JPS5818034B2 - AGC Zoufukuki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a community reception facility that receives broadcast signals of multiple channels and transmits the signals of those channels over a single transmission line.

This type of communal reception facility, which amplifies the signals of multiple channels received by a wideband antenna and transmits them using a wideband amplifier, has limited reception characteristics, so in order to obtain better characteristics, One method has been considered in which the signals of each channel are received by a dedicated antenna and further amplified by a dedicated AGC amplifier.

However, in AGC amplifiers used for this type of purpose, the AGC circuit works to maximize the gain of the amplifier when the transmission channel signal stops due to broadcasting interruptions or failures, etc. Noise and extraneous noise are amplified and the amplified loud noisy signal disturbs the normal signals of other ongoing channels and creates noise interference on the receivers of subscribers receiving those channels. There is a problem with giving.

Therefore, the present invention aims to provide a joint i-reception facility that eliminates the above-mentioned problems.

The drawings showing the embodiments of the present application will be described below.

In FIG. 1, which shows the head end of the joint reception facility as a block, %11. F , , j□ . . . 1N are antennas, each of which is used exclusively for each channel in the telephony transmission.

28, 2□...2N are AGC amplifiers, which, like the antenna, are dedicated to each channel.

Note that since these amplifiers have substantially the same configuration, only the amplifier 21 will be described below.

3 is an input terminal, and a plug is generally used.

Reference numeral 4 denotes a pre-amplifier circuit, which is used depending on the frequency band or level of the signal to be handled.

5 is a brancher, 6 and 7 are AGCs forming an AGC amplifier circuit.
The circuit and the post-stage amplifier circuit may have a separate structure as shown in this embodiment, or may have an integrated structure.

Reference numeral 8 is a branching device 1.9 is an output terminal, and like the input terminal 3, a plug is generally used.

Next, reference numeral 10 denotes an amplifier circuit that is used as needed, and is used to amplify the AGC signal branched by the splitter 8 to a sufficient level when the level of the signal for AGC is low.

Next, members indicated by reference numerals 11 and 12 constitute an AGC control circuit, and 11 indicates a detector, which is provided to convert a high frequency signal input as an AGC signal into a direct current.

Reference numeral 12 denotes a DC amplifier, which amplifies the AGC signal detected by the wave detector 11 and controls the AGC circuit 6.

13 is a switching circuit, 13a is an input end, 13b is an output end, and 13c is a control input end.

Next, 14 is a mixer, which includes a plurality of amplifiers 2. ．． 2□・・・・
...It is designed to mix the signals of each channel at 2N and send it to the transmission line.

Next, FIG. 2 showing an example of one circuit of the amplifier 21 will be explained.

Q1-Q are transistors, R1-R2I are resistors, C1
~C8 is a capacitor, L1-L3 is a coil, D1-D2
are diodes, which constitute an AGC circuit 6, an AGC control circuit 11, 12, and a switching circuit 13, as shown by the dot-dashed line.

Note that R1 is a variable resistor for level setting in the switching circuit 13, and the diode D1 has a property that its high frequency resistance decreases as the bias current flowing through it increases, such as a PIN diode. The diode with which it is used is used.

15 is an amplifier used as necessary; 16a to 16b;
is a power supply terminal, which is a terminal that receives DC power from a well-known power supply circuit.

In the amplifier having the above configuration, when the level of the signal to the input terminal 3 decreases, the output level of the amplifier circuit 7 also decreases.

Then, the input to the base of the transistor Q1 in the DC amplifier circuit 12 decreases, and as is clear from the circuit diagram, the collector currents of the transistors Q2 and Q7 decrease.

Along with this, the diode D1 of the AGC circuit 6. D2
As the biases of the diodes D and D change, the high frequency resistance of the diodes D decreases, and the amount of attenuation as an AGC circuit decreases.

Therefore, the input to the amplifier circuit 7 increases and its output also increases; compensating for the level drop mentioned above.

Note that even when the level of the signal to the input terminal 3 increases, as is clear, the output level of the amplifier circuit 7 is kept constant by performing the operation completely opposite to that described above.

Next, if the input level to input terminal 3 drops abnormally due to a stop in broadcasting, etc., the AGC operation as described above
The amplification degree of the GC amplifier circuit is about to increase to the maximum.

However, in this case, the input to the moderation input terminal 13c of the switching circuit 13 decreases, so the transistor Q4 is turned off.
%Q becomes 0N1Q6 becomes OFFν, its collector voltage rises, transistor Q7 is biased more deeply than during normal AGC operation through D4 provided as a switching diode, and its collector current increases.

This causes the diode D2 of the AGC circuit 6 to
It is biased more deeply than during C operation.

On the other hand, the diode D becomes almost unbiased as the diode D2 is biased, so the amount of high frequency attenuation of the AGC circuit 6 at this time increases significantly.

That is, this operation significantly reduces the gain of the entire amplifier, thereby preventing external noise and internal noise from being amplified and transmitted.

As is clear from the configuration shown in FIG.
It can also be reduced to about m5 or less using well-known technology.

