JP2791451B2 - FM processor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM processor which is provided, for example, at the head end of a public hearing facility and converts the frequency of an FM broadcast signal received by an antenna into a desired frequency.

[0002]

2. Description of the Related Art Conventionally, as a head end of a joint hearing facility, for example, there is one as shown in FIG. In this head end, the signal was received by the antenna 2 for FM broadcast reception.
For example, a plurality of FMs in the range of 76 MHz to 90 MHz
The broadcast signal is supplied to the FM processors 6 and 8 via the splitter 4. In the FM processor 6, a plurality of input F
A signal having a predetermined frequency f1 is selected from the M broadcast signals, converted into another predetermined frequency f1v within a range of 76 MHz to 90 MHz, and supplied to the mixing unit 10. The FM processor 8 also selects a signal having a frequency f2 different from that selected by the FM processor 6 from the plurality of input FM broadcast signals, and transmits the selected signal to the FM processor 6.
Is converted to a frequency f2v in the range of 76 MHz to 90 MHz, which is different from the conversion frequency in, and supplied to the mixing unit 10.

A plurality of television broadcast signals received by a television broadcast receiving antenna 12 are transmitted to respective television processors 16, 18, 2,
0,22. In the television processor 16, a predetermined frequency f3 of the plurality of television broadcast signals is set.
Is selected, converted to another predetermined frequency f3v, and supplied to the mixing unit 10. Similarly, the other television processors 18 to 22 similarly select television broadcast signals of frequencies f4, f5, and f6, convert these signals to f4v, f5v, and f6v, respectively.
Supply 0.

[0004] A plurality of satellite broadcast signals received by a satellite broadcast receiving antenna 24 and frequency-converted to an intermediate frequency signal by a converter (not shown) are sent to satellite broadcast receivers 28 and 30 via a splitter 26. Supplied. The satellite broadcast receiver 28 selects the satellite broadcast signal f7 and the satellite broadcast receiver 30 selects the satellite broadcast signal f8, demodulates them into baseband signals, and television signal modulators (TV modulators) 32, 34.
To supply. The TV modulator 32 modulates the carrier of the frequency f7v with the baseband signal based on f7, and the TV modulator 34 modulates the frequency f7 with the baseband signal based on f8.
The 8v carrier is modulated, and these modulated signals are supplied to the mixing unit 10.

A baseband signal for voluntary broadcast from a video tape recorder or a television camera 36 is a TV signal.
The carrier is supplied to the modulator 38, modulates the carrier having the frequency f9v with the baseband signal, and supplies the modulated carrier to the mixer 10.

[0006] The mixing unit 10 includes each of the FM processors 6, 8,
TV processors 16 to 22, TV modulators 32, 3
The output signals of 4, 38 are mixed and supplied to a main line provided in the area of the joint hearing facility. The number of FM processors, television processors, satellite broadcast receivers, video tape recorders or television cameras, and TV modulators depends on the number of FM broadcast signals, television broadcast signals, and satellite broadcasts that can be received at the installation location of this joint viewing facility. It is changed according to the number, etc., the number of independent broadcasts, and the like.

The FM processor 6 is configured, for example, as shown in FIG. That is, the two dividers 4 are connected to the input terminal 40.
Are supplied from the high frequency amplifier 4
After being amplified by 2, it is supplied to a variable band pass filter 46 via a variable attenuator 44. The variable band-pass filter 46 transmits the F
The pass band is adjusted so that the M broadcast signal f1 can pass.

The output signal of the variable band-pass filter 46 is supplied to a mixer 52 via high-frequency amplifiers 48 and 50. In the mixer 52, the first local oscillation circuit 54 outputs a first local oscillation signal (f1 is 76 MHz to 90 MHz because f1 is 76 MHz to 90 MHz, which is adjusted to a frequency necessary to convert f1 to an intermediate frequency signal of 10.7 MHz. This frequency is in the range of 65.3 to 79.3 MHz.), And f1 is converted to an intermediate frequency signal of 10.7 MHz.

The output signal of the mixer 52 is amplified by a high-frequency amplifier 56, and then fixed band-pass filter (B)
PF) 58 and only the 10.7 MHz intermediate frequency signal is selected. The configuration so far is the first frequency conversion unit.

The 10.7 MHz intermediate frequency signal is amplified by a high frequency amplifier 60, and then amplified by a second frequency converter 62.
Is converted to a frequency of 50 MHz. this is,
This is for preventing spurious from occurring from the output signal of the FM processor, for example, the FM processor 6.

