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22 votes
Accepted

How much power is radiated by cell towers?

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 ...
Marcus Müller's user avatar
17 votes

How did old mobile phones amplify signals lower than the noise floor?

As shown in the picture 1, the RxLevel sometimes is -101 dBm. This RxLevel is lower than the noise floor of electronic devices, which is around -90 to -80 dBm. Well there's your problem, the ...
Neil_UK's user avatar
  • 165k
16 votes
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Why do cell phones sometimes interfere with amplifiers

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 ...
Kevin White's user avatar
12 votes

If a module is "arduino compatible", does that necessarily mean it isn't compatible with other microcontrollers?

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 ...
Bimpelrekkie's user avatar
  • 80.8k
11 votes

Simulate bad cell phone reception in the lab

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 ...
Ale..chenski's user avatar
  • 40.1k
9 votes
Accepted

Simulate bad cell phone reception in the lab

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 ...
Sylvain's user avatar
  • 809
8 votes
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Impedence matching required for very short PCB trace?

That is a good question indeed, but the answer really depends on how much power you are willing to lose to the transmission line (TL) effects. Different people use different rules of thumbs for the ...
Big6's user avatar
  • 5,634
7 votes
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Does my PCB require a 50 ohm impedance trace even if I am using an external antenna?

When you send a signal along a trace, if the length of the trace is of the same order as the wavelength of the signal, then you have to match impedances or, you will get a "reflection". What this ...
Andy aka's user avatar
  • 453k
7 votes
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RF layout bend over Component

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 ...
Dave Tweed's user avatar
  • 172k
7 votes

Can smaller trace width limit the current flowing through the PCB?

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 ...
DKNguyen's user avatar
  • 56.4k
6 votes

What AT command should be sent to modem to get time?

AT+CLTS=1 ( Get local time stamp ) AT&W ( Save configuration ) Turn off modem and turn on modem(reboot to get local time from network) Next time when modem boots up you should be able to get ...
Sumit Dubey's user avatar
6 votes

Can you use a amplifier and a satellite antenna to boost a GSM signal?

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 ...
Chris Stratton's user avatar
6 votes

How did old mobile phones amplify signals lower than the noise floor?

Not a full answer, but some general ideas. I will suppose digital signal in "logic level". The reasoning could be extended to analog signals, but it's a bit more complicated. Let's suppose ...
Sandro's user avatar
  • 7,089
5 votes

Why do some GPS devices require a GSM SIM-card?

Because the first is a GPS tracker that you can call and it replies via IVR or SMS or has a data connection so you can see it online or periodic emails. Maybe automatic geo fencing warnings. The ...
Passerby's user avatar
  • 73k
5 votes

Will this PCB trace GSM antenna be affected by EMI?

Apart from EMI issues, I have a hard time believing that this will work at all. Is there a reference design available for something similar? From what I would guess (I'm not an antenna specialist at ...
Tom L.'s user avatar
  • 8,014
5 votes
Accepted

GSM Module gets into reboot loop

How are you powering that GSM module? [...] from the usb port Using a PC USB port for power is likely to be a problem, for the same reason I explained in my answer here to someone who (...
SamGibson's user avatar
  • 17.8k
5 votes

How to properly power sim800l module?

Everything you are reporting is consistent with insufficient power to the GSM module, when it tries to register with the network, even though you think your power supply is OK. Do you have access ...
SamGibson's user avatar
  • 17.8k
5 votes

Simulate bad cell phone reception in the lab

RF is tricky. I wouldn't mess with the antenna, I think the product should be tested in its final configuration. The reason for this is simple: when reception is really bad, your transmitter will ...
bobflux's user avatar
  • 75.9k
5 votes
Accepted

Why sometimes I have voice but no data on a GSM network?

GSM by itself does not support data, just voice (even SMS is put ontop of GSM). Data service, beyond the 9600baud CSD (which doesn't seem to be supported by most phones/mobile providers anymore) ...
Attila Kinali's user avatar
5 votes

Long term health effects of a gsm modem

The fears are unfounded - both technologies are fundamentally safe. The only conceivable damage from radio waves is heating of biological tissue and and Specific Absorption Rate (SAR) testing is ...
EasyOhm's user avatar
  • 4,649
4 votes

GPS consideration for PCB with GSM (interference, setup etc)

Amtenna signals shouldn't interfere since the GSM and GPS are on different bands. However, the electronics might interfere with each other. Put GPS and GSM modules on their own ground planes such that ...
student's user avatar
  • 551
4 votes
Accepted

Does A-GPS require a GPS antenna?

It is possible to get a location fix without a valid GPS signal. Cell phones often call this "network location". I wouldn't call it A-GPS, but sources are conflicted here. This fix is not very ...
Christian's user avatar
  • 1,283
4 votes

Does my PCB require a 50 ohm impedance trace even if I am using an external antenna?

I know this is a very old question, but whomever is interested, I actually think there is one important thing wrong in the previous answer. It was assumed that the speed of light within the PCB track ...
Monty's user avatar
  • 61
4 votes
Accepted

Will this PCB trace GSM antenna be affected by EMI?

I think a more reasonable way would be to use an external three way splitter and the old design to connect your three GSM modules to one antenna. You don't seem to have the knowledge to do RF PCB ...
JRE's user avatar
  • 71k
4 votes

Will this PCB trace GSM antenna be affected by EMI?

At the risk of giving a product recommendation you may want to look at an RF power splitter/combiner IC from someone like mini-circuits. Mini-circuits splitters These will allow you to combine the 3 ...
Andrew's user avatar
  • 6,912
4 votes
Accepted

SIM800 PWRKEY - Automatic start

To automate the startup of sim800/sim900 module just keep the pwrkey shorted to ground always. As the supply will be provided modem will be on.
Pi M's user avatar
  • 56
4 votes

How to properly power sim800l module?

General considerations regarding powering and interfacing the module, not related to OP's issues most likely. The module requires 4.0V nominal (recommended) with up to 2A peak consumption and as low ...
Spehro Pefhany's user avatar
4 votes
Accepted

GSM antenna inside metalic enclosure

As you say, the enclosure will block radio waves emitted inside of it. People often think that a shield should block all radio waves. Technically it does, but in practice it doesn't because the ...
Olin Lathrop's user avatar
4 votes

How to wake up SIM800 module from sleep, after entering sleep mode 2 (AT+CSCLK=2)?

According to this page, to wake it up, you need to send any AT command, which will be ignored by the module (so no response), followed (within 5 seconds) by AT+CSCLK=0 It took me all of one ...
DoxyLover's user avatar
  • 8,070
4 votes
Accepted

SIMCOM vs UBLOX

Your antenna supplier is probably also an U-blox reseller ;) Seriously - pretty much all cellular modules: Telit, U-blox, Gemalto [former Cinterion], Simcom, Quectel are basically the same (I've ...
filo's user avatar
  • 8,931

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