JPH05300107A - Radio transmitter for voice signal - Google Patents

Abstract

PURPOSE:To avoid interference jamming from the same type adjacent equipment at low cost by selecting a bias voltage to be supplied to a pair of FM modulators with a switch. CONSTITUTION:This device is provided with a signal forming means to form a pair of voice carrier signals SL and SR at a prescribed frequency interval and a frequency transiting means to transit the frequency of a pair of voice carrier signals just for an equal amount f in the same direction, and the frequency transiting means is composed of a pair of voltage sources 29a and 29b to supply deviated voltages Va and Vb to the frequency modulators and a switch Sch to select these voltage sources 29a and 29b. Namely, the frequency of a signal for frequency modulation to up convert the carrier frequency is not switched but the carrier frequency of the voice carrier signals SL, and SR to be inputted to a mixer circuit for frequency modulation is switched by the frequency modulators 22L and 22R. Therefore, the cost of the frequency transiting means can be reduced, and the space can be saved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal wireless transmission apparatus suitable for, for example, a headphone type stereo cassette player.

[0002]

2. Description of the Related Art Conventionally, as a headphone type stereo cassette player (hereinafter simply referred to as "player") such as a Walkman (registered trademark), there is known a wireless transmission system between the player and the headphones. ing.

FIG. 3 is a perspective view showing the appearance of an example of a wireless player, 1 is a player, and 6 is a dedicated receiver for the headphones thereof. In player 1, during playback,
When the left and right channel stereo audio signals L and R are reproduced from the tape cassette (not shown), these signals L and R are reproduced.
R is an FM signal SL using two carriers with a predetermined frequency interval,
Converted to SR, the FM signals SL and SR are transmitted to the receiver 6.

When the receiver receives the FM signals SL and SR from the player 1, the signals S and SR are received.
Audio signals L and R are demodulated from L and SR, and these audio signals L and R are acoustic units 7L and 7R on the left and right of the headphone 7.
Is supplied to each. In this case, the receiver 6 can be half the size of a business card or less.

Therefore, for example, when playing a cassette tape on a train for commuting, the player 1 is put in a bag, a bag, etc., and the receiver 6 is put in a chest pocket of a jacket, or a clip or a collar or a tie is put. The cord of the headphone 7 does not get in the way.

The distance that the receiver 6 can be used away from the player 1 is set in consideration of the Radio Law and the case where a nearby person is using a similar wireless player.
It is about 5 m.

References: Japanese Patent Application No. 61-254966 (Japanese Patent Application Laid-Open No. 63-108825) and Japanese Patent Application No. 62-280489.
No. etc.

[0008]

However, in the above-mentioned wireless player, since the FM signals SL and SR having the same pair of frequencies are transmitted from all the players, for example, in the adjacent seat in a commuter train. When the same type of wireless player is used, there is a problem that both receivers interfere with FM signals transmitted from the other player and interfere with normal reception.

As a means for avoiding such interference of interference due to the same frequency, for example, Japanese Patent Application Laid-Open No. Hei 2 (1998)
No. 179132 “Voice signal transmission device” is known. In this conventional device, in a headphone type stereo cassette player, when wireless transmission is performed between the player main body and headphones by two carriers, the frequencies of the two carriers on the player main body side are set in the same direction by almost half of the frequency interval. By providing an automatic tuning control circuit (AFC) in the receiver on the headphone side, which is capable of tracking the frequency shift of the carrier wave as well as the shift, it is possible to operate the receiver from other similar players in the vicinity without requiring any operation of the receiver. Interference interference can be avoided.

