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# Modem,modulator-demodulator electronic manufacturing PCB assembly

Modem,modulator-demodulator electronic manufacturing PCB assembly
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News wire services in the 1920s used multiplex devices that satisfied the definition of a modem. However, the modem function was incidental to the multiplexing function, so they are not commonly included in the history of modems. Modems grew out of the need to connect teleprinters over ordinary phone lines instead of the more expensive leased lines which had previously been used for current loop–based teleprinters and automated telegraphs.

In 1941, the Allies developed a voice encryption system called SIGSALY which used a vocoder to digitize speech, then encrypted the speech with one-time pad and encoded the digital data as tones using frequency shift keying.

Programmable features include the local oscillator divider ratio (2 or 4). The small, RF-optimised VQFN package and minimal external components make the device ideal for space-constrained applications.

The CMX973 forms the basis of a high-performance RF transceiver system combining a flexible IF/RF quadrature modulator and quadrature demodulator, in a single chip. Wide signal bandwidth at RF, 0dBm output, low noise and serial bus control delivers maximum flexibility and high-performance, all at an attractive low operating power.

The demodulator is suitable for superheterodyne architectures with IF frequencies of 20MHz to 300MHz and the device may be used in low IF systems or those converting down to baseband.

The modulator converts directly from baseband to the desired transmit frequency 20MHz to 1GHz and features quadrature phase correction to minimise unwanted spectral components. The CMX973 has an on-chip negative resistance amplifier that can form the basis of an on-chip VCO. The CMX973’s quadrature architecture supports a wide range of modulation formats and standards.

Of course, that still leaves the question of exactly how data is transferred from one computer to another; something that is more of a problem than might first appear mainly because the phone lines are analogue while computers are digital. In simple terms this means a telephone signal is constantly changing. To understand that just think of a sine wave as produced on an oscilloscope. The signal might be constant, but it is constantly changing from positive to negative and back again in a series of smooth curves. Computers, on the other hand, can only understand information when it is presented as a string of binary digits so the idea is to map digital output onto an analogue signal.

Without going into technical details this is done by superimposing different frequencies onto the analogue signal (which then becomes known as the carrier wave). Different frequencies can then represent different groups of binary digits in a process which is known as modulation when it is being transmitted and demodulation when it is decoded at the receiving end. Naturally two way communication is achieved by having a single device being capable of both modulation and demodulation, from which the unit takes its name: the modem.

Modems provide a Layer 1 service of delivering a bit stream between the two endpoints on the dialed circuit. To pass IP traffic, an appropriate data-link protocol must be used, typically PPP. The biggest negatives about using modems include their relatively low speed and the fact that you cannot use the phone at the same time as you send data.

flash memory : Some modems come with flash memory rather than conventional ROM, which means that the
communications protocolscan be easily updated if necessary.

Dial-up Modems were commonly used by computers to connect to the Internet through the early 2000's, until broadband Internet started to be more widely available. As broadband Internet became more popular and available, dial-up Modems were used by less computer users. Today, computers no longer come with a dial-up modem, requiring users who need one to purchase and install it.

Each modified element of the modulated carrier wave (for instance, a shift from one frequency to another or a shift between two phases) is known as a baud. In early voiceband modems beginning in the early 1960s, one baud represented one bit, so that a modem operating, for instance, at 300 bauds per second (or, more simply, 300 baud) transmitted data at 300 bits per second. In modern modems a baud can represent many bits, so that the more accurate measure of transmission rate is bits or kilobits (thousand bits) per second. During the course of their development, modems have risen in throughput from 300 bits per second (bps) to 56 kilobits per second (Kbps) and beyond. Cable modems achieve a throughput of several megabits per second (Mbps; million bits per second). At the highest bit rates, channel-encoding schemes must be employed in order to reduce transmission errors. In addition, various source-encoding schemes can be used to “compress” the data into fewer bits, increasing the rate of information transmission without raising the bit rate.

The word modem is actually made by combining parts of two different words – Modulator and demodulator. As this suggests, a modem is a device that both modulates and demodulates signals that encode and retrieve information, respectively. For starters, modulation is a process of adding meaningful information to a carrier wave so that it can be transmitted over long distances.

You see, when an electrical signal containing some meaningful information needs to be transmitted over a long distance, it is added to a carrier wave. This process of ‘mounting’ the original signal on a carrier wave is called modulation.

