or less by a single frequency conversion means to obtain an intermediate frequency signal, and the intermediate frequency signal is detected by the detection means. Then, a baseband signal is obtained. For example, the transmission signal is a 900 MHz band FM modulated signal, and is converted into an intermediate frequency signal having a carrier frequency of 10.7 MHz by a single frequency conversion means.

The audio transmission apparatus according to the present invention comprises a transmitter and a receiver, and the transmitter comprises a transmission signal forming means for modulating a carrier signal with an audio signal to form a transmission signal, and the transmission signal forming means. A transmitting antenna for transmitting the transmission signal formed by the signal forming means, and the receiver,
A receiving antenna for receiving a transmission signal, a single frequency conversion means for converting the frequency of the transmission signal received by the reception antenna to obtain an intermediate frequency signal, and an intermediate frequency signal output from the frequency conversion means. And a detection means for obtaining an audio signal, and in the frequency conversion means of the receiver,
The frequency of the transmission signal is reduced to 1/30 or less to obtain an intermediate frequency signal.

On the transmission side, a transmission signal is formed by modulation processing of the audio signal, and this transmission signal is transmitted from the transmission antenna to the reception side. On the other hand, on the receiving side, the frequency of the transmission signal received by the receiving antenna is converted to a frequency of 1/30 or less by a single frequency converting means to obtain an intermediate frequency signal, and the detecting means for this intermediate frequency signal. Then, the detection processing is performed to obtain an audio signal as a baseband signal. For example, the transmission signal is a 900 MHz band FM modulated signal, and is converted into an intermediate frequency signal having a carrier frequency of 10.7 MHz by a single frequency conversion means.

[0021]

Embodiments of the present invention will be described below. This embodiment is an example applied to an audio transmission device for transmitting an audio signal output from a television receiver in the United States. This audio transmission device is configured to include a transmitter 400 and a receiver 500.

First, referring to FIG. 1, a transmitter 400
Will be described. The transmitter 400 has input terminals 401L and 401L to which the left channel audio signal AL and the right channel audio signal AR output from the television receiver are respectively supplied.
R, buffer amplifiers 402L and 402R, and pre-emphasis circuits 403L and 403R for enhancing high frequencies of the audio signals AL and AR. The buffer amplifiers 402L and 402R have input terminals 401L and 4L, respectively.
01R and pre-emphasis circuits 403L and 403R.

Further, the transmitter 400 has a voice signal A which is high-frequency emphasized by the pre-emphasis circuits 403L and 403R.
It has a stereo modulation circuit 404 for obtaining a pilot tone type stereo modulation signal using L and AR. In this case, the subcarrier frequency is set to 4 fh in order to prevent the beat signal due to the horizontal frequency (fh) component of the video signal included in the audio signals AL and AR from being generated in the audible frequency band.

Also, the transmitter 400 includes an adder 405 for adding a bias voltage to the stereo modulation signal output from the stereo modulation circuit 404, and a variable resistor 406 for supplying the bias voltage to the adder 405. have. One end of the variable resistor 406 is connected to the power supply terminal (Vcc) and the other end is grounded. The voltage obtained at the mover of the variable resistor 406 is supplied as a bias voltage to the adder 405 via the resistor 407.

Further, the transmitter 400 has an FM modulation circuit 408 for performing FM modulation processing on the stereo modulation signal added with the bias voltage output from the adder 405. The FM modulation circuit 408 is composed of a voltage controlled oscillator, and the stereo modulation signal to which the bias voltage described above is added is supplied as a control signal, so that a transmission signal (FM modulation signal) having a carrier frequency of 900 MHz band.
Is obtained.

By the way, as will be described later, in the receiver of the present embodiment, the frequency of the 900 MHz band transmission signal is converted by the mixer, which is a single frequency conversion means, and the intermediate frequency signal having the carrier frequency of 10.7 MHz is converted. Is configured to obtain. Generally, in the frequency conversion by a single frequency conversion means, the intermediate frequency (carrier frequency of the intermediate frequency signal) is limited to about 1/30 of the reception frequency (frequency of the transmission signal) due to image interference. (Reference “Ohmsha, 1968 edition,“ Transistor radio design and calculation ”Authors: Kaichi Sato, Shozo Takahashi”).

