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JPH07283750

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPH07283750
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
wireless audio devices such as so-called headphone stereos.
[0002]
2. Description of the Related Art As a headphone type stereo cassette player (hereinafter referred
to as a "player") such as Walkman (registered trademark), a wireless system between the player
and headphones has been considered.
[0003]
FIG. 6 is a perspective view showing the appearance of an example of the wireless cassette
player, in which 1 is a player and 6 is a dedicated receiver for the headphone.
[0004]
Then, in the player 1, at the time of reproduction, stereo audio signals L and R of the left and
right channels are reproduced from a tape cassette (not shown), and these signals L and R are
converted into FM signals SL and SR of predetermined carrier frequencies. And the signals SL, SR
are transmitted to the receiver 6.
[0005]
Then, in the receiver 6, when the FM signals SL and SR from the player 1 are received, the audio
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signals L and R are demodulated from the signals SL and SR, and the signals L and R are the
sound of the left and right of the headphone 7. The units 7L and 7R are respectively supplied.
[0006]
In this case, the receiver 6 can be half the size or less of the name card.
Further, the distance in which the receiver 6 can be used away from the player 1 is about 1.5 m
in consideration of the radio law.
[0007]
Therefore, according to the wireless player, for example, when listening to the cassette in a
commuter train, the player 1 is put in a bag or bag, and the receiver 6 is put in the chest pocket
of the jacket or It can be fastened to a tie or the like, and the cord of the headphone 7 does not
get in the way.
[0008]
By the way, the transmission output of the FM signals SL and SR in the above-mentioned wireless
type player 1 is regulated by the Radio Law.
Then, when the Radio Law regulates the transmission output of this type of wireless device,
specify that the electric field transmitted from the target wireless device is received and that the
received electric field strength does not exceed the limit value. Regulates the transmission output.
Therefore, also in the player 1, the transmission output is designed (or adjusted) so that the
reception field strength of the FM signal SL, SR does not exceed the limit value.
[0009]
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However, when the player 1 plays back a new, silent tape, a silent section between songs and a
leader tape portion at the beginning or end of the tape, the audio signals L and R can not be
obtained. The FM signals SL and SR are not modulated, and as shown in FIG. 5A, the transmitted
signals SL and SR have only carrier components (fC is the carrier frequency of the signal SL or
SR).
Therefore, in the player 1, the transmission output is designed so that the reception electric field
strength of the carrier component does not exceed the limit value ES.
[0010]
However, in this design, when the audio signals L and R are obtained from the tape, and the FM
signals SL and SR have sideband components, as shown in FIG. 5B, the received field strengths of
the FM signals SL and SR are As a result, the reaching distance of the FM signals SL and SR
becomes disadvantageous by the distance corresponding to the level ΔE.
Alternatively, even within the reach distance, the disturbance characteristic and the S / N ratio of
the received audio signals L and R become disadvantageous because the reception electric field
strength decreases.
[0011]
The present invention is intended to solve such problems.
[0012]
Therefore, in the present invention, when the reference numerals of the respective parts
correspond to those of the embodiments described later, the audio apparatus L transmits the
audio signals L and R by radio waves. The modulation circuits 21L and 21R are supplied with the
signals L and R as modulation inputs and convert the audio signals L and R into modulated
signals SL and SR to be radio waves, and the audio signals L supplied to the modulation circuits
21L and 21R. , R, the modulated signal by the detection output S46 of the detection circuit 46 so
that the reception electric field strength of the radio wave becomes equal between when there is
no audio signal L, R and when there is an audio signal L, R Control of SL and SR is performed.
[0013]
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The effective transmission output in the reproduction mode is increased, and the reach of the
transmission signal is increased.
[0014]
1 and 2 show an example of a signal system of a wireless cassette player 1 and a dedicated
receiver 6 for headphones thereof.
In the player 1, 2 is a cassette magnetic tape, 10 is a reproduction circuit, 20 is a transmission
circuit, 31 is a tape running mechanism, 32 is a microcomputer for system control, 33 is an
operation key such as a reproduction key and a stop key. is there.
[0015]
In this case, although not shown, the tape transport mechanism 31 has a capstan, a pinch roller,
a capstan motor, a plunger, etc., and the plunger etc. is triggered by a lever etc. and uses the
trigger result and the rotational force of the capstan motor. Then, the mechanical state of the
player 1 is controlled or held in the stop mode, the reproduction mode or the like.
