KR0140965B1 - A rf modem for communication of catv - Google Patents

Abstract

The present invention relates to a communication modem of a cable broadcasting (CATV) system, that is, an RF modem of a converter (MODEM; modulator and demodulator) and an RF modem of a head end. The present invention relates to a modem having improved characteristics and broadband characteristics and, in the reverse direction, improved isolation characteristics.

Conventional RF modem is a technology that detects only the presence of communication error in performing two-way communication between subscriber-side converter and broadcasting station, and is required for two-way data communication, that is, the shape of noise characteristic and wideband characteristic in the forward direction. In addition, it was difficult to exclude the effect of the transmission system on the receiving system and the tuner and the effect of the receiving system on the transmission system, the tuner, and the cable because it was difficult to secure the insulation characteristics in the reverse direction. .

The present invention includes a transmission oscillator, a filter of a transmission signal, an amplifier of a transmission signal, a coupler for branching of a transmission / reception path, an amplifier of a reception signal, and a demodulator of an amplified reception signal. Noise and broadband characteristics in the forward direction while smoothly transmitting and receiving data by minimizing the effects of the transmission system on the receiving system and the tuner. RF modem improves the isolation characteristics in the reverse direction.

Description

RF modem for cable broadcasting (CATV) system

1 is a block diagram of an RF modem of a conventional bidirectional CATV.

2 is a circuit diagram of a first embodiment of an RF modem of a cable broadcasting (CATV) converter according to the present invention.

3 is a circuit diagram of an RF modem of a cable broadcasting (CATV) converter according to a second embodiment of the present invention.

4 is a circuit diagram of a third embodiment of the RF modem of the cable broadcasting (CATV) converter of the present invention.

5 is a circuit diagram of a fourth embodiment of an RF modem in a cable broadcasting (CATV) head end of the present invention.

6A is a circuit diagram of a first embodiment of a transmission oscillator used in the present invention.

(b) is a circuit diagram of a second embodiment of a transmission oscillator used in the present invention.

7 is a circuit diagram of an embodiment of a transmission amplifier used in the present invention.

8 is a circuit diagram showing the characteristics of the coupler used in the present invention.

9 is a circuit diagram of an embodiment of a wideband amplifier used in the present invention.

10 is a circuit diagram of an embodiment of a receiver amplifier used in the present invention.

11 is a diagram showing the technical conditions (specifications) of the subscriber converter

* Explanation of symbols for main parts of the drawings

20, 30, 40, 50: Transmit oscillator 21, 31, 41, 54: Low pass filter

22, 32, 42, 52: Transmitter 23, 25, 33, 36, 43, 48, 53: Coupler

24, 34, 44a, 44b: High pass filter 26, 35, 49: Broadband amplifier

27, 37, 45, 55: Receiver amplifiers 28, 38, 46, 56: Demodulator

29, 39, 47, 57: receiving oscillator 51: bandpass filter

The present invention relates to a communication modem of a cable broadcasting (CATV) system, that is, an RF modem of a converter (MODEM; modulator and demodulator) and an RF modem of a head end. The present invention relates to a modem that has improved characteristics and broadband characteristics and has improved isolation characteristics in the reverse direction.

The configuration of a conventional CATV RF modem (Korean Patent Publication No. 93-9184, September 23, 1993) is shown in FIG.

As shown in FIG. 1, a conventional modem 10 includes a filter (1) for receiving a signal from a cable, a filter (2) for transmission, and a demodulated signal received through the filter (1). A demodulator 3 input to the 20, a modulator 4 for modulating the signal transmitted from the computer 20 and input to the filter 2, and a level of the received signal demodulated by the demodulator 3; It can be seen that the configuration is provided with a level detector 5, and a microcomputer 6 for storing the detection data of the level detector 5 and providing the data so that the computer at the head end can determine whether there is a communication error.

The conventional modem 10 detects the level of the signal demodulated by the demodulator 3 via the filter 1 at the level detector 5 and inputs it to the microcomputer 6, and the microcomputer 6 inputs the detected level. The computer 20 receives the data transmission command through the modulator 4 and the filter 2 and provides the stored level information so that the computer 20 can determine whether there is a communication error.

However, such a conventional RF modem is a technology for detecting only the presence of a communication error in performing two-way communication between a subscriber-side converter and a broadcasting station, and is required for two-way data communication, that is, improving noise characteristics in a forward direction and wide area. (Wideband) characteristics could not be expected, and it is difficult to secure insulation characteristics in the reverse direction, so that the effect of the transmission system on the reception system and tuner and the effect of the reception system on the transmission system, tuner, and cable are excluded. There was a difficult problem.

The present invention solves the conventional problems as described above, and can minimize the effect of the transmission system on the receiving system and the tuner, as well as minimizing the effect of the receiving system on the transmission system, the tuner and the cable. It aims to provide an RF (RF) modem of a cable broadcasting (CATV) converter with smooth performance while improving noise and broadband characteristics in the forward direction and isolation characteristics in the reverse direction.

For RF modems that meet the above objectives, refer to the standard for Korean CATV systems (see Figure 11) .The data transceiver specification on the cable is 40 ± 4dBmV = -9 ± 5dBm with the output level and the input level It can be seen that 5 ± 10dBmV = -44 ± 10dBm, and also the return loss of 7dBm or more in the input characteristics of the signal receiver of the television receiver, the leakage electromagnetic wave is less than 20dBmμV at 5MHz to 30MHz = -89dBm or less, and 25dBmνV or less at 50MHz to 450MHz = It can be seen that it is -84 dBm.

Therefore, the RF modem should be configured to smoothly transmit and receive data while suppressing leakage electromagnetic waves as much as possible. The RF modem of the present invention satisfying this condition is implemented as an embodiment of FIGS. 2 to 4. There is no standard for the headend RF modem that communicates with Bertie's RF modem. However, it is clear that unnecessary electromagnetic interference or leakage on the cable should be suppressed as much as possible. Implemented by the embodiment of FIG.

In order to achieve the above object, the configuration, operation and effects of RF modem of the cable broadcasting (CATV) converter of the present invention are divided by each embodiment, and the transmission and reception operation in the forward direction is performed. In this order, the effect on the transmission system, the effect of the receiving system on the transmission system, the tuner and the cable is as follows.

[First Embodiment]

RF modem of a cable broadcasting (CATV) converter of the present invention, as shown in FIG. 2, generates a carrier to modulate the transmission data, and transmits the carrier data on the carrier and outputs the transmission data. Transmits an oscillator 20, a low pass filter 21 for filtering the transmit RF signal output from the transmit oscillator 20, and a transmit RF signal passing through the low pass filter 21 through a cable, The received RF signal is separated from the transmission system by a first coupler 23 passing through the reception path, a high pass filter 24 for filtering the received RF signal branched from the first coupler 23, and A second coupler 25 for branching the received RF signal passing through the high pass filter 24 into a tuner side for image and audio processing and a path for demodulating received data, and a reception passed through the second coupler 25. Amplify RF signal and input to tuner A wideband amplifier 26, a reception amplifier 27 for amplifying the data signal branched from the second coupler 25, a demodulator 28 for demodulating data on the signal amplified by the reception amplifier 27, The demodulator 28 includes a receiving oscillator 29 for generating and supplying an oscillation signal for data demodulation.

In the transmission system, the low pass filter 21 is configured in one stage, and the first low pass filter 21a is connected between the transmission oscillator 20 and the coupler 23, or the second low pass filter. 21b may be connected between the coupler 23 and the transmission oscillator 20, or may be configured by connecting a transmission amplifier 22 that amplifies a transmission RF signal at the front or the rear of the filter.

FIG. 2 shows a case where the two stage low pass filters 21a and 21b and the transmission amplifier 22 are formed between them.

The RF modem operation and effects of the cable broadcasting (CATV) converter as described above are as follows.

In the case of data transmission, the transmission oscillator 20 generates a carrier signal and loads the transmission data on it, and outputs the output RF signal. The output RF signal is passed through the low pass filter 21 to remove unwanted waves, and then the first coupler ( 23 is transmitted via a cable, and the low pass filter 21 is one stage of the first low pass filter 21a or the second low pass filter 21b or only one stage of filtering is used to remove the unwanted wave. In case of shortage, it is necessary to configure both stages of the filters 21a and 21b in order to secure a sufficient bandwidth, or if the output of the transmission oscillator 20 is not sufficient for the transmission of the transmission signal, the transmission amplifier 22 Amplify by intervention and transmit via coupler.

At this time, in order to send an output level of -98Bm from the transmission cable, the transmission oscillator 20 → the first low pass filter 21a → the transmission amplifier 22 → the second low pass filter 21b → the first coupler 23 → Since the total attenuation of the system leading to the cable is 10 dBm (coupler; 4 dBm, low pass filter; 3 dBm * 2), and the amplification degree of the transmission amplifier 22 is 13 db, the output level of the transmission oscillator 20 = -9 dBm-10 dBm + 13 dBm = -6 dBm.

On the other hand, in the case of reception, the signal input from the cable is branched by the first coupler 23 to remove the unwanted wave while passing through the high pass filter 24, and the signal passed through the tuner is again tuned by the second coupler 25. The RF broadcast reception signal to be sent to the side and the data signal to be sent to the demodulator are separated and transmitted to each system.The signal sent to the tuner is amplified by the broadband amplifier 26 and then supplied to the tuner, and the signal sent to the demodulator is received. Amplified to the required level at 27, the demodulator 28 receives the local oscillation signal of the receiving oscillator 29 and demodulates it.

At this time, when a signal is input at a force of -44 ± 10 dBm from the cable, the first coupler (23) → high pass filter (24) → coupler (25) → receiving amplifier (27) → demodulator (28) → receiving system Since the total attenuation of is 11 dBm (coupler 23, 25; 45 dBm, high pass filter 24; 3 dBm), and the amplification degree of the receiving amplifier 27 is 11 dBm, the local oscillation signal output level of the receiving oscillator 29 is It can be set from -3 to -20 dBm.

On the other hand, the signal force of the transmission system is not transmitted only to the cable from the first coupler 23, but also to the receiving system of the tuner and the demodulator. Since the output level of the low pass filter 21b is -54 dBm, the high pass filter ( 24) is input with a force of -25dBm.

This force flows into the tuner at -25dBm-40dBm-4dBm + 9dBm = -60dBm and does not affect the tuner.The harmonic forces generated by the transmission system are 40dBmc or more smaller than the transmit level, so the tuner is below -100dBm. Is passed to.

In addition, the transmission level is -25dBm-40dBm-4dBm + 11dBm = -58dBm at which the level input to the demodulator 28 in the receiving system is -34dBm to -54dBm or less.

The effect of the receiving system on the cable and tuner is that the local oscillating output level of the receiving oscillator 29 is -20 dBm, the reverse propagation characteristic of the demodulator 28 is -30 dBm, and the reverse propagation characteristic of the receiving amplifier 27 is -60 dBm. Therefore, the force leaking to the input terminal of the receiver amplifier 27 becomes -90 dBm.

The influence of this force on the tuner is -90dBm-20dBm + 16dBm = -94dBm, which is 50dBm less than the standard field strength of -44dBm.

In the cable, -90dBm-4dBm-3dBm-4dBm = -101dBm satisfies the specification of -84dBm or less at the leakage electromagnetic wave of the converter from 50 to 450MHz.

On the other hand, since the undesired electromagnetic wave generated by the tuner has a reverse amplification degree of -27 dBm of the wideband amplifier 26, the total attenuation becomes 38 dBm, and forces below -46 dBm are allowed.

Second Embodiment

In the second embodiment of the RF modem of the cable broadcasting (CATV) converter of the present invention, as shown in FIG. 3, a transmission for generating a carrier to modulate the transmission data and loading the transmission data on the carrier is output. Transmits the oscillator 30, the low pass filter 31 for filtering the transmit RF signal output from the transmit oscillator 30, and the transmit RF signal passing through the low pass filter 31 through a cable, The received RF signal is separated from the transmission system by a first coupler 33 passing through the reception path, a high pass filter 34 for filtering the received RF signal branched from the first coupler 33, and Broadband amplifier 35 for amplifying the received RF signal passed through the high-pass filter 34, and the signal amplified by the broadband amplifier 35 branched to the tuner side for image and audio processing and the path for demodulation of received data Second coupler (36) And a receiver amplifier 37 for amplifying the data signal branched from the second coupler 36, a demodulator 38 for demodulating data from the signal amplified by the receiver amplifier 37, and the demodulator 38. And a receiving oscillator 39 for generating and supplying an oscillation signal for data demodulation.

In the transmission system, the low pass filter 31 is configured in one stage, and the first low pass filter 31a is connected between the transmission oscillator 30 and the coupler 33, or the second low pass filter. 31b may be connected between the coupler 33 and the transmission oscillator 30, or may be configured by connecting a transmission amplifier 32 that amplifies a transmission RF signal at the front or the rear of the filter.

FIG. 3 shows a case where the two stage low pass filters 31a and 31b and the transmission amplifier 32 are formed between them.

The operation and effects of RF modem of the cable broadcasting (CATV) converter having such a configuration are as follows.

