JPH0441855B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a synchronization device in a frequency hopping system.

[Conventional technology]

Figure 2, Jatek Publishing, "Latest Spread Spectrum Communication System", written by RCDixon, November 30, 1978.
This is a wideband AGC amplifier + envelope detection method used in the synchronization device of the conventional frequency hopping communication method shown in Figures 7 and 6, published by Japan First Edition, page 246, Chapter 7. In the figure, 1 is the receiving antenna, 2
is a wideband AGC amplifier, 3 is a mixer, 4 is an IF filter, 5 is an IF amplifier, 6 is an envelope detector, 7 is an integrator, 8 is a synchronous detector, 9 is a hopping controller, and 10 is a synthesizer.

Next, the operation will be explained. A signal received from the antenna 1 is amplified to a certain level by a wideband AGC amplifier 2. This signal is mixed with the output signal of the synthesizer 10 by the mixer 3 and becomes an intermediate frequency (IF).
After being converted into a signal, the IF filter 4 removes frequencies other than the desired receiving frequency band. This signal is further
After being amplified by the IF amplifier 5 and detected by the envelope detector 6, it is integrated by the integrator 7. When this integrated value exceeds a certain threshold level, the synchronous detector 8 transfers the synchronous acquisition signal to the hopping controller. Give to 9. After receiving the synchronization acquisition signal, the hopping controller 9 shifts from the synchronization acquisition mode to the synchronization tracking mode, generates a frequency sequence equal to the frequency hopping sequence on the transmitting side, and controls the synthesizer 10 until the synchronization acquisition is completed.

[Problem to be solved by the invention]

Conventional frequency hopping synchronizers are configured as described above, so when a signal other than the desired signal wave is input from the antenna at a high level, the wideband AGC amplifier 2 instantly responds to the switching of the signal wave. Since the response speed could not be made as fast as possible, there was a drawback that the desired signal wave was suppressed.

This invention was made in order to solve the above-mentioned problem, and when an undesired signal wave of a large level is input, the signal wave of a level higher than the desired signal wave is suppressed without unnecessary suppression of the desired signal wave. It is an object of the present invention to provide a synchronization device that reduces the influence of large-level undesired signals by selectively clipping the amplitude of undesired signal waves.

[Means to solve the problem]

The frequency hopping type synchronizer according to the present invention has a limiter amplifier in the intermediate frequency stage, and after detecting the output with a linear detector, it is passed through a high-pass filter, and the desired signal is determined by the output level of the high-pass filter. This system detects the presence or absence of waves and performs synchronous detection.

[Effect]

The frequency hopping type synchronization device according to the present invention uses a limiter amplifier installed in the intermediate frequency stage to limit the amplitude of the input signal, so that when there is a desired signal wave or an undesired signal wave, the limiter amplifier itself compresses it instantly. The gain is controlled and its output is detected by a linear detector. Then, the desired signal wave, undesired signal wave, and high-frequency components that are the detection output are passed through a high-pass filter, and the presence or absence of the desired signal wave is detected based on the output level of the high-frequency component that can pass through this high-pass filter. Perform detection.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a frequency hopping synchronizer according to the present invention, and FIG. 2 is a diagram showing the time relationship between signal waveforms and gains of various parts of the present invention. In FIG. 1, numbers 1, 3 to 4, 6, and 8 to 10 are the same as in the conventional system (FIG. 3). 11 is a linear detector, 12 is a high-pass filter, 13 is a low-frequency amplifier, and 14 is a limiter amplifier. The limiter amplifier 14, the linear detector 11, and the high-pass filter 12
constitutes a noise squelch circuit.

Next, the operation will be explained. The signal received from the antenna 1 is mixed with the output signal of the synthesizer 10 by the mixer 3 and passes through the IF filter 4. The output waveform of the IF filter 4 at this time is shown in FIG. 2a.
The signal then passed through the limiter amplifier 14 is
As shown in Figure b, the amplitude is limited to a predetermined value and the amplitude modulation component is removed. The gain of the limiter amplifier 14 at this time sufficiently follows and responds to the pulsed IF filter 4 output waveform as shown in FIG. 2c. That is, when there is a desired signal wave, the gain is small, when there is no input, the limiter amplifier 14 has the maximum gain, and when there is a particularly large undesired signal wave, the gain is particularly small. Then linear detector 1
1, the high-frequency component (noise component) is extracted by the high-pass filter 12, and the waveform changes in proportion to the gain of the limiter amplifier 14 as shown in FIG. It turns out. The signal is then amplified by the low frequency amplifier 13 and then detected by the envelope detector 6. Thereafter, the signal is integrated by the integrator 7 as in the conventional example, and when this integrated value exceeds a certain threshold level, the synchronization detector 8 outputs a synchronization acquisition signal, and the hopping controller 9 receives this signal. The synchronization acquisition mode is changed to the synchronization tracking mode, a frequency sequence equal to the frequency hopping sequence on the transmitting side is generated, and the synthesizer 10 is controlled until the synchronization acquisition is completed.

In summary, during the period t1 in FIG. 2 when the desired signal wave is input from the reception antenna 1, the out-of-band noise of the high-pass filter 12 is suppressed to a low level.
During a period in which there is no signal wave, the out-of-band noise of the high-pass filter 12 is not suppressed and remains at a high level. Also, if we pay attention to the period t3 in Fig. 2 (when there is no desired signal wave and an undesired signal wave comes in), the out-of-band noise of the high-pass filter 12 is caused by the undesired signal wave existing in the intermediate frequency amplification stage. Therefore, if the time that the undesired signal wave exists in the intermediate frequency amplification stage is sufficiently short compared to the period t3, it is integrated by the integrator 7 and controlled by setting a predetermined threshold level. From the viewpoint of synchronization detection, the entire period t3 is equivalent to being at a high level.

By using the output of such a high-pass filter 12, the duration of the undesired signal wave is generally sufficiently short compared to the entire period of t3, and is equal to t1+t2.
It is even shorter than the entire period of +t3..., and synchronization detection can be performed without depending on the strength of the undesired signal wave.

〔Effect of the invention〕

As described above, according to the present invention, the frequency hopping type synchronization device is configured with a noise squelch circuit consisting of a limiter amplifier, a linear detector, and a high-pass filter, so that interference waves at a higher level than the desired signal wave can be generated. Even in the FH communication channel where there is an interference signal, it has the effect of bringing into a stable synchronization state without depending on the interference wave signal strength.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a frequency hopping synchronizer according to the present invention, FIG. 2 is a diagram showing the time relationship between signal waveforms and gains of various parts of the present invention, and FIG. 3 is a conventional frequency hopping synchronizer. 1...Receiving antenna, 3...Mixer, 4...IF
Filter, 6... Envelope detector, 8... Synchronous detector, 9... Hopping controller, 10... Synthesizer, 11... Linear detector, 12... High pass filter, 13... Low frequency amplification , 14...limiter amplifier. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1 In a frequency hopping type synchronization device,
A limiter amplifier is provided in the intermediate frequency stage, and after its output is detected by a linear detector, it is passed through a high-pass filter, and the presence or absence of the desired signal wave is detected based on the output level of this high-pass filter, and synchronous detection is performed. A frequency hopping type synchronization device featuring: