JPH0245857B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secret communication device used in a line with a large frequency deviation such as an SSB communication line.

Conventionally, this type of secret communication device has a method of dividing the voice spectrum into N equal subbands with a certain frequency bandwidth, and exchanging each divided subband and inverting the spectrum. There is a method in which swapping and spectrum inversion is performed in a certain time unit, or a method in which the audio signal is encoded and a secret conversation is performed by code conversion.

Among these various methods, in the method of dividing the spectrum into N subbands, if there is a frequency deviation in the transmission path as in the case of an SSB communication circuit, frequencies other than the audio that should originally be passed are divided into each subband. Because it passes through sub-bands, the intelligibility of the reproduced received audio deteriorates dramatically.

This becomes more noticeable as the number of divisions N increases to improve confidentiality.

The present invention aims to solve the conventional drawbacks of the method of dividing the spectrum into N subbands, swapping the subbands, and inverting the spectrum. A lock loop is used to remove frequency deviations in the transmission line. As a result, even when used on a transmission line with a frequency deviation, it is possible to output clear secret playback audio without frequency adjustment, so when talking to multiple radio stations with large frequency deviations in sequence, each It is possible to obtain a confidential communication device that does not require manual fine-tuning of the frequency deviation with respect to the station. Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, in which numeral 1 is a portion of a secret device having a function of a normal frequency switching method, and numeral 1 is a phase lock loop according to the present invention. Now, 1 is a switch that switches between microphone input M and secret speech input m, 2 is an amplifier, 3 is a mixer circuit that converts microphone input M or secret speech input m into an intermediate frequency, and 4 is a switch that changes the audio bandwidth to N, etc. 5 is a mixer circuit that returns the intermediate frequency of N etc. to the baseband, 6 is a low pass filter that removes harmonic components, 7 is the baseband signal to the intermediate frequency A local oscillation circuit 8 generates N outputs of different frequencies to be converted, and a local oscillation circuit 8 generates N or 2N outputs of different frequencies to return each intermediate frequency to the baseband. In , 9 is the secret playback output
a switch for switching m ₁ and secret speech output m ₂ ; 10 is an amplifier for secret speech input m; 11 is a first mixer circuit for converting the secret speech input into an intermediate frequency;
12 is a first local oscillator that converts the baseband secret speech into an intermediate frequency; 13 is an intermediate frequency bandpass filter; 14 is a second mixer circuit that returns the intermediate frequency signal to the baseband; 5 is a frequency deviation converter; a second local oscillator for returning a certain secret voice input (intermediate frequency) to the baseband; 16 is a control voltage holding circuit; 17 is a low-pass filter; 18
19 is a phase comparator, and 19 is a phase lock detector, which activates the control voltage holding circuit 16 when the phase lock is completed. A reference signal generator 20 generates an arbitrary frequency within the passband of the radio line. Reference numeral 21 denotes a switch for supplying a reference signal to the private speech output microphone line L for a certain period of time, and 22 a timer for controlling the switch 21.

Next, to describe the operation of this confidential voice device, first, switch 1 is set to the microphone input side A, and switch 9 is set to the confidential voice output side.
m ₂ side, and before transmitting a call, send a reference signal from the reference signal generator 20 to the secret output microphone line L using the timer 22 and switch 21 for a certain period of time so that the phase lock loop of the reception system can phase lock.
A baseband input M is then applied to amplifier 2.
The output of the amplifier 2 is divided by a mixer circuit 3 and an intermediate frequency bandpass filter 4. The N divided intermediate frequency signals are returned to the baseband by the local oscillator 8 and the mixer circuit 5, and the frequency is swapped and the spectrum is inverted depending on the frequency of the local oscillator 8 at this time. This swapping or inversion is a known fact as a normal spectrum inversion swapping method.

Next, we will discuss how to reproduce the audio with the secret message back to the original audio.

The switch 1 is switched to the secret speech input side B, and the switch 9 is switched to the secret speech reproduction output _m1 , and the received audio signal is applied to the secret speech input. Since the reference signal including the frequency deviation that has passed through the transmission path is input before the received audio signal, the received audio signal given to the amplifier 10 is
The first local oscillator 12 in the mixer circuit 11 of
is converted to an intermediate frequency through an intermediate frequency bandpass filter 13, and further
The second local oscillator 15 in the mixer circuit 14 of
output back to baseband. Here, the output of the second mixer circuit 14 is output to the phase comparator 18.
is compared with the reference signal of the reference signal generator 20, and the comparison output is converted into voltage by the low-pass filter 17, passed through the control voltage holding circuit 16, and serves as a control signal for the local oscillator 15. With this phase lock loop (15-19), the output of the second mixer circuit 14 can be synchronized with the reference signal of the reference signal generation circuit 20, and the frequency deviation of the transmission path can be removed. Here, the phase lock detector 19 obtains the comparison output from the phase comparator 18, and when a phase lock is detected, the control voltage holding circuit 16 is activated by the output of the phase lock detector 19, and the voltage is inputted following the reference signal. To prevent the phase lock loop from malfunctioning due to the received audio signal. Therefore, the output of the second mixer circuit 14 after receiving the reference signal becomes a clear voice by the known secret speech devices 1 to 6 shown next to the secret speech input signal without frequency deviation, and the secret speech reproduction output _m1 is reproduced.