ADSL (asymmetric digital subscriber line) modems, a more recent development, are not limited to the telephone's voiceband audio frequencies. Standard twisted-pair telephone cable can, for short distances, carry signals with much higher frequencies than the cable's maximum frequency rating. ADSL broadband takes advantage of this capability. However, ADSL's performance gradually declines as the telephone cable's length increases. This limits ADSL broadband service to subscribers within a relatively short distance of the telephone exchange.

Cable modems use infrastructure originally intended to carry television signals and therefore designed from the outset to carry higher frequencies. A single cable can carry radio and television signals at the same time as broadband internet service without interference. Newer types of broadband modems are also available, including satellite and power line modems.

Most consumers did not know about networking and routers when broadband became available. However, many people knew that a modem connected a computer to the Internet over a telephone line. To take advantage of consumers' familiarity with modems, companies called these devices broadband modems rather than using less familiar terms such as adapter, interface, transceiver, or bridge. In fact, broadband modems fit the definition of modem because they use complex waveforms to carry digital data. They use more advanced technology than dial-up modems: typically they can modulate and demodulate hundreds of channels simultaneously or use much wider channels than dial-up modems.
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modem, an acronym for modulator/demodulator, is a device that allows one computer to "talk" with another over a standard telephone line. Modems act as a kind of interpreter between a computer and the telephone line. Computers transmit digital data, expressed as electrical impulses, whereas telephones transmit voice frequencies as analog signals. To transmit digital data, the sending modem must first modulate, or encode, a computer's digital signal into an analog signal that can travel over the phone line. The receiving modem must then demodulate, or decode, the analog signal back into a digital signal recognizable to a computer. A modem transmits data in bits per second (bps), with the fastest modems transmitting at 56K (kilobits per second). An internal modem is housed within the computer itself, while an external modern is a separate device connected to the computer by cable.

ISDN is more than twice as fast as a dialup modem, but not nearly as fast as ADSL or DSL. ADSL can deliver data at 8 mbps, but is available only in selected urban areas. demodulator DSL transmits at a high rate of speed, but to ensure reliable service, the user must be located near the phone company's central office or outlying transmitters. In addition, a DSL connection is always "on" and thus modulator-demodulator electronic manufacturing PCB assembly makes a computer more vulnerable to attacks from hackers. To secure a DSL connection, a user must install either a software package called a firewall or a piece of hardware called a router. With either of these in place, the DSL connection cannot be detected by outsiders.

bonnie Lund states in Business Communication That Really Works!, "the speed with which we can exchange documents has revolutionized business communications," which in turn has enabled business to be done "faster, cheaper, and more efficiently." Modems, along with the related technologies, facilitate this rapid transfer of information between colleagues or customers, regardless of their location. Communications that, in the past, may have taken several days or even weeks to complete, can now be accomplished in a fraction of the time. For example, during a typical work day, an employee could use a modem to facilitate sending an email message to a customer, transmitting a spreadsheet containing the annual budget to a manager for review, or downloading a file from the Internet. On a busy day this will take place dozens of times.

Cable modems do not use phone lines. Instead, they utilize the same line that provides cable TV services to consumers. Offered by cable television companies, cable modems are about 50 times faster than a dialup modem, but transmission speed is dependent on the number of subscribers using the service at the same time. Because the service uses a shared connection, its speed decreases as the number of users increases. Satellite, or wireless, services are faster than a 56K modem, but slower than a DSL. In addition, the initial satellite installation is expensive. However, for users in rural areas who do not have access to other services, wireless service may be a viable option.

We searched our database and could not find a definition other than MOdulator/DEModulator for MODEM

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A variety of protocols (standards, rules) govern the conversion of data to and from digital and analog. These also govern error correction and data compression. Error correction is necessary to detect and correct data that may have become lost or garbled as the result of a poor telephone connection. Data compression speeds the data transfer by eliminating any redundant data sent between two modems, which the receiving modem then restores to its original form. Individual modems vary in the types of protocols they support, depending on such factors as manufacturer and age.

The first Modem, known as the Dataphone, was released by AT&T inIt later became more common for home users when Dennis Hayes and Dale Heatherington released the 80-103A Modem in

While the modem interfaces are standardized, a number of different protocols for formatting data to be demodulator transmitted over telephone lines exist. Some, like CCITT V.34, are official standards, while others have been developed by private companies. Most modems have built-in supportfor the more common protocols -- at slow data transmission speeds at least, most modems can communicate with each other. At high transmission speeds, however, the protocols are less standardized.