In the case of data transmission, the transmission oscillator 30 generates a carrier signal, loads the transmission data on it, and outputs it. The output RF signal is passed through a low pass filter 31 to remove unwanted waves, and then a first coupler ( 33) is transmitted via a cable, and the low pass filter 31 is one stage of the first low pass filter 31a or the second low pass filter 31b or only one stage of filtering is used to remove unnecessary waves. In case of shortage, both the filters 31a and 31b of two stages are configured to secure sufficient bandwidth, or if the output of the transmission oscillator 30 is not sufficient for transmission of the transmission signal, the transmission amplifier 32 Amplify by intervention and transmit via coupler.

At this time, in order to send an output level of -9 dBm from the transmission cable, the transmission oscillator 30 → the first low pass filter 31 a → the transmission amplifier 32 → the second low pass filter 31 b → the first coupler 33 → Since the total attenuation of the system leading to the cable is 10 dBm (coupler; 4 dBm, low pass filter; 3 dBm * 2), and the amplification degree of the transmit amplifier 32 is 13 dBm, the output level of the transmit oscillator 30 = -9 dBm-10 dBm + 13 dBm = -6 dBm.

On the other hand, in the case of reception, the signal input from the cable is branched by the first coupler 33 to remove the unwanted wave while passing through the high pass filter 34, and the signal passed here is amplified by the broadband amplifier 35 The second coupler 36 separates the RF broadcast reception signal to be sent to the tuner side and the data signal to be sent to the demodulator side, and is transmitted to each system. The signal sent to the demodulator side is amplified to the required level by the receiving amplifier 37. The demodulator 38 receives the local oscillation signal of the reception oscillator 39 and demodulates it.

At this time, when a signal is input with a force of -44 ± 10 dBm from the cable, the first coupler 33 → high pass filter 34 → wideband amplifier 35 → coupler 36 → receiver amplifier 37 → demodulator 38 → the total attenuation of the system leading to the received data is 11 dBm (couplers 33, 36; 4 dBm * 2, high pass filter 34; 3 dBm), and the amplification degree of the receive amplifier 37 is 11 dBm. The local oscillation signal output level can be set from 0 to -20dBm.

On the other hand, the signal force of the transmission system is not transmitted only to the cable from the first coupler 33, but also to the receiving system of the tuner and the demodulator. Since the output level of the low pass filter 31b is -5 dBm, the high pass filter ( 34) is input with a force of -25dBm.

This force flows into the tuner with -25dBm-40dBm-4dBm + 9dBm-60dBm and does not affect the tuner.The harmonic forces generated by the transmission system are over 40dBm smaller than the transmit level, so the tuner is below -100dBm. Delivered.

In addition, the transmission force input to the demodulator 28 in the receiving system is -58 dBm + 16 dBm = -42 dBm, and a standard electric field strength degree is introduced.

The effect of the receiving system on the cable and tuner is that the local well output level of the receiving oscillator 39 is -20 dBm, the reverse propagation characteristic of the demodulator 38 is -30 dBm, and the reverse propagation characteristic of the receiving amplifier 37 is -60 dBm. Therefore, the leakage force at the input terminal of the receiver amplifier 37 becomes -90 dBm. The influence of this force on the tuner is -90dBm-20dBm = -110dBm and -90dBm-27dBm-11dBm = -128dBm on the cable, which satisfies the specification of -84dBm or less at the converter's leakage electromagnetic wave 50 to 450MHz.

On the other hand, the undesired electromagnetic wave generated in the tuner is allowed a force of -46 dBm or less because the backward amplification degree of the broadband amplifier 35 is -27 dBm.

Third Embodiment

In the third embodiment of the RF modem of the cable broadcasting (CATV) converter of the present invention, as shown in FIG. 4, a transmission for generating a carrier to modulate the transmission data and loading the transmission data on the carrier is output. A path for transmitting the transmission RF signal passing through the oscillator 40, the low pass filter 41 for filtering the transmission RF signal output from the transmission oscillator 40, and the low pass filter 41 through a cable. And the received RF signal is a first coupler 43 for branching to a data receiving system and a first high pass filter 44a for filtering the data signal from the received RF signal branched from the first coupler 43. ), A receiver amplifier 45 for amplifying the received data passing through the first high pass filter 44a, a demodulator 46 for demodulating data from the signal amplified by the receiver amplifier 45, Demodulate data into the demodulator 46 A receiving oscillator 47 for generating and supplying an oscillation signal for a second signal; a second coupler 48 for branching a data transmission path to a cable, the first coupler 43, and a tuner; and the second coupler 48 A second high pass filter 44b for filtering the received RF signal branched at and a wideband amplifier 49 for amplifying a signal passing through the second high pass filter 44b and inputting a tuner.

In the transmission system, the low pass filter 41 is configured in one stage, and connects the first low pass filter 41a to the transmitter oscillator 40 and the coupler 43 at the same time, or the second low pass filter. 41b may be connected between the coupler 43 and the transmission oscillator 40, or may be configured by connecting a transmission amplifier 42 for amplifying a transmission RF signal at the front or the rear of the filter.

FIG. 4 shows a case where a two-stage low pass filter 41a (41b) and a transmission amplifier 42 are formed therebetween.

The operation and effects of RF modem of the cable broadcasting (CATV) converter having such a configuration are as follows.

In the case of data transmission, the transmission oscillator 40 generates a carrier signal, loads the transmission data on it, and outputs it. The output RF signal is passed through the low pass filter 41 to remove unwanted waves, and then the first coupler ( 43) and the second coupler 48 are transmitted via a cable, and the low pass filter 41 is connected to the first stage of the first low pass filter 41a or the second low pass filter 41b to remove the unwanted wave. Or if only one stage of filtering is insufficient, the two stages of filters 41a and 41b are configured to secure sufficient bandwidth, or the output of the transmission oscillator 40 is not sufficient for transmission of the transmission signal. This is amplified through the transmission amplifier 42 and transmitted through the coupler.

At this time, in order to send an output level of -9 dBm from the transmission cable, the transmission oscillator 40 → the first low pass filter 41a → the transmission amplifier 42 → the second low pass filter 41b → the first coupler 43 → The output of the transmission oscillator 40 because the total attenuation of the system from the second coupler 48 to the cable is 14 dBm (coupler; 4 dBm * 2, low pass filter; 3 dBm * 2), and the amplification degree of the transmission amplifier 42 is 13 dBm. The level is -2 dBm.

On the other hand, in the case of reception, the RF signal input from the cable is branched by the second coupler 48 and passed through the second high pass filter 44b to remove unwanted waves, and amplified by the broadband amplifier 49 and supplied to the tuner. On the other hand, the received data signal branched from the second coupler 48 is again branched from the second coupler 43, and the received data signal is filtered by the first high pass filter 44a. After amplifying to the required level in the receiving amplifier 45, the demodulator 46 receives the local oscillation signal of the receiving oscillator 47 and demodulates it.