As shown in FIG. 4, the above-described conventional player 1 includes an audio signal reproducing circuit 10 represented by magnetic heads 11L and 11R, and a transmitting circuit 20. The left and right audio signals reproduced from the tape MT by the magnetic heads 11L and 11R are equalized and amplified by the amplifiers 12L and 12R, and the emphasis circuits 21L and 2 of the transmission circuit 20.
Supplied to 1R. This emphasis circuit 21L, 21
The output audio signal of R is the FM modulator 22 as a modulation signal.
It is supplied to the L and 22R, and the original carrier waves by the oscillators 23L and 23R are modulated and converted into a pair of FM signals SL and SR. The FM modulators 22L and 22R include, for example, semiconductor elements such as variable capacitance diodes, and are configured integrally with the respective oscillators 23L and 23R.

In the conventional example of FIG. 4, a pair of FM signals SL,
SR frequency shift is, for example, 75k at 100% modulation
Set to Hz. Further, as shown in FIG. 5, the original carrier frequencies fLo and fRo of the FM signals SL and SR are considerably lower than the original transmission frequency (carrier frequency). Is set.

The FM signals SL and SR are supplied to the mixer 24.
The signal Sup for frequency conversion (up conversion) is supplied from the oscillator 25 to the mixer 24 while being supplied to the L and 24R.
It is supplied to L and 24R.

In the conventional example of FIG. 4, in the resonance circuit of the oscillator 25, one of the pair of solid resonators 26a and 26b having high stability, such as a lithium tantalate resonator, is selected by the changeover switch Sch. The solid-state resonator is used in the fifth harmonic mode, for example.

The switch Sch is connected to the a-side contact as shown, and the frequency fua of the frequency conversion signal Sup when the one solid resonator 26a is selected.
The frequency f of the signal Sup when ch is switched to the b-side contact contrary to the illustration and the other solid state resonator 26b is selected
As shown in FIG. 5, ub is set as, for example, fua = 64.00 MHz fub = 63.77 MHz Δfn = fua-fub = 230 kHz.

In the mixers 24L and 24R, the frequency converting signal Sup and the FM signals SL and SR are mixed, and the carrier frequencies of the FM signals SL and SR are as shown in FIG. Each of them is converted into a high frequency, and they are taken out from the bandpass filters 27L and 27R, respectively.

The carrier frequencies fLa and fRa of the FM signals SL and SR when the switch Sch is connected to the a-side contact (A channel) as shown in the figure are fLa = 75.29 MHz and fRa = 75.75 MHz. On the other hand, the FM signal SL, SR when the switch Sch is connected to the b-side contact opposite to that shown in the drawing (B channel)
Carrier frequencies fLb and fRb are as follows: fLb = 75.06MHz fRb = 75.52MHz, both of which are equal to the frequency difference Δfn of the frequency conversion signal Sup compared to when the switch Sch is connected to the a-side contact. It has moved to a lower direction.

The FM signal SL, SR of either the A or B channel is supplied to the high frequency amplifier 28L,
The signal is transmitted from the antenna Ant via 28R.

On the headphone side, when the frequencies of the two carrier waves on the player body side are changed, the local oscillation frequency of the receiver is changed by the AFC following the frequency change of the two carrier waves to change the selection characteristics of the receiver. , Interference from adjacent similar players is avoided.

However, in the conventional example of FIG. 4, as described above, it is necessary to use two solid state resonators on the player side, and although stable operation can be obtained, there is a problem that the cost is high. there were.

Further, the present applicant has not yet made it public in order to solve the inconvenience caused by the local oscillation circuit of the receiver including the variable capacitance diode for AFC in the above-mentioned conventional example. "Wireless transmission type audio signal reproducing device" has already been proposed.

In this proposed example, a transmitter side superimposes a pilot signal on a voice signal and switches a pair of resonators of an oscillator for up-converting a carrier voice signal, and a receiver side pilot signal discriminating circuit. By activating the control circuit that switches the resonator type local oscillator based on the output of, the transmission characteristic of the receiver is automatically changed by following the frequency change of the carrier wave on the transmission side. However, similar to the conventional example of FIG. 4, two solid state resonators are used on the player side, and although stable operation can be obtained, the problem of high cost remains.