The equation for calculating the image interference ratio α is shown in the equation (6.2) of the reference document.

[0028]

(Equation 1)

Here, since the intermediate frequency amplifier circuit is a general double-tuned circuit, n = 2, and since the actual range of the goodness of the tuned circuit is 20 to 30, Q = 2.
5, fs (reception frequency) = 900 MHz, fm
When the image interference ratio α is selected when (intermediate frequency) = 10.7 MHz is calculated, it becomes α≈−3.0 dB, which is a practical range of the image interference ratio α (−20 dB to −26 dB).
It is a large deviation from. On the other hand, under the same conditions, f
When the image interference ratio α in the case of selecting s = 900 MHz and fm = 30 MHz is calculated, α≈−20.9 dB, which barely falls within the practical range.

As described above, the configuration of converting the frequency of the transmission signal in the 900 MHz band to obtain the intermediate frequency signal having the carrier frequency of 10.7 MHz by the mixer which is the single frequency conversion means is equivalent to the image interference ratio. It is not normally performed because α does not fall within the practical range. However, in the present embodiment, such a configuration can be achieved by selecting the use band of the frequency of the transmission signal as follows.

That is, the frequency allocation around 900 MHz in the United States is determined as shown in FIG. 869M
Hz to 894 MHz is the band used by the cellular phone,
894 MHz to 896 MHz is the aviation radio band, 896 MHz to 902 MHz is the in-vehicle repeater input band, and 902 MHz to 928 MHz is the personal communication band.
MHz to 935 MHz is a pager (pager) usage band, 935 MHz to 941 MHz is a vehicle repeater output usage band, and 941 MHz to 944M
Hz is a publicly used band, 944 MHz to 950 M
Hz is the bandwidth used by the studio transmitter link. Therefore, in the present embodiment, basically, the frequency of the above-mentioned 900 MHz band transmission signal is 902M.
The band of 4 to 5 MHz is used in the band used for personal communication of Hz to 928 MHz.

Here, when the local oscillation frequency is set to the lower side of the transmission frequency, the image interference frequency band for the use band of personal communication of 902 MHz to 928 MHz is 880.6 MHz to 906.6 MHz.
Therefore, the band of 902 MHz to 906.6 MHz is included in the band used for personal communication. Therefore, 923.4 MHz to 928
When selecting the band of (MHz) as the used band, use 9
Since the band of 02 MHz to 906.6 MHz is the image interference frequency band, the rate of strong image interference is low.

When the local oscillation frequency is set to the upper side of the transmission frequency, the image interference frequency band for the personal communication use band of 902 MHz to 928 MHz is 923.4 MHz to 949.4 MHz, and the band of 923.4 MHz to 928 MHz. (Band) is included in the band used for personal communication. Therefore, 902MHz to 906.6M
When selecting the band of (Hz) as the used band, 92
Since the image interference frequency band is in the band of 3.4 MHz to 928 MHz, the rate of strong image interference is low.

Further, when the local oscillation frequency is set to the upper side of the transmission frequency, it is included in the use band of personal communication of 902 MHz to 928 MHz.
The image interference frequency band corresponding to (the band of) 2.6 MHz to 928 MHz is 944 MHz to 949.
It becomes a band of 4 MHz. Therefore, 92
When selecting the band of 2.6 MHz to 928 MHz as the used band, the band of 944 MHz to 949.4 MHz becomes the image interference frequency band, and this band is the band used by the studio transmitter link and is used indoors with a small output. Since it is considered to be in operation and used in a small number, the image interference rate is very low.

As described above, when the local oscillation frequency is set to the upper side of the transmission frequency, the band of or can be selected as the used band to reduce the rate of image interference, while the local oscillation frequency can be set below the transmission frequency. When it is set to the side, it is possible to reduce the rate of image interference by selecting the band as the used band. In the present embodiment, it is assumed that the receiver sets the local oscillation frequency to the upper side of the transmission frequency.
The band of 28 MHz is selected as the band to be used.