At this time, when a signal is input at a force of -44 ± 10 dBm from the cable, the second coupler 48 → the first coupler 43 → the first high pass filter 44a → the receiver amplifier 45 → the demodulator 46 → the receiver. The total attenuation of the system leading to the data is 11 dBm (couplers 48, 43; 4 dBm * 2, high pass filter 44a; 3 dBm), and the amplification degree of the receive amplifier 45 is 11 dBm. The local oscillating signal output level is set to -20dBm.

On the other hand, the signal power of the transmission system is not transmitted only by the cable, but also flows into the reception system of the tuner and the demodulator. The transmission power transmitted to the tuner is -5 dBm calculated from the loss and amplification degree of each stage as described above. Harmonic forces are below -96 dBm, which satisfies the above specification.

In addition, the transmission force transmitted to the demodulator 46 is -5dBm is input to the input terminal of the high pass filter 44a, which is -5dBm-40dBm-4dBm + 11dBm = -34dBm, which is quite a cone force.

In addition, the influence of the receiving system on the cable and the tuner is -94dBm-20dBm-20dBm-4dBm + on the tuner since the leakage force at the input of the first high pass filter 44a is -20dBm-30dBm-60dBm-4dBm = -9dBm. 16dBm = -122dBm, and -94dBm -20dBm-4dBm = -118dBm over the cable.

On the other hand, the unwanted electromagnetic wave generated in the tuner is allowed a force of -50 dBm or less because the backward amplification degree of the broadband amplifier 49 is -27 dBm.

[Example 4]

RF (Modem Modem) Embodiment 4 of the present invention is a head-end modem. As shown in FIG. 5, a transmission oscillator which generates a carrier to modulate transmission data and loads transmission data on this carrier is outputted. 50), a band pass filter 51 for filtering the transmitted RF signal output from the transmission oscillator 50, and a transmission RF signal passing through the band pass filter 51 through a cable, and receiving The RF signal to be separated from the transmission system passes through the coupler 53, a low pass filter 54 for filtering the received RF signal branched from the coupler 53, and the high pass filter 54 A demodulator 56 for amplifying the received RF signal passing through the amplified RF signal to the tuner, a demodulator 56 for demodulating data from the signal amplified by the receiver amplifier 55, and a demodulator 56 demodulating the data. Oscillation signal for It consists of a receiving oscillator 57 which produces and supplies.

In the transmission system, the band pass filter 51 is configured in one stage to connect the first band pass filter 51a between the transmission oscillator 50 and the coupler 53, or the second band pass filter. 51b may be connected between the coupler 53 and the transmission oscillator 50, or may be configured by connecting a transmission amplifier 52 that amplifies a transmission RF signal at the front or the rear of the filter.

5 shows a head-end RF model in the case where a two-stage band pass filter 51a, 51b and a transmission amplifier 52 are formed therebetween.

Head-end RF (RF) modem operation and effects of this configuration will be described as follows.

In the case of data transmission, the transmission oscillator 50 generates a carrier signal and loads the transmission data on it, and outputs the output RF signal. The output RF signal is passed through the band pass filter 51, and then the coupler 53 is removed. Is transmitted via a cable through the cable, and the bandpass filter 51 is formed as one stage of the first bandpass filter 51a or the second bandpass filter 51b to eliminate unnecessary waves, or when only one stage of filtering is insufficient. Configure both filters 51a and 51b in two stages to ensure sufficient bandwidth, or if the output of the transmission oscillator 50 is not sufficient for the transmission of the transmission signal, send it through the transmission amplifier 52 After amplification it is transmitted through a coupler.

At this time, in order to send an output level of -9 dBm from the transmission cable, the transmission oscillator 50 → the first band pass filter 51 a → the transmission amplifier 52 → the second band pass filter 51 b → the coupler 53 → the cable. Since the total attenuation of the following system is 10 dBm (coupler; 4 dBm, band filter; 3 dBm * 2), and the amplification degree of the transmission amplifier 52 is 13 dBm, the output level of the transmission oscillator 50 = -9 dBm-10 dBm + 13 dBm =-6 dBm Becomes

On the other hand, in the case of reception, the signal input from the cable branches from the coupler 53, passes through the low pass filter 54, removes the unwanted wave, amplifies to the required level in the receiver amplifier 55, and then in the demodulator 56 The local oscillation signal of the reception oscillator 57 is input and demodulated.

At this time, if a signal is inputted with a force of -44 ± 10 dBm from the cable, the total attenuator of the system leading to coupler (53) → low pass filter (54) → receiving amplifier (55) → demodulator (56) → receiving data is 7 dBm (coupler). (53); 4 dBm, low pass filter 36; 3 dBm), and since the amplification degree of the receiving amplifier 55 is 11 dBm, the input level of the demodulator 56 is 4 dBm amplified to the cable input level.

At this time, if the local oscillation output level of the receiving oscillator 57 is set to -2 dBm, the intensity of the receiving oscillator 57 leaked by the cable becomes -20 dBm-30 dBm-60 dBm-3 dBm-4 dBm = -117 dBm, and the transmitting force is a demodulator ( 56) the incoming level is -25dBm-40dBm + 11dBm = -54dBm, so the local oscillation output level of the receiving oscillator 57 can be raised to the limit of leakage electromagnetic wave, if 5-30MHz is below -89dBm Therefore, it is necessary to have an allowance of 28dBm and complement the reception sensitivity to obtain an appropriate value.

Transmitter Oscillator

(A) and (b) of FIG. 6 are diagrams showing the circuit configuration of the transmission oscillator applied in the first to fourth embodiments, in which (a) is an oscillation circuit by one PLL type, and (b) is Oscillation circuit by fixed type and PLL type.

The transmission oscillator shown in FIG. 6A includes a modulation oscillator 60a for modulating and outputting transmission data to an oscillation signal, a reference oscillator 60b for generating a reference local oscillation signal, and the oscillator 60a ( A PLL unit 61 for controlling the loop filter by comparing the phases of 60b) and a loop filter 62 for controlling the oscillation frequency of the modulation oscillator 60a under the control of the PLL unit 61.

The transmission oscillator having such a configuration loops the signals when the PLL section 61 compares the phases of the oscillation signals input from the modulation oscillator 60a and the reference oscillator 60b and outputs a signal corresponding to the phase difference. The filter 62 converts the voltage to fix the carrier frequency of the oscillator 60a to a constant value, thereby fixing to a desired frequency.

In this circuit, when the transmission channel is a plurality of channels, it is difficult to obtain an even FM characteristic according to the channel because FM modulation is performed depending on the linearity of the variable capacitance capacitor inside the modulation oscillator 60a.

