JP2908683B2 - Booster for receiving television broadcast signals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a booster for amplifying a television broadcast signal and supplying the amplified signal to a television receiver. In particular, an amplifier is provided outdoors, and a power supply for this amplifier is provided indoors. To be separated.

[0002]

2. Description of the Related Art Hitherto, there has been an isolated booster as described above in which an input attenuator and a manual gain adjustment circuit are provided in an amplification section installed outdoors. After installing such a booster, first check the screen of the television receiver to see if there is any reception failure,
If a failure has occurred, whether the cause is due to the input level over in the amplification unit or the input level over in the receiver is determined by adjusting the input attenuator or manual gain adjustment circuit of the amplification unit outdoors. ,
Judging from the state of the screen of the receiver, the input attenuator and the manual gain adjustment circuit have been appropriately adjusted.

[0003]

However, there has been a problem that the above-mentioned adjustment cannot be accurately performed unless a person having a certain level of electrical knowledge and experience performs the adjustment. In addition, to perform the above-mentioned work, a person who adjusts the outdoor amplification unit and a person who is near an indoor receiver and checks the state of the screen on the receiver and informs the outdoor worker. At least two people are required, and there is also a problem that the operation cost is high. It is also possible for one worker to go back and forth between indoors and outdoors, but in that case, there is a problem that efficiency is poor and much time is required. In addition, the outdoor amplifying unit is generally installed at a high place directly below the antenna, such as a rooftop, and there is a problem that the adjustment operation itself involves danger.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a separated television having an amplifying unit installed outdoors and a power supply unit installed indoors. In the booster for receiving a broadcast signal, the amplification unit includes:
Gain adjusting means for supplying a plurality of television broadcast signals and adjusting the gain in accordance with the gain control signal; level detecting means for detecting the level of an output signal of the gain adjusting means; and input to the gain adjusting means Signal generating means for generating reference signals having different values corresponding to different wave numbers of the television broadcast signal to be transmitted, selecting means for selecting one of the reference signals having different values, and selecting means for selecting the reference signals. Control means for generating the gain control signal in accordance with the reference signal and the output signal of the level detection means. Further, a means for manually adjusting the level of the output signal of the amplifying unit transmitted indoors may be provided indoors.

[0005]

In general, the upper limit of the maximum output level of the gain adjusting means is set by a distortion component appearing in the output signal. Although there are various types of distortion components, the third-order intermodulation component and the intermodulation component are very important factors in defining the output level of the booster. These two distortion components also have a large change amount. The interference ratio of these distortion components worsens in inverse proportion to the square of the output level. The intermodulation component and the tertiary intermodulation component are affected by the wave number of the television broadcast signal supplied to the gain adjusting means. Therefore, in the present invention, reference signals corresponding to different wave numbers are generated by the reference signal generation means, and among these, a reference signal corresponding to a wave number close to the wave number currently input to the gain adjustment means is selected by the selection means. The gain of the gain adjusting means is controlled based on the reference signal thus obtained. Such automatic gain control
Since the amplification is performed inside the amplification section outdoors, the maximum output level with respect to distortion can be maintained in this amplification section, and it is unnecessary to adjust the input level over the amplification section.

[0006]

FIG. 1 shows an embodiment of the present invention. The booster of this embodiment is of a power supply separated type, in which the amplification unit 2 is provided outdoors and the power supply unit 4 is provided indoors. Amplifier 2
The multi-wave television broadcast signal supplied to the input terminal 5 is amplified by the amplifying unit 2, transmitted to the power supply unit 4 via the coaxial cable 6, and supplied from this to a television receiver (not shown). . The operating power for operating the amplifying unit 2 from the power supply unit 4 is supplied by the coaxial cable 6.
Is supplied to the amplifying unit 2 via the.

[0007] The amplification section 2 adjusts the level of a plurality of television broadcast signals supplied from the input terminal 5 to a gain adjustment means 7.
Adjust by The gain adjustment means 7 is a cascade connection of a wideband amplifier 8, a variable attenuator 9 and a wideband amplifier 10 capable of amplifying a plurality of television broadcast signals.
The amount of attenuation of the variable attenuator 9 is changed based on a gain control signal described later.

