JPS6016775B2 - Multiplex communication device with common automatic frequency control function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a communication device used in a frequency division multiple access communication system using individual carrier modulation in satellite communication, and particularly to a multiplex communication device having a common automatic control function in a receiving circuit.

This frequency division multiple access system using individual carrier modulation is generally called SCPC/FDMA (SingleChaneIP).
er Camier/Frequency, DMsio
nMultipleAccess),
This is a communication method that uses independent transmitting and receiving radio frequency carrier waves for each channel for signal transmission, and is different from conventional frequency division multiplexing, frequency modulation, and frequency division multiple access (FDM).
The FM/FDMA) system is more flexible than the system that first multiplexes several channels and modulates one carrier wave with the multiplexed signal for communication, and also makes the communication bandwidth of the satellite repeater more effective. Since it can be used for transmission of small-capacity traffic, it has recently been in the spotlight not only for international communication but also as a domestic and intra-regional satellite communication system.

Among such SCPC/FDMA communication systems, there is a system called SUBED system to which the PCM-ORK system is applied for international communication.

This spade method is called SPADE (Singe chan
nel percarrier Pcmmultipl
e Access Demand, assigned
It was put into practical use under the name "Equipment".
Subsequently, as an application of this SPADE technology and concept, several simpler SCPC/FDMA systems have been proposed, and some of them have been put into practical use. First, S as a conventional technology
Regarding SCPC/FDMA devices including PADE method,
This will be explained with reference to FIGS. 1 to 6.

FIG. 1 shows a general frequency arrangement of signals in the SCPC/FDMA communication system.

In other words, a large number of frequencies are set for the permissible frequency band TB of the satellite repeater, with a mutual frequency interval of fs, and each earth station selects which of these frequencies to transmit for each channel of the signal to be transmitted. Communicate using a carrier wave with a frequency equal to Of course, one frequency can only be used to transmit one signal at a time. FIG. 1 can be thought of as showing the entire spectrum when the signal 2 transmitted from each earth station in this manner is input to the satellite repeater. Generally, pilot signal 1 is transmitted from one of the earth stations (reference station) to the center of the allowable frequency band, and this is used to perform automatic frequency control (AFC) and automatic gain control (AGC) during reception as described later. ) used for Specifically SPADE
In the case of the communication method, the allowable frequency band TB is 38M
The mutual spacing fs of the frequencies assigned to the carrier waves is 4 HZ, which allows about 800 carrier frequencies for the frequency band.

In this method, the frequency band TB is divided into a band UB above the frequency of the central pilot signal 1 and a band LB below the frequency of the central pilot signal 1.
Frequencies are divided into upper band UB and lower band L.
The frequencies belonging to B constitute a frequency pair for transmission and reception, and are used as one set. In other words, if a certain station uses a certain frequency 2' in the lower band LB as a transmission frequency for a certain channel, the other station will always use the frequency 2'' in the upper band UB that forms a frequency pair with 2'. Transmit using frequency.
The interval fF between the two frequencies forming this frequency pair is constant and is 18.048 MH2. Figure 2 shows SCPC
This is a conceptual diagram of a multiplex communication device for communication, in which a baseband signal 50 such as an audio signal or data is connected to a different communication circuit 100 for each channel, and modulation and demodulation are performed here. The input/output signal 15 (m) is connected to a composite spectrum signal 250 by a combining/distributing circuit 200. The common intermediate circuit 30 includes amplifiers, attenuators, filters, AFC/AGC circuits, etc. shared by all communication circuits, and has an interface with the station IF input/output signal 350 as a multiplexer. The number of communication circuits 100 connected to one common IF circuit 300 is variable, but is up to 60 in the case of a SPADE device. In order for the carrier waves transmitted separately from each station to be arranged correctly as shown in Figure 1, each communication circuit,
Various frequencies of the common IF circuit or up converter must be kept stable and accurate. SP
In the application example of the ADE system, this frequency error on the transmitting side is suppressed within 200 to 250 days2 in total.
However, from the earth station to the satellite repeater, the signal undergoes Doppler transitions caused by the movement of the satellite. Satellite transponders have errors due to instability in the internal local oscillator, and are also subject to Doppler transitions on the downlink from the satellite to the earth station. Furthermore, even within the earth station, there are errors due to instability of the local oscillator in the down converter, and the frequency may fluctuate significantly when looking at the entire system. Among these frequency fluctuations, the fluctuations after the input to the satellite repeater occur commonly for the entire spectrum shown in FIG. Therefore, relying on the pilot sent from the reference station, the receiving side uses a common AF for the entire spectrum.
By performing C, these common frequency transitions can be corrected. This frequency correction range is SPADE
In the case of the method, it is about ±6 female HZ. Common AF like this
Subordinate SPADE or SCPC/F, including C circuits
A configuration diagram of the DMA communication device is shown in FIG.