The transmission oscillator shown in (b) of FIG. 6 includes a PLL-type transmission local oscillator 63 for outputting a local oscillation signal for modulating and outputting transmission data to an oscillation signal, and a reference oscillator for generating a PLL reference local oscillation signal. (64), the PLL section 65 for controlling the loop filter by comparing the phases of the oscillators (63) and 64, and the PLL transmission local oscillator (63) under the control of the PLL section (65). A loop filter 66 for fixing an oscillation frequency, a fixed transmission local oscillator 67 for modulating and outputting a transmission data signal, an output of the fixed transmission local oscillator 67, and the PLL transmission local oscillator 63; And a band pass filter 69 for filtering the mixed signal from the mixer 68 to an appropriate band and outputting the mixed signal.

The transmission oscillator having such a configuration compares the phases of the oscillation signals input from the transmission local oscillator 63 and the reference local oscillator 64 with each other, and outputs a signal corresponding to the phase difference. The loop filter 66 converts the voltage into a voltage to fix the local oscillation frequency of the oscillator 63 to a constant value, wherein the fixed local oscillation signal carrying the transmission data in the fixed transmission local oscillator 67 is mixed with a mixer ( 68) and then output the filtered and modulated transmission data signal at the desired frequency by filtering through the band pass filter (69).

In this circuit, since the fixed oscillator 63 is employed, the FM modulation is performed at the fixed oscillation 63, and the channel change is performed by the PLL type oscillators 63, 64, 65, and 66. Constant FM characteristic can be obtained.

[Transmitter]

FIG. 7 illustrates a circuit configuration of the transmission amplifier applied to FIGS. 2 to 5. As shown in FIG. 7, the input coupling capacitor C1 and the coupling capacitor C1 are described. A transistor Q1 for amplifying the transmission signal input through the resistor, a resistor R1 (R2) for setting a bias of the transistor Q1, and a coupling capacitor for outputting the signal amplified by the transistor Q1. (C2) and a resistor (R3) for reducing the load variation when the transmission amplifier circuit is turned on and off at the output terminal, VCC is the power supply, C3 is a capacitor for removing the power ripple.

The above-described transmission amplifier sets the bias by the resistors R1 and R2, and the 1 dB gain compression point is -4 dBm or more, and the amplification degree is about 13 dB so that the input coupling capacitor ( The signal to be transmitted input through C1) is amplified by the transistor Q1 and then output through the coupling capacitor C2 of the output terminal.

At this time, since the transmission amplifier is turned on or off as necessary, it is necessary to minimize the impedance variation during on and off, and through the resistor R3 based on the necessity, when the amplifier is turned on, the resistor R3 and the capacitor ( The impedance value of C2) and the transistor Q1 acts as a load, and when the amplifier is turned off, the transistor Q3 becomes high impedance and causes the resistor R3 to act as a load so that the resistor R3 is turned on or off. ) Always intervenes to minimize load fluctuations.

[Coupler]

8 shows an exemplary circuit of the coupler used in FIGS. 2 to 5 and its characteristics.

This coupler circuit has -4dB transfer characteristic in the reverse / reverse direction between P1 and P2 when viewed from three terminals (P1, P2, P3), -4dB transfer characteristic in the reverse / reverse direction between P1 and P3, and P2 Between P3 and P3, a transmission characteristic of -20dB in the reverse / reverse direction was satisfied to satisfy the above-described specifications in the first to third embodiments.

[Wideband Amplifier]

9 shows a circuit configuration of an embodiment of a broadband amplifier applied to the first to third embodiments.

As shown in FIG. 9, the coupling capacitor C1 of the input terminal, the transistor Q1 for amplifying the signal input through the coupling capacitor C1, and the bias of the transistor Q1 are set. The first stage includes the bias resistors R1, R2, R4, and coil L1, and a capacitor C2, a coil L2, and a resistor R3, which are connected to secure the broadband characteristics of the transistor Q1. A transistor (Q2) for constituting an amplifying circuit and amplifying the coupling capacitor (C3) of the signal amplified by the first stage amplifier circuit, the signal input through the coupling capacitor (C3), in two stages; Bias resistors R5, R6, R8 and coil L3 for setting the bias of Q2, and capacitors C4 and coil L4 connected to adjust the broadband characteristics of the transistor Q2. And a second stage amplifying circuit with a resistor R7 and a coupling capacitor C5 of the output signal amplified by the transistor Q2. It was constructed.

The wideband amplifier of this configuration amplifies the received signal input through the coupling capacitor C1 in the transistor Q1 by one stage according to the bias set by the resistors R1, R2, R4 and coil L1, At this time, the capacitor C2, the coil L2, and the resistor R3 give the broadband characteristics in the 50 to 450MHz band, and the coil L1 has a high impedance between the power line and the signal line.

In this way, the signal amplified by the first stage of the transistor Q1 is input to the second stage amplifying transistor Q2 of the rear stage through the coupling capacitor C3, and the transistor Q2 is connected to the resistors R5, R6, and R8. And amplifies the input signal in two stages according to the bias set by the coil L3 and outputs the resultant signal through the coupling capacitor C5. At this time, the broadband characteristics are obtained by the capacitor C4, the coil L4, and the resistor R7. By adjusting, the two-stage amplified signal is set to converge around 75Ω in a desired band, has an even amplification characteristic of about 14dB to 14.5dB, and has an even characteristic of about -27dB at 40 to 450MHz.

[Receiving amplifier]

10 is a diagram illustrating a circuit configuration of a receiver amplifier applied to the first to fourth embodiments, wherein the receiver amplifier is input through an input coupling capacitor C1 and a resistor R1 and the coupling circuit. A transistor Q1 for amplifying the received signal by one step, resistors R2 and R3 for setting a bias of the transistor Q1, and a feedback loop for securing wideband input characteristics of the transistor Q4. A resistor R5 and a capacitor C4 for forming a first stage amplification circuit comprising a condenser C2, a coil L1, and a resistor R4, and coupling the first stage amplification circuit and the rear stage amplification circuit; The second stage amplification circuit is composed of a transistor Q2 for amplifying the signal input through the coupling resistor and the capacitor in two stages, and resistors R6 and R7 for setting the bias of the transistor Q2. For coupling between the output stage and the demodulator of the second stage amplification circuit. An impedance conversion circuit composed of a capacitor C6, C7 and a coil L2 was provided.

In the figure, VCC is the power supply, and C2 and C3 are the power ripple rejection capacitors.