The output signal of 50 MHz from the second frequency converter 62 is supplied to a third frequency converter 64 where it is converted to an arbitrary frequency f1v within the range of 76 to 90 MHz and mixed from an output terminal 66. It is supplied to the unit 10.

The fixed band-pass filter 58-1
The 0.7 MHz intermediate frequency signal is detected by the IF-AGC detection circuit 68 and supplied to the AGC control circuit 70. A
The GC control circuit 70 adjusts the attenuation of the variable attenuator 44 so that the level of the 10.7 MHz intermediate frequency signal becomes a predetermined constant level.

The FM processor 8 has the same configuration, and includes a pass band of the variable band-pass filter 46,
When the frequency of the first local oscillation signal of the first local oscillation circuit 54 is
The only difference from the FM processor 6 is the difference in the frequency of the FM broadcast signal to be received.

In such an FM processor, the variable band-pass filter 46 is used for the purpose of suppressing image interference and attenuating an undesired signal, but the FM processor can receive a signal of any frequency. To achieve this, the passband is made variable as indicated by the arrow in FIG. Therefore, the FM you want to receive
If the signal cannot be a narrow band that allows only the broadcast signal to pass therethrough, and if there are undesired signals U1 to U4 close to the desired reception signal D as shown in FIG. As shown in FIG. 3C, undesired signals U1 to U4 appear at the output of the variable bandpass filter 46.
These are also supplied to the mixer 52, and the mixer 52
Undesired intermediate frequency signals other than 0.7 MHz will also be generated.

On the other hand, since the fixed band-pass filter 58 has a constant passing frequency of 10.7 MHz, it can have a relatively narrow band as shown in FIG. As shown in FIG.
Even if the intermediate frequency signals IF2 and IF3 other than the desired ones are generated from the mixer 52, the output of the fixed band-pass filter 58 will be the desired intermediate frequency signal IF1 as shown in FIG. Only output.

[0016]

In such an FM processor, an intermediate frequency signal output from the fixed band-pass filter 58 is detected, and automatic gain control is performed based on the detected output. That is, IF-AGC is performed. Therefore, as shown in FIG. 11A, for example, when the desired reception signal D1 is lower in level than the undesired signals U1 and U2, the desired reception signal D1 having a lower level is output to the mixer 52.
The IF-AGC which raises the level so as to be input as an appropriate input operates, and accordingly, the level of the undesired signal which was originally higher is also raised.

However, since the undesired signal cannot be completely removed by the variable band-pass filter 46 as described above, the undesired signal whose level has been increased is also supplied to the mixer 52. As a result, distortion is generated in the mixer 52 as shown by a dotted line in FIG. 3B, and among these distortions, those having a frequency within the band of the desired reception signal are indicated by a dotted line in FIG. As described above, the fixed bandpass filter 5
However, there is a problem that the signal cannot be removed by the method No. 8 and the reception of the desired signal is affected.

Normally, each FM is controlled so that the level of the desired reception signal does not become lower than the level of the non-desired signal.
Although the frequency allocation of the broadcasting stations is set separately for each service area, the FM processor at the head end of the joint hearing facility is desired to receive an FM broadcast signal that does not set the location of the joint hearing facility as a service area. May be
In such a case, the above-described problems occur.

The above problems can be improved by using RF-AGC instead of IF-AGC. But,
If it is configured to always use RF-AGC, AG
C controls the sum based on the sum of the levels of the desired signal and the undesired signal so that the sum does not exceed the optimum input level in the mixer 52. If the level is lower than the level, the input level of the desired reception signal to the mixer 52 is lower than the optimum input level of the mixer 52, and the C / N ratio is deteriorated.

Since the FM processor is versatile, it may be used in a state where the level of a desired signal to be received is higher than that of an undesired signal or in a state where it is lower. Therefore, AGC cannot be fixed to RF-AGC.

[0021]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and has a pass band for passing a desired one of a plurality of FM broadcast signals received by an antenna. A variable bandpass filter that is variable,
Signal passing and level adjusting means comprising level adjusting means for adjusting the level of each FM broadcast signal according to a control signal; and an output of the signal passing and level adjusting means and a local oscillation signal of a predetermined frequency. An FM processor comprising a mixer for mixing and a band-pass filter having a fixed pass band for selecting an intermediate frequency signal having a desired frequency from the output of the mixer. A second high-frequency detecting means for detecting an output of the band-pass filter having a fixed pass band.
And the signal selecting means for selecting one of the outputs of the first and second detecting means, and the control signal corresponding to the signal selected by the signal selecting means is supplied to the level adjusting means. And control means for performing the control.

