JPH02159136A - Am stereo transmitter and receiver - Google Patents

Abstract

PURPOSE:To ensure the compatibility by modulating the amplitude of a signal obtained by setting an RZ SSB modulated wave at a fixed amplitude via a sum signal and therefore receiving a monaural signal via a conventional AM receiver. CONSTITUTION:An amplitude limiter 105 limits substantially the amplitude of a modulated wave obtained by an RZ SSB modulation wave generating circuit 104. An amplitude modulator 106 serves as a 2nd modulation means which modulates the amplitude of the output of the limiter 105 as a carrier wave with a sum signal. An amplitude limiter 202 sets the amplitude of the output signal of an RF/IF conversion circuit 201 at a fixed level. A frequency detector 203, an integrator 204, and a linearizer 205 demodulate a difference signal out of the output of the limiter 202. An envelope curve detector 206 uses the output signal of the circuit 201 as an envelope curve detection wave and outputs a sum signal. A matrix circuit 208 produces the right and left signals from the demodulated sum and difference signals and outputs both produced signals to a right signal output terminal 209 and a left signal output terminal 201 respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is used for transmitting stereo signals. In particular, it relates to signal transmission by amplitude modulation. The present invention is suitable for use in a medium wave amplitude broadcasting device.

The present invention provides an AM system that transmits stereo signals by amplitude modulation.
In stereo transmitters and receivers, high quality can be achieved with a relatively narrow modulation spectrum by performing sideband modulation on all carrier waves using the difference signal, and using a signal with a constant amplitude of this modulated wave as the carrier wave and amplitude modulating it using the sum signal. It transmits stereo signals.

[Prior art] As a method for transmitting stereo signals using amplitude modulated waves,
Conventionally, a sum signal (R) of a right signal (R) and a left signal (L)
10L) and angle modulation (phase modulation or frequency modulation) by the difference signal (R-L), or quadrature modulation by the sum signal and difference signal, and remove the amplitude modulation component of the composite wave. A method has been proposed in which a carrier wave is used as a carrier wave and amplitude modulated using a sum signal.

[Problem that the invention seeks to solve]

However, conventional methods have drawbacks such as a wider frequency spectrum when transmitting a stereo signal, distortion in the demodulated signal, and a lower degree of stereo separation than when amplitude modulating only a monaural signal.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide an AM stereo transmitting device and a receiving device that transmit a stereo signal without expanding the radio frequency band required when amplitude modulating a monaural signal. .

[Means for solving problems]

The AM stereo transmitter of the present invention converts the carrier wave into a difference signal (R
-L), the full carrier single sideband wave (FullCarrie
r SSB or RZ 5SB) A first modulating means for modulating, an amplitude limiter for limiting the amplitude of the modulated wave obtained by the first modulating means to a substantially constant value, and a summation of the output of the amplitude limiter as a carrier wave. and a second modulation means for amplitude modulating the signal (R+L). Here, RL (RL) is substantially equivalent as a difference signal, and an equivalent modulated wave can be obtained by using either of them. In this specification, a positive sign error signal (R-L) will be used for explanation.

The transmission signal of this transmitting device has a sum signal that is almost equivalent to a normal amplitude modulated wave, and can be received as a monaural signal even by a conventional AM receiving device.

However, in order to receive it as a stereo signal, it is necessary to be able to receive a phase modulated wave.

That is, the AM stereo receiver of the present invention sums the outputs of the amplitude modulated wave demodulating means for demodulating the received signal as an amplitude modulated wave, the phase modulated wave demodulating means for demodulating the received signal as a phase modulated wave, and the output of the amplitude modulated wave demodulating means for demodulating the received signal as a phase modulated wave. The output of the phase modulated wave demodulating means is used as a difference signal to be input to a circuit that reproduces the left signal and the right signal.

[For production]

A wave obtained by making a signal subjected to full carrier single sideband modulation to a constant amplitude using an amplitude limiter becomes a pseudo-angle modulated wave with a modulation index sufficiently higher than 1. As a result, the spread of the modulation spectrum is sufficiently reduced compared to the angle modulated wave obtained by the conventional method, and can be made comparable to that of a monaural signal. Furthermore, since the angle modulated wave and the amplitude modulated wave can be demodulated without being influenced by each other, a high quality stereo signal can be obtained.