Referring to the operation of the reception amplifier having such a configuration, in the first stage amplification circuit to perform the amplification of 11dB in the forward direction, -60dB in the reverse direction to have a wideband input characteristics, the capacitor (C1) and the resistor (R1) The transistor Q1 is amplified by the bias set by the resistors R2 and R3 in a very short time, and the wideband input characteristics are provided by the feedback circuits of the capacitor C3, the coil L1, and the resistor R4. Secured.

In addition, the second stage amplification circuit including the transistor Q2 and the peripheral element has a low forward amplification degree and a reverse amplification degree of about -40 dB, so that the first and second stages are coupled to the capacitor C4 and the resistor R5. The signal input through the R5 and the capacitor C4 is amplified and output by the transistor Q2 according to the bias set by the resistors R6 and R7.

The signal output from the transistor Q2 is supplied to the demodulator as described above. Since the demodulator is high impedance and the output terminal of the receiver amplifier is low impedance, an impedance conversion circuit composed of capacitors C6, C7 and coil L2 is used. To convert the impedance.

Therefore, the signal amplified by the receiving amplifier is input to the demodulator through an impedance conversion process.

As described above, according to the RF modem of the cable broadcasting (CATV) converter of the present invention, it is possible to minimize leakage electromagnetic waves and to transmit and receive data in a configuration that has the least effect on the video and audio signals of the TV. It is possible to minimize the distortion of the video and audio signals due to the addition of communication.

In addition, the head end RF modem that communicates with the RF modem of the cable broadcasting (CATV) converter is not specified in the standard, but it can provide a head end RF modem with a simplified configuration with the least impact on the CATV network.

Claims (31)

