Hot answers tagged

24

This is partially not entirely true anymore. With increasing bandwidth requirements and as we are getting really close to the theoretical limit of omnidirectional picojoules/bit, in order to increase bandwidth in cell phones it will definitely be necessary to go back to directional antennas again. The way this is solved in the next generation of radios (and ...


21

There seems to be a remarkable lack of relevant on-web material. Maybe just hiding. This looks highly apposite Design of New Multi Standard Patch Antenna GSM/PCS/UMTS/HIPERLAN for Mobile Cellular Phones with an interesting appearance And tri-band !!! GSM Dipole antenna - very informative Designing a GSM dipole antenna Commercial product. LOOKS simple....


20

There are no antennas that are truly omnidirectional without a lot of complication especially for a cell-phone. However, if you think about it, you do want to be able to hold your handset and turn in any direction to face north, south, east or west and expect it to work. A directional loop antenna defeats the objective of being able to face any direction and ...


19

There's no general answer. First of all, you have a misconception about GSM, 3G, 4G: The frequency bands you list are some of the frequency allocations for these networks. These are different between different operators and in different countries. Then: Cellular networks are not broadcast transmitters. They don't work with constant output powers. The ...


11

Normally, the WWLAN testing and debug is done in electromagnetically shielded cages in labs when external tower signals (or local 3G-4G repeaters/re-translators) are too strong. The tests are usually done with special instruments like Agilent LTE tester, which has all abilities to change signal levels and simulate weak reception. In normal operation the LTE ...


11

The term "Arduino compatible" basically means nothing. Many sellers use the term more as marketing ("You can make this work with your Arduino!") than anything else. The Arduino is (usually) just an ATMega microcontroller on a board, that ATMega is very similar to many other microcontrollers. Nearly all of them work with a supply between 2 V and 5 V as does ...


10

There are at least two commonly used civilian mechanisms for long range control of UAVs or RC cars: Public-band TX/RX radio, and mobile packet data, depending on the capabilities onboard the remotely controlled vehicle. For public-band RF control at long range, modules such as the Xtend 900 1 Watt RSPMA by digi work well at 5+ miles, giving between 10 kbps ...


9

To "simulate" a poorer cell reception you can use RF attenuators between your board and the antenna. They are composed of multiples resistances building a network that will attenuate RF power very predictably, both in RX and TX, while maintaining the proposer RF impedance as seen from the modem and antenna. They have a limited power rating. Do not run your ...


7

I have used the following command: AT+CCLK? which returns the date and time, like: +CCLK: "00/01/12,05:44:53+00" successfully in products using three different cell modules: Enfora, Telit, and Sierra. The fact that it uses a + character after the AT implies it is a common (as opposed to proprietary) command, and should be available on most if not all ...


7

It isn't the metal mesh leaking so much as the joint around the door. Rather than employing a continuous metal-to-metal contact around the edge of the door to seal it when closed, most microwave ovens use a quarter-wave "trap" — basically a shaped "groove" of the correct dimensions that surrounds the door opening (usually hidden behind a dielectric ...


7

No, they cannot. Cell phones contain cell modems, like the green module pictured in the question. They are controlled using "AT" commands, patterned after (but greatly extending) the AT commands developed in the original Hayes modems thirty years ago. There is a core set of AT commands that are common across all cell modems; these generally have a prefix ...


7

The dual-tone multi-frequency (DTMF) system of transmitting data via. standardized audio tones is baked into the GSM standard and works similar to that of a land-line. When a call is in progress, pressing a number button generates a combination of audio frequencies based on which button is pressed (seen here.) If you have the ability to receive and interpret ...


7

The usual problem with interference from GSM cell phones is caused by rectification of the strong RF signal at the semiconductor junctions at the input of the amplifier. GSM uses Time Domain Multiplexing to share the RF frequency with other uses - it only turns the RF signal on for a short time at a 217Hz rate with other users and the base station using the ...


7

Yes, a smooth bend would be better for signal integrity than the square corner. All other things being equal, that corner sticking out represents an unnecessary impedance "bump" in the transmission line. Although in this case, the dimensions are so short that you'd probably never be able to measure the difference. The solder fillets on the nearby components ...