〔Example〕

FIG. 1 is a block diagram of an AM stereo transmitter according to an embodiment of the present invention.

This transmitter receives the right signal (R) and left signal (L) of the stereo signal, and the sum signal (R+L) and the difference signal (
A matrix circuit 10 as a means for generating
2. Here, the feature of this transmitting device is that the local oscillation signal supplied from the local oscillator 103 is used as a carrier wave, and this carrier wave is modulated by a difference signal into all carrier waves and single sideband. As a first modulation means, an RZ SSB modulated wave generation circuit is used. 104, this RZ SSB modulated wave generation circuit 104
The present invention includes an amplitude limiter 105 that limits the amplitude of the modulated wave obtained by substantially constant, and an amplitude modulator 106 as a second modulation means that uses the output of the amplitude limiter 105 as a carrier wave and modulates the amplitude with a sum signal. That's true.

The right signal input terminal 100 and the left signal input terminal 101 include
A right signal and a left signal of the stereo signal are respectively input. M) The IJ Fuchs path 102 generates a sum signal and a difference signal from the right signal and left signal.

The RZ SSB modulated wave generation circuit 104 includes a local oscillator 10
3 and the difference signal to generate an RZ SSB modulated wave. The amplitude limiter 105 makes the amplitude of this RZ SSB modulated wave constant. Amplitude modulator 106 amplitude modulates the output signal of amplitude limiter 105 using a sum signal. IF/RF
The conversion circuit 107 converts the amplitude modulated wave obtained by the amplitude modulator 106 into a radio frequency, removes unnecessary waves, amplifies it, and radiates it from the transmitting antenna.

- FIG. 2 is a block diagram of an AM stereo receiving apparatus according to an embodiment of the present invention.

This receiving device includes a matrix circuit 208 as a circuit that receives a sum signal and a difference signal of stereo signals and reproduces a right signal and a left signal. Here, the features of this receiving device include an envelope detector 206 as an amplitude modulated wave demodulating means for demodulating the received signal as an amplitude modulated wave, and a phase modulated wave demodulating means for demodulating the received signal as a phase modulated wave. It is equipped with an amplitude limiter 202, a frequency detector 203, an integrator 204, and a linearizer 205, and the output of the amplitude modulation wave demodulation means is used as a sum signal, and the output of the phase modulation wave demodulation means is used as a difference signal and input to the matrix circuit 208. There is a particular thing.

The RF/IP conversion circuit 201 converts the signal received by the receiving antenna 200 to an intermediate frequency and compensates for loss in the propagation path. The amplitude limiter 202 is the RF/IF conversion circuit 201
Keep the amplitude of the output signal constant. frequency detector 203,
The integrator 204 and the linearizer 205 are the amplitude limiter 2
The difference signal is demodulated from the output of 02.

The envelope detector 206 performs envelope detection on the output signal of the RF/IF conversion circuit 201 and outputs a sum signal. Delay circuit 2
07 compensates for the delay time caused by the demodulation of the difference signal. The IJx circuit 208 generates a right signal and a left signal from the demodulated sum signal and difference signal, and outputs them to a right signal output terminal 209 and a left signal output terminal 210, respectively.

FIG. 3 is a block diagram showing details of the R2SSB modulated wave generation circuit 104.

Difference signal input terminal 3 of RZ SSB modulated wave generation circuit 104
The difference signal generated by the matrix circuit 102 is input to 00. This difference signal is divided into two, one of which is supplied to the amplitude modulator 302 as is, and the other is subjected to Hilbert transformation by the Hilbert transformation circuit 303 and then supplied to the amplitude modulator 304.

The output signal of the local oscillator 103 is input to the carrier input terminal 301 . This signal is divided into two by a distributor 305, one of which is input to a distributor 306, and the other is supplied to a combining circuit 309 via a level adjustment circuit 308. The signal input to the divider 306 is further divided into two, one of which is supplied to the amplitude modulator 302, and the other is supplied to the amplitude modulator 302.
The signal is supplied to an amplitude modulator 304 via a degree phase shifter 307 .