A transmission oscillator 20 for generating a carrier and loading transmission data on the carrier, a low pass filter 21 for filtering a transmission RF signal output from the transmission oscillator 20, and the low pass filter ( A first coupler 23 which transmits the transmitted RF signal through the cable 21 and passes the received RF signal to the reception path separately from the transmission system; and a reception branched from the first coupler 23. A high pass filter 24 for filtering the RF signal, and a second coupler for branching the received RF signal passing through the high pass filter 24 into a tuner side for image and audio processing and a path for demodulating received data ( 25), a wideband amplifier 26 for amplifying a received RF signal passing through the second coupler 25 and inputting it to a tuner, and a receiving amplifier for amplifying a data signal branched from the second coupler 25 ( 27) and amplification in the receive amplifier 27 A demodulator for demodulating the data from the signal 28 and the demodulator 28, cable TV (CATV) communication, RFID (RF) modem system composed of a receiving oscillator 29 for supplying to generate an oscillation signal for data demodulation. A transmission amplifier (22) according to claim 1, characterized in that it comprises a transmission amplifier (22) for amplifying a transmission RF signal between the output terminal of the transmission oscillator (20) and the input terminal of the low pass filter (21) and supplying it to the low pass filter (21). RF modem for cable broadcasting (CATV) system. The RF amplifier for communication of a cable broadcasting (CATV) system according to claim 1, further comprising a transmission amplifier (22) for amplifying an RF signal and supplying it to the coupler (23) at the output terminal of the low pass filter (21). (RF) modem. The low pass filter (21) according to claim 1, characterized in that the low pass filter (21) consists of two stage filters (21a) and (21b), and a transmission amplifier (22) for amplifying a transmission RF signal between the filters of each stage. RF modem for cable broadcasting (CATV) system. The PLL type local oscillator 63 for outputting a local oscillation signal for modulating and transmitting transmission data to an oscillation signal, and a reference oscillator for generating a PLL reference local oscillation signal. (64), the PLL section 65 for controlling the loop filter by comparing the phases of the oscillators (63) and 64, and the PLL transmission local oscillator (63) under the control of the PLL section (65). A loop filter 66 for fixing an oscillation frequency, a fixed transmission local oscillator 67 for modulating and outputting a transmission data signal, an output of the fixed transmission local oscillator 67, and the PLL transmission local oscillator 63; Mixing the output of the mixer 68 and the band pass filter 69 for filtering and outputting the signal mixed in the mixer 68 to the appropriate band, characterized in that the RF for communication of the cable broadcasting (CATV) system ( RF) modem. 2. The transistor of claim 1, wherein the wideband amplifier 26 includes a coupling capacitor C1 at an input terminal, a transistor Q1 for amplifying a signal input through the coupling capacitor C1, and the transistor Q1. Bias resistors R1, R2, R4, and coil L1 for setting the bias of the capacitor; and capacitors C2, coil L2, and resistors (C2) connected to secure the broadband characteristics of the transistor Q1. A transistor configured to form a first stage amplification circuit (R3), and amplifying a two-stage amplification signal from the coupling capacitor C3 of the signal amplified by the first stage amplification circuit and the coupling capacitor C3; Q2), bias resistors R5, R6, E8 and coil L3 for setting the bias of the transistor Q2, and a capacitor C4 connected to adjust the broadband characteristics of the transistor Q2. ), The coil L4 and the resistor R7, and the coupling capacitor C5 of the output signal amplified by the transistor Q2. Cable television, characterized in that the two-stage configuration of the amplifier circuit (CATV) communication, RFID (RF) modem system. 2. The receiver of claim 1, wherein the receive amplifier 27 comprises: an input coupling capacitor C1 and a resistor R1, a transistor Q1 for amplifying a received signal input through the coupling circuit in one step; Resistors R2 and R3 for setting the bias of transistor Q1, and capacitors C2 and coil L1 and resistor R4 forming a feedback loop to secure wideband input characteristics of transistor Q4. A transistor for constructing a first stage amplification circuit, the resistor R5 and the capacitor C4 for coupling the first stage amplification circuit and the rear stage amplification circuit, and a transistor for amplifying a signal input through the coupling resistor and the capacitor in two stages. Q2 and a resistor R6 (R7) for setting the bias of the transistor Q2 constitute a second stage amplification circuit, and a capacitor C6 for coupling between the output stage of the second stage amplification circuit and a demodulator. And an impedance conversion circuit composed of C7 and coil L2. Cable TV (CATV) communication, RFID (RF) modem of the system of ranging. The transmission amplifier (22) according to claim 2, wherein the transmission amplifier (22) comprises: an input coupling capacitor (C1), a transistor (Q1) for amplifying a transmission signal input through the coupling capacitor (C1), Resistor R1 (R2) for setting the bias of the transistor Q1, a coupling capacitor C2 for outputting the signal amplified by the transistor Q1, and a transmission amplifier circuit on and off at the output terminal. RF modem for communication of a cable broadcasting system (CATV) system, characterized in that it consists of a resistor (R3) to reduce the load fluctuation. Transmitted through the transmission oscillator 30 for carrying the transmission data on the carrier wave, the low pass filter 31 for filtering the transmission RF signal output from the transmission oscillator 30, and the low pass filter 31 Transmitting the transmitted RF signal through a cable, and the received RF signal is separated from the transmission system to filter the first coupler 33 and the received RF signal branched from the first coupler 33 A high pass filter 34, a wideband amplifier 35 for amplifying a received RF signal passing through the high pass filter 34, and a tuner for image and audio processing of the signal amplified by the wideband amplifier 35. A second coupler 36 branching to the side and a path for demodulating the received data, a receiver amplifier 37 amplifying the data signal branched from the second coupler 36, and amplified by the receiver amplifier 37 A demodulator 38 for demodulating data in the signal; And an RF modem for communication in a cable broadcasting (CATV) system, comprising a reception oscillator (39) for generating and supplying an oscillation signal for data demodulation to the demodulator (38). The transmission amplifier 32 of claim 9, further comprising a transmission amplifier 32 that amplifies a transmission RF signal between the output terminal of the transmission oscillator 30 and the input terminal of the low pass filter 31 and supplies the amplified RF signal to the low pass filter 31. RF modem for cable broadcasting (CATV) system. 10. The RF signal for communication in a cable broadcasting (CATV) system according to claim 9, further comprising a transmission amplifier (32) which amplifies an RF signal and supplies it to the coupler (33) at an output terminal of the low pass filter (31). (RF) modem. The low pass filter (31) is composed of two stage filters (31a) and (31b), and a transmission amplifier (32) for amplifying a transmission RF signal between the filters of each stage is characterized in that it comprises. RF modem for communication of CATV system. 10. The transmission oscillator (30) according to claim 9, wherein the transmission oscillator (30) includes a PLL type transmission local oscillator (63) for outputting a local oscillation signal for modulating and outputting transmission data to an oscillation signal, and a reference for generating a PLL reference local oscillation signal. PLL section 65 for controlling the loop filter by comparing the phases of the oscillator 64 and the oscillators 63 and 64, and the PLL transmission local oscillator 63 under the control of the PLL section 65. A loop filter 66 for fixing the oscillation frequency of the antenna, a fixed transmission local oscillator 67 for modulating and outputting a transmission data signal, an output of the fixed transmission local oscillator 67, and the PLL transmission local oscillator 63 And a band pass filter 69 for filtering and outputting the mixed signal from the mixer 68 to an appropriate band. (RF) modem. 10. The transistor of claim 9, wherein the wideband amplifier 35 comprises: a coupling capacitor C1 at an input stage, a transistor Q1 for amplifying a signal input through the coupling capacitor C1, and the transistor Q1; Bias resistors R1 (R2) (R4) and coils (L1) for setting the bias of the capacitor, and capacitors (C2) (L2) and resistors (R3) connected to secure the broadband characteristics of the transistor (Q1). A first stage amplification circuit and a transistor (Q2) for amplifying a signal input through the coupling capacitor (C3) and the signal input through the coupling capacitor (C3) in two stages. ), A bias resistor R5, R6, R8 and coil L3 for setting the bias of the transistor Q2, and a capacitor C4 connected to adjust the broadband characteristics of the transistor Q2. And the second stage with the coupling capacitor C5 of the coil L4 and the resistor R7 and the output signal amplified by the transistor Q2. RF modem for communication of a cable broadcasting system (CATV) system comprising an amplifying circuit. 10. The receiver of claim 9, wherein the receive amplifier 37 comprises: an input coupling capacitor C1 and a resistor R1, a transistor Q1 for amplifying a received signal input through the coupling circuit in one step; Resistors R2 and R3 for setting the bias of transistor Q1, and capacitors C2 and coil L1 and resistor R4 forming a feedback loop to secure wideband input characteristics of transistor Q4. A transistor for constructing a first stage amplification circuit, the resistor R5 and the capacitor C4 for coupling the first stage amplification circuit and the rear stage amplification circuit, and a transistor for amplifying a signal input through the coupling resistor and the capacitor in two stages. Q2 and a resistor R6 (R7) for setting the bias of the transistor Q2 constitute a second stage amplification circuit, and a capacitor C6 for coupling between the output stage of the second stage amplification circuit and a demodulator. (C7) and the coil (L2) with an impedance change circuit composed of Cable TV (CATV) communication, RFID (RF) modem of the system of ranging. 