JPH077479A - Signal generator for testing mutual modulation distortion - Google Patents

Abstract

PURPOSE:To previously check the transmission of eight waves in a BS-IF amplifier or the like can be transmitted or not by providing this signal generator with plural signal generating means for intermittently generating signals with specific frequency and a mixing means for mixing output signals from respective signal generating means with a BS-IF signal. CONSTITUTION:Four VCOs 5 generate test signals (sine waves) to be outputted by the ON/OFF of a driving power supply in each second. Four PLL circuits 6 corresponding to respective VCOs 5 stabilize the frequency of output signals by frequency division data outputted from a control data ROM 7. Output signals from respective VCOs 5 are mutually mixed by a mixing circuit 11 and a mixed signal is inputted to an amplifier 8 through a variable attenuator 3. The amplifier 8 is a high level input and high level output amplifier matched with the broadcasting level of a BS-IF (broadcasting signal) and output signals from respective VCOs 5 are amplified and then mixed with a BS-IF signal inputted from a BS converter by an AC coupling directional coupler as a test signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a BS obtained by frequency-converting satellite broadcast wave signals in satellite broadcast reception, for example.
-Intermodulation distortion test signal generator for testing intermodulation characteristics of a BS-IF amplifier that amplifies an IF signal.

[0002] Therefore, the field of use of the present invention is to provide satellite broadcasting receiving equipment, a joint receiving system in apartment housing,
It covers CATV and home co-listening facilities.

[0003]

2. Description of the Related Art There is no conventional technique for checking the intermodulation distortion of a transmission system by mixing a test signal of a current broadcast wave and a test signal of a future channel in the BS-IF band of satellite broadcasting.

[0004]

In the BS-IF joint reception facility in a condominium, intermodulation distortion is newly generated in the BS-IF amplifier every time the number of satellite broadcasting channels increases, and the reception becomes difficult. Sometimes it caused a defect. Despite the fact that the satellite broadcasting is FM system, BS at the high level like the conventional AM signal is used.
-Construction problems of transmitting IF signals are raised. On the other hand, in the actual construction, the equipment for measuring the transmission level has gradually spread, but the actual situation is not sufficient.
The final check is the image quality check on the current 4 waves. If we continue to broadcast 8 channels, BS-I
It is expected that reception failures will occur at the same time in the F joint reception facility, and it will be difficult to deal with this.

Therefore, the object of the present invention is to solve the above problems, for example, by simply comparing the image quality after the transmission of the current 4 waves with the image quality after the transmission of the future 8 waves by subjective evaluation, for example, BS. -To provide an intermodulation distortion test signal generator capable of checking whether eight-wave transmission is possible in an IF amplifier.

[0006]

In order to achieve the above object, the present invention provides a plurality of signal generating means for intermittently generating a signal having a frequency near the center frequency of a plurality of channels not broadcast in the BS-IF signal band. And mixing means for mixing the output signals from the plurality of signal generating means with the BS-IF signal.

Further, the present invention is preferably characterized in that the mixing means has means for adjusting the levels of output signals from the plurality of signal generating means.

More preferably, the means for sweeping the frequency of the output signals from the plurality of signal generating means at a predetermined speed or more, and the level of the output signals from the plurality of signal generating means in a peak hold line of a predetermined spectrum. And a means for controlling so as to match.

[0009]

According to the present invention, for example, four BS-IF signals obtained by subjecting the existing satellite broadcast wave signal to low frequency conversion and a test signal (carrier wave of BS-IF band corresponding to an empty channel generated every one second, for example) Only) Mixing with 4 waves, eg BS
-Transmit to IF joint reception facility. As a result, if there is intermodulation distortion, a signal will appear intermittently (every 1 second) on the screen, so it will be possible to identify the problematic facility only by checking the image quality without a measuring instrument. On the other hand, it becomes possible to simulate the transmission state of eight satellite broadcast waves to be used in the future and subjectively evaluate the intermodulation distortion in the receiving equipment when receiving the satellite broadcast wave signals to be used in the future.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A BS-IF signal generator according to an embodiment of the present invention will be described with reference to FIG.

This device is arranged between the BS antenna (BS converter) and the head end of the joint reception facility, and the input terminal 1 has a BS antenna, that is, a B antenna.
Connect the output cable from the S converter to output terminal 2
Is connected to the headend input terminal of the joint reception facility. Since the input terminal 1 and the output terminal 2 pass DC,
The S converter receives power from the head end and operates under the same conditions as before the insertion of this unit.