[0016]
Then, when the reproduction key of the operation keys 33 is pressed, the traveling mechanism
31 is controlled by the microcomputer 32, the mechanical operation mode of the player 1 is set
to the reproduction mode, and the tape 2 is made to travel at a constant speed. Audio signals L
and R of the left and right channels are reproduced from the tape 2 by 11R.
Then, the reproduction signals L and R are supplied to the FM modulation circuits 21L and 21R
through the signal lines of the reproduction equalizer amplifiers 12L and 12R and the preemphasis circuits 13L and 13R and the addition circuits 14L and 14R, respectively, to the FM
signals SLO and SRO. It is converted.
[0017]
In this case, the frequency shift of the FM signals SLO and SRO is set, for example, to 75 kHz with
100% modulation, and the carrier frequencies fLO and fRO of the FM signals SLO and SRO are
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the transmission frequencies of the actual transmission signals SL and SR. (Carrier frequency) fL
and fR are set considerably lower, for example, fLO = 11.29 MHz fRO = 11.75 MHz
[0018]
The FM signals SLO and SRO are supplied to the mixer circuits 22L and 22R, and a local
oscillation signal S23 for beat-up from the local oscillation circuit 23 is supplied to the mixer
circuits 22L and 22R.
The frequency f23 of the signal S23 is, for example, f23 = 64.00 MHz.
[0019]
Thus, in the mixer circuits 22L and 22R, the signals SLO and SRO are frequency modulated to the
FM signals SL and SR of the carrier frequencies fL and fR, for example, fL = fLO + f23 = 75.29
MHz fR = fRO + f23 = 75.75 MHz. It is converted.
[0020]
Then, the FM signals SL and SR are supplied to the antenna 26 through the band pass filters 24L
and 24R and the power amplifiers 25L and 25R, and are transmitted to the receiver 6.
[0021]
On the other hand, in the receiver 6, the FM signals SL and SR transmitted from the player 1 are
received by the antenna 61, and the signals SL and SR are supplied to the mixer circuit 64
through the antenna tuning circuit 62 and the high frequency amplifier 63. At the same time, the
local oscillation signal S65 is supplied from the local oscillation circuit 65 to the mixer circuit 64.
In this case, the frequency f 65 of the signal S 65 is, for example, f 65 = 65.05 MHz
[0022]
Thus, the FM signals SL and SR are converted by the signal S65 in the mixer circuit 64 to the
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intermediate frequency signals SLI and SRI whose frequencies fLI and fRI are, for example, fLI =
fL-f65 = 10.24 MHz fRI = fR + f65 = 10.70 MHz. It is frequency converted.
[0023]
Then, the signals SLI and SRI are supplied to the FM demodulation circuits 68L and 68R through
the intermediate frequency filters 66L and 66R and the amplifiers 67L and 67R to demodulate
the audio signals L and R, and the signals L and R are de-emphasis circuits 69L. , 69R and the
output amplifiers 71L, 71R, respectively, to the sound units 7L, 7R of the headphones 7
respectively.
[0024]
Furthermore, in order to set the reception electric field strength in the reproduction mode of the
player 1 as the limit value ES, in this example, the player 1 is configured as follows.
[0025]
That is, in general, the processing contents of the microcomputer 32 are not so complicated, and
the processing speed is not required to be so fast.
Also, although the original oscillation frequency of a so-called digital watch is 32.768 kHz, quartz
oscillators for oscillation are mass-produced and are low cost.
For these reasons, in the player 1, the clock frequency of the microcomputer 32 is 32.768 kHz.
[0026]
Therefore, the clock signal SCK is taken out from the microcomputer 32, and the clock signal SCK
is supplied to the multiplication circuit 42 through the buffer amplifier 41 and multiplied by, for
example, a signal S42 having a triple frequency, and this signal S42 is supplied to the switch
circuit 43. Be done.
In this case, since the clock signal SCK is a rectangular wave signal and has a harmonic
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component, the multiplying circuit 42 can be configured by a band pass filter that uses the
frequency of the signal S42 as a pass band, and an amplifier The characteristics of the band pass
filter may not be so strict.
[0027]
Further, the signals L and R from the reproduction equalizer amplifiers 12L and 12R are supplied
to the detection circuit 46 through the addition circuit 44 and the amplifier 45, and the detection
signal S46 indicating the presence or absence of the audio signals L and R is extracted.
That is, when at least one of the audio signals L and R is equal to or higher than a predetermined
level, a detection signal S46 is extracted which is "1" and both of the signals L and R are lower
than a predetermined level.
