JPS588621B2 - The first thing you need to know is how much you can do - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency reversal privacy system used in mobile radio lines that transmit voice bands.

FIG. 1 is a block diagram showing an example of a conventional confidential communication system.

In other words, from the input side 1 to the transmission line, f1 (KHz) to f
The input signal fv within the audio band of 2 (KHz) is transmitted through the transmission path 2.
The signal is received at the output side 3 of the transmission path with the frequency shifted by Δf (KHz).

This frequency-shifted signal of fv+Δf (KHz) is frequency-converted by supplying a frequency fs higher than the f2 (KHz) from the oscillator 5 to the frequency converter 4, and is then passed through the low-pass filter 6.
Only the lower sideband is extracted by transmitter 7, antenna 8,
After being transmitted by the radio propagation path 9, antenna 10, and receiver 11, the frequency is converted by the frequency converter 12 using the output f's of the local oscillator 13, and only the lower sideband is extracted by the low-pass filter 14 and received. It is output from the end output terminal 15.

In this case, the receiving end side output signal frequency is the input signal frequency fv
is not equal to fv+Δf+f's-fs.

Therefore, although there is almost no problem with audio signals, there is a drawback that it is impossible to transmit signals that require precise frequency accuracy, such as individual selection signals.

The present invention focuses on the fact that a relatively large frequency shift occurs in a wired transmission line, while almost no frequency shift occurs in a wireless transmission line, and aims to solve these drawbacks. f1 (KH
z) Send a pilot signal with a higher frequency fs (KHz) to the transmission line, separate this signal at the output side of the wired transmission line, convert the frequency of the audio signal using this signal, and output an inverted frequency signal. Then, the wireless transmitter sends out the inverted frequency signal to the wireless transmission path, the sent signal is received by the wireless receiver, and is inverted again to obtain the same signal as the audio band input signal at the receiving end output side. Its purpose is to realize the transmission of precision frequency signals and the generation of inverted frequency signals, as well as to
It is an object of the present invention to provide a secret communication system having a frequency correction function that can prevent the band of a wireless channel from expanding.

The present invention will be explained in detail below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which 1 is the transmission line input side;
2 is a transmission line, 3 is a transmission line output side, 4 is a frequency converter, 5
13 is an oscillator, 6, 14 and 16 are low pass filters, 7 is a radio transmitter, 8 is a transmitting antenna, 9 is a radio propagation path, 10 is a receiving antenna, 11 is a radio receiver, 1
2 is a frequency converter, 15 is a receiving end output side, 17 is a sending end input side, 18 is a combiner, 19 is a distributor, and 20 is a band pass filter.

In this embodiment, the input signal fv (KHz) within the audio band from f1 (KHz) to f2 (KHz) is passed through the low-pass filter 1.
6, is combined by a synthesizer 18 with the output signal of the oscillator 5 having a frequency fs higher than f2 (KHz), and is sent to the transmission line 2.

The low-pass filter 16 filters the audio signal at a frequency fs (KHz
) to prevent interference with pilot signals.

By passing through the transmission path 2, the audio signal fv (KHz) and the pilot signal fs (KHz) are affected by the frequency deviation in the transmission path 2, and are shifted by Δf (KHz) to the receiving end 3 of the transmission path 2. will be received.

These received signals are divided into two by a distributor 19, and one pilot signal of fs+Δf (KHz) is extracted through a band pass filter 20, and this pilot signal is used as a signal for frequency conversion. In the device 4, the frequency of the other fv+Δf (KHz) audio signal is converted, and an inverted frequency signal of fs−fv (KHz) is sent to the radio transmitter.

In this way, even if a frequency shift of Δf occurs in the transmission path 2, the input signal of fv (KHz) can be converted to a frequency of fs-fv (KHz) and sent to the radio transmitter 7 without undergoing a frequency shift.

The signal transmitted by the radio transmitter is only an inverted frequency signal and does not include a pilot signal.

Therefore, in order to correct slight frequency deviations in the wireless transmission path, the band per wireless channel can be narrower compared to a method in which pilot signals are also sent on the wireless transmission path in the same way as in the wired transmission path. .

In other words, it becomes possible to effectively utilize radio frequencies.

However, the oscillator 13 for frequency conversion on the radio receiver side
Although a frequency deviation due to the difference in the oscillation frequency between the oscillator 5 and the oscillator 5 on the sending end side is unavoidable, the accuracy of these oscillators can be made sufficiently high (for example, 0.1 Hz or less), and the method of the present invention According to this method, since it is almost unaffected by frequency shifts in the transmission path, it is possible to transmit signals that require precise frequencies, such as individual selection signals.

In addition, if the transmission path from the wireless receiver 11 is a wired transmission path that requires correction of frequency deviation, after this wireless receiver 11, from the input end 17 to the low-pass filter 6 in the same way as the transmitter side. It may be configured as follows.

As explained above, the present invention makes it possible to transmit a precise frequency to any transmission path as long as the frequency deviation is within the passband of the pilot signal detection bandpass filter.
Furthermore, the band per radio channel in the radio transmission path can be narrowed, and radio frequencies can be used effectively.

Furthermore, since it has a frequency correction function and a frequency inversion function at the same time and the number of inversions can be reduced, it has the advantage of being economical and having excellent transmission frequency characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional confidential communication system, and FIG. 2 is a diagram showing an embodiment of the present invention. Reference symbols in each figure are as follows. 1... Transmission line input side, 2... Transmission line,
3... Transmission line output, 4... Frequency converter, 5... Oscillator, . 6...Low pass filter, 7...Radio transmitter, 8...
Transmitting antenna, 9...Radio transmission path, 10...
...Receiving antenna, 11... Radio receiver,
12... Frequency converter, 13... Oscillator, 14... Low pass filter, 15...
...Receiving end, output side, 16...Low pass filter,
17... Sending end input side, 18... Combiner, 19... Distributor, 20... Band pass filter.

Claims (1)

[Claims] 1 On the input side of the wired transmission line, f1 (KHz) to f2 (
f2 along with signals in the audio frequency band in the range of KHz).
(KHz) transmits a pilot signal with a higher frequency,
On the output side of the wired transmission line, the pilot signal is detected, the signal in the voice frequency band is frequency-converted using the detected pilot signal, the frequency of the voice is inverted by the frequency conversion, and the signal is transmitted wirelessly by the wireless transmitter. The method is characterized in that only a frequency-inverted signal containing no pilot signal is sent to the transmission path, and the frequency-inverted signal is received by a wireless receiver to obtain the same signal as the signal in the audio frequency band on the input side of the wired transmission path. Confidential communication method with frequency correction function.