In the figure, a baseband signal 60 to be transmitted is applied to a communication circuit transmitting section 110 and a modulating local oscillator 111.
The output 40 of the frequency fTL is modulated by the modulator 112 to become a modulated wave of the frequency fTL. This modulated wave is combined with the output 30 of the frequency synthesizer 115 in the frequency mixer 113 and frequency-converted to become an IF output 160. SP
In the example of the ADE device, the output frequency f of the modulation local oscillator 111 is 45.9875 MHZ, and the output frequency of the frequency synthesizer 115 is 78 MHZ and 115 MHz.
is any one of approximately 80 frequency outputs occurring at 4 Hz intervals in the range of . As a result, IF output 1 60
is a signal in the range of 70MHZ to 18MH2. The m outputs 160 of multiple communication circuits in one station are connected to transformers.
The signals are synthesized by a combining circuit 210', which is a hybrid circuit, to become a transmitting combined spectrum signal 260, which is added to a transmitting common circuit 310, and subjected to necessary amplification, level adjustment, shaping by a filter, etc., and then becomes a station IF output 360. This station IF frequency is generally 70 MHZ frequency 2, which is the same as the output 160 of the communication circuit transmitter 110, and this is added to the up converter 1 and further passed through the power amplifier from the antenna to the satellite. Sent.
Next, on the receiving side, the radio waves received by the antenna are detected by a low-noise amplifier, then converted to the station IF by a down converter, and sent to the SCPC as the station M input 370.
input into the device.

Station IF input 370 is also typically chosen to be 70MHZ±18MHZ. The station m input 370 is input to the reception common circuit 320' and subjected to amplification, level adjustment, filter shaping, etc., but the most important function of the reception common circuit 320 is to perform automatic frequency control based on the aforementioned pilot signal. It is. [At the F input 37 and the mixer 323, the AFC
The received spectrum signal 270 is mixed with the output 20 (frequency is f^Fc) of the voltage controlled oscillator (VCO) 322 and frequency-converted to become the received spectrum signal 270. The pilot component in the received spectrum signal 270 is detected by the AFC circuit 321, compared with the reference frequency signal in the AFC circuit, and an error signal is output so that the two match, and the AFC operation is performed by controlling the VC0322. . For SPADE devices, f
^Fc is the same as fTL 45. It changes in the range of 6 female HZ centered around 79 MHZ. As a result, the received spectrum signal 270 is 3
It becomes a spectrum signal of 8 MHZ width. This received spectrum signal 27 is distributed through a distribution circuit 22 formed by a transformer hybrid in a number corresponding to the number of communication circuits, and becomes an IF input signal 170, which is applied to each communication circuit receiving section 120. Here, "input signal 1
First, the signal 70 is combined with the output 30 of the frequency synthesizer 115 by the mixer 121 and frequency-converted. The frequency-converted output passes through a filter 122 and is converted into an internal IF signal 80 with center frequencies f, F, and then sent to a demodulation circuit 1.
23 and becomes a baseband signal output 70. In the demodulation circuit 123, there is a channel filter that extracts only the carrier wave of the required channel from the received spectrum. Frequency conversion may be performed in order to realize this channel filter, but since it is not directly related to the present invention, it is omitted here. Let us continue the explanation assuming that there is a carrier wave of the desired channel. For SPADE equipment, f,F is 18.048M
H2, which is characterized by matching the interval fP between the frequency pairs mentioned above, and as a result, the frequency synthesizer 1
15 can be shared by the transmitting and receiving sides of the communication circuit, which is a significant advantage. Next, the frequency relationship of each part in this device will be further explained with reference to FIG.