Aside from the transmission protocols that they support, the following characteristics distinguish one modem from another:
bps : How fast the modem can transmit and receive data. At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher speeds, modems are measured in terms of bits per second (bps). The fastest modems run at 57,600 bps, although they can achieve even higher data transfer ratesby compressing the data. Obviously, the faster the transmission rate, the faster you can send and receive data. Note, however, that you cannot receive data any faster than it is being sent. If, for example, the device sending data to your computer is sending it at 2,400 bps, you must receive it at 2,400 bps. It does not always pay, therefore, to have a very fast modem. In addition, some telephone lines are unable to transmit data reliably at very high rates.

voice/data: Many modems support a switch to change between voice and data modes. In data mode, the modem acts like a regular modem. In voice mode, the modem acts like a regular telephone. Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice communication.

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US$1 / Piece 1 Piece (Min. Order) Freight Cost Available Supplier Details Inquire Now Add this product to Inquiry Basket Professional demodulator Customized PCBA OEM Manufacturer Electronic ... China Professional Customized PCBA OEM Manufacturer Electronic Circuit Board The next major advance in modems was the Hayes Smartmodem, introduced in 1981. The Smartmodem was an otherwise standard 103A 300-bit/s direct-connect modem, but it was attached to a small microcontroller that watched the data stream for certain character strings representing commands. This allowed both data and commands to be sent through a single serial port. The now-standard Hayes command set included instructions for picking up and hanging up the phone, dialing numbers, and answering calls, among others. This was similar to the commands offered by the internal modems, but unlike them, the Smartmodem could be connected to any computer with an RS-232 port, which was practically every microcomputer built. Any interest in these proprietary improvements was destroyed during the lengthy introduction of the 28,800 bit/s V.34 standard. While waiting, several companies decided to release hardware and introduced modems they referred to as V.FAST. In order to guarantee compatibility with V.34 modems once the standard was ratified (1994), the manufacturers were forced to use more flexible parts, generally a DSP and microcontroller, as opposed to purpose-designed ASIC modem chips. The ITU standard V.34 represents the culmination of the joint efforts. It employs the most powerful coding techniques including channel encoding and shape encoding. From the mere four bits per symbol (9.6 kbit/s), the new standards used the functional equivalent of 6 to 10 bits per symbol, plus increasing baud rates from 2,400 to 3,429, to create 14.4, 28.8, and 33.6 kbit/s modems. This rate is near the theoretical modulator-demodulator electronic manufacturing PCB assembly Shannon limit. When demodulator calculated, the Shannon capacity of a narrowband line is {\displaystyle {\text{bandwidth}}\times \log _{2}(1+P_{u}/P_{n})} , with {\displaystyle P_{u}/P_{n}} the (linear) signal-to-noise ratio. Narrowband phone lines have a bandwidth of 3,000 Hz so using {\displaystyle P_{u}/P_{n}=1000} (SNR = 30 dB), the capacity is approximately 30 kbit/s.[4] Without the discovery and eventual application of trellis modulation, maximum telephone rates using voice-bandwidth channels would have been limited to 3,429 baud × 4 bit/symbol = approximately 14 kbit/s using traditional QAM. To begin with the Data Terminal Equipment or DTE (better known as a computer) sends a Ready To Send or RTS signal to the Data Communication Equipment or DCE (better known as a modem). This is sometimes known as a wakeup call and results in the modem sending a Data Carrier Detect or DCD signal to the receiving modem. There then follows a series of signals passed between the two until the communication channel has been established. This process is known as handshaking and helps to explain why, even now, some companies like CompuServe use the symbol of two hands grasping each other to mean being on-line. Of course, after that all it takes is for the second modem to send a Data Set Ready or DSR signal to its computer and wait for the Data Terminal Ready or DTR reply. When that happens the first modem sends a Clear To Send or CTS signal to the computer that started the whole process off and data can then be transmitted. It is as simple as that. Alternatively, for anyone confused by what the entire Internet industry dubs TLA's which means Three Letter Acronyms, the following diagram should help. The introduction of the Smartmodem made communications much simpler and more easily accessed. This provided a growing market for other vendors, who licensed the Hayes patents and competed on price or by adding features. Through the 1980s, a number of new higher-speed modems, first 1,200 and then 2,400 bit/s, greatly improved the responsiveness of the online systems, and made file transfer practical. This led to rapid growth of online services with their large file libraries, which in turn gave more reason to own a modem. The rapid update of modems led to a similar rapid increase in BBS use, which was helped by the fact that BBSs could control the modem simply by sending strings, rather than talking to a device driver that was different for every direct-connect modem. Mass-produced modems in the United modulator-demodulator electronic manufacturing PCB assembly States began as part of the SAGE air-defense system in 1958 (the year the word modem was first used[1]), connecting terminals at various airbases, radar sites, and command-and-control centers to the SAGE director centers scattered around the U.S. and Canada. SAGE modems were described by AT&T's Bell Labs as demodulator conforming to their newly published Bell 101 dataset standard. While they ran on dedicated telephone lines, the devices at each end were no different from commercial acoustically coupled Bell 101, 110 baud modems. Freight Cost Available Supplier Details Inquire Now Add demodulator this product to Inquiry Basket Professional PCBA OEM/ODM PCBA PCB and PCBA Add to Compare Similar Products Contact Supplier Leave Messages csp-1601 16 way fixed channel modulators 10 Pieces (Min. 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Various data compression and error correction algorithms are required to support the highest speeds. Other optional features are auto-dial (auto-call) and auto-answer which allow the computer to initiate and accept calls without human intervention. Most modern modems support a number of different protocols, and two modems, when first connected, will automatically negotiate to find a common protocol (this process may be audible through the modem or computer's loudspeakers). Some modem protocols allow the two modems to renegotiate ("retrain") if the initial choice of data rate is too high and gives too many transmission errors.

