JPS5855456B2 - C/N measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a C/N measuring device for measuring the ratio of carrier level C to noise level N of an external input signal.

Conventionally, there has been a C/N measuring device having a frequency tracking function as shown in FIG.

In this figure, a frequency mixer 1 applies an external input signal to one input terminal, and applies the output of a variable local oscillator 5 to the other input terminal to generate an intermediate frequency signal f.

Outputs 1. The phase difference detector 3 receives the intermediate frequency signal f at one input terminal.

1, and the frequency signal output from the reference oscillator 2 is added to the other input terminal for phase comparison, and the output of the difference is fed back to the variable local oscillator 5 via the filter 4 for phase synchronization.

The filter 4 changes the frequency of the external input signal applied to the frequency mixer 1 at a high speed, for example, 4MHz/3m5 (when measuring the C/N of satellite communication, the carrier wave is changed, for example, to suppress the influence on the terrestrial line. Control frequency 150Hz,
It is configured to ensure phase characteristics up to about 60 MHz in order to achieve phase synchronization with a sweep width of 4 MHz.

Therefore, the output frequency of the reference oscillator 2 is also approximately 60KHz.
I have to do more than that.

The demultiplexer 6 uses the intermediate frequency f output from the frequency mixer 1.
.

1 is received and separated into a carrier component c (=f01) and a noise component N (>fot).

Carrier component element. For example, C/H6 (C/H6 per IHz)
N) To separate errors of 0.02 dB or less in a range of -70 aB or more, the carrier extraction bandwidth of the demultiplexer 6 should be set to 25K.
It needs to be below Hz.

For this reason, if the limit of the BPF of the duplexer 6, for example, by LC, is set to 20% or more of the fractional band, the carrier extraction center frequency, that is, the output frequency of the reference oscillator 2, must be kept to 125 KHz or less.

Considering the phase characteristics of the filter 4 and the carrier extraction error of the duplexer 6 mentioned above, for example, the output frequency of the reference oscillator 2 is set to 100 KHz, and the carrier wave extraction bandwidth of the duplexer 6 is set to 100 KHz.
Set to KHz±10KHz.

In addition, the noise extraction bandwidth of the duplexer 6 is set to 0.6 MHz, for example.
Set to ~1.4 NHZ.

The level ratio detector 7 receives the carrier wave component and the noise component outputted from the branching filter 6 and determines the carrier wave level C of the external input signal.
Detect the noise level N ratio.

An indicator 8 receives the output of the level ratio detector 7 and indicates the C/N of the external input signal applied to the frequency mixer 1.

However, in such a conventional example, the output frequency of the reference oscillator 2 cannot be made very high, about 100 KHz, compared to the frequency of 60 KHz that ensures the phase characteristics of the waveform generator 40. Frequency signal f.

1 and its harmonic components are not completely attenuated by the filter 4 and are applied to the variable local oscillator 5.

Therefore, the variable local oscillator 5 operates in a frequency modulating manner using this harmonic component, etc., and generates the intermediate frequency signal f of the frequency mixer 1.

Waveform distortion occurs in 1. This distortion component, ie, the intermediate frequency signal f.

1 (100 KHz) falls within the noise extraction band 1 of the duplexer 6, which causes a measurement error when the ratio of the carrier level C to the noise level N is large.

This invention was made in view of the above problems.
The frequency of the intermediate frequency signal applied to the phase difference detector is generated separately from the frequency of the intermediate frequency signal applied to the splitter,
Furthermore, the objective is to provide a C/N measuring device with less measurement and determination errors by suppressing waveform distortion generated in the phase-locked loop by selecting a frequency sufficiently higher than the frequency of the intermediate frequency signal applied to the duplexer.

This invention will be explained below.

FIG. 2 shows a first embodiment of the invention.

In this figure, the first frequency mixer 9 applies an external input signal to one input terminal, adds the output of the variable local oscillator 5 to the other input terminal, and outputs a 'first intermediate frequency signal f1. .

The reference oscillator 10 generates the same frequency as the first intermediate frequency f1 with good frequency stability, for example, 10
It consists of a MHz crystal oscillator.

The phase difference detector 11 receives the reference frequency signal of the reference oscillator 100 and the first intermediate frequency signal f1 output from the first frequency mixer 9, compares the phases thereof, and outputs the signal.

The filter 12 secures phase characteristics up to about 60 KHz, and receives the output of the phase difference detector 11 and removes the first intermediate frequency signal f1 and its harmonic components contained in this output, and then changes the output. It is fed back to the local oscillator 5.

The local oscillator 13 has good frequency stability, for example, 9.9M.
It consists of a Hz crystal oscillator.

The second frequency mixer 14 adds the first intermediate frequency signal f1 outputted from the first frequency mixer 9 to one input terminal, adds the local oscillator 130 frequency signal to the other input terminal, and receives the first intermediate frequency signal f1 output from the first frequency mixer 9. A second intermediate frequency signal f2 smaller than the intermediate frequency signal f1 is output.

The splitter 15 receives the second intermediate frequency signal, f2, and divides it into a carrier wave component.

and a noise component element N.

In this case, it is assumed that fc is selected so that f2, f2 x fN<fl.

Note that 7 and 8 are the same as in FIG.

Here, if the first intermediate frequency signal f1 is 10 MHz and the local oscillator 130 frequency is 9.9 MHz, then
The second intermediate frequency signal f2 output from the second frequency mixer 14 is 100 KHz.