[0022]

According to the present invention, one of the output signals of the first and second detection means is selected by the selection means,
Supplied to the control means, the control means controls the level adjusting means. That is, in the present invention, the RF-AGC based on the output of the first detector and the IF-AGC based on the output of the second detector are used.
-AGC can be arbitrarily switched.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The FM processor of this embodiment is used for the head end of a joint hearing facility, like the FM processors 6 and 8 shown in FIG. 7, and is equivalent to the FM processor 6 shown in FIG. The same reference numerals are given to the portions, and the description is omitted.

The second frequency converter 62 has a high frequency amplifier 68 for amplifying the 10.7 MHz intermediate frequency signal supplied from the high frequency amplifier 60. The output signal of the high frequency amplifier 68 is a variable attenuator 71. , High frequency amplifier 72
Is supplied to the mixer 74 via the. The mixer 74 is supplied with a local oscillation signal of 60.7 MHz from the second local oscillation circuit 76.
The frequency conversion of the intermediate frequency signal of 50 Hz to 50 MHz. The 50 MHz intermediate frequency signal is amplified by a high frequency amplifier 78 and supplied to a fixed band-pass filter 80 having a narrow band of 50 MHz.
Are extracted. In addition, this 50M
The intermediate frequency signal of Hz is detected by an AGC detection circuit 82, and the detection output is supplied to an AGC control circuit 84. The AGC control circuit 84 performs variable attenuation so that the level of the 50 MHz intermediate frequency signal becomes constant. Control unit 71.

The third frequency converter 64 has a high-frequency amplifier 86 for amplifying the 50 MHz intermediate frequency signal from the fixed band-pass filter 80. The output of the high-frequency amplifier 86 is supplied to a mixer 88. The mixer 88 has 1
A third local oscillation signal having a frequency selected from the range of 26 MHz to 140 MHz is supplied from the third local oscillation circuit 90, and the mixer 88 converts the 50 MHz intermediate frequency signal to an arbitrary frequency within the range of 76 MHz to 90 MHz. Convert. After the output signal of the mixer 88 is amplified by the high frequency amplifiers 92 and 94, a fixed band pass filter 96 having a pass band fixed at 76 MHz to 90 MHz.
After removing unnecessary harmonics and the like, the signal is amplified by the high-frequency amplifier 98 and supplied to the output terminal 66.

The feature of the present invention resides in that an IF-AGC detection circuit 68 for detecting an intermediate frequency signal is provided on the output side of the fixed band-pass filter 58, and that the output side of the high-frequency amplifier 48 is RF- for detecting each FM broadcast signal
An AGC detection circuit 100 is provided, and both detection circuits 68 and 100 are provided.
Is selected by the changeover switch 102,
The point is that it is supplied to the AGC control circuit 70.

As shown in FIG. 1, the variable attenuator 44
Obtained by using the PIN diodes 104, 106, 108 of the present, PIN diode 104, 106 is AC grounded by a capacitor 1 10, 111, P
The IN diodes 104 and 106 exhibit a constant high-frequency resistance value when current flows from the power supply terminal 113 to the resistors 112 and 114, the PIN diode 104, the high-frequency blocking coil 116, the PIN diode 106, and the resistor 118.

The PIN diode 108 has a resistance value according to the current supplied through the resistor 119. Therefore, a π-type variable attenuator is configured, and the amount of attenuation changes according to a change in the high-frequency resistance value of the PIN diode 108. The capacitors 120, 122, and 124 are for AC coupling.

The RF-AGC detection circuit 100 rectifies the voltage of the output of the high-frequency amplifier 48 by diodes 126, 128 and a capacitor 130. This RF-AG
The detection output of the C detection circuit 100 is supplied to a changeover switch 102. This changeover switch 102 has an IF-
The detection output from the AGC detection circuit 68 (the detection output of the output of the fixed band-pass filter 58) is also supplied.

A selected by the changeover switch 102
The detection output of the GC detection circuit 68 or 100 is supplied to the comparator 132 of the AGC control circuit 70. The comparator 132 is supplied with a reference signal by a variable resistor 134, and the comparator 132 generates a signal corresponding to a deviation between the detection signal supplied from the changeover switch 102 and the reference signal. This signal is supplied to the base of the transistor 135, and this transistor 13
5 is changed. According to the conduction state of the transistor 135, a current is supplied from the collector of the transistor 135 to the PIN diode 108 via the resistor 119, and the high-frequency resistance value of the PIN diode 108 is changed.