A modem may either be internal (connected to the computer's bus) or external ("stand-alone", connected to one of the computer's serial ports). The actual speed of transmission in characters per second depends not just the modem-to-modem data rate, but also on the speed with which the processor can transfer data to and from the modem, the kind of compression used and whether the data is compressed by the processor or the modem, the amount of noise on the telephone line (which causes retransmissions), the serial character format (typically 8N1: one start bit, eight data bits, no parity, one stop bit).

modem_reset(q) resets the internal state of the object. This method is really only relevant to LIQUID_MODEM_DPSK (differential phase-shift keying) which retains the phase of the previous symbol in memory. All other modulation schemes are memoryless.
modem_gen_rand_sym(q) generates a random integer symbol in {0,M−1}{0,M−1} .
modem_get_bps(q) returns the modem's modulation depth (bits/symbol).

modem_modulate(q,symbol,*x) modulates the integer symbol storing the result in the output value of xx . The input symbol value must be less than the constellation size MM .

modem_demodulate(q,x,*symbol) finds the closest integer symbol which matches the input sample xx . The exact method by which liquid performs this computation is dependent upon the modulation scheme. For example, while LIQUID_MODEM_QAM4 , and LIQUID_MODEM_PSK4 are effectively equivalent (four points on the unit circle) they are demodulated differently.

modem_demodulate_soft(q,x,*symbol,*softbits) demodulates as with modem_demodulate() (see above) but also populates the mm -element array of unsigned char as an approximate log-likelihood ratio of the soft-decision demodulated bits

While computer technology is purely digital, i.e., it relies on numbers to transmit and receive information, telephone technology, even to this day, is partly analog, meaning that it uses continuously varying electrical signals to transmit information.

Now, we have telephone lines that are partly analog and a lot of computer tech (e.g., laptops, desktops etc.) that is purely digital. How do you make them talk to each other and exchange information?

Simple! Use a modem.

A modem has two plugs in it, one that connects it to the telephone line (or the cable provided by your Internet service provider) and the other connecting it to your computer (or a WiFi router).

The modulator-demodulator, aka the modem, was enhanced by Bell Laboratories to improve upon the Teletype speed of approximately 150 bits per second (bps).

It was in 1962 that the first commercial modem, the Bell 103, was released by AT&T. Including full-duplex transmission, frequency-shift keying (FSK) and a speed of 300 bps (baud). These modems were designed to hold a telephone's receiver in a cradle with wire connections running from the cradle to the computer.

