JPH022337B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a confidential communication device that allows a user to talk to a specific party without any trouble in wireless telephone communication, while keeping the content of the call unintelligible to a third party. It is.

[Prior art and its problems]

2. Description of the Related Art A variety of secret communication systems for wireless telephones for the purpose of keeping the contents of a call secret from a third party other than a specific party have been developed and put into practical use for a long time. Normally, it is impossible to listen if the radio wave format is different, so when AM communication was at its peak, SSB
Both FM and FM used to have confidentiality, but today, apart from the radio wave format, some kind of common key has been established,
This refers to a transmitting/receiving method and device in which listening and listening is not possible unless the keys match. Secret key methods include a method of inverting the modulation frequency spectrum for the transmission carrier, a method of inverting only one of both sidebands, and a method of dividing the modulation frequency band and inverting part of it to rearrange the arrangement. There is a method to change the combination in time division. However, a simple combination of keys has the disadvantage that once the key is recognized, the secret communication effect is lost, and a complete secret communication device is complicated and large, making it difficult to employ in mobile devices and the like.

[Purpose of the invention]

It is an object of the present invention to provide a confidential communication device that can provide a high-level confidential communication effect in a compact and lightweight manner by adding recent digital technology to the conventional analog confidential communication system.

[Summary of the invention]

This invention transmits a normal modulated signal (non-inverted) and a frequency-inverted signal by switching between a normal modulation signal (non-inverted) and a frequency-inverted signal according to a specific bit pattern on the transmitting side, and transmits the inverted signal and non-inverted signal on the receiving side using the same bit pattern as the transmitting side. The operating principle is to reproduce the original audio signal by switching between
(Read Only Memory) and furthermore, by selecting the frequency division ratio of a programmable frequency divider that sets the timing of pattern switching, it has double confidentiality.

On the transmitting side, as illustrated in Figure 1, the configuration is such that the modulation carrier frequency 61 is the upper modulation frequency (usually 3kHz for SSB communication, for example), and the band is limited to below that frequency (for example, 2.7kHz), and A frequency that is half the modulating carrier frequency (e.g.
1.5kHz), LPF ( _c = 2.7kHz)
1 and the audio signal 21 passed through a notch filter ( _o = 1.5 kHz) 2 are passed through a double-balanced modulator 3 to create a frequency inverted signal 31, and a synchronization switch 4 is switched by the output of the ROM 5 in which a specific bit pattern is written to transmit the secret message. A composite signal 41 is obtained. An example of this arrangement is shown in 1 of the timing chart of FIG.

Further, the output 61 of the modulated carrier oscillator 6 is divided into two, and the output 71, which has been appropriately divided by the programmable frequency divider 7, is inputted to the hexadecimal counter 8.
The output 4 bits 81 (FIG. 3 2) are input to the ROM 5 and the bit pattern output 51 is applied to the synchronization switch 4. Separately, if the frequency divided by 2 of the modulated carrier frequency is added to the secret synthesis signal 41 (through an appropriate synthesis network 10) through the carrier output of the hexadecimal counter and the AND gate 9, the timing becomes the third
It becomes as shown in FIG. 3 and operates as a pilot signal for synchronization. The final composite signal is in the audio band.
Unwanted components generated by switching etc. are removed through the LPF ( _c = 2.7 kHz) 10 (the sum component in the balanced modulator output 31 can also be removed) and added to the modulator of the transmitter.

On the receiving side, the demodulated output is passed through LPF ( _c = 2.7kHz)
After removing unnecessary components such as noise and the pilot signal through a notch filter ( _o = 1.5kHz), a double balanced modulator adds the output (3kHz) of the same modulated carrier frequency oscillator 6 as that on the transmitting side, and generates a frequency inverted signal 31.
The non-inverted signal 21 and the signal output restored by switching with the synchronization switch 4 are passed through the audio band LPF ( _c = 2.7k
Hz) 10 to the audio output circuit.

Further, the output 61 of the modulated carrier oscillator 6 is divided by two, and further divided into the same frequency as that on the transmitting side by the programmable frequency divider 7 and inputted to the hexadecimal counter 8, and the output 4 bits 81 are inputted to the ROM 5. The bit pattern output 51 is applied to the synchronization switch 4. In addition, in order to match the switching timing of the synchronization switch with the transmitting side, BPF ( _p = 1.5kHz) is applied from the demodulated output.
The pilot signal 111 [4 in Figure 3] is separated through 11 to trigger the one-shot multivibrator 12, and its output 121 [5 in Figure 3]
Reset the programmable frequency divider 7 with
121 positive edge 121P [6 in Figure 3]
Load the preset input F into the hex counter with
121 negative edge 121N [Figure 3 7]
gives a pseudo clock to hexadecimal counter 8, but
Modulated carrier 61 (3kHz) as regular clock
The output 71 obtained by dividing the frequency by 2 (1.5kHz) by the programmable frequency divider 7 to the same frequency as the transmitter
By combining at gate 13 and inputting to hexadecimal counter 8, the output 4 bits of hexadecimal counter 81
By inputting [Fig. 3 8] into the ROM 5 in which the same bit pattern as that on the transmitting side is written, and controlling the switching operation of the synchronization switch 4 according to the output bit pattern 51, the frequency of the demodulated signal can be changed. This confidential communication device is characterized in that it is configured to switch between an inverted signal and a frequency non-inverted signal in synchronization with the transmitting side.