), therefore, even if a noise signal enters from the input terminal 3, it will not be amplified and a large noise signal will be input to the mixer 14 from the terminal 9, and the output signal from the mixer 14 will be received. There is no disturbance to the receiver screen.

Note that the degree of increase in this attenuation amount is selected depending on the size of the circuit element or other equipment used.

In addition, the above operation is performed so that the signal level to the control input terminal 13c is within a normal level fluctuation range due to changes in the transmission state of radio waves or changes in temperature (inputs within this range are referred to in this specification). This is called a prescribed input.

) so that the variable resistor Y
It is regulated by R1.

Therefore, it does not affect the normal AGC operation as described above.

As described above, in the present invention, when receiving signals of a plurality of channels, each channel has a dedicated antenna 1□
, 1□...... are amplified by the dedicated channel amplifiers 21, 2□..., so it is even more difficult to receive the signals of those multiple channels with a wideband antenna. Compared to the conventional configuration in which the signal is amplified using a wideband amplifier, each channel can be received with better reception characteristics.

Moreover, in the case of reception, the amplifier 2 dedicated to each channel is
1, 22..., the signals of each channel are amplified by AGC, so the signals of any channel can always be received at a stable level, resulting in even better reception characteristics. There is an effect that can be received.

Moreover, in the present invention, even if the signals of a plurality of channels are individually received by antennas dedicated to each channel as described above and further amplified individually by amplifiers dedicated to each channel, Since the signals of each channel are mixed in the mixer 14, when transmitting the signals of the plurality of channels, a single transmission line is sufficient for the transmission, which is economical with low facility costs. There is sex.

Moreover, the present invention receives signals using antennas dedicated to each channel and amplifiers dedicated to each channel, as described above.

Even if the amplified signals of multiple channels are mixed by the mixer 14 and sent to a single transmission line, each channel-dedicated amplifier 21, 2□... has a switching circuit, respectively. 13, and when the prescribed input is gone, about husband k.

Since the amplification degree of the amplifier circuit is significantly reduced, even if the signal of any channel disappears due to the end of broadcasting or other reasons, all the signals (mainly noise signals) related to the channel where the signal disappeared will be transferred to the mixer. It is advantageous to be able to mix and send only the normal signals of the ongoing channels that are sent to the mixer 14 from other amplifiers, as if they had been disconnected. .

That is, to explain this in detail, in each channel-dedicated amplifier 21, 2□..., the control input terminal 13c of the switching circuit 130 is turned off by stopping the wave of that channel.
As soon as the input value to falls below the specified minimum value (the lowest value of the specified inputs),
Since switching is performed to a state where the amplification degree of the GC amplifier circuit is significantly reduced, there is a feature that it is possible to prevent a large noise signal from being input to the mixer 14 from the AGC amplifier circuit, and vice versa. When the signal of the stopped channel is restored and the input value to the control input terminal rises and exceeds the specified minimum value, the AGC amplifier circuit immediately returns to the state where it performs normal AGC operation. Since switching is to be performed,
It has the advantage that the signal of that channel can be immediately sent to the mixer at a normal level.

These things mean that the screen of the television receiver receiving the signals of other channels output from the above-mentioned combiner 14 is always stable without being adversely affected by the stoppage and restoration of the above-mentioned specific channel. It has the effect of making it more appealing.

[Brief explanation of drawings]

The drawings show an embodiment of the present application, and FIG. 1 is a block diagram of a head end, and FIG. 2 is a circuit diagram of an amplifier. 11.12...AGC control circuit, 6,7...AGC
Amplifying circuit, 13... Switching circuit, 13a...
Input end, 13b...output end, 13c...control input end.

Claims (1)

[Claims] 1 An antenna dedicated to multiple channels, a mixer that mixes the signals of multiple channels and sends it to a single transmission line, and the mixer that sends the signal from the mixer to the next stage. It consists of a single transmission line connected to each channel, and each channel-dedicated amplifier interposed between the above-mentioned channel-dedicated antenna and the above-mentioned mixer, so that the signal received by the above-mentioned channel-dedicated antenna is In a common reception facility where each channel is individually amplified by an amplifier, and the amplified signals are mixed by the mixer and sent out to a single transmission line, in the amplifier dedicated to each channel, An AGC amplifier circuit is connected between each input terminal and output terminal, and an AGC control circuit is connected to a stage subsequent to the AGC amplifier circuit, and on the other hand,
It has a control input terminal, an input terminal, and an output terminal, and when the input value to the control input terminal is equal to or higher than the specified minimum value, the signal from the AGC control circuit that enters the input terminal is sent out as it is to the output terminal, while the control input terminal When the input value to the control input terminal is less than the specified minimum value, the output terminal sends out a signal that significantly reduces the amplification degree of the AGC amplifier circuit, and the switching of these states is controlled by the input to the control input terminal. a switching circuit configured to perform conversion immediately when the value changes from a value less than the specified minimum value to a value exceeding the specified minimum value and vice versa, and the switching circuit The control input terminal is connected to the stage before the AGC amplifier circuit, and the input terminal is connected to the output terminal of the AGC control circuit,
A communal reception facility characterized in that the output end is connected to the AGC amplifier circuit.