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Questions tagged [modem]

A modem (modulator-demodulator) is a device used to transmit and receive digital data over an analog communications channel. Common examples are PC modems that use an analog telephone line and wireless modems that use RF (radio frequency).

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SimCom SIM800C modem - How to reattach to GPRS by AT commands [closed]

I'm working with a SIM800C modem of SimCom and my main doubt here is: how can I reconnect/re-attach to GPRS network after the connection goes down, without doing a hardware reset? Here is my ...
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1answer
42 views

Problem with 2G Modem's supply power

I want to run a 2G Modem HL6528RD. I provide it with 3.6 V, got from the following circuit : I finally manage to make it work but the problem is that if R108 is mounted, the modem doesn’t work, (the ...
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1answer
358 views

Audio filtering circuit with capacitor shorted

I was looking at the Adafruit FONA cellular network modem breakout board schematic and found something that I can't quite understand. The breakout board has an audio input and output that both goes ...
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2answers
131 views

(When) Can I use Cat5e wiring to carry a POTS signal to a DSL modem?

According to this answer by @asndre, It is very bad idea to use Cat5e-based wiring/cabling to establish a xDSL connection. However, my telephone/internet provider technician recommended -- and ...
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57 views

Confusion between analog & digital signal and modem

Telephone wire is a lowpass chaneel so the process looks like below. (Maybe right?) Voice(analog signal) → Sampling(digial data) → Coding(digial signal) → transmit There's no need to convert digital ...
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1answer
74 views

Would it be energy efficient for phones to include actual GPS chip? [closed]

None of the smartphones today have dedicated GPS chips in them, they only have a GPS capability that stems from byproduct features of the modem chips. Because of that, the GPS capability is very ...
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2answers
60 views

Force cellular modem to transmit at maximum power [duplicate]

I want to force my cellular modem to transmit at maximum power so that I can see if that is the cause of microSD card crashes that I have been experiencing in an embedded application. My modem is a ...
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1answer
83 views

MoCa - Ethernet over Coaxial

This is specifically a high-level hobbyist question, I'm not really looking for schematics or anything of the sort. To deliver Ethernet over Coaxial, what sort of high-level designs or common issues ...
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2answers
96 views

How does things work between MODEM and PC on the RJ45 ethernet cable? [closed]

I am a newbie in electronic and i would like to ask why there is Transmitter and Receiver in the RJ45 cable connecting the MODEM and Computer? Which one goes first From Modem --> Receiver Receive ...
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1answer
90 views

How did dial-up modems make noise when initializing internet connection

A 56k modem sounded like this. I read somewhere that the reason for these whistles and chirps and buzzes is to give the user the feedback that something was happening during the handshake. I guess ...
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2answers
74 views

Dialup Modem To Generate Musical Tones [closed]

Just brainstorming here but would it be possible to control the actual audio band signals emitted by a modem like an old US Robotics V.90 or similar? I'm guessing not without somehow rewriting the ...
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66 views

Is this warning about wireless modules interfering with aircraft systems true?

I see the following warning for Sierra wireless (cellular) modems: Do not operate the Sierra Wireless modem in any aircraft, whether the aircraft is on the ground or in flight. In aircraft, the ...
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3answers
158 views

Superimpose a High Frequency AC Small Signal on a DC Power Signal

I am facing a challenging problem with a circuit that I am currently working on, I would like others input and thoughts. I have a DC power signal that I am injecting a AC small signal this mixed ...
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1answer
55 views

Can a 3G usb modem be used as a mini Cellphone Tower [closed]

I am curious to know whether small USB 3G modems could be used as cellular towers, and if you would need special firmware to do it or if it is not possible at all. They can communicate with the tower, ...
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2answers
427 views

SIM7100 GSM Modem Unreliable Connection

I am trying to communicate with SIM7100 GSM modem but I could just rarely communicate with it across UART interface. I am observing the signal with an oscilloscope, I am giving 5V as High and 0V as ...
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1answer
88 views

Isolate UART Signal Pins

I'm working with an embedded cell modem that will be living on a battery, hopefully for a long period. It only wakes up and sends data occasionally. To that end, my plan is to cut power to it when ...
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1answer
42 views

What is effect of echo canceller on QAM signals?

