JPH04104537A - Modem - Google Patents

Abstract

PURPOSE:To make the reception frequency characteristic flat on the reception side of a high channel signal of a land mobile radio telephone line or the like to keep stable demodulation by switching a switch to insert a line equalizer which corrects the degradation in characteristic of a signal due to attenuation on the high band side of the line. CONSTITUTION:A modulator 100 and a demodulator 116 are switched to a wire line or a land mobile radio telephone line by switches 107 and 113. When they are switched to the land mobile radio telephone line and the response mode is set, a high channel signal of the modulator 100 is transmitted after the degradation of the frequency characteristic due to line attenuation is corrected by a first line equalizer 104 for high band inserted by a switch 105. When the call originating mode is set, the high channel signal subjected to line attenuation from the land mobile radio telephone line is inputted to the demodulator 116 after the degradation of the frequency characteristic is corrected by a second line equalizer 112 for high band inserted by a switch 111. Thus stable demodulation is always kept in demodulators of the local station and the other-party station.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a full-duplex modem modulator and demodulator using a frequency division method that can be used commonly for car telephones and wired telephones.

(Prior Art) FIG. 2 is a block diagram showing the configuration of a conventional frequency division full duplex modem, which operates as a calling mode modem or an answering mode modem.

The calling mode modem receives the high channel signal and transmits the low channel signal, and is connected to the switch 20.
1 and 203 to each side, and a high channel band pass filter (BPF (H
)) 202 is connected, and a low channel band pass filter (BPF(L)) 208 is connected to the input side of the demodulator 209. In addition, the response mode modem receives a low channel signal and transmits a high channel signal, and switches 201 and 203 to the b side to connect a BPF (L) 208 to the output side of the modulator 200. A BPF(H) 202 is connected to the input side of the demodulator 209.

Next, the operation of the modem in response mode will be explained with reference to FIG.

The high channel signal output from the modulator 200 passes through the BPF (H) 202 connected by a switch 201, and then passes through the transmitting amplifier 2 connected by a switch 203.
04 and is amplified. The amplified signal undergoes impedance conversion from a four-wire system to a two-wire system by a hybrid circuit 205, and is input to a line equalizer 206 for line equalization. The line-equalized signal is transmitted to the other party's station via a general public telephone line.

On the other hand, a low channel signal sent from the other party through a public telephone line is equalized by a line equalizer 206, impedance converted from a 2-wire system to a 4-wire system by a hybrid circuit 205, and input to a receiving amplifier 207. and amplified. The amplified signal passes through a BPF (L) 208 connected by a switch 203, is input to a demodulator 209 connected by a switch 201, and is demodulated into a digital signal. The operation of the calling mode modem is basically the same as that of the answering modem described above.

In the modem shown in FIG. 2, the line equalizer 206 is provided between the hybrid circuit 205 and the general public telephone line, but it may be provided separately on the transmitting side and receiving side of a four-wire system.

Further, the line equalizer 206 has a function of correcting attenuation due to communication lines for high channel and low channel signals.

(Problem to be Solved by the Invention) However, since the line equalizer 206 does not take into account attenuation on the high frequency side due to the band limitation of a car phone, when the modem is used in a car phone, the reception There was a problem that deterioration occurred on the high frequency side of the signal.

Figure 3 shows an example of the frequency characteristics of Japan's NTT high-capacity car phone, in which (a) shows the frequency characteristics on the receiving side for a transmission signal that has a flat frequency characteristic from the car phone to the wired phone; b) is the frequency characteristic on the receiving side for a transmission signal having a flat frequency characteristic from a wired telephone to a car telephone.

In either case, it can be seen that the high frequency side is severely degraded.

In this case, it is conceivable to correct the attenuation on the high frequency side using the transmitting amplifier 204 or the receiving amplifier 207 shown in FIG. However, when the gain on the high frequency side is increased by the transmission amplifier 204, the gain on the low frequency side decreases and the signal on the low frequency side is attenuated unless the number of amplification stages is increased. Furthermore, if the gain on the high frequency side is increased by the receiving amplifier 207, noise on the high frequency side will also be amplified, which is undesirable for demodulation, and neither of these methods can be adopted.