The transmission signal A is converted into an IF output 160 by frequency-converting a modulated wave having a frequency equal to the output frequency f of the modulating local oscillator using the frequency synthesizer output, that is, the output 30 of the local oscillator C. This frequency becomes the station IF output signal as it is. On the other hand, regarding received signal B 0, IF output 160 and fP are used as station IF input signal 370.
only different frequencies are received. This signal undergoes a frequency transition by f^Fc due to the AFC action in the receiving common circuit and becomes an IF input signal 170. By using this and the output 30 of the frequency synthesizer as they are and frequency converting, the difference frequency is f, F. get. fTL=
Since f^Fc, f, F=fp. SP like this
While the ADE device has the great advantage of simultaneously controlling the transmitting and receiving frequencies with a single frequency synthesizer by defining frequency pairs and matching the difference frequency of the frequency pairs with the internal IF frequency in the communication circuit, the ADE device has the following advantages: There are drawbacks such as.

First, since the frequency pairs are reversely specified by the internal IF, there is no flexibility, and if the entire 38 MHz band of the satellite repeater cannot be used, some bands such as SMHZ and 1 HZ can be used. Can't communicate. In this case, it is common to use one frequency synthesizer and use the transmitting side and the receiving side independently, but in this case, the characteristics of the SPADE device are lost, so we will consider this as a drawback. As a result, the following three drawbacks remain. The first drawback is that it is difficult to conduct loopback tests that target only the communication circuits of the transmitting and receiving sections installed at one station. In FIG. 3, considering the folding loop 365 as a device, since the frequencies for transmission and reception are originally different by fP, it cannot be received by a paired communication circuit, and is received by another communication circuit, but as mentioned above, It is necessary to prepare two frequency synthesizers. Moreover, when checking the most important communication circuit after operation has started, it is even more difficult to connect the folding loop 165 because the transmitting and receiving frequencies are different. As shown in FIGS. 4 and 5, this corresponds to the IF output 160 and the input 170.
This is because the frequencies differ by either f^Fc-fP or f^pc+fP, and complex frequency conversion is required to eliminate this difference. The second drawback is also the fifth
As shown in the figure, the received signal 17 towards the end of the satellite repeater
When 0 is located, this is received and the internal IF of fIF
The local oscillation signal to be converted into a signal, that is, the output 30 of the frequency synthesizer, is located in the center of the 38 MHZ band, and the noise in the part shown as 171, which is outside the band of the received signal but in the vicinity, is This means that it is converted into f and F at the same time as image noise.

For this reason, SPADE devices and similar conventional SC
In the PC/FDMA device, the received spectrum signal 270 shown in FIG.
These two 1'
They are exploring ways to select which Akutai Castle signal to use, making the device even more complex. The third drawback will be explained with reference to FIG.

In FIG. 6, the transmitter up converter - 410
The RF output 460 of is typically a Z-band signal. On the receiving side, the RF input 470 is usually selected for signals in the 4GHZ band.
is added to the down converter-420. By the way, the specifications of the SPADE device are determined assuming a standard earth station for international communications, and according to this, the SPADE device and the up converter and down converter connected to it are installed in separate locations. They are often installed in the same area, and the two sides are usually connected by a coaxial line with several plates to several dozen sails. On the other hand, recent demand is mostly for local or domestic communication, and in this case earth stations are also becoming smaller and S
The distance between the CPC device and the up/down converter is close, and in some cases, they may even be installed in the same rack. FIG. 6 shows an example of application in the case of such a small station, in which the transmission common section 310 and the reception common section 320 are
It is possible to simplify. down converter
It is a double conversion type and has frequency conversion circuits in two places. In other words, 40Hz band RF
The input signal 470' is mixed with the output of the local oscillator 421 in the first mixer 422 and converted into a frequency of, for example, about 85 MHZ, and further mixed with the output of the second local oscillator 423 in the second mixer 424. The signals are mixed and converted to a local IF in the 7mMHZ band. This second frequency conversion part can be used as it is as an AFC circuit. That is, only the AFC circuit 321 that monitors the pilot and generates an error signal is installed in the reception common circuit 320', and the AFC VCO
In this case, the local oscillator 723 is changed to an appropriate voltage control device. However, in this case, the received spectrum signal 27
Since 0 becomes a signal in the 7MHZ band, the frequency of the input IF of each communication circuit also changes, making it impossible to share the same type of communication device for standard stations and simple devices for small stations. SUMMARY OF THE INVENTION An object of the present invention is to eliminate these drawbacks and provide a multiplex communication device having a common automatic frequency control function, which is highly flexible in terms of device testing and use, and can reduce manufacturing costs.