13. The transmitter of claim 10, wherein the transmission amplifier 32 comprises: an input coupling capacitor C1, a transistor Q1 for amplifying a transmission signal input through the coupling capacitor C1, and Resistor R1 (R2) for setting the bias of transistor Q1, coupling capacitor C2 for outputting the signal amplified by transistor Q1, and when the transmission amplifier circuit is turned on and off at the output terminal. RF modem for communication in a cable broadcasting system (CATV), characterized in that it consists of a resistor (R3) to reduce the load variation. A transmission oscillator 40 for carrying and outputting transmission data on a carrier wave, a low pass filter 41 for filtering a transmission RF signal output from the transmission oscillator 40, and a low pass filter 41 which passes through the low pass filter 41. The transmission RF signal is branched to a path for transmitting through a cable, and the received RF signal is divided into a first coupling 43 for branching to a data reception system and data from a received RF signal branched from the first coupling 43. A first high pass filter 44a for filtering a signal, a receive amplifier 45 for amplifying a received data signal passing through the first high pass filter 44a, and a signal amplified by the receive amplifier 45 A demodulator 46 for demodulating the data, a reception oscillator 47 for generating and supplying an oscillation signal for data demodulation to the demodulator 46, a cable, data transmission to the first coupler 43, and a tuner. The second coupler 48 for branching the path A second high pass filter 44b for filtering the received RF signal branched from the second coupler 48; and a wideband amplifier 49 for amplifying and inputting a signal passing through the second high pass filter 44b RF modem for communication of CATV system. 18. A transmission amplifier (42) according to claim 17, further comprising a transmission amplifier (42) for amplifying a transmission RF signal between the output terminal of the transmission oscillator (40) and the input terminal of the low pass filter (41) and supplying it to the low pass filter (41). RF modem for cable broadcasting (CATV) system. 18. The RF signal for communication in a cable broadcasting (CATV) system according to claim 17, characterized in that a transmission amplifier (42) is provided at an output of said low pass filter (41) to amplify an RF signal and supply it to said coupler (43). (RF) modem. The low pass filter (41) is composed of two stage filters (41a) and (41b), and has a transmission amplifier (42) for amplifying a transmission RF signal between the filters at each stage. RF modem for cable broadcasting (CATV) system. 18. The transmission oscillator (40) according to claim 17, wherein the transmission oscillator (40) includes a PLL type transmission local oscillator (63) for outputting a local oscillation signal for modulating and outputting transmission data to an oscillation signal, and a reference for generating a PLL reference local oscillation signal. PLL section 65 for controlling the loop filter by comparing the phases of the oscillator 64 and the oscillators 63 and 64, and the PLL transmission local oscillator 63 under the control of the PLL section 65. A loop filter 66 for fixing the oscillation frequency of the antenna, a fixed transmission local oscillator 67 for modulating and outputting a transmission data signal, an output of the fixed transmission local oscillator 67, and the PLL transmission local oscillator 63; RF mixer for communication of the CATV system, characterized in that it comprises a mixer 68 for mixing the output of the) and a band pass filter 69 for filtering and outputting the signal mixed in the mixer 68 to the appropriate band. (RF) modem. 18. The transistor of claim 17, wherein the wideband amplifier 49 comprises: a coupling capacitor C1 at an input stage, a transistor Q1 for amplifying a signal input through the coupling capacitor C1, and the transistor Q1; Bias resistors R1, R2, R4, and coil L1 for setting the bias of the capacitor, and capacitors C2, coil L2, and resistors (C2) connected to secure the broadband characteristics of the transistor Q1. A transistor configured to form a first stage amplification circuit (R3), and amplifying a two-stage amplification signal from the coupling capacitor (C3) of the signal amplified by the first stage amplification circuit and the coupling capacitor (C3); Q2), bias resistors R5, R6, R8 and coil L3 for setting the bias of the transistor Q2, and a capacitor C4 connected to adjust the broadband characteristics of the transistor Q2. ), The coil L4 and the resistor R7, and the coupling capacitor C5 of the output signal amplified by the transistor Q2. An RF modem for communication of a cable broadcasting (CATV) system, comprising a second stage amplifying circuit. The method of claim 17, wherein the receiving amplifier 45, the input coupling capacitor (C1) and the resistor (R1), a transistor (Q1) for amplifying the received signal input through the first coupling circuit one-step, and Resistors R2 and R3 for setting the bias of transistor Q1, and capacitors C2 and coil L1 and resistor R4 forming a feedback loop to secure wideband input characteristics of transistor Q4. A transistor for constructing a first stage amplification circuit, the resistor R5 and the capacitor C4 for coupling the first stage amplification circuit and the rear stage amplification circuit, and a transistor for amplifying a signal input through the coupling resistor and the capacitor in two stages. Q2 and a resistor R6 (R7) for setting the bias of the transistor Q2 constitute a second stage amplification circuit, and a capacitor C6 for coupling between the output stage of the second stage amplification circuit and a demodulator. Comprising an impedance conversion circuit consisting of (C7) and the coil (L2) Cable TV (CATV) communication, RFID (RF) modem system according to claim. 21. The transmission amplifier according to claim 18, wherein the transmission amplifier (42) comprises: an input coupling capacitor (C1), a transistor (Q1) for amplifying a transmission signal input through the coupling capacitor (C1), and Resistor R1 (R2) for setting the bias of transistor Q1, coupling capacitor C2 for outputting the signal amplified by transistor Q1, and when the transmission amplifier circuit is turned on and off at the output terminal. RF modem for communication in a cable broadcasting system (CATV), characterized in that it consists of a resistor (R3) to reduce the load variation. The transmission oscillator 50 for carrying and outputting transmission data on a carrier wave, a band pass filter 51 for filtering the transmission RF signal output from the transmission oscillator 50, and the band pass filter 51 A coupler 53 for transmitting a transmit RF signal through a cable and receiving the received RF signal from a transmission system and passing it through a receive path, and a low pass filter for filtering the received RF signal branched from the coupler 53. (54), a receive amplifier (55) for amplifying a received RF signal passing through the high pass filter (54) and inputting it to a tuner, and a demodulator (56) for demodulating data from the signal amplified by the receive amplifier (55). And a receiving oscillator (57) for generating and supplying an oscillation signal for data demodulation to the demodulator (56). A transmission amplifier (52) is provided between the output terminal of the transmission oscillator (50) and the input terminal of the band pass filter (51) to amplify a transmission RF signal and supply it to the band pass filter (51). RF modem for cable broadcasting (CATV) system. 27. The communication amplifier of claim 25, further comprising a transmission amplifier 52 that amplifies an RF signal and supplies the RF signal to the coupler 53 at an output terminal of the band pass filter 51. RF) modem. 26. The apparatus of claim 25, wherein the band pass filter (51) comprises two stage filters (51a) and (51b), and a transmission amplifier (52) for amplifying a transmission RF signal between the filters of each stage. RF modem for communication of CATV system. The transmission oscillator 50 includes: a PLL-type transmission local oscillator 63 for outputting a local oscillation signal for modulating and outputting transmission data to an oscillation signal; and a reference for generating a PLL reference local oscillation signal; PLL section 65 for controlling the loop filter by comparing the phases of the oscillator 64 and the oscillators 63 and 64, and the PLL transmission local oscillator 63 under the control of the PLL section 65. A loop filter 66 for fixing the oscillation frequency of the antenna, a fixed transmission local oscillator 67 for modulating and outputting a transmission data signal, an output of the fixed transmission local oscillator 67, and the PLL transmission local oscillator 63; RF mixer for communication of the CATV system, characterized in that it comprises a mixer 68 for mixing the output of the) and a band pass filter 69 for filtering and outputting the signal mixed in the mixer 68 to the appropriate band. (2) modem. The receiver of claim 25, wherein the receive amplifier 55 comprises: an input coupling capacitor C1 and a resistor R1, a transistor Q1 for amplifying a received signal input through the coupling circuit in one step; Resistors R2 and R3 for setting the bias of transistor Q1, and capacitors C2 and coil L1 and resistor R4 forming a feedback loop to secure wideband input characteristics of transistor Q4. A transistor for constructing a first stage amplification circuit, the resistor R5 and the capacitor C4 for coupling the first stage amplification circuit and the rear stage amplification circuit, and a transistor for amplifying a signal input through the coupling resistor and the capacitor in two stages. Q2 and a resistor R6 (R7) for setting the bias of the transistor Q2 constitute a second stage amplification circuit, and a capacitor C6 for coupling between the output stage of the second stage amplification circuit and a demodulator. And an impedance conversion circuit composed of C7 and coil L2. RF modem for communication of cable broadcasting (CATV) system. 29. The transmitter of claim 26, wherein the transmission amplifier 52 comprises: an input coupling capacitor C1, a transistor Q1 for amplifying a transmission signal input through the coupling capacitor C1, and Resistors R1 and R2 for setting the bias of the transistor Q1, a coupling capacitor C2 for outputting the signal amplified by the transistor Q1, and a transmission amplifier circuit on and off at the output terminal. RF modem for communication of a cable broadcasting system (CATV) system, characterized in that it consists of a resistor (R3) to reduce the load fluctuation.