FIGS. 2A to 2G illustrate a comparison between the intelligibility improvement effect of the present invention and the conventional method, so FIG. 2A represents the microphone input audio signal as a spectrum.
Here, B ₁ ~ B ₈ is the audio signal of 300Hz ~ 2700Hz.
The name of each band when divided into 8 parts per Hz, B ₁
is 300Hz to 600Hz band, similarly B ₂ is 700Hz to 900
Hz band. _B8 is in the 2400Hz to 2700Hz band. A spectrum obtained by subjecting this spectrum to frequency inversion and replacement is shown in FIG. 2B. Here B ₁ ~
B ₈ with a dash indicates spectral inversion. Figure 2C shows the confidential voice transmitted by the transmitter with a frequency deviation of △ as a baseband signal, and the confidential voice demodulated by the receiver with a frequency deviation of △ is shown in Figure 2C. Shown in D. Therefore, each band is shifted from each other by 2Δ. Figure 2 (E) shows the secret speech playback audio played by a secret speech device that does not have a frequency deviation correction function. It can be seen that the signal that moves to a distant frequency and returns to the original band is also shifted by 2Δf, which disturbs the harmonic relationship of the audio signal and significantly deteriorates the clarity. FIG. 2(F) shows the spectrum before reproduction of the confidential speech after frequency deviation has been removed by the reference signal according to the present invention, and FIG. 2G shows the output spectrum of the reproduction of the confidential speech by the present apparatus, so that the original voice can be faithfully reproduced.

As described above, the present invention is a system that provides a phase lock loop function in addition to the functions of a normal frequency switching system, so when a confidential device is used in a transmission line with a large frequency deviation such as an SSB communication line, You can obtain clear confidential playback sound without having to adjust the frequency deviation with each radio station every time you make a call.
The larger the value, the more the clarity deteriorates due to frequency deviation, but the present invention has an improvement effect without such drawbacks.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIGS. 2A to 2G are diagrams showing the spectral relationship between the conventional system and the confidential communication process of the present invention. 1,9,21...Switcher, 2,10...Amplifier, 3,5,11,14...Mixer circuit, 4,1
3...Intermediate frequency band pass filter, 6, 17...
...Low pass filter, 7, 8...Local oscillation circuit,
12... Local oscillator, 15... Voltage controlled local oscillator, 16... Control voltage holding circuit, 18... Phase comparator, 19... Phase lock detector, 20... Reference signal generator, 22... Timer.

Claims (1)

[Claims] 1. In a secret speech device using a band division swapping inversion method that divides the audio spectrum into multiple subbands, swaps the divided multiple subbands, and inverts the spectrum, the demodulator of the receiver converts the signal to the baseband at the time of reception. a frequency conversion means comprising a first mixer circuit, a first local oscillator, and an intermediate frequency bandpass filter for converting the frequency of the demodulated confidential voice signal into an intermediate frequency signal, and converting the intermediate frequency signal back to the baseband. a second mixer circuit for outputting the signal to the private voice input terminal of the private voice input terminal of the band division exchange and inversion method; a voltage-controlled second local oscillator that supplies a local oscillation frequency to the second mixer circuit; a reference signal generator that generates a signal; a phase comparator that compares the phase of the output of the second mixer circuit with the phase of the reference signal; and a control voltage holding circuit that smoothes the output of the phase comparator to direct current. a low-pass filter that provides a control voltage to the second local oscillator via the phase lock detector; a phase lock detector that detects phase lock using the output from the phase comparator; the control voltage holding circuit that holds the control voltage from the pass filter; and a timer that adds the reference signal of the reference signal generator for a certain period of time to the confidential signal output output from the band division exchange inversion type confidential signal device to the transmitter during transmission. What is claimed is: 1. A confidential communication device comprising: a communication device for removing a frequency deviation of an input confidential communication audio signal due to a transmission path;