[0028]
Further, in this case, a capacitor 47 for time constant is connected to the detection circuit 46, and
the detection signal S46 becomes "1" immediately when at least one of the signals L and R
becomes a predetermined level or more. When both L and R fall below a predetermined level,
they are made to become "0" after a predetermined time.
[0029]
The detection signal S46 is supplied as the control signal to the switch circuit 43. When S46 =
"0", the switch circuit 43 is turned on to extract the signal S42, and the signal S42 extracted from
the switch circuit 43. Are supplied to the adder circuits 14L and 14R.
[0030]
According to such a configuration, when the player 1 is in the reproduction mode, the audio
signals L and R are obtained, so S46 = “1”, and the switch circuit 43 is off.
Thus, as described above, the FM signals SL, SR are modulated by the audio signals L, R and
transmitted to the receiver 6.
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[0031]
However, even when the player 1 is in the playback mode, when the tape 2 is silent, when the
silent section of the tape 2 is played back, or when the leader tape portion is played back, the
audio signals L and R are used. Is not obtained, S46 = “0”, and the switch circuit 43 is turned
on.
[0032]
Therefore, in this case, the signal S42 is supplied as the modulation signal to the FM modulation
circuits 21L and 21R through the switch circuit 43 and the addition circuits 14L and 14R, so that
the FM signals SL and SR are modulated by the signal S42 and transmitted. For example, as
shown in FIG. 3A, the FM signals SL and SR include not only the carrier component but also the
sideband component by the signal S42.
[0033]
At this time, as shown in FIG. 3A, the transmission output can be designed (or adjusted) such that
the reception electric field strength of the FM signal SL, SR in this state becomes equal to the
limit value ES.
[0034]
Then, when the audio signals L and R are obtained from the tape 2, the FM signals SL and SR are
similarly modulated by the audio signals L and R, for example, as shown in FIG. 3B, sideband
components other than carrier components. Therefore, the received electric field strengths of the
FM signals SL and SR in this case are approximately equal to the limit value ES.
[0035]
That is, the FM signals SL and SR in the state in which the audio signals L and R can not be
obtained, and the FM signals SL and SR in the state that can be obtained are also signals in a
modulated state, and the audio signals L and R can be obtained. Since the reception field
strengths of the FM signals SL and SR in the absence state are set to the limit value ES, the
reception field strengths of the FM signals SL and SR in the state where the audio signals L and R
are obtained are also substantially equal to the limit value ES. Become.
[0036]
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Thus, according to the player 1, since the actual reception electric field strength in the
reproduction mode can be set to the limit value ES, the reach distance of the FM signals SL and
SR can be extended.
Alternatively, even within the reach distance, the received electric field strength is high, so that
the interference characteristic and the S / N of the received audio signals L and R are
advantageous.
[0037]
According to experiments, the received electric field strength in the reproduction mode can be
increased by about 5 to 6 dB, and therefore, the reach distance of the FM signals SL and SR can
be approximately doubled.
Also, even if the transmission output is set such that the received electric field strength of the FM
signals SL and SR in the case where the audio signals L and R can not be obtained is about 3 dB
lower than the limit value ES, with a margin. Since the reception electric field strength when L
and R are obtained can be increased by about 3 dB, the reach distance of the FM signals SL and
SR can be expanded by about 1.4 times.
[0038]
Furthermore, since the switch circuit 43 is controlled in accordance with the presence or absence
of the audio signals L and R, the reception electric field strengths of the FM signals SL and SR do
not exceed the limit value ES.
That is, it is possible to take out a signal indicating the operation mode of the player 1 from the
microcomputer 32 and to supply the signal S42 to the modulation circuits 21L and 21R by
turning on the switch circuit 43 except in the reproduction mode.
[0039]
However, in such a case, when the ordinary tape 2 is reproduced, the audio signal L, R causes the
side band component in the FM signal SL, SR so that the received electric field strength does not
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exceed the limit value ES. Also, when playing a silent tape, a silent section of the tape 2, a leader
tape portion, etc., the audio signals L and R can not be obtained, so the FM signals SL and SR
have only carrier components and the received electric field strength is limited. It exceeds ES and
violates the Radio Law.
[0040]
However, since the switch circuit 43 is controlled according to the presence or absence of the
audio signals L and R in the above-described player 1, the audio signal can be obtained by
reproducing a silent tape, a silent section of the tape 2, a leader tape portion, etc. When L and R
can not be obtained, the signal S42 is instead supplied to the modulation circuits 21L and 21R,
so that the reception field strengths of the FM signals SL and SR do not exceed the limit value ES.
