JPH04135359A - Frequency dividing modem - Google Patents

Abstract

PURPOSE:To reduce cost, to improve performance, to make the device compact and light in weight and to facilitate operations by providing a distributor to be connected to a hybrid transformer in the case of a two wire line and to be connected to a reception side line in the case of a four wire line. CONSTITUTION:A low-pass filter 14 for transmission connects a hybrid transformer 7 and cuts a frequency higher than 2KHz from an audio signal. A hybrid transformer 17 is connected to a mixer 12, mixes transmitted and received signals and connects them to the line. A distributor 13 is connected to the hybrid transformer 17 in the case of the 2W line and connected to the reception side line in the case of the 4W line. A low-pass filter 15 for reception is connected to the distributor 13 and cuts a frequency higher than 2KHz, and a reception amplifier 9 is connected to the low-pass filter 15 for reception, and amplifiers the received signal up to a suitable level so as to transmit it to the hybrid transformer 7. Thus, a line filter having a bidirectional filter function is unnecessitated, the device is made compact and light in weight, the cost is reduced, the performance is improved and the operations is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a modem that performs data communication and telephone calls simultaneously among modems that use a frequency-divided voice band.

2. Description of the Related Art Conventionally, this type of modem has been comprised of a modem capable of full-duplex data communication, a line filter, and a telephone interface circuit. The line filter is used to frequency-divide a voice band line (<0.3 to 3.4 KHz) into frequencies below 2 KHz for telephone calls and above 2 KHz for data communication. The reason why data and voice are multiplexed onto a single line by frequency division is to reduce line costs and to communicate during maintenance and inspection without stopping data communications. Audio frequencies above 2KF (Z are removed, but there is no problem with intelligibility. This type of modem aims to reduce line costs, so it uses a 2-wire (hereinafter abbreviated as 2W) line. In this case, a line filter is inserted between the modem and the 211i line to divide the frequency and use it.However, when the line quality is extremely poor, a 4-wire (hereinafter abbreviated as 4W) line is used. However, in this case, a line filter is inserted on the transmitting side of one modem, and a line filter is inserted on the receiving side of the other modem to enable calls.

FIG. 2 is an explanatory diagram of a frequency division method of a frequency division modem, and FIG. 3 is a block diagram showing a frequency division modem using a conventional technique.

First, the principle of a frequency division modem will be explained with reference to FIG. 0.3-2K) Iz to call, 2-3, 4
KHz is used for data communication. Data communication is 2.4K
It uses two frequencies: Hz and 2.8 KHz. This allows full-duplex communication while making a phone call.

Next, the operation of a frequency division modem using conventional technology will be explained with reference to FIG. 2! Use with 11 lines and 4W
Can be used on line. First, the operation on the 2111 line will be explained. 2W/4111 selector switch 16 a
Switch to the side. Switch the call selector switch 18 to a. Regarding the data transmission signal, the SD double signal sent from the terminal equipment is frequency modulated by the modulator 1,
The transmission BPF 2 removes unnecessary transmission components, the hybrid transformer 5 mixes the transmission carrier, the line filter 6 mixes it with the audio signal, and the signal is transmitted via the repeater coil 10 to a 21'1 line of NTT or the like. Regarding the data reception signal, the reception carrier from the 291 line passes through the repeater coil 1°, is separated from the voice signal at the line filter 6, is separated from the transmission carrier at the hybrid transformer 5, and unnecessary noise is removed from the reception BPF. 4, the demodulator 3 demodulates the RD signal and sends it to the terminal equipment. The transmission signal passes through hybrid transformers 7 and 8, is mixed with a data transmission/reception carrier at line filter 6, and is sent out via repeater coil 10 to line 21'. The received signal from the 21Ii line is passed through the repeater coil 10 to the line filter 6.
The signal is separated from the data signal by the hybrid transformer 8, separated from the transmitting signal by the hybrid transformer 8, amplified to an appropriate level by the receiving amplifier, mixed with the transmitting signal by the hybrid transformer 7, and sent to the telephone set.