Amplitude modulators 302 and 304 amplitude-modulate carrier waves whose phases differ by 90 degrees from each other using difference signals and their Hilbert transforms, and generate amplitude-modulated waves in which the carrier waves are suppressed. A synthesis circuit 309 synthesizes the outputs of the amplitude modulators 302 and 304 and the carrier wave whose level has been adjusted by the level adjustment circuit 308, and outputs an RZ SSB wave to an output terminal 310.

Here, the difference signal (R-L) is g (t) and the modulation index is m
, mg(t) as m'g(t), 1
Let mg(t)<1. At this time, RZ SSB waves
(t) is 5(t)=(1+mg(t)) cosωt
+mg(t) 5ina+ t=Ao cos ((
Ll t +tan-'m1(t)/(1+mg(t)
)) becomes. By making this amplitude constant using an amplitude limiter and removing unnecessary harmonics, we get 5(t) = CO9((LJ t 〇jan 'm'g
(t)/(1+mg (t)) ). however,
Amplitude coefficients are omitted. Here, when m(1, S (t
) is approximated as 5(t) = CO8((IJ t + mg(t)). In other words, it is a phase modulated wave with a modulation index m. Since m(1), the spectrum of this modulated wave is , very compact.

〔Effect of the invention〕

As explained above, the AM stereo transmitting device and the receiving device of the present invention have the following advantages. (2) The amplitude-limited RZ SSB modulated wave becomes a pseudo-angle modulated wave with a modulation index sufficiently higher than 1, and is mutually influenced by the amplitude modulated wave. (3) Unlike conventional angle modulation, the pseudo-angle modulation used in the present invention causes less distortion due to the delay characteristics of the filter; (4) The sum signal The amplitude modulation used for transmission and the R2 SSB modulation used for transmitting the difference signal are the same linear modulation, and their demodulation characteristics are the same even if the received electric field strength changes, so stereo It has the effect that the characteristics do not change.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an AM stereo transmitter according to an embodiment of the present invention. FIG. 2 is a block diagram of an AM stereo receiver according to an embodiment of the present invention. FIG. 3 is a block diagram showing details of the RZ SSB modulated wave generation circuit. 100... Right signal input terminal, 101... Left signal input terminal, 102... Matrix circuit, 103... Local oscillator, 104... RZSSB modulated wave generation circuit, 1
05.202...Amplitude limiter, 106.302.30
4... Amplitude modulator, 107... IP/RF conversion circuit, 200... Receiving antenna, 201... RF/IF
Conversion circuit, 203... Frequency detector, 204... Integrator, 205... Linearizer, 206... Envelope detector, 207... Delay circuit, 208... Matrix circuit, 209...・Right signal output terminal, 210...
Left signal output terminal, 300...Difference signal input terminal, 301
. . . Carrier wave input terminal, 303 . . . Hilbert transform circuit, 305. 306 . ...Output terminal. Patent applicant: Nippon Telegraph and Telephone Corporation Agent, Patent attorney Naotaka Ide Transmission station Figure 1 Transmission station Figure 2

Claims (1)

[Claims] 1. AM stereo including means for receiving a right signal (R) and a left signal (L) of a stereo signal and generating a sum signal (R+L) and a difference signal (R-L) thereof. In the transmitting and receiving device, a first modulating means for performing all-carrier single sideband modulation on a carrier wave by the difference signal; an amplitude limiter for limiting the amplitude of the modulated wave obtained by the first modulating means to a substantially constant value; An AM stereo transmitter comprising: second modulation means for amplitude modulating the sum signal using the output of the amplitude limiter as a carrier wave. 2. Sum signal (R+L) and difference signal (R
- L) as an input, and is equipped with a circuit for reproducing right and left signals, comprising amplitude modulated wave demodulation means for demodulating the received signal as an amplitude modulated wave, and demodulating the received signal as a phase modulated wave. AM stereo, characterized in that the output of the amplitude modulation wave demodulation means is used as a sum signal, and the output of the phase modulation wave demodulation means is input as a difference signal to the reproducing circuit. Receiving device.