The present invention was made in order to solve the above-mentioned problem that when a modem is used for a car phone, the received signal on the high frequency side is degraded, and the line equalizer is switched depending on the line used. The purpose of the present invention is to provide a modulator/demodulator that can always maintain optimal line characteristics by using the same.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a full-duplex modulator and demodulator using a frequency division method, in which a modulator and a demodulator are
A switch for switching between a wired line or a car telephone line, first and second high-frequency line equalizers that correct deterioration of frequency characteristics due to line attenuation of high channel signals, and a switch connected to the car phone line and in response mode. a switch for inserting the first high-frequency line equalizer into the modulator side; and a switch for inserting the second high-frequency line equalizer into the demodulator when connected to a car telephone line and in calling mode. It is equipped with a switch inserted on the side.

(Function) Switching of the modulator and demodulator to a wired line or a car telephone line can be easily performed using a switch.

When switched to a car telephone line and set to response mode, the high channel signal of the modulator is processed by the first high frequency line equalizer inserted by the switch, which reduces the deterioration of frequency characteristics due to line attenuation. The minutes are corrected in advance and sent. In addition, when set to calling mode, the deterioration of the frequency characteristics of the high channel signal that has undergone line attenuation from the car telephone line is corrected by a second high frequency line equalizer inserted by a switch. and input it to the demodulator. As a result, the demodulators of the other station and the local station can always maintain stable demodulation.

Note that since the low channel signal has almost no frequency characteristic deterioration due to line attenuation, there is no need for correction.

(Embodiment) FIG. 1 is a block diagram of an embodiment of the present invention.
1 is a modulator that outputs a low channel signal or a high channel signal, 101 and 103 are switches, 102 is a band pass filter for high channel signals (BPF (H)),
104 and 112 are high-frequency line equalizers (IBE), 10
5, 107, 111, 113 are switches, 106 is a transmitting amplifier, 10B is a hybrid circuit, 109 is a line equalizer, 110 is an attenuator (ATT), 114 is a receiving amplifier, 115 is a bandpass filter for low channel signals (B
PF (L) ), 116 is a demodulator that demodulates the low channel signal or the high channel signal.

Next, the operation of this embodiment will be explained based on FIG.

First, it is assumed that the modem shown in FIG. 1 is connected to a car telephone line and set as a response mode modem. At this time, switches 101, 103° 105, 107, 11
1 and 113 are respectively switched to the a side as shown in FIG. Modulator 100 outputs a high channel signal. This signal is input to a high channel BPF (H) 102 connected by a switch 101, and out-of-band signals are removed. The output of the BPF(I()) 102 is input to the transmission amplifier 106 through the HBE 104 connected by switches 103 and 105, and is amplified.The amplified signal is sent to the ATTI connected by the switch 107.
After the level is adjusted by IO, it is output to the car telephone line. The upper limit of the transmission power output to the car phone line varies depending on the type of car phone, so the above ATTI
The transmission power is adjusted by IO.

By the way, the frequency characteristics of the above-mentioned car telephone line are greatly attenuated on the high frequency side, as shown in FIG. 3(a). Therefore, the high channel signal output from the modem undergoes significant deterioration in its characteristics while passing through the car telephone line. Therefore, in this embodiment, HBE 1 is provided on the transmitting side.
04 is inserted, and the transmitting side corrects the high channel signal so as to cancel out the characteristic deterioration caused by the car telephone line, and then transmits the signal. Figure 4 shows this HBE1
04, in which the low frequency side of the high channel signal band is lowered and the high frequency side is raised.