The first feature of the present invention is that a plurality of frequencies are set within the permissible frequency band with a mutual frequency interval of a constant value fs, and each station selects one of these frequencies for each baseband signal. is used for SCPC communication in which all stations perform automatic frequency control (AFC) for a common frequency transition included in the received signal by a pilot signal transmitted within the band from one of the stations, A station modulated by one baseband signal using the output of a transmitting frequency synthesizer that generates any one of a plurality of frequencies with a fixed frequency interval fs.
Frequency fT of the frequency band (for example, supine MHZ, soil handling HZ)
a communication circuit transmitting section that generates an SCPC signal of , a transmitting common circuit that outputs the output of this communication circuit transmitting section as a transmission spectrum signal of the frequency band of station m, and a voltage controlled oscillator (that generates a signal of frequency f^Fc). VCO), a frequency converter that uses the output signal of this VCO to convert the frequency f of any SCPC signal desired to be received in the received spectrum signal in the frequency band of the station to a frequency fo that differs from it by f^Fc, and this frequency A common AFC that extracts the pilot signal from the received spectrum signal at the output of the converter, detects its frequency transition, and corrects the frequency with respect to the received spectrum signal by controlling the f^Fc.
By adding the output of a reception common circuit comprising a circuit and a reception frequency synthesizer that generates any one of a plurality of frequencies with a constant frequency interval fs, the frequency fo in the spectral signal of the output of the reception common circuit is determined. SC you would like to receive
In an SCPC communication device having a communication circuit receiving section that converts a PC signal into a signal with fixed intermediate frequencies f, F and demodulates the same into a baseband signal, the VCO output frequency f^Fc of the receiving common circuit is set to A value that is twice the intermediate frequency fIF, or a value that differs from the double value by an integral multiple of the certain frequency interval fs, and further, the communication circuit receiving section independently selects the output frequency of the receiving frequency synthesizer as appropriate to generate not only the received SCPC signal of frequency fo that is being output from the receiving common circuit, but also the SCPC signal of frequency f that is being output from the communication circuit transmitter. , the receiving common circuit is configured to convert any of the received SCPC signals of the frequency fl that are generated when the frequency conversion circuit is omitted into a signal of the same intermediate frequency fIF. .

Furthermore, a second feature of the present invention is that in the multiplex communication device having the first feature, noise outside the allowable frequency band,
Alternatively, in order to suppress unnecessary signals from being converted into signals in the frequency bands f and F, the intermediate frequencies f and F of the communication circuit receiving section are sufficiently set compared to 1/2 of the allowable frequency bandwidth. This is due to the fact that it was highly selected.

Next, referring to FIG. 7, the SCPC/FDM according to the present invention
An example of a multiplex communication device for A will be described.

In FIG. 7, the frequency synthesizer 115 mentioned in FIG. There is a difference in the illustration in that there is a difference in the illustration, but other things are the same. As mentioned above, the use of independent frequency synthesizers on the transmitting side and the receiving side has already been put into practical use as an SCPC/FDMA device based on an application and modification of the SPADE technology, and the configuration is well known. However, in conventional such devices, the transmit frequency synthesizer 11
6 and reception frequency synthesizer 117, the same type of synthesizer is used, so the above-mentioned SPADE
It inherits the defects of the device. However, the present invention eliminates these drawbacks by selecting specific conditions for the frequency relationship of each part inside the SCPC/FDMA device. One of the features of the present invention is the input and output IF of the reception common circuit including the common AFC function.
Even if a specific relationship is established between the signal frequency and the output frequency of the reception frequency synthesizer, and the station IF input signal 370 of the reception common circuit is introduced into the communication circuit at the same frequency, it will not work as it would under normal usage conditions. , the output of the common AFC circuit is to obtain the same internal IF signal frequency f, F as in the case where the signal 270 is led to the communication circuit 120.

Now, it is assumed that the receiving station IF input 0 signal 370 includes a signal following the permissible frequency arrangement with the frequency interval fs as shown in FIG. 1, and the carrier frequency of any signal among the signals is f. Assume that the signal is converted to frequency fo by the AFC function of the reception common circuit. On the other hand, the output signal 32 of the reception frequency synthesizer 117 for receiving this signal and converting it into the frequency fIF
The frequency of is set as fR, and the darkness of each frequency mentioned above has the following relationship. fR=(1'2)(f, ten f.

) ten (1'2) N・fs●--1 However, N is a positive or negative integer including 0.