6

In my work on hearing implants I found that the buzzing is caused by magnetic radiation from the battery wires in the phone which carry pulses of maybe 2A. This magnetic field is relatively intense and can couple into low frequency EMI susceptible circuitry of nearby devices. The noise in my case wasn't from the RF and antenna at all. This is why RF ...


6

Solution is to reflash SIM900A with SIM900 software and it works like a charm. Here is the page that shows the solution. Flashing is no trickery, just a right sequence of operations, there is detailed instruction for arduino-like approach, my way required just a few major steps: Power up your SIM900A module to respond to AT commands in auto-...


6

These things are all PIFA (planar inverted F) antennas. They all perform exactly the same, though they have to be carefully designed to fit into the enclosure and have the correct resonances. The basic idea is to add cuts in such a way that the path the current takes through the antenna cause it to resonate at a lower frequency than the overall size would ...


6

Would using a typical high frequency audio amplifier that is connected to a satellite antenna boost the signal? No, absolutely not. In fact it would make things worse. An audio amplifier has absolutely no capability at the (near/-) microwave frequencies used by GSM. Quite likely it will function as a very effective attenuator and block almost all of the ...


6

This might not be the only issue, but is almost certainly is one of them: the LM317 cannot supply 2A (its output transistor simply cannot pass that much current). But even if it could, it probably would go into thermal shutdown. It is a linear regulator and linear regulators work by turning excess voltage to heat. That means the higher your input voltage is ...


5

Firstly, you have to accept that your device will be bigger and more expensive than a comparable cellphone. If you want to assemble something out of modules, you're already at the smallest point. To get smaller, you'll have to do your own PCB and attach a suitable GSM module and microcontroller. (You can get programmable modules which may suffice: Sierra ...


5

One way is to use for this purpose cheap USB TV tuner. I've read that ppl have good results with it. Here is the link: http://hackaday.com/2012/03/30/working-software-defined-radio-with-a-tv-tuner-card/ Obviously it is viable only for receiving (so no, it is not possible to make GSM base station with it). However GPS receiver is doable: http://hackaday....


5

How can the tiny bit of EM emitted by a cellphone radio cause a speaker system, designed to operate off of a fluctuating 1 v signal, produce such a loud buzzing noise? The interference is not driving the speakers directly; it is finding its way back into the electronics, through some path where it ends up amplified. Here is one way. The speaker is actually ...


5

First of all, it is the power that matters in this situation. Any small speakers are going to be only a few watts, if not loss. The power out from the handset in cell applications can be as large as 33dBm (or 2 Watts). This is the case for both UMTS and GSM; however, for GSM there are bursts that are around 217 Hz (which is in the audible range) This 2 ...


5

The most important reason for the distinction is quality of service, which has very different requirements for both modes of operation. In voice transmissions, you need to have the packets to arrive in order and they have to take the same short time to transmit. In voice chat, a few dozen milliseconds sound like a long time: "are you still there?". Circuit ...


5

How many functions? That depends on a few factors. First, will I have enough pins? The GPS module will probably take up two PWM pins (Rx and Tx) but I recommend you hook the Rx and Tx of the GPS directly into the hardware serial Rx and Tx of the Uno. The senors will probably use a single analog pin each. The Arduino Uno has six. I'm not sure how many pins ...


5

First of all, NITZ is poorly supported in many networks (can you say COST-CUTTING). I would not rely on it at all as 1 in 10 networks use it, especially in far flung places. Secondly +CCLK command is for the internal RTC of the modem. Some modems have facilities to update this clock from the network. Relying on this is risky. The above HTTP request is ...


5

An omnidirectional aerial is simply a convenience. If you are prepared to locate the direction of the nearest/strongest cell site and point a directional aerial at it, it will work just fine. I used to do just that. As Andy says, needing to do this is generally unacceptable to typical users. In niche cases it can be extremely useful, and these prove the "...


5

2A bursts are 577 ┬Ás every 4.6 ms The power for those bursts is equivalent to about 1.25 watts\$^1\$ - if the 4.1V supply were 100% efficient at taking energy from the 5V traco then the power needed would be 1.028 watts but because you are using a linear voltage regulator to create the 4.1 volts then it's 1.25 watts from the traco. The question is, from ...


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