Modulator-demodulator. Electronic device that allows computers to communicate over telephone wires or cable-TV cable. One computer's modem converts its digital signals (which cannot be sent efficiently over phone lines) into analog signals (which can be). The other computer's modem reconverts the analog signals (that the computer cannot understand) into digital signals (that it can). Conversion of one type of signals to another is called modulation, their reconversion to the original type is called demodulation. Modern modems work at 56 thousand bits per second (Kbps) or higher data transfer speeds, perform automatic error correction, and allow voice and fax communications.

Early modems were classified as point-to-point connections. When a dialup connection was setup between two computers, that connection was only shared between them. That means that the transmission medium (the phone line) didn’t have to be shared by other resources- only the two computers communicating.

Using the NS3000, customers achieve the highest data rates of up to 716Mbps whilereducing dish and HPA sizes and/or required satellite leased bandwidth. The NS3000offers a fully Integrated IP solution incorporating routing capability. Further utilizationof allocated bandwidth can be accommodated using NovelSat optimized ACM mode.The NS3000 comes with IF/extended L-Band input/output interfaces and can supportBUC and LNB, offering a compact and cost effective solution in a space-saving 1Upackage.

Supporting the highest data rates in the industry, the NS3000 Modem achieves up to 365Mbps in each direction (730Mbps) using 70Msym/sec transmission. Duet™, NovelSat's next generation Echo Cancellation embedded within the modem, drives this increased data rate. Powered by award winning NS3™ technology, the NS3000 Modem delivers significantly higher spectral efficiency and capacity expansion than any other modem in the market, including DVB-S2, while enabling robust immunity against channel impairment including satellite jamming.

This modem delivered more characters and introduced a very simple data compression that worked well with text but didn't have great results with images.

Running along in the background was also some hefty legal action and competition as AT&T initially prevented customers from connecting devices from other companies to their telephone lines.

However, thanks to Tom Carter the Carterfone Decision of 1968 soon saw this unfair advantage taken away from AT&T.

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From this it becomes obvious that the more frequencies that can be superimposed on the carrier wave the faster data can be transmitted. Alternatively, to take a different point of view, the more data there is to be transmitted so the more frequencies are needed.

Unfortunately it is only possible to send a limited number of frequencies at the same time, known as the bandwidth, which means communication takes that much longer as the size of the signals steadily increases. Now that pictures, sound and even video sequences are transmitted over the Internet on a regular basis, and as these all call for massive data files, the amount of available bandwidth is likely to be a problem for some time.

The CDM-710 Broadcast Satellite Modem is intended for operation in Digital Video Broadcast (DVB) and generic data transmission applications. It operates over satellite links and provides programmable symbol / data rates up to 45 Msps in DVB-S21, DVB-S and DVB-DSNG modes.

Telephone lines that are used in a conventional phone system are designed to transmit human speech with analog signals. Analog signals vary continuously, like waves, along their length. Computers store and process data in digital format and communicate both internally and with each other in binary digits

When two computers communicate with each other over a conventional phone line, a modem translates the binary information from the computer at the sending end to an analog signal that can pass over the phone line. At the receiving end, another modem translates the analog signal back to binary information that can be used by the computer. The conversion from binary to analog information is called modulation, and the conversion back from analog to binary is called demodulation. The word modem, short for modulator/demodulator, is the name for the device that performs these conversions.

Both standard modems and fax modems perform this conversion. There are also ISDN, DSL, and cable modems that provide digital communication. These modems do not convert digital and analog signals. They enable computers to transmit digital information directly without the conversion. When you communicate over analog telephone lines, you need standard modems.

The speed at which modems transmit data is called the throughput. This is measured in bits per second (bps)
The conversion between digital and analog data is governed by proprietary and international standards, called modem protocols. Improving protocols have allowed faster data throughput rates. Besides using the available bandwidth more effectively, protocols have incorporated data compression to speed the throughput and error control for greater reliability. The protocols for modems operating at 56 kilobits per second (Kbps) are now designed to support receiving data from an Internet service provider connected to a digital line, but send with the standard digital-to-analog conversion.

The modulation types supported include QPSK, 8-PSK, 16-QAM, 16-APSK and 32-APSK. Constant Coding and Modulation (CCM) operation with a single input stream is provided for DVB-S2 operation. The unit is available in modulator only, demodulator only, and modem configurations.

The terrestrial data interfaces are field-removable to allow swap out of interface types. The data interfaces include the CDI-40 with ASI, CDI-70 Gigabit Ethernet and CDI-60 HSSI.