Now, if N=0 fR−f,=f.

-fR=(1/2)(f.-f,)3fIF
...It can be seen that the above purpose can be achieved by 2.

FIG. 8 corresponds to an example of using this frequency relationship, in which a signal transmitted by the own station is looped back at the IF stage or after passing through a satellite. That is, the transmission signal A is the IF output signal 160 of the communication circuit transmitter represented by fl.
However, in terms of frequency, this signal becomes the station IF output signal 360 as it is, and this is folded back to become the station IF input signal 370 to the receiving common circuit, which eventually becomes the frequency of f. This signal transitions by f^Fc by the reception common circuit, and the IF input signal 170 in the communication circuit reception section
f as shown in the received signal B in the figure. The frequency will be . Therefore, the frequency synthesizer output frequency fR indicated by the receiving station oscillation signal C is equal to the above-mentioned two frequencies, f and f. If you choose an intermediate value between , f. -fR and fR-f are converted into the same f and F. Conversely, if f and F are determined first, this corresponds to selecting f^Fc as aIF. As a result, the first drawback of the conventional apparatus mentioned above, namely the difficulty of repeat testing, is eliminated. In other words, in FIG. 7, the return loop 165 inputs a signal with a carrier frequency of f to the communication circuit receiving section, while the return loop at the station IF signal 365 inputs a signal with a carrier frequency fo. This is because it will happen. At the same time, the third drawback, that is, the problem of flexibility of the communication circuit with respect to the presence or absence of the AFC function in the receiving common circuit is also solved.

That is, if a device made based on the frequency relationship of the present invention includes an AFC function in the reception common circuit, the communication reception section will have f. However, if the AFC function is not included, the carrier frequency f of the station IF signal is input as is. Another feature of the present invention is to change the frequency of the internal IF signal to the allowable frequency band T of the satellite repeater.
It should be made sufficiently larger than 1'2 of B.

This is to solve the second drawback of the conventional device mentioned above, that is, the problem caused by image noise.
This condition is almost automatically derived from the first feature of the present invention. That is, when frequency converting the station IF input signal spectrum in the receiving common circuit, it is desirable that the spectrum of the input signal 370 and the spectrum of the output signal 270 do not overlap with each other, so f^Fc is naturally T.
Since it is larger than B, f and F are also larger than (1'2)TB. However, it may be desirable to select f and F somewhat arbitrarily due to other reasons, such as restrictions on the parts used. This case can be solved by using an appropriate value for N in equation 1 above. This frequency relationship is shown in FIG. 9, and the reception frequency synthesizer is different when receiving the frequency f of the transmission signal 160 and when receiving the frequency fo of the reception common circuit output 170. 32 fR and 32'fR'. However, since the frequency synthesizer can generate any frequency at fs intervals, there is no particular problem in its use. However, the operating range of the frequency synthesizer must be wider by INl·fs than in the case shown in FIG. 8, that is, when N=0. Note that the frequency synthesizer used in normal SCPC/FDMA equipment has an output of 1/M (M
is a positive integer) and compares it with a reference frequency equal to fs to stabilize the frequency.

In such a case, fR=M・fs...3 becomes.

Therefore, from formula 1 and formula 3 f, ten f.

= (2M-N) fs ...4 also fo-f・=
Substituting fAFc, we get fAFC=(2M-N)fs-.
...5 is obtained.

As an example, if you choose N=0, fl=70±1 Tsumugi MH2, and 21.4MHZ band as fIF, fRII91.4
±18MHZ and fAF.

is a frequency near 42.8 MHZ. In addition, fIF,
Accurate values such as fR and fAFc require detailed modification according to the frequency allocation plan corresponding to Figure 1. For example, SCPC/PSK/FDM, which is currently used internationally,
Considering the case of communication method A, fs = 49KH2, f, F
=21.4179MHZ, fAFc-42.839MH
2, fR=91.4175±捌MHZ, etc. can be considered as a specific example. Note that in the configuration of the present invention, the transmission frequency synthesizer can be designed completely independently, except that it has the same frequency interval fs standard as the reception frequency synthesizer.

For example, the frequency fTL of the modulation local oscillator 111 in FIG.
By setting the frequency to a higher frequency than the output frequency band of the frequency synthesizer, for example 187.987 MHZ, another drawback of the conventional device, namely the problem of spurious in the transmission output, can be solved.