Further, the transmitter 400 has a comparator 409 for comparing the levels of the stereo modulated signals output from the stereo demodulation circuit 404 and monitoring the modulation rate (modulation degree). This comparator 409 has an output terminal 410.
a, 410b, 410c are provided. The output terminal 410a is grounded via the anode / cathode of the light emitting diode 411a that emits orange light. The output terminal 410b is a light emitting diode 411 that emits green light.
It is grounded through the anode / cathode of b. The output terminal 410c is grounded via the anode / cathode of the light emitting diode 411c that emits red light.

In this case, the output terminal 410 of the comparator 409
A signal having a high level "H" when the level of the stereo modulation signal exceeds the level corresponding to the modulation rate of 20% and a low level "L" at other times is obtained in a. Further, at the output terminal 410b of the comparator 409, a signal having a high level "H" when the level of the stereo modulation signal exceeds the level corresponding to the modulation rate of 50%, and a signal having a low level "L" otherwise is obtained. . Further, at the output terminal 410c of the comparator 409, a signal having a high level "H" when the level of the stereo modulation signal exceeds a level corresponding to the modulation rate of 100%, and a signal having a low level "L" otherwise is obtained. .

As a result, when the level of the stereo modulated signal is below the level corresponding to the modulation rate of 20%, the comparator 409
No high level “H” signal is obtained from any of the output terminals 410a to 410c of the light emitting diodes 411a to 411c.
None of 11c emits light. When the level of the stereo modulation signal exceeds the level corresponding to the modulation rate of 20% and is equal to or lower than the level corresponding to the modulation rate of 50%, a high level “H” signal is obtained at the output terminal 410a of the comparator 409. The light emitting diode 411a is in a state of emitting light. Also, the level of the stereo modulated signal is 50%.
Above the level corresponding to 100% and below the level corresponding to the modulation rate of 100%, the output terminal 410a of the comparator 409,
A high level "H" signal is obtained at 410b, and the light emitting diodes 411a and 411b are in a state of emitting light. Further, when the level of the stereo modulation signal exceeds the level corresponding to the modulation rate of 100%, the output terminal 4 of the comparator 409 is used.
A high level "H" signal is obtained at 10a to 410c,
The light emitting diodes 411a to 411c are in a state of emitting light. Therefore, the modulation rate can be adjusted to an appropriate value (for example, 50%) by changing the level of the stereo modulation signal in the stereo modulation circuit 404 while confirming the light emitting states of the light emitting diodes 411a to 411c.

Further, the transmitter 400 includes an FM modulation circuit 40.
It has an RF amplifier 412 that amplifies the transmission signal output from 8 to a level that can be transmitted from the transmission antenna, and a transmission antenna 413 that transmits the transmission signal amplified by this RF amplifier 412 to the receiving side.

In the above configuration, the input terminals 401L,
The audio signals AL and AR supplied to the 401R are supplied to the pre-emphasis circuits 403L and 403R via the buffer amplifiers 402L and 402R, respectively, are high-frequency emphasized, and then are supplied to the stereo modulation circuit 404, and are of the pilot tone type. A stereo modulated signal is formed. Then, a bias voltage is added to this stereo modulated signal by the adder 405 and then supplied to the FM modulation circuit 408 to generate F
M-modulation processing is performed to form a transmission signal (FM modulation signal) having a carrier frequency of 900 MHz band. Here, by moving the mover position of the variable resistor 406 and adjusting the bias voltage, the carrier frequency and hence the transmission frequency can be adjusted. Then, the F output from the FM modulation circuit 408
The M modulation signal is amplified by the RF amplifier 412 and then supplied to the transmission antenna 413 and transmitted to the reception side.

Next, referring to FIG. 2, the receiver 500
Will be described. The receiver 500 receives a transmission signal sent from the transmission side, a reception antenna 501, an RF amplifier 502 for amplifying the transmission signal received by the reception antenna 501, and an RF amplifier 502 amplified by the RF amplifier 502. Bandpass filter 5 for extracting transmission signal
03 and the frequency of the transmission signal extracted by the bandpass filter 503 are converted to obtain a carrier frequency of 10.7.
It has a mixer 504 for obtaining an intermediate frequency signal of MHz, a local oscillation circuit 505 for supplying a variable local oscillation signal to this mixer 504, and a variable resistor 506 for obtaining a tuning voltage.