Therefore, if the changeover switch 102 is set to the IF-AG
When the detection output from the C detection circuit 68 is supplied to the AGC control circuit 70, the IF-AGC operation is performed, and the changeover switch 102 supplies the detection output of the RF -AGC detection circuit 100 to the AGC control circuit 70. RF-AG
C operation is performed.

Use this IF-AGC or RF-AG
Whether to use C is changed according to the state of the input FM broadcast signal. For example, as shown in FIG. 3A, when the level of the reception desired signal D is higher than the levels of the undesired signals U1 and U2, the output of the variable band-pass filter 46 is set as RF-AGC. b)
The output of the mixer 52 is as shown in FIG. 3C, and the output of the fixed band-pass filter 58 is as shown in FIG. In the case of IF-AGC, the output of the variable band-pass filter 46 becomes as shown in FIG. 11E, the output of the mixer 52 becomes as shown in FIG. Is as shown in FIG. That is, even in the case of IF-AGC, RF-AGC
Even in the case of (1), since the AGC operation is performed based on the level of the desired signal, either AGC may be used.

As shown in FIG. 4 (a), when the level of the desired signal D is substantially equal to the levels of the undesired signals U1 to U4, if the signal is RF-AGC, the desired signal D
The AGC operation is performed based on the sum of the non-desired signals U1 to U4, so that the output of the variable band-pass filter 46 (input to the mixer 52) as shown in FIG.
The input level of the desired reception signal D falls below the optimum level,
Although the C / N ratio may deteriorate, no distortion occurs in the mixer 52. FIG. 3C shows the output of the mixer 52, and FIG. 4D shows the output of the fixed band-pass filter 58.

On the other hand, in the case of the IF-AGC, the AGC operation is performed based on the level of the desired reception signal D, so that the output of the variable band-pass filter 46 (input to the mixer 52) as shown in FIG. In (2), the input level of the desired reception signal D becomes the optimum level, but the level of the undesired signal also rises along with this, so that the output of the mixer 52 is distorted as shown by the dotted line in FIG. However, there is no problem when the distortion is outside the pass band of the fixed band-pass filter 58 or when the reference signal in the AGC control circuit 70 is set so as to be within the allowable limit. Therefore, IF-AGC is mainly used, but in some cases R-AGC is used.
Use F-AGC. FIG. 9G shows the output of the fixed band-pass filter 58. From the viewpoint of suppressing distortion within the allowable limit, it is desirable to use the variable resistor 134 for generating the reference signal.

As shown in FIG. 5A, the level of the desired signal D is lower than the levels of the undesired signals U1 to U3, and the relationship between the frequencies of the desired signal D and the undesired signals U1 to U3 is determined. If distortion is likely to occur in the pass band of the fixed band-pass filter 58, the RF-AGC
Then, the desired reception signal D and the undesired signals U1 to U3
The AGC operates on the basis of the sum of the signals, so that the output of the variable band-pass filter 46 (input to the mixer 52) is, as shown in FIG.
ＵU3 is the optimum input level to the mixer 52. Accordingly, no distortion occurs in the output of the mixer 52 as shown in FIG. 11C, and, naturally, no distortion occurs in the output of the fixed band-pass filter 58 as shown in FIG. The / N ratio deteriorates.

On the other hand, if the IF-AGC is used, the AGC operates so that the level of the desired reception signal D becomes the optimum input level to the mixer 52. Therefore, the output of the variable band-pass filter 46 (input to the mixer 52). Are proportional to the level of the desired signal D being the optimum input level of the mixer 52 as shown in FIG.
Level 3 is also higher. Therefore, the output of the mixer 52 is distorted as shown in FIG. 7 (f), and the frequency of the undesired signals U1 to U3 and the desired signal D is fixed, as shown in FIG. Distortion occurs in the pass band of the band pass filter 58. In such a case, RF-AGC is used.

As shown in FIG. 6A, the desired reception signal D
May be smaller than the levels of the undesired signals U1 to U3, and distortion may occur in the pass band of the fixed band-pass filter 58 due to the frequency relationship between the received desired signal D and the undesired signals U1 to U3. If there is no RF-AGC, the AGC operates based on the sum of the desired signal D and the undesired signals U1 to U3, so that the output (input to the mixer 52) of the variable band-pass filter 46 is As shown in (b), the reception desired signal D and the undesired signal U1
ＵU3 is the optimum input level to the mixer 52. Therefore, no distortion occurs in the output of the mixer 52 as shown in FIG. 11C, and naturally no distortion occurs in the output of the fixed band-pass filter 58 as shown in FIG. Deterioration of the C / N ratio occurs.