During data call or fax call echo cancellers are switched off in entire path from phone to exchange and exchange to phone. Echo canceller are used to cancel echo during voice call. Modulation in data ...
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101 views

What frequency is used for 2400 bps modem on pstn lines?

If dial-up modem is working in 2400 bps .please correct me in the following it can use 1200 hz and 2400 hz or higher till 3400 hz (at max )frquency depending on modulation technque .am I right ? If ...
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54 views

GSM module not registering

I'm doing a project that uses GSM/GPRS to communicate. The problem is that the modem sometimes fails to register in the network. I've done some testing and this happens even with a good RSSI, but it's ...
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1answer
369 views

Usb 3G, 4G modems, power supply

I have read that usually a gsm module requires a power supply capable to provide up to 2A. But how can 3g modems sticks work properly when they are powered through usb port which provides only up to ...
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2answers
5k views

Difference between Hirose U.FL and IPEX connectors

Both these connectors are used to connect antenna to Mini PCI cards. Wikipedia does not explain the difference between those naming issues: U.FL, IPEX, IPAX, IPX,[1] AMC, MHF and UMCC is a ...
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1answer
81 views

Accessing the filesystem of a modem

My goal is to access the file system of a modem/router i have. On the circuitboard i found connectors (refdes J13 and J203) that the factory likely used to program or test the device. J13 has solder ...
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1answer
42 views

GL868 Modem Reboot problem

I am working on a IOT based Project which uses GL868 Modem & minimizing power consumption is very important goal for me now. One way of minimizing the power consumption is to turn off GL868 Modem ...
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1answer
303 views

Power line communication by inducing a signal into a wire

I would like to make a small board with a simple MCU that just repeatedly sends a message via a modem on one end of a power line wire (14awg or so). On the other end will be a similar device for ...
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2answers
119 views

What technology to use to send data/Ethernet (about 128 kbps) over copper cable (4km)?

What thechnologies can i use to send data/ethernet (w/ a symmetrical traffic throuput of about 128kbps) over copper cable (4km)? 1)SHDSL would be an option !!(but I couldn't find any chip with ...
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1answer
87 views

What triggered the need for VLSI chips in modems post 1200 baud?

I was chatting to my boss today and he said: My first job was electrical working in a factory for a modem company. The last model modem we made was the 1200 baud. After that they needed ...
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3answers
1k views

Reading data from 3.5mm audio jack

I wonder if it'd be a relatively straightforward exercise to read data from a 3.5mm audio jack using an Arduino and a raspberry pi. The communication will be one-way only: raspberry pi transmits data ...
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1answer
571 views

Where can I get MDM9615 modem chipset datasheet?

I've been looking for this datasheet in the internet but I found nothing. I reaaly need this MDM9615 datasheet. Thank you.
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1answer
529 views

In Fiber Optic Telephone line, how light signals are converted to the voice signals? [closed]

I have been learning how internet data travels in different kind of Broadband access. In case of telephone broadband, voice signals travels through the telephone line. At the user premise, the modem ...
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2answers
220 views

Why are telephone/internet lines less susceptible to surges than power lines?

(I know nothing about electronics, so excuse my ignorance.) I understand surge protection for power outlets are necessary, or at least recommended, for expensive electronics. But are telephone lines ...
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2answers
2k views

AT+CSQ without Disconnecting PPP Connection in ARCH Linux

I have a Telit GL865 GSM/GPRS module which is connected to a SBC (running ARCH Linux.) via Serial Port. For GPRS connection, PPP connection as indicaten on this page. I want to read Cell Tower Signal ...
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1answer
432 views

What would prevent DTMF tones being recognised (modem to modem)? [closed]

A bit of back story: the SEGA Dreamcast had a dial up modem which was used for online play, in the absence of dialup ISPs it's now common practice to directly connect the DC to a USB dial up modem and ...
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1answer
428 views

