JPS6340925Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a communication device that uses double modulation for wired or wireless communication to reduce noise and enable communication with a good S/N ratio. be.

In conventional communication devices that modulate the carrier wave with the transmitted signal, that is, the modulation signal itself, noise components in the same frequency band as the modulation signal cannot be removed even with the use of high-performance filters, so in order to extend the communication distance, I had to increase the output on the transmitter side.

This invention modulates the carrier wave of the transmitted signal with a signal that is AM-modulated with another signal.
The present invention provides a communication device that can perform communication with a good S/N ratio by reducing noise through a combination of filters on the receiving side.

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, which is composed of a transmitting system Y and a receiving system Z. Second
The figure shows the waveforms of each part in FIG. 1, and FIG. 2 a to g correspond to a to g in FIG. 1.

First, data input a input from the data input terminal 1 passes through the mixer 3 that receives the output b of the subcarrier oscillator 2, becomes an AM modulated signal c, and the main carrier oscillator 4 modulates the carrier wave. Y
The output is c. The modulation of the main carrier wave oscillator 4 can be either FM modulation or AM modulation, but in this embodiment, a case where FM modulation is performed will be described.

The output c of the transmitting system Y is transmitted to the receiving system Z through a wired or wireless signal transmitting means 11. The transmitted data is selectively received by a receiver 5 tuned to the transmission system carrier wave, and subjected to FM detection by an FM detector 6. The detected signal d is applied to a high pass filter 7, where noise components below the cutoff frequency are removed. At this time, the cutoff frequency is set to a value at which the subcarrier wave is not attenuated. The signal e that has passed through the high-pass filter becomes an AC signal, and is subjected to AM detection by an AM detector 8. This signal f
is further applied to a low-pass filter 9 to remove noise components higher than the data signal frequency and subcarrier frequency components. The cutoff frequency of this low-pass filter 9 is set to a value at which the data signal is not attenuated.

In Fig. 3, F1 is the frequency characteristic of the low-pass filter 9, F _L is its cutoff frequency, and F2
is the frequency characteristic of the high-pass filter, _FH indicates its cutoff frequency, and the frequency characteristic obtained by combining these filters is F3. That is, in the end, the data signal a itself is not attenuated, and only the noise component is attenuated in accordance with the characteristics of F3 in the entire reproduction frequency band, including the noise component distributed in the same frequency band as the data signal frequency, and the reproduction output It is output from the terminal 10 as a signal g.

At this time, it is necessary that the function F _L < F _H and the data signal frequency be set to a value lower than F _L , and the configuration order is high pass filter 7, AM detector 8, low pass filter 9. It is necessary that the order is as follows.

FIG. 4 is a block diagram of a conventional communication device shown for comparison with the present invention, and FIG. 5 shows waveforms of each part thereof.
Corresponds to a, d to g in the figure. When compared with the communication device of the present invention, the conventional communication device does not have the mixer 3 and subcarrier oscillator 2 shown in FIG. 1 in the transmission system, and has the same circuit configuration in the reception system.
FIG. 6 shows the frequency characteristics F1 and F2 of the high-pass filter 7 and low-pass filter 9 required in a conventional communication device, and their cutoff frequencies must satisfy F _H <F _L. However, noise components distributed between the data signal frequency band F _H and F _L cannot be removed at all.

In other words, according to the present invention, noise can be removed over a wide frequency range, including noise components distributed in the target signal frequency band, so communication with a good S/N ratio can be performed with less power. . This is particularly advantageous for communication devices in which the signal transmission means is wireless and uses weak radio waves stipulated by the Radio Law.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a dual modulation communication device according to an embodiment of the present invention, Fig. 2 is a waveform diagram of each part in Fig. 1 used to explain the present invention, and Fig. 3 is a frequency diagram of a filter used in the present invention. Explanatory diagram showing characteristics, 4th
6 to 6 relate to a conventional example, FIG. 4 is a block diagram, FIG. 5 is a waveform diagram, and FIG. 6 is an explanatory diagram showing the frequency characteristics of the filter. 1...Data input terminal, 2...Subcarrier oscillator,
3...Mixer, 4...Main carrier wave oscillator, 5...Receiver, 6...FM detector, 7...High pass filter, 8
...AM detector, 9...Low pass filter, 10...Reproduction output terminal, 11...Signal transmission means.

Claims (1)

[Scope of utility model registration request] In the transmitting system, data input is supplied to the main carrier oscillator via a mixer that receives the output from the subcarrier oscillator for FM or AM modulation, and in the receiving system, the data received and detected by the FM or AM detector is passed through a high-pass filter. After passing through, AM detection is performed,
Next, a double modulation communication device is characterized in that a reproduced output is obtained through a low-pass filter.