On the other hand, if the IF-AGC is used, the AGC operates so that the level of the desired reception signal D becomes the optimum input level to the mixer 52. Therefore, the output of the variable band-pass filter 46 (input to the mixer 52). Are proportional to the level of the desired signal D being the optimum input level of the mixer 52 as shown in FIG.
Level 3 is also higher. As a result, distortion is generated in the output of the mixer 52 as shown in FIG. However, due to the frequency relationship between the undesired signals U1 to U3 and the desired signal D, no distortion occurs in the pass band of the fixed band-pass filter 58 as shown in FIG. In such a case, IF-AGC is used.

Although the variable attenuator 44 is used in the above embodiment, a variable gain amplifier can be used instead. Further, in the above embodiment, the variable band-pass filter 46 is provided after the variable attenuator 44, but the variable attenuator 44 may be provided after the variable band-pass filter 46.

[0040]

As described above, according to the present invention, the output of the signal passing and level adjusting means is detected by the first detecting means, and the output of the band-pass filter having a fixed pass band is detected by the second detecting means.
And one of the outputs of the first and second detection means is selected by the signal selection means and supplied to the control means for controlling the level adjustment means. Therefore, depending on the relationship between the level of the signal desired to be received and the level of the undesired signal and the frequency relationship between these two signals, IF-AGC or R-
Among the F-AGCs, an AGC that can receive the desired signal in the best condition can be used.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of one embodiment of an FM processor according to the present invention.

FIG. 2 is a block diagram of the embodiment.

FIG. 3 is a frequency characteristic diagram of each unit when the RF-AGC and the IF-AGC are used when the level of a desired signal to be received is higher than that of a non-desired signal in the embodiment.

FIG. 4 is a frequency characteristic diagram of each unit when the RF-AGC and the IF-AGC are used when the level of a desired signal to be received and the level of a non-desired signal are equal in the embodiment.

FIG. 5 shows the RF-AGC and the RF-AGC when the level of the desired signal to be received is lower than that of the non-desired signal and the frequency relationship between the desired signal and the undesired signal causes distortion in the output of the fixed band-pass filter. FIG. 5 is a frequency characteristic diagram of each unit when IF-AGC is used.

FIG. 6 shows the RF-AGC and the RF-AGC when the desired reception signal is lower in level than the undesired signal and the frequency relationship between the desired reception signal and the undesired signal does not cause distortion in the output of the fixed band-pass filter. FIG. 5 is a frequency characteristic diagram of each unit when IF-AGC is used.

FIG. 7 is a block diagram of a joint hearing facility headend.

FIG. 8 is a block diagram of a conventional FM processor.

FIG. 9 is a diagram showing frequency characteristics of a variable band-pass filter used in a conventional FM processor, and an input signal and an output signal to the filter.

FIG. 10 is a diagram showing frequency characteristics of a fixed band-pass filter used in a conventional FM processor, and an input signal and an output signal to the filter.

FIG. 11 is a frequency characteristic diagram of each unit when the level of a desired signal to be received is smaller than the level of a non-desired signal in a conventional FM processor.

[Description of Signs] 44 Variable Attenuator (Level Adjusting Means) 46 Variable Bandpass Filter 52 Mixer 68 IF-AGC Detection Circuit (Second Detection Means) 70 AGC Control Circuit (Control Means) 100 RF-AGC Detection Circuit ( First detection means)

Claims (1)

(57) [Claims] 1. A variable band-pass filter whose pass band is varied so as to pass a desired one of a plurality of FM broadcast signals received by an antenna, and a level of each of the FM broadcast signals according to a control signal. A signal passing and level adjusting means comprising: a mixer for mixing the output of the signal passing and level adjusting means with a local oscillation signal of a predetermined frequency; and And a band-pass filter having a fixed pass band for selecting an intermediate frequency signal having a frequency of
High-frequency detection means, a second intermediate frequency detection means for detecting the output of the band-pass filter having a fixed pass band, a signal selection means for selecting one of the outputs of the first and second detection means, And a control unit for supplying the control signal according to the signal selected by the signal selection unit to the level adjustment unit.