In view of the above points, the present invention reduces the cost of the frequency shifting means for shifting the frequencies of the two carrier waves on the player body side in the same direction by an equal amount in order to avoid interference from nearby similar players. In addition, it is an object of the present invention to provide a wireless transmission device for audio signals, which can save space.

[0023]

In order to solve the above-mentioned problems, the audio signal wireless transmission apparatus according to the present invention corresponds to the reference symbols of the embodiments described later, and a pair of audio signals reproduced from the recording medium MT. Signals L and R are respectively supplied 1
A signal forming means that includes a pair of frequency modulators 22L and 22R and forms a pair of carrier audio signals SL and SR at a predetermined frequency interval, and a frequency that shifts the frequencies of the pair of carrier audio signals in the same direction by an equal amount Δf. A voice signal wireless transmission device comprising a shift means and a voice signal for wireless transmission, wherein the frequency shift means includes a bias voltage Va,
It is composed of a pair of voltage sources 29a and 29b for supplying Vb and a switch Sch for selecting this voltage source.

[0024]

According to the present invention, instead of switching the frequency of the frequency conversion signal for up-converting the carrier frequency, the carrier audio signals SL and SR to be input to the frequency conversion mixing circuit in the frequency modulators 22L and 22R.
Carrier frequency is switched.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a voice signal wireless transmission apparatus according to the present invention will be described below with reference to FIGS. The configuration of an embodiment of the present invention is shown in FIG. In FIG. 1, parts corresponding to those in FIG. 4 described above are denoted by the same reference numerals, and redundant description will be omitted.

In FIG. 1, reference numeral 20A denotes a transmission circuit, and the FM modulators 22L and 22R are provided with the resonance circuits of the original carrier oscillators 23L and 23R. Variable-capacitance diode 22 forming the resonance circuits 22L and 22R
The outputs of the emphasis circuits 21L and 21R are supplied to dl and 22dr, respectively, and 1 is shared by both variable capacitance diodes 22dl and 22dr via the changeover switch Sch.
An appropriate bias voltage Va of the pair of voltage sources 29a, 29b,
Either Vb is supplied. In addition, the oscillator 25,
The single solid state resonator 26 is directly connected. The other structure is the same as that shown in FIG.

Next, referring to FIG. 2 as well, a frequency shift operation according to an embodiment of the present invention will be described.

In this embodiment, the switch Sch is connected to the a-side contact as shown in the figure, and when one of the voltage sources 29a is selected, the switch Sch is switched to the b-side contact opposite to the one shown in the figure. , When the other voltage source 29b is selected, different bias voltages Va and Vb are applied to the FM modulator 2.
The original carrier frequencies of the FM signals SL and SR are changed by being supplied to the variable capacitance diodes 22dl and 22dr of 2L and 22R, respectively.

That is, the original carrier wave frequencies faLo and faRo when the switch Sch is connected to the a-side contact and the voltage source 29a is selected are, for example, faLo = 11.29 MHz faRo = 1.29, as shown in FIG. It is set to 75MHz. Further, the FM signal S when the switch Sch is switched to the b-side contact and the voltage source 29b is selected.
As shown in FIG. 2, the original carrier frequencies fbLo and fbRo of L and SR are set as, for example, fbLo = 10.37 MHz and fbRo = 10.83 MHz. Therefore, in this example, Δfw = faLo−fbLo = faRo−fbRo = 920 kHz.

On the other hand, the frequency of the frequency conversion signal Sup for up-conversion is set, for example, as fup = 64.00 MHz as shown in FIG.

In the mixers 24L and 24R, the beatup signal Sup and the FM signals SL and SR are mixed, and the carrier frequencies of the FM signals SL and SR extracted from the bandpass filters 27L and 27R are as shown in the figure. Two
As shown in, each is converted to high.