Portions indicated by the same symbols in FIG. 1 (transmitting side) and FIG. 2 (receiving side) have the same operational performance.

[Embodiments of the invention]

As described in the previous section, since there are many parts with the same performance indicated by the same symbols on the transmitting side and the receiving side of the present invention, FIG. Shown below.

In Figure 4, the dedicated section during transmission is an AND gate and its output synthesis circuit, and the dedicated section during reception is
BPF11・One-shot multivibrator 1
2, OR gate 13, negative edge detector, positive edge detector;
The ROM 5, modulated carrier oscillator 6, programmable frequency divider 7, hexadecimal counter 8, and LPF 10 are commonly used for transmission and reception. The operation of each component has been described in detail in the previous section, so the explanation will be omitted.

〔Effect of the invention〕

Basically, this invention writes a secret key in ROM and shares it for sending and receiving, and calls can only be made between a group of devices that have the same ROM.
By replacing the ROM, the combination of call groups can be easily changed. Also the same
Even within a group made up of ROM, it has a dual privacy feature that allows calls to be made only between specific devices by changing the division ratio of the programmable frequency divider, so it has a wide range of applications as a privacy device. It is something.

The ROM is mass-produced at a low cost as a digital storage device by using an IC, and since writing can be performed individually using a writer, it is both mass-producible and unique for each application.

Since the transmitted wave includes a pilot signal and is used as a synchronization signal on the receiving side, the secret key on the receiving side is synchronized automatically, so no synchronization operation is necessary. However, it is also possible to adjust the pulse width adjuster 122 of the one-shot multi 12 more precisely.

The pilot signal has a constant frequency (1.5kHz)
Since it has a constant amplitude, it can be used for frequency synchronization of the modulated carrier (3kHz) on the receiving side,
In SSB communication, it is also effective as a pilot signal for local oscillation AFC and AGC.

Since there are many parts that operate in the same way on the transmitting side and the receiving side, it has been shown in the embodiment that these parts can be shared.

It is also possible to use it as an independent private communication device by attaching it externally to an existing transmitter/receiver.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of the transmitting side of the present invention, FIG. 2 is a configuration diagram of the receiving side, FIG. 3 is a synchronization timing diagram of confidential operation, and FIG. 4 is an example of the implementation configuration of the present invention. In each figure, the same symbols indicate the same operating parts. 1, 10...LPF, 2...Notchi filter,
3...double balanced modulator, 4...synchronous switch, 5
...ROM, 6...Modulation carrier oscillator, 7...
Programmable frequency divider, 8...Hex counter, 9
...AND gate, 11...BPF, 12...one-shot multivibrator.

Claims (1)

[Claims] 1 On the transmitting side, the modulation carrier frequency of the modulation upper limit frequency and the audio signal whose band is limited to below the modulation carrier frequency and half the frequency of the modulation carrier frequency are removed are passed through a double balanced modulator to generate a frequency inverted signal. The configuration is such that the transmitted wave is modulated by adding a pilot signal with a frequency half the modulation carrier frequency to a composite output signal in which a frequency inverted signal and a frequency non-inverted signal are switched according to a specific bit pattern. The pattern is to input the frequency obtained by dividing the carrier frequency using a programmable frequency divider into a hexadecimal counter, and output the 4
The bit pattern is written in advance.
The pilot signal is input to the ROM and obtained as its output, and the pilot signal is output only during the carrier output period of the hexadecimal counter.On the receiving side, the audio signal with the pilot signal removed from the demodulated output and the carrier frequency are A frequency-inverted signal is created through a double-balanced modulator, the frequency-inverted signal and the non-inverted signal are passed through a switching circuit that operates according to a specific bit pattern to restore the audio signal, and the pilot signal is separated from the demodulated output to produce a one-shot signal. By triggering the multivibrator, resetting the programmable divider with its output, loading the preset input F into the hex counter with its positive edge, and providing a pseudo-clock to the hex counter with its negative edge, the 16 By inputting the 4-bit output of the forward counter into a ROM in which the same bit pattern as that on the transmitting side is written, and controlling the operation of the switching circuit according to the output bit pattern, the demodulated signal is converted into a frequency-inverted signal. A secret communication device characterized in that it is configured to switch between a frequency non-inverted signal and a frequency non-inverted signal in synchronization with a transmitting side.