DVB-S2 offers new opportunities for broadcast applications. With a broad range of modulation and coding formats, it permits the user to tailor a link for the available bandwidth and power to modulator-demodulator electronic manufacturing PCB assembly optimize link performance. Whether a link is for Direct-to-Home (DTH) or Digital Satellite News Gathering (DSNG), contribution or distribution, there is a format available to suit each application.

auto-answer :An auto-answer modem enables your computer to receive calls in your absence. This is only necessary if you are offering some type of computer service that people can call in to use.

Built with the highest quality components and processing power, the NS3000 passes a rigorous regimen of over 10,000 automatic tests, ensuring reliability that's second to none.

But as your may well know, this type of dialup connection isn’t very desirable. Connections made through a phone line are much slower than other counterparts such as Ethernet or fiber optic cable. But since the original modems used phone lines, they became vastly popular. After all- if you have a global telephone line system, why not take advantage of that and use it for internet access?

As far as Cisco exams go, just remember how modulation and demodulation works. Cisco doesn’t include a lot of material or exam questions on modems, so there isn’t much of a need to go into further detail.

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data compression :Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique.

The term Modulation is Process of converting the Digital Signal in Analog form to tranmit on Telephone Line. And Term Demodulation is process of converting the Analog Signals in Digital Signals.Modems create an analog signal when sending data.

term, baud, often is used to describe the speed of a modem. modulator-demodulator electronic manufacturing PCB assembly In fact, some people say things like “That modem runs at 33 kilo baud per second,” really meaning 33 kilobits per second (kbps), thinking that “bits per second” and “baud per second” are the same thing. But the two terms are not synonymous. The term baud refers to a single encoded energy signal that can represent 1 or more bits. In this final example, a baud happens to represent 2 bits. Baud is not an acronym; it is taken from the name of the inventor (Baudot) of one of the first modulation schemes that implied more than 1 bit. So, the modem running at 28,000 bps, with a modulation scheme that sends/receives 2 bits per baud, is running at 14,000 baud per second.

modem_create_arbitrary(*table,M) creates a generic arbitrary modem ( LIQUID_MODEM_ARB ) with the MM -point constellation map defined by the float complex array table . The resulting constellation is normalized such that it is centered at zero and has unity energy. Note that MM must be equal to 2m2m where mm is an integer greater than zero.

Typically, two cords modulator-demodulator electronic manufacturing PCB assembly connect to the modem – one brings it the Internet, and the other takes the Internet to a router or a computer (Photo Credit : Simon A. Eugster / Wikipedia Commons)
Basically, what the modem does is take the digital signal from the computer and add it on top of an analog telephone signal (i.e., modulates it) so that it can be transferred through the telephone line.

Since your modem sends information through a telephone line by modulating digital signals, it also needs to have another kind of translator that helps it demodulate the analog signals it receives via the telephone line.

modem_destroy(q) destroys a modem object, freeing all internally-allocated memory.
modem_print(q) prints the internal state of the object.

Modems are distinguished primarily by the maximum data rate they support. Data rates can range from 75 bits per second up to 56000 and beyond. Data from the user (i.e. flowing from the local terminal or computer via the modem to the telephone line) is sometimes at a lower rate than the other direction, on the assumption that the user cannot type more than a few characters per second.

Future Electronics has a full selection of the best modulators / demodulators from several manufacturers that can be used for a modulator / demodulator circuit such as an rf modulator / demodulator, balanced modulator / demodulator circuit, HD RF modulator / demodulator or digital radio frequency modulator / demodulator. Simply choose from the modulator / demodulator technical attributes below and your search results will quickly be narrowed in order to match your specific modulator / demodulator application needs.

When the US Air Force needed a convenient way of transmitting hundreds of radar images to command centres during the Cold War in the late 1940s they turned to the telephone system as a solution.

Fortunately modems, already in action in Teletype since the 1920s, were the perfect tool for taking the digital radar images and converting them into analogue transmissions and then back again so that they could be sent across the network of telephone systems already in place.

If you have a preferred brand, we deal with several manufacturers such as Digi International, Freescale Semiconductor, Hittite Microwave, New Japan Radio, NXP, STMicroelectronics or ON Semiconductor. You can easily refine your modulator / demodulator product search results by clicking your preferred modulator / demodulator brand below from our list of manufacturers.