Broadcast wave signal (BS-
The IF signal) is mixed with the test signal generated by this device and input to the head end. The variable attenuator 3 can attenuate the level of the test signal generated by the device with a uniform attenuation amount in the range of 65 to 80 dB to a desired level.

The timer circuit 4 has a function of turning on / off the direct current power source generated by the power source circuit 10 by an electronic relay device every one second, and directly applies it to the VCO 5 as a driving power source for the four VCOs 5. The four VCOs 5 generate a test signal (sine wave), which is an output, every 1 second by turning on / off the driving power supply. The oscillation frequency of each VCO 5 is 1.04948 GHz (ch-1), which is obtained by converting each channel into BS-IF, 1.08784.
GHz (ch-3), 1.27964 GHz (ch-1
3) and 1.31800 GHz (ch-15), and the error is within ± 300 kHz. The error is ±
The reason for setting the frequency within 300 kHz will be described later ((3) Frequency accuracy).

For future channel changes, the VCO
5 can be dealt with by changing the control data ROM 7 and the control data ROM 7. The VCO 5 has a frequency variable range of about 2
By narrowing the frequency to 1 MHz (center frequency ± 1 MHz), the frequency pull-in after power-on is prevented from deviating, and the time required for stabilization is shortened. 4 Ps corresponding to each VCO
The LL circuit 6 can stabilize the frequency of the output signal by the frequency division ratio data of the control data ROM 7. The time required for the stabilization is 0.
It was possible within 3 seconds.

The output signals of the respective VCOs 5 are mixed by the mixing circuit 11, and are mixed via the variable attenuator 3 into the amplifier 8.
Entered in. The amplifier 8 is for adjusting the broadcast wave level of the BS-IF and is a high-level input and high-level output amplifier. The output signal from each VCO 5 is amplified, and then the broadcast wave signal (BS-IF) from the BS converter is used as a test signal by the AC coupling directional coupler 9.
Signal). The insertion loss of the test signal in the directional coupler 9 is about 20 dB.

In this example, the timer circuit 4 is configured to turn on and off every second, but without being limited to this, the timer circuit 4 is turned on and off with a time constant such that the four-wave state and the eight-wave state can be alternately compared. Of course, all you have to do is do it. Further, of the subjective evaluation of image quality, the evaluation of the SN ratio is as follows.
It is very difficult to accurately evaluate a slight difference in SN ratio at different points in time and place. However, the determination as to whether the image quality is relatively good or bad with respect to a certain SN ratio serving as a reference does not change can be compared to some extent accurately if the image quality is switched in the same place in a short time. Utilizing this fact, the entire receiving screen was alternately switched to demodulation in the 4-wave state and demodulation in the 8-wave state, and an interval of several seconds was optimally evaluated and an experiment was conducted to see if the intervals could be distinguished.
Detecting noise and waiting for noise in the next state is one cycle, and if it is 2 seconds or more, the next state cannot be waited, which is often inappropriate. Further, it was found from the visual characteristics that the entire screen is alternately switched between the four-wave state and the eight-wave state for less than 1 second as in the present embodiment, it is difficult to detect low-level noise.

Next, the accuracy of this device will be described.

(1) Quality of test signal In intermodulation distortion between BS and IF signals generated in an amplifier, a distortion product generated between carriers having the highest level in a channel is dominant. Therefore, the test signal may be only a sine wave serving as a carrier wave. Of course, each test signal may be FM-modulated on the input side of the mixing circuit 11.

Further, the CN ratio is 27 dB or more (noise bandwidth is 27 MHz), and the spurious characteristic is − within the BS-IF band.
50 dB or less is secured.

(2) Generation and Level of Intermodulation Distortion of Amplifier in BS-IF8 Wave FIG. 2 shows an input / output characteristic diagram of a general amplifier. In an actual joint reception facility, amplifiers are connected in cascade, but for simplicity, if the gain gain and transmission loss are equal, the total characteristics can also be represented in FIG. In the same figure, the upper curve shows the input / output characteristics of the fundamental wave, and in the area A, the slope is a line. Also, the lower curve in the figure is the characteristic of the third-order distortion with respect to the input, and in the area A, it becomes a line with a slope of 3. Of these, the region where the input / output relationship is linear is A, the region near saturation is B, and the saturated region is C.

Assuming that the levels of the BS-IF channels are all equal and input to the amplifier within a specified value, the third-order distortion has characteristics in the area A of FIG. That is,
If the input level of 8 waves is increased by 1 dB, the third-order distortion will be 3 d.
B becomes larger and the DU ratio deteriorates by 2 dB. Conversely, if the input level of 8 waves is lowered by 1 dB, the third-order distortion will be reduced by 3 dB, and the DU ratio will be improved by 2 dB.