Next, the operation on the 4W line will be explained. 21'l/411
1 changeover switch 16 is switched to the b side. The call changeover switch 18 is set to "a" for one modem and to "b" for the other modem. On the other hand, the modem receives an SD double signal sent from the terminal equipment, frequency modulates it in the modulator 1, removes unnecessary transmission components in the transmission BPF 2, and sends the data transmission signal to the hybrid transformer 5 and the call selector switch 18. The signal is mixed with the audio signal in the line filter 6, and then passed through the repeater coil 10 to the 4W of NTT etc.
sent to the line.

Regarding the data reception signal, the reception carrier from the 4111 line passes through the repeater coil 11, the call changeover switch 18, unnecessary noise is removed by the reception BPF 4, and the demodulator 3 demodulates the RD double signal. Sent to the terminal device. The transmission signal is from hybrid transformers 7 and 8.
The signal is mixed with the data transmission carrier at the line filter 6, and sent out to the 4111 line via the repeater coil 10. The received signal from the 4W line is passed through the repeater coil 10 to the line filter 6.
It is separated from the transmitting carrier at , separated from the transmitting signal at hybrid transformer 8 , amplified to an appropriate level at receiving amplifier 9 , mixed with the transmitting signal at hybrid transformer 7 , and sent to the telephone set.

The other modem differs from one modem in that a line filter 6 is inserted on the receiving side.

Problems to be Solved by the Invention In the conventional frequency division modem described above, in order to insert a line filter between the modem and the line capable of full-duplex data communication, it is necessary to perform frequency division for bidirectional signals. Instead, passive filters such as LC filters were used. This LC filter has disadvantages in that it is expensive and cannot reduce the size and weight of the modem because it requires a high precision coil and capacitor, requires a lot of adjustment time, is large in size and heavy.

Furthermore, when using a 4W line, the line into which the line filter is inserted is the data sending side for one modem and the data receiving side for the other modem, so a switch must be installed inside the modem, which is cumbersome to handle.
The disadvantage is that it increases costs.

Also, instead of a line that uses two 21' lines to form a 4W line, a line that uses two unidirectional transmission lines to form a 41' line requires a line filter to be inserted in each line. However, it has the drawbacks of being more expensive and larger.

The present invention has been made in view of the above-mentioned conventional circumstances, and therefore, an object of the present invention is to provide a novel frequency division modem that makes it possible to eliminate the above-mentioned drawbacks inherent in the conventional technology. be.

Means for Solving the Problems In order to achieve the above object, a frequency division modem according to the present invention includes a modulator that modulates a data transmission signal from a terminal device, and a modulator that is connected to the modulator and removes unnecessary transmission components from a transmission carrier. a high frit transformer A that mixes the transmitting signal from the telephone and the receiving signal to the telephone; and a high frit transformer A that is connected to the high frit transformer A and cuts frequencies higher than 20% from the audio signal. a mixer connected to the transmitting pan-F pass filter and the transmitting lonipass filter to mix the transmitting carrier and the transmitting signal; and a mixer connected to the mixer to mix the transmitting signal and the receiving signal. A hybrid transformer B that mixes and connects to the line, a distributor that is connected to the hybrid 1 to Lance B when it is a 2111 line and connected to the receiving side line when it is a 41'1 line, and a distributor that is connected to the distributor and removes unnecessary noise. a reception bandpass filter, a demodulator connected to the reception bandpass filter and outputting a data reception signal to a terminal device, and a 2KH demodulator connected to the distributor.
It is configured to include a low-pass filter for receiving a call that cuts frequencies above z, and a receiving amplifier that is connected to the low-pass filter for receiving a call and amplifies the received signal to an appropriate level and sends it to the hybrid transformer A.

Embodiment Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a frequency division modem according to the present invention.