However, since this configuration is not directly related to the present invention, further explanation will be omitted. As described above, according to the present invention, by using a frequency synthesizer on the receiving side that is independent of the transmitting side, and by appropriately selecting the frequency relationship of each part, It eliminates various disadvantages, facilitates testing of local equipment, improves performance, provides flexibility in equipment usage, and reduces manufacturing costs, and its effects are significant.

[Brief explanation of drawings]

Figure 1 is a general frequency allocation diagram of signals in SCPC/FDMA communication system, Figure 2 is a general conceptual diagram of SCPC/FDMA communication equipment, and Figure 3 is a conventional SCPC/FD communication system.
FIG. 4 is an explanatory diagram showing the frequency relationship of the main parts of the communication device shown in FIG. 3, and FIG. An explanatory diagram showing the frequency relationship, Figure 6 is a conventional SCPC/
A partial configuration diagram for explaining one of the problems of the FDMA communication device, FIG. 7 is an SCPC/FDMA communication device according to the present invention.
A configuration diagram showing an embodiment of the communication device, FIG. 8 is an explanatory diagram showing the frequency relationship of the main parts of the communication device of the present invention shown in FIG. 7, and FIG. 9 is also shown in FIG. 7. FIG. 6 is an explanatory diagram showing another frequency relationship of main parts in the communication device of the present invention. Explanation of symbols, 60: Transmission baseband signal, 15 10
: Communication circuit transmitter, 116: Transmission frequency synthesizer, 160: Transmission IF output, 210: Transmission synthesis circuit,
310: Transmission common circuit, 360: Transmission station IF output, 3
70: Receiving station "input (f,), 320: Receiving common circuit,
270: Reception spectrum IF signal output of reception common 0 circuit, 220: Reception distribution circuit, 170: Distributed reception I
F signal output, 117: Reception frequency synthesizer, 12
0: Communication circuit receiving section, 70: Reception baseband signal. Figure 1 Figure 2 Figure 4 Figure 3 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. A plurality of frequencies are set within the permissible frequency band so that the mutual frequency interval is a constant value f_s, and each station transmits each baseband signal using one of these frequencies as a carrier wave, and A pilot signal transmitted in the band by one of the stations causes all stations to perform automatic frequency control (
The frequency of the station IF modulated by one baseband signal using the output of a transmitting frequency synthesizer that generates any one of a plurality of frequencies with a fixed frequency interval f_s. A communication circuit transmitter that generates a transmit SCPC signal of frequency f_T in the frequency band (for example, 70 ± 18 MHz_z), a transmit common circuit that outputs the output of this communication circuit transmitter as a transmit spectrum signal of the station IF frequency band, and a frequency f_A_F_C. A voltage controlled oscillator (VCO) that generates a signal, and a frequency that uses the output signal of this VCO to convert the frequency f_I of any SCPC signal desired to be received in the reception spectrum signal of the frequency band of the station IF to a frequency f_O that differs from it by f_A_F_C. converter and extracting the pilot signal from the received spectrum signal at the output of the frequency converter;
a receiving common circuit including a common AFC circuit that detects the frequency transition and corrects the frequency for the received spectrum signal by controlling the f_A_F_C; By adding the output of the reception frequency synthesizer generated, the frequency f in the spectrum signal of the reception common circuit output is
_O's desired SCPC signal to be received at a certain intermediate frequency f_
In the SCPC communication device, the output frequency f_A of the VCO of the receiving common circuit is
_F_C is selected to be twice the intermediate frequency f_I_F, or a value that differs from the double value by an integral multiple of the certain frequency interval f_s, and further, the communication circuit receiving section By appropriately selecting the output frequency of the reception frequency synthesizer independently of the output of the reception frequency synthesizer, not only the reception SCPC signal of frequency f_O in the output of the reception common circuit but also the frequency f_T of the output of the communication circuit transmission section can be adjusted. It is configured to convert either an SCPC signal or a received SCPC signal of frequency f_I that occurs when a frequency conversion circuit is omitted in the receiving common circuit into a signal of the same intermediate frequency f_I_F, and The intermediate frequency f_I_F of the communication circuit receiving section is selected to be sufficiently large compared to 1/2 of the allowable frequency bandwidth, and noise or unnecessary signals outside the allowable frequency band are converted to signals in the frequency band of f_I_F. What is claimed is: 1. A multiplex communication device having a common automatic frequency control function, characterized in that the device is configured to suppress such occurrences.