On the other hand, the low channel signal sent from the other party's station is input from the car phone line through switch 111 and switch 113 to receiving amplifier 114, where it is amplified. As shown in the figure, since there is no attenuation on the low frequency side, the above-mentioned low channel signal does not suffer from characteristic deterioration.Therefore, in this case, HBE112
is not used. The signal amplified by the reception amplifier 114 is input to the HBE 115 via the switch 103, the out-of-band signal is removed, and the signal is sent to the demodulator 1 via the switch 101.
16 and demodulated into a digital signal.

Next, a case will be described in which the modem shown in FIG. 1 is connected to a car telephone line and set to calling mode.

In this case, the modem will transmit a low channel signal and receive a high channel signal, so switch 101
, 103 to the b side, a BPF (L) 115 is connected to the output side of the modulator 100, and a BPF (H) 102 is connected to the input side of the demodulator 116. Furthermore, since the low channel signal transmitted from the modem is hardly affected by the frequency characteristics of the car telephone line, the switch 1
05 to the b side, and no equalization by the HBE 104 is performed. However, the high channel signal sent from the other party's station is affected by the frequency characteristics of the car telephone line, and its characteristics have deteriorated. Therefore, in this embodiment, the switch 111
is switched to the b side, an HBE 112 having the same characteristics as the HBE 104 is inserted, and high-frequency line equalization is performed to prevent characteristic deterioration of the high channel signal from the car telephone line.

Note that the switches 107 and 113 are naturally switched to the a side.

Next, a case where the modem shown in FIG. 1 is connected to a public telephone line will be described. In this case, switch 105
, 107, and 111 are respectively switched to the b side, and the configuration thereof becomes the same as that shown in FIG. 2, and therefore the operation is also the same. Note that FIG. 5 shows an example of the characteristics of the line equalizer 106.

As explained above, when this embodiment is used by connecting to a car telephone line, the high frequency line equalizer tlBE104,
112 is used to correct characteristic deterioration due to the frequency characteristics of the car telephone line, flatten the frequency characteristics of the signal, and maintain good characteristics.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to easily insert a line equalizer for correcting signal characteristic deterioration due to attenuation on the high frequency side of the line by switching a switch. Therefore, even when used on a line with significant attenuation on the high frequency side, such as a car telephone line, the line equalizer can flatten the receiving frequency characteristics on the receiving side of the high channel signal, ensuring stable demodulation. can be maintained.

Furthermore, by changing the switch, it is possible to easily support both public telephone lines, etc., which have low attenuation on the high frequency side, and automobile telephone lines, which have high attenuation on the high frequency side.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a block diagram of a conventional full-duplex modem, Fig. 3 is a diagram showing the frequency characteristics of a car telephone, and Fig. 4 is a diagram showing high-frequency line equalization. FIG. 5 is a diagram showing the frequency characteristics of the line equalizer. 100...Modulator, 101, 103, 105°107
．． 111, 113...Switch, 102...Band pass filter for high channel signal, 104°112...
High-frequency line equalizer, 106... Transmission amplifier, 108.
...Hybrid circuit, 109...Line equalizer, 11
0...Attenuator, 114...Reception amplifier, 115...
・Band pass filter for low channel signal, 116...
Demodulator. Patent applicant: Oki Electric Industry Co., Ltd. Agent: Toshiaki Suzuki, Figure 1: Full-duplex modem by Shishiba (Figure 1) Masu no Oka j skin Makimochi, pressure 4th figure, direction) δ shi 8, 薯ii (, slow 3 mi σ) Zhouyu skin Maki 1 1,000'
i 5th v! J

Claims (1)

[Claims] In a full-duplex modem using a frequency division method, there is provided a switch for switching the modulator and demodulator to a wired line or a car telephone line, and a switch for correcting deterioration of frequency characteristics due to line attenuation of high channel signals. first and second high-frequency line equalizers; a switch for inserting the first high-frequency line equalizer into the modulator side when connected to a car telephone line and in response mode; and a car phone. A modulator/demodulator comprising: a switch for inserting the second high-frequency line equalizer into the demodulator side when connected to a line and in a calling mode.