Referring to FIG. 1, in the present invention, 2! It can be used on the +1 line and the 4111 line, and first, the operation on the base line will be explained. 21+1/41'l selector switch 16 is switched to the a side. Regarding the data transmission signal, the SD signal sent from the terminal equipment is frequency modulated by the modulator 1, unnecessary transmission components are removed by the transmission BPF 2, mixed with the transmission signal by the mixer 12, and transmitted by the hybrid transformer 17. The carrier and the received carrier are mixed and sent via the repeater coil 10 to a 2vJ line such as NTT. Regarding the data reception signal, the reception carrier from the 2111 line is passed through the repeater coil 10,
The signal is separated from the transmission carrier by a hybrid transformer 17, and distributed in two directions by a distributor 13. One of the distributed signals is sent to the receiving BPF 4, and the other is sent to the receiving LPF 15. The signal sent to the reception BPF 4 has unnecessary noise removed by the reception BPF 4, is demodulated into an RD signal by the demodulator 3, and is sent to the terminal equipment. The transmitting signal has frequencies of 2 kHz or more cut off by the transmitting LPF 14, is mixed with the transmitting carrier by the mixer 12, the transmitting carrier and the receiving carrier are mixed by the hybrid transformer 17, and then transmitted via the repeater coil 10 to NTT, etc. 2W line. The reception signal from the 21'1 line is separated from the transmission carrier by the hybrid transformer 17 via the repeater coil IO, and is distributed in two directions by the distributor 13. The receiving signal sent to the receiving LPF 15 is 2KH.
After frequencies above z are cut off, the signal is amplified to an appropriate level by a receiver amplifier 9, mixed with a transmitter signal by a hybrid transformer 7, and sent to the telephone set.

Next, the operation in 41'1 line will be explained. 21'l/41
Switch the +1 selector switch 16 to the b side. Regarding the data transmission signal, the SD signal sent from the terminal device is frequency modulated by the modulator 1, unnecessary transmission components are removed by the transmission BPF 2, and mixed with the transmission signal by the mixer 12. and 4. of NTT etc. via the repeater coil 10. It is sent to the l'1 line. Regarding the data reception signal, the reception carrier from the first line 41' passes through the repeater coil 11 and is distributed in two directions by the distributor 13. One of the distributed signals is B for reception.
The signal is sent to PF4, and the other is sent to LPFI 5 for listening. The signal sent to receiving BPF 4 removes unnecessary noise from receiving BPF4.
It is removed by PF4, demodulated into an RD signal by demodulator 3, and sent to the terminal device. The transmitting signal is sent to the mixer 12 after the transmitting LPF 14 cuts frequencies of 2KHz or more.
is mixed with the transmitting carrier in the hybrid transformer 17
The signal is transmitted via the repeater coil 10 to a 41'1 line such as NTT. The reception signal from the 4W line passes through the repeater coil 11 and is distributed in two directions by the distributor 13. The receiving signal sent to the receiving LPF 15 is 2KH.
After the components above z are cut off, the signal is amplified to an appropriate level by the receiver amplifier 9, mixed with the transmitter signal by the hybrid transformer 7, and sent to the telephone set.

As described in detail, according to the present invention, a line filter having a bidirectional filter function is no longer necessary, and a small, low-cost, high-performance active filter can be used, resulting in significant cost reduction, small size, and light weight. This has the effect of making it easier to use and operate.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram showing an embodiment of a frequency division modem according to the present invention, FIG. 2 is an explanatory diagram of a frequency division method of a frequency division modem, and FIG. 3 is a frequency division modem using conventional technology. FIG. 1... Modulator, 2... BPF for transmission, 3... Demodulator, 4... BPF for reception, 5... Hybrid transformer, 6... Line filter, 7... Hybrid transformer, 8... Hybrid transformer, 9... Receiving amplifier, 10... Repeater coil, 11... Repeater coil, 12... Mixer, 13... Distributor, 14
...LPF for sending calls, 15...LPF for receiving calls, 1
6...21'l/4W changeover switch, 17...Hybrid transformer, 18...Call changeover switch Patent applicant: NEC Corporation Patent applicant: NEC Robot Engineering Link Co., Ltd. Agent: Yuta Kumagai, patent attorney Department

Claims (1)

[Claims] A modulator that modulates the data transmission signal from the terminal equipment and outputs the transmission carrier, and a 2KHz transmission signal from the telephone.
A transmitting low-pass filter that cuts frequencies above
a mixer connected to the modulation section and the transmitting low-pass filter to mix the transmitting carrier and the transmitting signal; a hybrid transformer connected to the mixer to mix the transmitting signal and the receiving signal and connecting to the line; and a two-wire line. A distributor that is sometimes connected to the hybrid transformer and connected to the receiving line in the case of a 4-wire line, a demodulator that is connected to the distributor and outputs a data reception signal to the terminal equipment, and a demodulator that is connected to the distributor and that outputs a data reception signal to a terminal device. 1. A frequency division modem comprising a receiving low-pass filter that cuts a frequency and outputs a receiving signal to a telephone set.