JPS60242743A - Intermediate frequency amplifier - Google Patents

Abstract

PURPOSE:To measure the transmission characteristic even if a broad band sweep signal is inputted by detecting the presence or absence of an AM component from an output of the 2nd level detecting means and providing a squelch control means not executing squelch control only when a signal with the AM component is received. CONSTITUTION:An AM dection section 13 detects the AM component appearing an output of the 2nd level detection section 10 so as to output the presence or absence of the AM component. Further, the detection section 13 has a time constant function giving an output of the presence of AM component only when the AM component is generated continuously for a prescribed time or over. A squelch control section 14 executes the same operation as a conventional squelch control section when the output of the detection section 13 has no AM component, while an output sigal transmission of a fixed gain amplifier section 5 is kept regardless of an output of the detection section 10 and the automatic gain control section 8 when the AM component exists. Thus, even if the output of the detection section 10 is zero, the transmission of the outut signal of the amplifier 5 is not blocked and the measurement of the transmission characteristic is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an intermediate frequency amplifier used in a heterodyne radio receiving device.

[Prior art]

Conventionally, in heterodyne wireless receiving equipment that takes into account the influence of unnecessary waves near the receiving frequency, when a wideband sweep signal is input to measure transmission characteristics, the output of this intermediate frequency amplifier is switched on and off. In some cases, it became impossible to measure.

FIG. 1 is a block diagram of such a conventional intermediate frequency amplifier. In the figure, 1 is a variable gain amplifier section in which variable gain amplifiers 3 to 4 are connected in series to amplify and output the input signals inputted to the input terminal 2; The variable gain amplification section 1 and the fixed gain amplification section 5 form an intermediate frequency amplification section.

Further, the output of the variable gain amplification section 1 is sent to the first level detection section 6.
．． It is also connected to the input side of the buffer amplifier section T. and,
The output of the first level detection section 6 is input to an automatic gain control section 8, and the output of this automatic gain control section 8 controls the gains of the variable gain amplifiers 3 to 4. Amplification section 7
The output of is input to a narrowband p-tech section 9 that outputs only signals in a predetermined frequency band, and the output of the narrow-band F-tech section 9 is input to a second level detection section 10. The buffer amplification section 7, the narrow band F technique section 9, and the second level detection section 10 together form a second level detection means. And the second
The output of the level detection unit 10 and the output of the automatic gain control unit 8 are input to the squelch control unit 11, and based on these two inputs, the squelch control unit 11 controls the output of the automatic gain control unit 8 to be Control is performed so that when a multi-threshold value is exceeded or when the output of the second level detection section 10 decreases, it is determined to be a squelch state and the output signal of the fixed gain amplification section 5 is prevented from being transmitted.

In the conventional intermediate frequency amplifier configured in this way,
When an input signal is input from the input terminal 2, an amplified output signal is sent from the output terminal 12, but when the following two conditions occur, the squelch control unit 11 determines the squelch state. The determination is made and the output signal of the fixed gain amplification section 5 is prevented from being transmitted.

(1) When the input level falls below the squelch level when there are no unnecessary waves near the reception frequency or when the level of unnecessary waves is low enough to cause a problem.

Since the unnecessary wave level is low, all fluctuations in the input level due to fading are absorbed by the automatic gain control section 8, and the output of the second level detection section 10 is always constant. However, when the input level falls below the squelch level, the output of the automatic gain control section 8 exceeds a correspondingly large multi-threshold value.
This time is determined to be a squelch state.

(2) When the signal wave level falls below the squelch level while the unnecessary wave level near the reception frequency is high enough to cause a problem.

The output of the first level detector 6 is proportional to the total level of the signal wave and unnecessary waves, so even if the signal wave level changes, the output of the first level detector 6 is proportional to the signal wave level. It doesn't change. Therefore, even if the signal wave level falls below the unnecessary wave level and further below the squelch level, the output of the automatic gain control section 8 will not exceed the threshold value and will not enter the squelch state.

However, since the second level detection section 10 at the output of the narrowband p-tech section 9 detects the signal excluding unnecessary wave components, its output decreases when the signal wave level becomes below the squelch level. This time is determined to be a squelch state.0 Now, suppose that a sweep signal is input to this intermediate frequency amplifier for transmission characteristic measurement. In this case, the output of the automatic gain control section 8 does not exceed the threshold value, but the output of the second level detection section 1
The zero output varies significantly as the frequency of the sweep signal varies within and out of the band of the narrowband F-tech section 9.

Therefore, the squelch control section 11 turns on and off the output of the fixed gain amplification section 5 without being able to distinguish from the case (2) described above, making it impossible to measure the transmission characteristics. In order to prevent this, it is possible to make the band of the narrowband F-technical section 9 the signal transmission bandwidth, and also set the sweep signal frequency range to the signal transmission bandwidth.
There are problems such as having to prepare a device with a different band, and also having to have a steep attenuation characteristic.

[Summary of the invention]

The present invention has been developed in view of these points, and its purpose is to provide an intermediate frequency amplifier that does not become unmeasurable even when a wideband sweep signal is input to measure transmission characteristics. It is about providing.

In order to achieve such an object, the present invention detects the presence or absence of an AM component appearing in the output of the second level detection means by an AM detection means, and only when a signal indicating the presence of an AM component is received from the AM detection means. A squelch control means for not performing squelch control is added to the squelch control section.

