JPS59158136A - Detector for ratio of carrier to electric noise power - Google Patents

Abstract

PURPOSE:To detect C/N accurately without any influence of an IM (intermodulation product) noise by setting the passing band width of a base band band-pass filter (BPF) to such a narrow band that the influence of the IM noise due to the nonlinearity of a transmission line is not exerted. CONSTITUTION:The passing band width of the base band BPF8 is set within DELTAf so that an intermodulation product IM is not extracted, and the band is set to a narrow band so that the spread of a spectrum due to the modulation of IM is not extracted; and either of areas ( I ) and (II) shown by dotted lines is used as the passing band width. Electric noise power extracted as mentioned above except the IM noise is extremely small, so the gain of the base band BPF8 which inputs the electric noise power except the IM noise from the filter 8 should be extremely large. In this case, the base band BPF9 should have extremely high stability or is provided with an additional automatic level control function.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carrier-to-noise power ratio (hereinafter abbreviated as C/N) detector provided on the receiving side of a satellite communication system.

Conventionally, this type of C/N detector consists of an automatic gain control (abbreviated as AGO) amplifier that receives an intermediate frequency (hereinafter abbreviated as IF) band reception input signal containing a carrier wave and noise, and this AGC.
It has a local oscillator and mixer for converting the output of the IF band of the amplifier into the baseband band, and a baseband band pass filter and splitter for extracting noise from the output of the baseband band. A wide band width was used as the pass band width of the band pass filter to facilitate C/N detection. However, due to the wide passband width of the baseband bandpass filter, in the conventional C/N detector.

It is not possible to extract only the noise power, and intermodulation products (hereinafter referred to as I
(abbreviated as lvl) When the noise is large, i2 is accurately C/N.
The disadvantage was that it could not be detected.

The object of the present invention is to solve the above-mentioned conventional drawbacks.

The object of the present invention is to provide a C/N detector that can accurately detect C/N without being affected by Ilvi noise.

According to the present invention, an AGC amplifier receives an IF band reception input signal including a carrier wave and noise, and means for converting the 11° band output of the AGC amplifier into a baseband band;
In a C/1 detector having a baseband bandpass filter that extracts noise from the baseband Ili power, the passband width of the baseband bandpass filter or the nonlinearity of the transmission path A C/N detector is obtained which is characterized in that it is set to a narrow band that is not affected by the resulting IM noise.

Please refer to the following nine drawings.
1 is a block diagram showing an example of the configuration of a C/N detector applied to a C/N detector (abbreviated as C) method. In the figure, 1 is I
2 is an AOC amplifier, 6 is a distributor, 4 is an IF band narrow band pass filter, 5 is a detector, 6
7 is a local oscillator, and 8 is a baseband bandpass filter.

9 indicates a baseband amplifier, and 10 indicates a detector.

Next, the operation of the circuit shown in FIG. 1 will be explained.

The received input signal Sin in the IF band including the carrier wave and noise is I
It passes through the li'' band receiving bandpass filter 1 and the AGC amplifier 2 and is divided into two by the 9-band divider 6.Here, in the 5cpc method, an unmodulated IF band pilot signal SP is generally used;
The rc amplifier 2 is controlled so that the level of the IF band pilot signal Sp among its outputs is always constant. Therefore, one of the IF band ratio outputs divided into two by the 9-distributor 5 is
The IF band pilot signal is inputted to the band narrow band pass Il and e detector 4, and only the IM pilot signal Sp is rejected.The IF band pilot signal is passed through the detector 5, and the AGC voltage output from the detector 5 is used to convert the AC) C amplifier. By controlling 2, AGC
The signal output from amplifier 2 is
The level of the F-band pilot signal Sp is controlled to be always constant.

On the other hand, the other IF band ratio output divided into two by the two-way divider 6 is input to the mixer 6 and converted into a baseband band by the two-way local oscillator 7. Then, noise power is extracted from this baseband output SB by a baseband band pass filter 8, and this extracted noise power passes through a baseband band amplifier 9 and is input to a detector 10. den j king 5
is output as our.