What is the speed of a baud rate? - RN42

After wondering/researching about this for days, I finally ask this question: What is the speed (bits per second) of a bluetooth SPP RN-42 device? Is 1 baud = 1 bit (thus 9600 baud = 9600 bits per ...
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1answer
447 views

How a modem really works? [closed]

I really searched a lot and couldn't find a detailed answer(s), what happens when the Network Interface Card sends a Ethernet frame to the modem? Does the frame directly go inside modem's cpu or ...
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1answer
79 views

A conceptual question on turning power on/off for a wireless communication

I want to interface a wireless modem with a micro-controller. What I want to achieve is that when I send a signal to the wireless modem I want the power to be turned on and when the modem does not ...
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1answer
128 views

Simulate modems and leased line over ethernet

I am using a leased line with two modems on the edges. Those modems receive x.21 protocol from db25 connector on their back and transmit to each other over the leased line. For some pairs of leased ...
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2answers
327 views

Modem to Modem via GPRS

I am working on a GPRS communication design. What I want to do to connects two modems together via GPRS. But I found that i could not connect. I was able to connect both modems to the internet using ...
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3answers
2k views

FCC certification for nrf24l01+

Is nrf24l01+ from Nordic Semiconductors FCC certified ? It is hard to find out from their datasheet whether FCC approved ? Is it FCC approved ? If it is approved and I use it in my PCB and control it ...
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1answer
397 views

How to handle nested final result code in AT-command text?

I am writing a parser (a finite state machine to be more precise) for AT-commands and I don't see how to handle a particular corner case: Here is the specifications of the modem communication: When ...
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1answer
81 views

Modem power usage versus signal strength

Is it true that a modem (such as a 3G dongle) will use more power when signal strength is weak that when signal strength is strong? Also, can someone link me to a resource that discusses this? What is ...
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2answers
678 views

TTL Long Distance Transmission Alternatives

I am working on a system that gets data from a sensor via a TTL connection. Currently, the data that is gathered from the sensor is sent to another part of the system via a set of modems. The ...
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1answer
530 views

simple GSM SIM modem

I'd like to build a prototype of simplest possible GSM device - a simple modem with SIM holder, capable of logging on to the SIM's provider network and nothing else. It's meant to be used as a GSM ...
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1answer
468 views

is 'Ok' important when sendin AT commands to modem

I'm currently using VHDL to program the FPGA Spartan 3AN Kit-set. The objective is create a programme to send an SMS to a mobile phone, using the Kit-set via the modem. I'm done with the transmit ...
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2answers
822 views

Which NTP server should I use for my product to update time?

I am developing a GPRS enabled embedded device.To synchronize time with the network I have to use NTP protocol. The nature of the product is such that I have to Hardcode the NTP server address inside ...
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3answers
5k views

LDO vs switching regulator

We've currently got a PCB that needs to power a modem and a microcontroller. The PCB is powered via a battery (12V - 30V range). The modem and the microcontroller have separate power lines. The ...
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2answers
410 views

How ADSL Demodulates (restores the order) the signal for dummies

I am not an electric engineer so sorry for questions that might miss some fundamentals. I am trying to understand the ADSL modem. The ADSL modem sends the data over different frequencies in parallel....
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2answers
2k views

GPRS data call using GSM/GPRS modem (Siemens TC35 and/or MC35)

I'm developing a data aquisition module, that amongst other things, it have to comunicate through GSM/GPRS module, since it will be a mobile application. I can connect to the module and send sms's ...
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2answers
100 views

Do you really need all of the sigals for a general RS-232 port?

I know that having TX, RX, GND, RTS, CTS are good. What about all of the others? Do devices these days even make use of the other pins (DSR, RI, DCD, DTR)? Is it safe to generally leave out these pins?...
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1answer
441 views

Receiving empty data from gprs module? [closed]

I am trying to send a string from a Huawei MU509 GPRS modem to a Linux server over the internet. I am using an AT command tester to simulate AT commands. After giving the ...
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1answer
173 views

What is the proper GPRS / GSM modem setup to work with 5 voltage sensors?

I've been looking at modems and most of them come in RS232/485 input only. I need to hook up 5 different power cables to the modem to monitor their voltage. Some of the modem's I've found have 4 to ...