When the switch Sch is connected as shown in the figure (channel A), the carrier frequencies fLa and fRa of the FM signals SL and SR are, for example, fLa = 75.29 MHz and fRa = 75.75 MHz. Further, the FM signals SL and SR when the switch Sch is switched to the connection opposite to that shown in the figure (B channel)
Carrier frequencies fLb and fRb are, for example, fLb = 74.37 MHz and fRb = 74.83 MHz, and FM signals SL and S compared to the case of A channel.
The original carrier frequency difference Δfw of R shifts in the same direction.

As described above, in this embodiment, the original carrier wave frequencies faLo to fbRo of the FM signals SL and SR are set to be considerably lower than the original carrier wave frequency. The influence of temperature change, aging change, etc. is reduced, and stable frequency change is performed.

Further, in this embodiment, since the single solid-state resonator is used to generate the up-converting signal Sup, the frequency is reduced even if a slight increase in cost for one bias voltage source of the modulator is subtracted. The cost for the transition is greatly reduced. In addition, since there is only one solid resonator, space can be saved accordingly.

In this embodiment, FM signals SL, S
Although the carrier frequencies fLa to fRb of R are the sum of the original carrier frequencies faLo to fbRo in a frequency band lower than that frequency band and the frequency fup of the frequency conversion signal relatively close to the predetermined frequency band, FM broadcasting The original carrier frequencies faLo to fbRo depending on the frequency allocation of the TV broadcast and the television broadcasting.
And the frequency fup of the beat-up signal.

[0036]

As described above, according to the present invention, in a device for wirelessly transmitting a stereo audio signal as a two-carrier FM signal, a bias voltage supplied to a pair of FM modulators is selected by a switch. , The original carrier frequencies of a pair of FM signals at a predetermined frequency interval are equally shifted in the same direction, and then up-converted to a predetermined carrier frequency, so that interference from adjacent similar devices can be produced at low cost. It is possible to obtain a wireless transmission device for audio signals, which can be avoided by.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a wireless transmission device for audio signals according to the present invention.

FIG. 2 is a frequency spectrum diagram for explaining the operation of the embodiment of the present invention.

FIG. 3 is a perspective view showing a configuration example of a conventional audio signal wireless transmission device.

FIG. 4 is a block diagram showing an electrical configuration of a conventional example.

FIG. 5 is a frequency spectrum diagram for explaining the operation of the conventional example.

[Explanation of symbols]

 10 audio signal reproduction circuit 20, 20A transmission circuit 22L, 22R frequency modulator 29a, 29b bias voltage source

Claims (4)

[Claims] 1. A signal forming means for forming a pair of carrier audio signals having a predetermined frequency interval, the signal forming means including a pair of frequency modulators to which a pair of audio signals reproduced from a recording medium are respectively supplied, And a frequency shifter that shifts the frequencies of the pair of carrier voice signals by the same amount in the same direction, wherein the voice signal is wirelessly transmitted, and the frequency shifter is the frequency shifter. A wireless transmission device for an audio signal, comprising: a modulator for switching carrier frequencies of the pair of carrier audio signals. 2. The sum of a pair of original carrier frequencies in a low frequency band in which the carrier frequencies of the pair of carrier audio signals are separated from a predetermined frequency band and a single fixed frequency relatively close to the predetermined frequency band. Alternatively, the audio signal wireless transmission device according to claim 1, wherein the difference is provided. 3. The frequency modulator according to claim 1, further comprising an oscillator of an original carrier having a variable capacitance diode as its resonance circuit, and a bias voltage is switched to the variable capacitance diode of the resonance circuit of the oscillator. Audio signal wireless transmission device. 4. A reproducing device including a mechanism for reproducing an audio signal from a recording medium, the signal forming means, the frequency shifting means, and a wireless transmitting means for the audio signal, and a transmission signal received from the reproducing apparatus. 2. The wireless transmission device for an audio signal according to claim 1, further comprising a receiver that demodulates the original audio signal and reproduces the audio in the acoustic unit.