Here, the biloft signal level is always kept constant by the AGO amplifier 2.

When C/N changes, the output noise of A OC amplifier 2 changes to C/N.
Since the output voltage 5out of the detector 10 also changes in response to the change in N, the change h1 in the output voltage 5Out is one to one with the C/14 change meter.
This will correspond to the following.

C/N can be detected by reading the output voltage 5out.

In FIG. 1, in the conventional C/N detector.

The passband width of the baseband bandpass filter 8 was set to a wide band because the wider the passband width 9, the greater the noise power that can be taken out as an output and the easier C/N detection.

Figure 2 shows this situation.

Referring to FIG. 2, generally in the 5CPC method.

Baseband carrier waves C are lined up for each △f.

In the vicinity of the baseband pilot signal P.

In order to perform automatic frequency control of reception using this pilot signal P, a guard band OB is provided. Therefore, in a conventional C/14 detector.

The baseband band pass 71j in FIG. 1 and the pass band width of the transducer 8 are changed to the gart band () as shown by the dotted line in FIG.
B was set as a whole, and the noise power of this guard band GB was extracted.

However, in an actual satellite loop, as shown in Figure 6,
Due to the non-linearity of the transmission path called the satellite loop, Ilvi noise exists within the Gartband ()B.
is coming down. here.

The IM positions are at intervals of Δf, but each level is constantly changing depending on the frequency of the baseband carrier c, voice activation, etc. Therefore.

Conventional C/N detectors cannot detect only noise power excluding IM noise, and cannot accurately detect C/N when the influence of IM is large.

In the present invention, do not take out ``Second Book I lvi''.

The passband width of the baseband bandpass filter 8 in Fig. 1 should be within △f, and the width of the spectrum caused by the modulation of Ilvf should also be avoided. Take this into consideration and set it to a narrow band. An example of this situation is shown in FIG.

Referring to FIG. 4, in the present invention, the area indicated by a dotted line [
Either I] or [■].

Baseband range in FIG. 1; Passage through bandpass filter 8:
;;Used as bandwidth. I extracted in this way
Since the noise power excluding M noise is very small, the I output from the baseband/output band pass i1/'3
It is necessary to considerably increase the gain of the baseband amplifier 9 to which the noise power excluding M noise is input. In this case, the stability of the baseband amplifier 9 becomes a problem, but it can be solved by using an extremely stable amplifier as the baseband amplifier 9, or by adding an automatic level control function to the baseband amplifier 9. ,” - can solve the problem of mating quality.

As is clear from the above description, according to the present invention, by setting the passband width of the baseband bandpass filter to a narrow band that does not extract IM, the

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of the configuration of a C/N detector applied to the 5CPC method, and Fig. 2 shows the passband width of a baseband bandpass filter in a conventional C/N detector. 6 is a diagram showing the 1M positional relationship caused by the non-linearity of the satellite loop, and FIG. 4 is a diagram showing the passband width of the baseband bandpass a filter in the C/N detector according to the present invention. It is a figure showing one example of this. 5...Detector, 6...Mixer, 7.Local oscillator. 8...Baseband band pass filter, 9...Baseband band amplifier, 10...Detector If2 device. Ii 1 person (71 Yu 1) Patent attorney ± fjA% Yo) r frequency

Claims (1)

[Claims] 1. An automatic gain control amplifier that receives a received input signal in an intermediate frequency band containing a carrier wave and noise, a means for converting the output of the intermediate frequency band of the automatic gain control amplifier into a baseband band, and a means for converting the output of the intermediate frequency band of the automatic gain control amplifier into a baseband band; In a carrier-to-noise power ratio detector having a baseband bandpass filter for extracting noise, the passband width of the baseband bandpass filter is equal to the intermodulation product noise caused by nonlinearity of the transmission path. A carrier-to-noise power ratio detector characterized in that it is set to a narrow band that is not affected by.