This device mixes a broadcast wave signal (BS-IF signal) with a test signal to generate a broadcast wave signal (BS-IF signal).
Since a mixer passage loss of 1 dB occurs on the (IF signal) side,
In order to obtain a true DU ratio in the future, it is desirable to adjust the variable attenuator 3 and transmit the test signal (output of the amplifier 8) at a level slightly higher than the broadcast wave signal. In the following, this will be described in detail by taking the case of raising it by 1 dB as an example.

The spectrum on the left side of FIG. 3 shows the true desired wave level of ch-7 or ch-9 and the future true third-order distortion (one wave) level when this device is not used. This difference is the true DU ratio for one distorted wave.

The spectrum on the right side of FIG. 3 shows that the levels of ch-5, 7, 9, and 11 are ch by using this device.
Ch-7 when 1 dB smaller than -1, 3, 13, 15
Alternatively, it is the level of the desired wave of ch-9 and the generated third-order distortion. The level of the third-order distortion is the combination of frequencies that create distortion that falls into the channel (see Table 1 below).
1 dB within the range of -3 to 0 dB depending on the number of channels of broadcast waves included in ch-7 or ch-9).
Occurs in steps. (Figure 3)

[0025]

[Table 1]

Table 1 shows the channel number and the channel number of the third-order distorted wave generated in each channel during BS-IF8 wave transmission.

Here, the relationship between the channel number and the frequency will be described. The frequency of each wave that causes third-order distortion is a, b,
If c, the frequency of the third-order distortion is represented by a + bc. For example, the distortion that falls on ch-1 due to ch-3, ch-5, and ch-7 signals is

[0028]

[Equation 1]

It becomes Also, this calculation can be substituted for the calculation for each channel number, so (the formula is 3 + 5-
(7 = 1 is substituted) In Table 1, all are represented by calculation by channel number.

In Table 1, (ch-1, 3, 13, 15)
Is a channel that is currently free and will be broadcast in the future. According to this combination, the channel where the influence of the third-order distortion is the largest (the wave number of the distortion is large) is located in the center ch-7.
Or, since it is ch-9, when 8 waves can be received at almost the same level, these two channels should be checked.

In Table 1, when considering the combination of the channel distortions of ch-7 or ch-9 divided into the broadcast wave signal and the test signal, none of the test signals are generated by three waves, and the test signal of two waves is broadcast. Eight waves generated by one wave, one test signal, five waves generated by two broadcast waves,
It can be seen that two waves are generated by three waves of broadcast waves. These levels are 0, -1, -2, and -3 dB in order based on the true strain level.

It is known that when the distortion product is obtained from a plurality of distorted waves, the power sum is adopted because the phase of each distorted wave is random.

The distortion product when n waves are generated at the same level (adB) is a value obtained by adding the electric powers of the n waves, and is a + 10 log (n) [dB]. Therefore, the true third-order distortion product of 15 waves is a + 10log (15) = a + 11.76 [dB].

When they occur at different levels, the difference from the reference level is corrected to a true value, and the power is added according to the wave number to be the addition amount to the distortion product. For example, a-1
If there are 8 waves at the level of [dB], then a + 10log (8.
10 ^-1/10 ). Actually, a-1, a-2, a-
Since 3 [dB] waves generate 8, 5 and 2 waves,

[0035]

[Number 2] ^{a + 10log (8 · 10 -1/10} +5 · 10 -1/20 +2 · 10 -1/30) = a + 10.22 a [dB].

Therefore, comparing the true strain product with the strain product when this device is used, the true strain product is 10 log15, that is, 11.log for the strain level of one wave.
Compared to 76 dB being added, when using this unit, 10 ^log (8 · 10 ^−1/10 + 5 · 10 ^−2/10 +
2 · 1 ^−3/10 ), that is, 10.22 dB is added. This difference is 1.54 dB, and since the desired wave is lowered by 1 dB, the DU ratio is 0.54 dB, which is practically negligible.

Since the output C is in a saturated state in the operating region of FIG. 2, a slight fluctuation of the input signal does not affect the amount of distortion. The operating area B is in the middle of A and C, and in the area of A with the largest error, DU is applied by the above method.
If the ratio has an error of 0.54 dB, the area of B becomes less than this value.

Therefore, the test signal is set to 1 rather than the broadcast wave.
The DU ratio obtained by increasing the dB is less than 0.54 dB with respect to the true DU ratio in the future in all the operation regions of the amplifier including the head end.