The pass band of the band pass filter 503 is
The frequency band of the transmission signal is set to match the band used, that is, the band of 922.6 MHz to 928 MHz (the band shown in FIG. 3) in the present embodiment. The bandpass filter 503 is provided instead of providing the tuning circuit.

A variable capacitance diode 507 is connected to the local oscillator circuit 505. Further, one end of the variable resistor 506 is connected to the power supply terminal (Vcc) and the other end is grounded. The tuning voltage obtained by the mover of the variable resistor 506 is applied to the cathode of the variable capacitance diode 507 via the resistor 508. In this case, by moving the mover position of the variable resistor 506 to adjust the tuning voltage, the frequency of the local oscillation signal output from the local oscillation circuit 505 can be adjusted, which enables the tuning operation. As described above, the local oscillation frequency output from the local oscillation circuit 505 is set to be above the transmission frequency.

The receiver 500 also includes an intermediate frequency amplifier 50 for amplifying the intermediate frequency signal output from the mixer 504.
9 and an FM detection circuit 510 for performing FM detection processing on the intermediate frequency signal amplified by the intermediate frequency amplifier 509 to obtain a stereo modulated signal as a baseband signal.
A stereo demodulation circuit 511 for performing stereo demodulation processing on the stereo modulated signal output from the FM detection circuit 510 to obtain a left channel audio signal AL and a right channel audio signal AR, and an output from this stereo demodulation circuit 511. De-emphasis circuits 512L and 512R for performing high-frequency attenuation processing on the audio signals AL and AR to restore flat frequency characteristics, and the de-emphasis circuit 512.
And output terminals 513L and 513R for deriving the audio signals AL and AR output from the L and 512R, respectively.

In the above configuration, the receiving antenna 501
The 900 MHz band transmission signal received from the transmission side is amplified by the RF amplifier 502, passes through the band pass filter 503, and is supplied to the mixer 504 to be converted into an intermediate frequency signal having a carrier frequency of 10.7 MHz. To be done. The intermediate frequency signal output from the mixer 504 is amplified by the intermediate frequency amplifier 509 and then FM detected by the FM detection circuit 510 to obtain a pilot tone stereo modulation signal. Then, this stereo modulated signal is supplied to the stereo demodulation circuit 511 and subjected to stereo demodulation processing to obtain audio signals AL and AR. These audio signals AL and AR are respectively de-emphasis circuits 512L and 512L.
It is led out to output terminals 513L and 513R via 512R. Therefore, by connecting headphones to the output terminals 513L and 513R, for example, the audio signals AL and AR
It is possible to obtain a stereo audio output by.

As described above, in the present embodiment, in the receiver 500, the mixer 504 as a single frequency conversion means is used.
, The frequency of the 900 MHz transmission signal is converted to obtain an intermediate frequency signal with a carrier frequency of 10.7 MHz, and a conventional tuning circuit is not inserted before the mixer 504, but a bandpass filter is used. 503
Has a merit that it can be configured easily and inexpensively as compared with the conventional receiver.

In this case, in the receiver 500, the local oscillation frequency is set to the upper side of the transmission frequency, and when the local oscillation frequency is set to the upper side of the transmission frequency on the receiver side, the rate of occurrence of image interference is high. 922.6 lower
Since the band used for the frequency of the transmission signal is selected in the band of MHz to 928 MHz (the band shown in FIG. 3), the mixer 5
Even if it is configured such that the frequency of the transmission signal in the 900 MHz band is converted by 04 to obtain the intermediate frequency signal having the carrier frequency of 10.7 MHz, the occurrence of image interference can be avoided with high probability. When image interference has occurred, the occurrence of image interference can be avoided by changing the mover position of the variable resistor 407 of the transmitter 400 to change the transmission frequency.