[0041]
FIG. 4 shows another example of the present invention. In this example, by controlling the
transmission output itself of the FM signals SL and SR, the reception field strength in the case
where the audio signals L and R can be obtained is limited value ES In this case,
[0042]
That is, in this example, audio signals L and R from the pre-emphasis circuits 13L and 13R are
supplied to the modulation circuits 21L and 21R without passing through the addition circuits.
[0043]
In the power amplifier 25L, Q21 represents a transistor at the output stage, and the transistor
Q21 is grounded at its emitter, and a resistor R21 is connected between its emitter and the
ground.
The collector and emitter of the transistor Q22 are connected in parallel to the resistor R21, and
the detection signal S46 of the detection circuit 46 is supplied to the base.
Furthermore, although not shown, the power amplifier 25R is also configured in the same
manner as the power amplifier 25L, and a signal S46 is supplied.
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[0044]
According to such a configuration, when the audio signals L and R can not be obtained, S46 =
“0”, and the transistor Q22 is off.
Therefore, current negative feedback is applied to the transistor Q21 by the resistor R21 and the
gain thereof decreases, so that the transmission output of the FM signal SL decreases to a
predetermined value, and the reception electric field strength becomes the limit value ES.
Similarly, the reception electric field strength of the FM signal SR also becomes the limit value ES.
[0045]
However, when the audio signals L and R are obtained, S46 = "1", and the transistor Q21 is
turned on.
Therefore, the transistor Q21 is not subjected to current negative feedback by the resistor R21,
and its gain is increased. Therefore, the transmission output of the FM signal SL is increased to a
predetermined value, and the FM signal SL has a sideband component. However, the received
electric field strength increases to the limit value ES.
Similarly, the reception field strength of the FM signal SR also increases up to the limit value ES.
[0046]
Therefore, also in this example, the reach distance of the FM signals SL and SR when the audio
signals L and R can be obtained can be extended.
Alternatively, even within the reach distance, the received electric field strength is high, so that
the interference characteristic and the S / N of the received audio signals L and R are
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advantageous.
[0047]
Furthermore, since the magnitude of the transmission output is controlled according to the
presence or absence of the audio signals L and R, the audio signals L and R can be obtained by
reproducing a silent tape, a silent section of the tape 2, a leader tape portion, etc. Even when this
is not the case, the reception field strengths of the FM signals SL and SR do not exceed the limit
value ES.
[0048]
In the above description, the present invention is applied to a headphone-type stereo cassette
player, but the present invention is also applied to a player using a CD, an MD, a DAT, a DCC or
the like as a recording medium. Can.
[0049]
Furthermore, although the signal 42 for modulation is obtained by multiplying the clock signal
SCK of the microcomputer 32 in the above description, the signal S42 may be formed by another
circuit as long as it is a signal of a frequency outside the audible band. .
[0050]
According to the present invention, since the actual received electric field strength in the
reproduction mode can be set to the limit value ES, the reach distance of the FM signals SL and
SR can be extended.
Alternatively, even within the reach distance, the received electric field strength is high, so that
the interference characteristic and the S / N of the received audio signals L and R are
advantageous.
According to experiments, the received electric field strength in the reproduction mode can be
increased by about 5 to 6 dB, and therefore, the reach distance of the FM signals SL and SR can
be approximately doubled.
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[0051]
Further, when the audio signals L and R can not be obtained by reproducing a silent tape, a silent
section of the tape 2, a leader tape portion and the like, the signal S42 is supplied to the
modulation circuits 21L and 21R instead. The received electric field strengths of the FM signals
SL and SR do not exceed the limit value ES, and the Radio Law is not violated.
[0052]
Brief description of the drawings
[0053]
1 is a system diagram showing an example of the present invention.
[0054]
2 is a system diagram showing an example of a receiver that can be used for the player of FIG.
[0055]
3 is a diagram showing the frequency spectrum of the transmission signal of the player of FIG.
[0056]
4 is a system diagram showing another example of the present invention.
[0057]
5 is a diagram showing a frequency spectrum of the conventional example.
[0058]
6 is a perspective view for explaining the present invention.
[0059]
Explanation of sign
[0060]
1 headphone type stereo cassette player 2 magnetic tape 6 dedicated receiver 7 headphone 10
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reproduction circuit 20 transmission circuit 21L, 21R FM demodulation circuit 22L, 22R mixer
circuit 23 local oscillation circuit 24L, 24R band pass filter 25L, 25R power amplifier 31 tape
traveling Mechanism 32 microcomputer 42 multiplier circuit 43 switch circuit 46 detection
circuit
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