The output signal of the gain adjusting means 7 is supplied to the power supply unit 4 via the one-branch device 12, the DC blocking capacitor 13, the output terminal 14, the coaxial cable 6, and the input terminal 16. Further, the output signal of the gain adjusting means branched by the one-branch unit 12 is amplified by the wideband amplifier 18 and then supplied to the detector 20, where wideband detection is performed. This detection voltage is supplied to a control means, for example, a voltage comparison circuit 2.
2 is supplied.

The voltage comparison circuit 22 is supplied with a reference voltage via a selection means, for example, a changeover switch 24.
The changeover switch 24 includes a contact 24a, contacts 24b, 24
c, 24d, and the contact 24a is manually connected to any of the contacts 24b, 24c, 24d. The contacts 24b, 24c and 24d are supplied with reference values of different values generated by reference signal generating means, for example, a reference voltage generating circuit 26.

The contact 24b is supplied with a high reference voltage used when, for example, a four-wave television broadcast signal is supplied to the input terminal 5, and the contact 24c is supplied with a six-wave television broadcast signal. An intermediate reference voltage used in such a case is supplied, and a low reference voltage used when eight television broadcast signals are supplied is supplied to the contact point 24d.

The voltage comparison circuit 22 compares the detection output detected by the detector 20 with one of the reference voltages supplied through the changeover switch 24, and makes the output level of the gain adjusting means 7 equal to the reference voltage. Thus, the amount of attenuation of the variable attenuator 9 is adjusted.

As described above, the output signal of the gain adjusting means 7 whose gain has been adjusted is supplied to the one-branch device 12, the DC blocking capacitor 13, the output terminal 14, the coaxial cable 6,
The power is supplied to the power supply unit 4 via the input terminal 16, and is supplied to the output terminal 30 via the DC blocking capacitor 26 and the manual variable attenuator 28 in the power supply unit 4, and is supplied to a television receiver (not shown). Is done.

A power supply circuit 32 for stepping down a commercial AC voltage is provided in the power supply unit 4, and the stepped-down voltage is supplied via a high-frequency blocking coil 34, an input terminal 16, a coaxial cable 6, and an output terminal 14. And supplied to the amplification unit 2,
In the amplifying unit 2, the DC power is supplied to the rectifying / smoothing circuit 38 via the high-frequency blocking coil 36, and the DC power obtained here is used for the wideband amplifiers 8, 10, 18,
The reference voltage generation circuit 26 and the like are driven.

The most significant feature of this embodiment is that the value of the reference voltage can be selected according to the wave number of the television broadcast signal supplied to the input terminal 5. The upper limit of the maximum output level of the amplifier 2 is set by a distortion component appearing in the output signal. In a booster for receiving a television broadcast, the third-order intermodulation component and the intermodulation component among the distortion components are very important factors for defining the output level. The third-order intermodulation components and the intermodulation components also have a large variation with respect to a variation in the output level of the amplifier 2. For example, the increase in the output level of the amplifier 2 is αd
B, the increase of the two distortion components is twice 2α dB.
Becomes That is, the interference ratio of these two distortion components worsens in inverse proportion to the square of the output level.

For example, if the number of received signal waves is n, the intermodulation component is:
It increases in proportion to (n-1). That is, 20 log (n-
1) Increase by dB. Actually, since the modulation contents are different, the rate of increase is smaller than this, and about 10 log (n-
1) It is about dB. In any case, as the number of received signal waves increases, the cross-modulation component increases.

Further, when the frequency of the third-order intermodulation distortion component is arranged at equal intervals as in a television broadcast signal, the amount of the increase in the amount of distortion is 20 l when the number of received signal waves is n.
og (n-1), but considering the frequency accuracy of the carrier of the television broadcast signal, the increase is about 10 l.
og (n-1) dB. In any case, as the number of received signal waves increases, the third-order intermodulation component distortion increases.

Therefore, although the wave number of the television broadcast signal supplied to the input terminal 5 is set to n and the gain of the gain adjusting means 7 is set, the signal is supplied to the input terminal 5 of the amplifier 2 when actually used. The wave number of the television broadcast signal is m
When (m> n), if the gain of the gain adjusting means 7 is kept as it is without changing the value of the reference voltage, the interference ratio of the distortion component is inversely proportional to the square of the output level as described above. Getting worse. Therefore, it is necessary to lower the output level of the gain adjusting means 7. The extent to which it is lowered is represented by Equation 1.