In the present embodiment, the transmitter 4
When the stereo modulation circuit 104 of 00 forms a stereo modulation signal of the pilot tone system, the subcarrier frequency of this stereo modulation signal is set to the horizontal frequency (f
Since the frequency is 4 times the frequency (4fh) of h), the audio signal A
It is possible to favorably prevent the beat signal due to the horizontal frequency component of the video signal included in L and AR from occurring in the audible frequency band.

Although the above-described embodiment is applied to an audio transmission device for transmitting an audio signal, the present invention can be similarly applied to a transmission device for transmitting a video signal and other signals. is there.

[0050]

According to the present invention, since the frequency of the transmission signal is converted to 1/30 or less by the single frequency conversion means to obtain the intermediate frequency signal, the frequency conversion means of two stages is provided. It has the advantage of being simpler and cheaper to configure. In this case, the occurrence of image interference can be avoided with high probability by selecting the transmission frequency and the like.

Further, by inserting a bandpass filter for passing the transmission signal in the preceding stage of the single frequency converting means, the construction can be made simpler and cheaper than the case where the tuning circuit is inserted. In addition, by setting the subcarrier frequency of the stereo modulation signal of the pilot tone system formed on the transmitter side to a frequency four times the horizontal frequency of the video signal, the beat signal due to the horizontal frequency component of the video signal becomes audible frequency band. It can be effectively prevented from occurring inside.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a transmitter of an audio transmission device as an embodiment.

FIG. 2 is a block diagram showing a receiver of an audio transmission device as an embodiment.

FIG. 3 is a diagram showing frequency allocation around 900 MHz in the United States.

FIG. 4 is a block diagram showing an example of a transmitter of an audio transmission device.

FIG. 5 is a block diagram showing an example of a receiver of an audio transmission device.

[Explanation of symbols]

 400 transmitter 404 stereo modulation circuit 408 FM modulation circuit 413 transmission antenna 500 receiver 501 reception antenna 503 band pass filter 504 mixer 505 local oscillation circuit 510 FM detection circuit 511 stereo demodulation circuit

Claims (7)

[Claims] 1. A reception antenna for receiving a transmission signal, a single frequency conversion means for converting the frequency of the transmission signal received by the reception antenna to obtain an intermediate frequency signal, and an output from the frequency conversion means. And a detection means for detecting the intermediate frequency signal to obtain a baseband signal, wherein the frequency conversion means reduces the frequency of the transmission signal to 1 /
A receiver characterized in that the intermediate frequency signal is obtained at 30 or less. 2. The transmission signal is a 900 MHz band signal, and the intermediate frequency signal has a carrier frequency of 10.7M.
The receiver according to claim 1, wherein the receiver is a Hz signal. 3. The receiver according to claim 1, wherein a bandpass filter for passing the transmission signal is inserted before the frequency conversion means. 4. A transmitter and a receiver, wherein the transmitter comprises a transmission signal forming means for modulating a carrier signal with an audio signal to form a transmission signal, and a transmission formed by the transmission signal forming means. The receiver has a transmitting antenna for transmitting a signal, and the receiver has a receiving antenna for receiving the transmitting signal and a single antenna for converting the frequency of the transmitting signal received by the receiving antenna to obtain an intermediate frequency signal. The frequency conversion means includes a frequency conversion means and a detection means for detecting the intermediate frequency signal output from the frequency conversion means to obtain the audio signal. The frequency conversion means of the receiver reduces the frequency of the transmission signal to 1 / An audio transmission device characterized in that the intermediate frequency signal is obtained at 30 or less. 5. The transmission signal is a 900 MHz band signal, and the intermediate frequency signal has a carrier frequency of 10.7 MH.
The audio transmission device according to claim 4, wherein the audio transmission device is a z signal. 6. The audio transmission device according to claim 4, wherein a band pass filter for passing the transmission signal is inserted before the frequency conversion means. 7. The audio signal is a pilot tone stereo modulation signal, and the subcarrier frequency of the stereo modulation signal is set to a frequency four times the horizontal frequency of the video signal. Audio transmission equipment.