[Embodiments of the invention]

Hereinafter, the intermediate frequency amplifier according to the present invention will be explained in detail based on the drawings. FIG. 2 is a block diagram showing one embodiment of the intermediate frequency amplifier of the present invention. In the figure, the same reference numerals as in FIG. 1 indicate the same parts, and the explanation thereof will be omitted. 13 is the second
An AM detection section which receives the output of the level detection section 10 as an input,
The AM component appearing in the output of the second level detection section 10 is detected and the presence or absence of the AM component is output. In addition, in order to distinguish between the generation of an AM component due to fading and the generation of an AM component due to sweep signal input, the AMM output unit 13 outputs an AM component only when the AM component continues to occur for a predetermined period of time or more. It has a time constant function that outputs a certain value. 14 is a squelch control unit which receives the output of the above-mentioned AMM output unit 13 as input, and when the output of the detection unit 13 has no AM component, it operates in the same manner as the conventional squelch control unit 11, but when it has an AM component, it operates in the same manner as the squelch control unit 11. has a squelch control means that maintains the output signal of the fixed gain amplification section 5 regardless of the outputs of the second level detection section 10 and the automatic gain control section 8.

When a wideband sweep signal is input to the intermediate frequency amplifier configured in this way through the input terminal 2 in order to measure the transmission characteristics, the output of the second level detection section 10 will be similar to the conventional one, in which the frequency of the sweep signal is narrow. It varies significantly due to variations within and outside the band of the band Okigibu 9. That is, when the frequency of the sweep signal is a frequency outside the band of the narrowband P liquid section 9, the output of the second level detection section 10 becomes almost zero, and the squelch control section 14 sends out the output signal of the fixed gain amplifier section 5. to prevent Next, when the frequency of the sweep signal changes to the frequency within the band of the narrow band sweep technique section 9, the output of the second level detection section 10 returns to the original state, and the squelch control section 14
The output signal is maintained. Next, when the frequency of the sweep signal becomes an out-of-band frequency again, transmission of the output signal of the fixed gain amplification section 5 is blocked. Thereafter, this operation is repeated, and eventually the signal turns on and off repeatedly as the frequency of the sweep signal changes. However, when the repetition of the arrow continues for a predetermined time, the AMM output section 13 detects the AM component and outputs the AM component comb output to the squelch control section 14. When the squelch control section 14 receives this AM component comb output, it holds the output signal of the fixed gain amplification section 5 regardless of the outputs of the second level detection section 10' and the automatic gain control section 8.

Therefore, even if the output of the second level detection section 10 becomes zero, the output signal of the fixed gain amplification section 5 is not blocked, and various transmission characteristics can be measured. In addition, only if the AM component continues to occur for a predetermined period of time or longer, A
Since the MM output section 13 sends out the AM component comb output, it does not operate due to the generation of the AM component due to fading.

Note that the output signal from the fixed gain amplification section 5 fluctuates until it is maintained, but this can be prevented by inserting a time constant circuit between the line squelch control section 14 and the fixed gain amplification section 5. However, in this case, the reaction speed to the squelch state is limited by this time constant, and the reaction speed is extremely slow, which is not advantageous in practice. Rather, it would be advantageous to not impair the reaction speed even if some fluctuation occurs during transmission characteristic measurement.

Furthermore, when a normal signal is input to the intermediate frequency amplifier instead of a sweep signal, the output of the second level detection section 10 is always kept constant by the automatic gain control section 8. The input is always in a state with no AM component, j), and the AMM output section 13 is never activated.
The operation is the same as that of a conventional intermediate frequency amplifier.

In this way, the conventional intermediate frequency amplifier having a narrowband level detection function is provided with the AMM output section 13 for detecting the AM component, and the conventional squelch control section 11 is further provided with the fixed gain amplifier section 5.
Since a function to maintain the transmission of output signals has been added, transmission characteristics can be measured without impairing conventional functions. In addition, since the frequency change of the sweep signal is detected as an AM component by the AM detection section, there is no need to change the band of the narrowband P-tech section 9 depending on the capacity of the transmission signal, and it is suitable for most systems. However, it is also possible to deal with this problem using the same narrow band F liquid part 9.

〔Effect of the invention〕

As explained above, according to the intermediate frequency amplifier according to the present invention, the AM component is detected by the AM component detection section, and only when the AM component is continuously detected for a predetermined period of time, a signal with an AM component is output to the squelch control means. As a result, the output signal of the fixed gain amplification section is maintained, so even if a wideband sweep signal is input to measure the transmission characteristics, measurement will not become impossible.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional intermediate frequency amplifier, and FIG. 2 is a block diagram showing the configuration of an embodiment of the intermediate frequency amplifier according to the present invention. 1... Field/variable gain amplification section, 5... Fixed gain amplification section, 6... First level detection section, 1... Buffer amplification section, 8. φ... Automatic gain amplification section , 9a... narrowband F technical section, 10#... second level detection section, 13...A
M detection section, 14...Q squelch control section. Patent Applicant NEC Corporation Agent Kazubin Yamakawa (and 2 others) Figure 1

Claims (1)

[Claims] an intermediate frequency amplification section that amplifies and outputs an input signal; a first level detection section that detects the signal level of the intermediate frequency amplification section; and an intermediate frequency amplification section that detects the signal level of the intermediate frequency amplification section according to the output of the first level detection section. automatic gain control means for controlling the gain of the intermediate frequency amplification section; second level detection means for receiving the signal of the intermediate frequency amplification section and detecting only the signal level of a predetermined bandwidth; In the intermediate frequency amplifier, the intermediate frequency amplifier includes an output of the automatic gain control means and a squelch control unit that performs squelch control based on the output of the automatic gain control means, and an AM detection means for detecting the presence or absence of an AM component appearing in the output of the second level detection means. 1. An intermediate frequency amplifier comprising: a noise detection means; and a squelch control means for not performing squelch control only when receiving a signal with a JAM component.