(3) Frequency accuracy The frequency accuracy of the test signal is within ± 300 kHz, but considering that the frequency spread signal of ± 300 kHz is added to the broadcast wave, the test signal is always an intermediate value of the video signal. Is present in the range where frequency is spread, and it can be considered practically equivalent to the behavior of the true intermodulation distortion product in the future, and therefore it can be practically used.

FIG. 4 shows another embodiment of the present invention. In this embodiment, a more accurate simulation can be obtained by the configuration shown below. 4, those parts which are the same as those corresponding parts in FIG. 1 are designated by the same reference numerals. The four sweep voltage generating circuits 12 are VCO
A sawtooth wave voltage is generated so that the frequency range of 5 becomes 27 MHz width which is the regulation of the broadcast wave, and is input to the VCO 5. The frequency of this sawtooth wave is 60Hz and 4 VCOs
A phase difference is added between the sawtooth waves so that 5 can sweep independently of each other.

A modulation circuit and a bandpass filter are indispensable for actually FM-modulating a test signal in a 27 MHz width. If these are used, four VCOs are required for each VCO, which increases the circuit scale. Therefore, by sweeping the carrier wave of the test signal in accordance with the peak hold line of the standard spectrum of the broadcast wave signal (BS-IF signal), it is possible to simulate the intermodulation distortion equivalent to the actual broadcast wave signal.

If the sweep signal from the sweep voltage generating circuit 12 is 60 Hz or higher, the intermodulation distortion product in which the power is added for each wave number is close to the true behavior. Moreover, by tracing the envelope of the standard spectrum, the frequency change of the intermodulation distortion becomes close to the actual behavior of the spread spectrum signal and the video signal. Further, from the visual afterimage characteristic, if it is 60 Hz or more, the noise level after demodulation has the same effect as in the true state.

Reference numeral 13 is a broadcast wave signal (BS-IF) obtained by modulating the output signal level of each VCO 5 with, for example, a color bar signal.
The four level control circuits are controlled so as to match the peak hold line of the frequency spectrum of the (signal), and the repetition timing thereof is input from the sweep voltage generation circuit 12. The output signals from the level control circuits 13 are mixed by the mixing circuit 11,
It is supplied to the high-speed switching circuit 14 via the variable attenuator 3 and the amplifier 8, is switched at high speed here and is intermittently supplied to the directional coupler 9, and is used as a test signal for a broadcast wave signal (BS-IF signal) from the BS converter. ) Is mixed.

The high-speed switching circuit 14 turns on / off the test signal input here by 120H.
This is done at the frequency of z, so that when the signal from the output terminal 2 mixed with the test signal is demodulated by the BS receiver (via the joint reception equipment etc.), about half of the vertical direction of the screen is The screen in which the test signals are mixed, and the other half is the screen in which only the current broadcast wave signal is transmitted, and both can be simultaneously compared in one screen.

[0045]

The intermodulation distortion amount can be estimated only by the test signal in the vicinity of the center frequency of the BS-IF signal corresponding to each vacant channel instead of the future broadcast wave. The circuit for that is simple and lightweight. Furthermore, the results can be obtained visually without a measuring instrument, so that it can be easily used, for example, by the construction personnel of the joint reception equipment.

As a result, the substantial improvement work was carried out by
Since the wave service can be started earlier than the start time, it is possible to avoid the temporary confusion that is concentrated in the future and improve the technical level of the construction related industry as a whole.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing input / output characteristics and third-order distortion characteristics of an amplifier.

FIG. 3 is a diagram illustrating a comparison of the amount of third-order distortion generated by a test signal and a broadcast wave signal (BS-IF signal).

FIG. 4 is a block diagram of another embodiment of the present invention.

[Explanation of symbols]

 3 Variable attenuator 4 Timer circuit 5 VCO 6 PLL 7 PLL control data ROM

Claims (3)

[Claims] 1. A plurality of signal generating means for intermittently generating signals of frequencies near the center frequencies of a plurality of channels not broadcast in the BS-IF signal band, and output signals from the plurality of signal generating means. A signal generator for intermodulation distortion test, comprising: mixing means for mixing with a BS-IF signal. 2. The intermodulation distortion test signal generator according to claim 1, wherein said mixing means has means for adjusting the levels of output signals from said plurality of signal generating means. 3. The means according to claim 1, further comprising means for sweeping the frequencies of the output signals from the plurality of signal generating means at a predetermined speed or higher, and levels of the output signals from the plurality of signal generating means. And a means for controlling so as to match the peak hold line of the spectrum of 1.