"While we could visualize what should be possible and how it could change the shape of the communications industry, our first thought, however, was for self preservation... I approached a number of communications equipment manufacturers for financial support, but they were all afraid of jeopardizing current or potential Bell contracts," said Tom.

After he won the case the market was suddenly left wide open with companies like General Electric entering the field with glee.

The NovelSat NS3000 incorporates both the NS1000 Modulator and NS2000 Demodulator into one unit, offering advanced packet processing and routing capabilities, and includes TCP acceleration and compression for IP packet streams. For ISPs seeking satellite cost reduction, the NS3000 delivers an ideal solution by combining outstanding data transmission rates with minimal bandwidth requirements, providing reliable and cost-effective satellite data links where lack of infrastructure and challenging geography make wire links infeasible.

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US $3.0-5.0 / Piece 1000 Pieces (Min. Order) Material: PP/ABS/PC/PA etc Plastic Modling Type: Injection Model Number: JY-P462 Brand Name: JUNYI Place of Origin: Guangdong,China (Mainland) Color: Black custom made modulator-demodulator case supplier/plastic modulator-demodulator manufacturer Dongguan Junyi Hardware & Plastic Co., Ltd. China (Mainland) Response Rate 21.1% Add to Compare Similar Products Contact Supplier Leave Messages New and Used Satellite Equipment US$500-1000 / Piece
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A Modem is a type of a hardware device. It converts between analog and digital data in real time for the two-way network communication. The expansion of the term MODEM is MODulator dEModulator. The speed of these modems was historically measured in baud (a unit of measurement named after Emile Baudot) and after the development of computer technology, it was converted into bits per second (bps).

Internal Modems in PC or Laptops might come with a modem built in or simply might use a convenient type of internal modem called a PCMCIA card, or simply PC card. PC cards are roughly the size of a credit card and easily can be inserted and removed from a PC. Most PC hardware comes with either a serial communications port, called a COM port, or a Universal Serial Bus (USB) port. Both USB and COM ports are intended to support external devices that communicate using a serial bit stream.

COM ports usually consist of either a female RS-232 connector, which is a D-shell connector with 25 pins, or a DB-9 connector, which uses 9 pins. USB ports are rectangular female connectors about one quarter inch by 1 inch long. In either case, the computer sends a serial bit stream to the external modem over the cable, expecting the modem to send the data. At the same time, the modem forwards bits received from the phone line back to the PC.

Modems operate in part by communicating with each other, and to do this they must follow matching protocols, or operating standards. Worldwide standards for voiceband modems are established by the V-series of recommendations published by the Telecommunication Standardization sector of the International Telecommunication Union (ITU). Among other functions, these standards establish the signaling by which modems initiate and terminate

communication, establish compatible modulation and encoding schemes, and arrive at identical transmission speeds. Modems have the ability to “fall back” to lower speeds in order to accommodate slower modems. “Full-duplex” standards allow simultaneous transmission and reception, which is necessary for interactive communication.

“Half-duplex” standards also allow two-way communication, but not simultaneously; such modems are sufficient for facsimile transmission.

Internal modems do not require the use of an RS-232, DB-9, or USB cable—they simply connect directly to the phone line. In the United States, that means using the same type of cable that is used to connect to an analog phone, with an RJ-11 connector. However, the installation of an internal modem still uses the logical concept of a COM port. That is true of internal modems that are installed in an expansion card slot and of PCMCIA modems that simply can be inserted into the convenient PC card slot in the side of a laptop computer. The operating system in the computer still uses the concept of sending data serially, but instead of it physically being sent over a cable to an external modem, it simply goes to the internal modem card.

The 201A and 201B Data-Phones were synchronous modems using two-bit-per-baud phase-shift keying (PSK). The 201A operated half-duplex at 2,000 bit/s over normal phone lines, while the 201B provided full duplex 2,400 bit/s service on four-wire leased lines, the send and receive channels each running on their own set of two wires.

The famous Bell 103A dataset standard was also introduced by AT&T in . It provided full-duplex service at 300 bit/s over normal phone lines. Frequency-shift keying was used, with the call originator transmitting at 1,070 or 1,270 Hz and the answering modem transmitting at 2,025 or 2,225 Hz. The readily available 103A2 gave an important boost to the use of remote low-speed terminals such as the Teletype Model 33 ASR and KSR, and the IBM 2741. AT&T reduced modem costs by introducing the originate-only 113D and the answer-only 113B/C modems.