(1/2) {10log (n-1) -10log (m-1)} = 5log {(m-1) / (n-1)}

In this embodiment, as described above, four waves, six waves
By selecting a reference voltage close to the wave number of the television broadcast signal actually supplied to the input terminal 5 by the changeover switch 24, the reference voltage of the amplifying unit 2 is always maintained. The output level can maintain the maximum output level with respect to distortion. That is, the maximum output level can always be maintained by selecting and designing the reference voltage value in advance so as to lower the output level by the value of Equation 1 according to the wave number of the received television broadcast signal.

In addition, since the gain in the amplifier 2 is controlled automatically, the output signal level of the amplifier 2 becomes constant even if the level of the input signal supplied to the input terminal 5 fluctuates. The obtained image can be obtained.

Further, even if a new television broadcasting station is opened after the installation and adjustment once, and the number of reception waves increases, the set reference voltage value is within the number of reception television broadcast signal waves. The value of the detection voltage at 20 is
That is, the output level of the amplifying unit 2 decreases to a value represented by Equation 2 as a calculated value.

20 log 数 (m + x) / m｝ dB where m is the wave number of the received television broadcast signal at the time of setting,
x is the increasing wave number. However, actually, the phases of the received television broadcast signals do not completely coincide with each other, so that the values are reduced to values that can be approximated by Expression 3.

[Equation 3] 15 log ｛(m + x) / m｝ dB

This decrease in the output level is larger than the decrease in the output level due to the equation (1) required when the number of television broadcast signals increases, and even when the number of received television broadcast signals increases, a failure occurs in the image. do not do.

In this embodiment, a manual variable attenuator 28 is provided in the power supply unit 4. The output level of the amplifier 2 is also set on the assumption that the output signal of the amplifier 2 is supplied to the power supply 4 via a coaxial cable of a predetermined length. However, in practice, the output signal of the amplification unit 2 may be supplied to the power supply unit 4 with a length shorter than a predetermined length. In such a case, if a signal is supplied from the output terminal 30 of the power supply unit 4 to the television receiver as it is, an input level over on the input side of the television receiver may occur and an image failure may occur. To prevent this, a manual variable attenuator 28 is provided.

In the above embodiment, the gain adjusting means 7 adjusts the gain by the variable attenuator 9. However, the wideband amplifier 8 or 10 is a variable gain amplifier, and the gain is adjusted by the output signal of the voltage comparing circuit 22. You may make it change. The manual variable attenuator 28 is connected to the power supply unit 4.
Although provided inside, it may be provided outside.

[0024]

As described above, according to the present invention, by selecting the reference signal according to the number of received waves by the selecting means, the automatic output of the automatic gain adjusting means in the amplifying unit is automatically adjusted to the maximum output level according to the distortion. Since the output level is adjusted, there is no need to adjust the input level over for the amplifier, and installation can be performed without the installer having the knowledge and experience of the adjustment, and it is necessary to go outside and adjust the amplifier. Since it is not necessary, the operation cost can be reduced and it is safe. Moreover, as described above, the input level over to the amplifying section is automatically adjusted. When an image failure occurs in the television receiver, the input level over to the receiver is caused. By simply adjusting the adjusting means, it is possible to easily eliminate the image trouble.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of a television broadcast signal booster according to the present invention.

[Explanation of symbols]

 2 Amplifying section 4 Power supply section 6 Coaxial cable 7 Gain adjusting means 20 Detector (level detecting means) 22 Voltage comparing circuit (control means) 24 Changeover switch (selecting means) 26 Reference voltage generating circuit (reference signal generating means) 28 Manual Variable attenuator (level manual adjustment means)

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03G 3/20 H04B 3/06 H04B 1/18

Claims (2)

(57) [Claims] 1. A separate type television broadcast signal receiving booster comprising an amplification unit installed outdoors and a power supply unit installed indoors, wherein the amplification unit comprises a plurality of television broadcast signals. Is supplied, the gain is adjusted according to the gain control signal, a level detecting means for detecting a level of an output signal of the gain adjusting means in a wide band, and a television broadcast signal inputted to the gain adjusting means. Reference signal generating means for generating reference signals having different values corresponding to different wave numbers of
Selection means for manually selecting one of the reference signals having different values, and control for generating the gain control signal in accordance with the reference signal selected by the selection means and the output signal of the level detection means Means for receiving a television broadcast signal. 2. The television broadcast signal receiving booster according to claim 1, further comprising means for manually adjusting the level of the output signal of the amplifying section transmitted indoors indoors. Receive booster.