Furthermore, the output of the phase difference detector 11 includes the first intermediate frequency signal f, -10 MHz and its harmonic components;
Since it is attenuated by the filter 12, no waveform distortion occurs in the first intermediate frequency signal f 1 =10 MHz of the first frequency mixer 9.

That is, no waveform distortion occurs in the second intermediate frequency signal f2-100KH2 of the second frequency mixer 14.

Even if distortion occurs in the first intermediate frequency signal f1, the
z and its harmonic components do not fall within the noise extraction band of 0.6 MHz'-1.4 MHz of the duplexer 15.

FIG. 3 shows a second embodiment of the invention.

In this figure, the second frequency mixer 17 has one input terminal connected to the first frequency mixer 17.
The first intermediate frequency signal f output from the frequency mixer 9 of
I' and the local oscillator 130 frequency signal is added to the other input terminal to generate a first intermediate frequency signal f, a second intermediate frequency signal f, which is greater than '
It outputs an intermediate frequency signal f2'.

The phase difference detector 18 receives the reference frequency signal of the reference oscillator 100 and the second intermediate frequency signal f2' which is also output from the second frequency mixer 17, compares the phases thereof, and outputs the signal.

The filter 19 receives the output of the phase difference detector 18, removes the second intermediate frequency signal f2' contained in this output and its harmonic components, and returns the output to the variable local oscillator 5.

The splitter 20 receives the first intermediate frequency signal 1, / and separates it into a carrier wave acid efc and a noise component N.

In this case, f□= f1', f1'< f N
< f 2'.

Here, the first intermediate frequency signal 1, / is 100KHz
If the frequency of the local oscillator 13 is 1.9MHz,
The second intermediate frequency signal f2' output from the second frequency rationalizer 17 is 2 MHz.

Therefore, the output of the phase difference detector 18 contains the second intermediate frequency signal f2'-2 MHz and its harmonic components, but since they are attenuated by the filter 19, the second intermediate frequency signal f2'-2MHz and its harmonic components are attenuated by the filter 19. No waveform distortion occurs in the first intermediate frequency signal f,'=100 KHz.

Even if distortion occurs in the intermediate frequency signal f1',
MHz and its harmonic components do not fall within the noise extraction band 0, 6 ME (z~1.4 MHz) of the duplexer 20.

As explained above, in this invention, the intermediate frequency signal applied to the phase difference detector is set separately from the intermediate frequency signal applied to the splitter, and the value is selected to be sufficiently larger than the intermediate frequency signal applied to the splitter. Since the circuit configuration is designed to suppress the waveform distortion generated in the phase-locked loop, the variable local oscillator does not operate in a frequency modulating manner and causes waveform distortion in the intermediate frequency signal applied to the duplexer. Never.

Further, even if waveform distortion occurs, the intermediate frequency signal and its harmonic components applied to the phase difference detector are outside the noise extraction band of the duplexer, so it does not affect the noise level.

Therefore, there is an effect that the C/N can be measured with less measurement error.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a conventional C/N measuring device, Figure 2 is a block diagram showing a conventional C/N measuring device.
The figure is a block diagram showing a first embodiment of the invention, and FIG. 3 is a block diagram showing a second embodiment of the invention. In the figure, 9 is a first frequency mixer, 10 is a reference oscillator, 1
1 and 18 are phase difference detectors, 12 and 19 are filters, 13 is a local oscillator, 14 and 17 are second frequency mixers, 15.
20 is a duplexer.

Claims (1)

[Claims] 1. a variable local oscillator; a first frequency mixer for receiving the output of the variable local oscillator and an external input signal and outputting a first intermediate frequency signal f1; a local oscillator; ; the frequency signal of this local oscillator and the first intermediate frequency signal f
a second frequency rationalizer for receiving the frequency signal of the reference oscillator and the first intermediate frequency signal f1 and outputting the second intermediate frequency signal f2; a phase difference detector for comparison and output; the output of this phase difference detector is received, and the output obtained by removing the first intermediate frequency signal f1 and its harmonic components contained in this output is sent to the variable local oscillator; a filter for feeding back the second intermediate frequency signal f2; a branching filter for receiving the second intermediate frequency signal f2 and separating it into a carrier component component c and a noise component component N; a carrier component component c of this branching filter; and a level ratio detector for receiving a noise component element N and detecting a carrier level to noise level ratio of the external input signal. However, f2<fl, fc=f2, and f2<fN<fl are selected. 2 a variable local oscillator; a first frequency mixer for receiving the output of this variable local oscillator and an external input signal and outputting a first intermediate frequency signal f1'; a local oscillator; a frequency signal and the first intermediate frequency signal f
a second frequency mixer for receiving the frequency signal of the reference oscillator and outputting the second intermediate frequency signal f2'; a reference oscillator; a phase difference detector for receiving, comparing phases, and outputting;
a filter for receiving the output of the phase difference detector and feeding back the second intermediate frequency signal f2' and its harmonic components included in the output to the variable local oscillator; a carrier component element receiving the first intermediate frequency signal f1'; and a noise component N; a level for receiving the carrier wave component O and the noise component N of the duplexer and detecting the carrier level to noise level ratio of the external input signal; A C/N measuring device equipped with a ratio detector. However, f2'>f1', fc: f1', fl<fN
<f2' shall be selected.