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38 votes
Accepted

Why do many laptops run on 19 volts?

The choice of 19 volts is because is it comfortably below 20 volts which is the maximum output voltage of power supplies that can be certified as LPS (Limited Power Source) with non-inherent power ...
Graham Davies's user avatar
37 votes
Accepted

Why are there no WiFi earbuds?

Because wifi is the wrong technology for audio transport. The highly nondeterministic, large-burst approach to data networking introduces a need for a large buffer. This inherently means high latency ...
Marcus Müller's user avatar
36 votes

Why doesn't higher frequency mean higher data rate?

It's not a bad question and shows quite a common misunderstanding of how Radio Frequency (RF) Systems work. The 900MHz and 2600MHz signals are called Carrier Frequencies. The actual information is ...
Vance's user avatar
  • 888
18 votes

Why doesn't higher frequency mean higher data rate?

Because the bandwidth of the channel determines how rapidly the symbols on that channel can change, not the carrier frequency. It is the bandwidth of the channel which determines how fast the channel ...
TimWescott's user avatar
  • 46.6k
14 votes

Why are there no WiFi earbuds?

Although the answer from Marcus Müller is good, he leaves out an important factor: standardization. This is not the same thing as market share. Wi-fi is a general-purpose protocol designed to carry ...
fluffysheap's user avatar
12 votes

Wiring power banks in series for 25V output to power e-bike

Your power banks provide 5V 2A output or 10W, and cost about $10. To power a 250W motor, you'll need 25 power banks which will cost you $250. Why not just buy a $200 battery then? Also, think how ...
Dmitry Grigoryev's user avatar
11 votes

Why doesn't higher frequency mean higher data rate?

By quick analogy (the other answers are sufficient in their detail): If you own a hotel where all the rooms are the same size (bandwidth), it doesn't matter how high a floor (frequency) they're on--...
Cristobol Polychronopolis's user avatar
9 votes

How is 4g much faster than 3g?

I understand that increasing the frequency band means increasing the data rate. You should make a distinction between the frequency band which is sets the frequency range that the cellular signal is ...
Bimpelrekkie's user avatar
8 votes
Accepted

Why is LM2596 buck converter output current low when used as a mobile charger?

Phones do USB power negotiation to see what current the USB power source is capable of providing; your buck converter doesn't negotiate so the phone assumes a maximum, and this maximum is below what ...
ocrdu's user avatar
  • 9,260
6 votes

Which chip remains on when the phone is switched off but it has to detect if the power button is pressed to switch it on?

This is a very broad question, a proper answer could be given only on a per-device basis, only by an expert engineer from the company that makes the device and probably only by someone that works on ...
Vladimir Cravero's user avatar
6 votes
Accepted

Why can't the orthogonal PN codes help in the near-far effect?

the orthogonal PN sequences used in CDMA be able to handle this? Orthogonal PN sequences could. In reality, you don't get these – frequency and timing offsets, and trade-offs during the design ...
Marcus Müller's user avatar
6 votes

Why doesn't higher frequency mean higher data rate?

Consider Morse Code modulation applied to human audio as one of many possible examples. With input - . . . - . . . - . - . First, 880 Hz carrier frequency: ...
mephisto's user avatar
6 votes
Accepted

How to explain mathematically 2.4 GHz and 5 GHz WiFi coverage and maximum range?

why 5Ghz has less coverage and more susceptible to attenuation in long range? It doesn't. The limitation you might be thinking of is because as frequency increases, the receive antenna size gets ...
Andy aka's user avatar
  • 462k
5 votes

How does the phone detect if 3.5 mm jack circuit is closed?

There have been quite a few answers on this, but still some additional clarifications may be helpful: yes, quite a few headset jacks include still an insert detect switch, which may also be a signal ...
Juha Backman's user avatar
5 votes

How to power a phone with no battery properly?

There should be no big problem to replace internal battery with external DC source. In my former place of work the software people routinely (and without any reservations!) used various benchtop ...
Ale..chenski's user avatar
  • 40.9k
5 votes

Can mobile reception 4G/5G signal reception be affected by atmospheric changes?

Yes, microwave propagation, like any other electromagnetic wave, is affected by medium properties – especially moisture/water content. As a tendency, the higher you go in frequency, the more you ...
Marcus Müller's user avatar
5 votes
Accepted

Is it possible to transfer provider from one SIM card to another?

If that "another" SIM card is not a blank one then most likely no, you can't. Even if you can, the new SIM will likely fail on network authentication due to the unknown or mismatched ...
Rohat Kılıç's user avatar
4 votes

How to power a phone with no battery properly?

In theory, I don't see why applying the specified battery voltage on the correct battery terminals would not work. Try to avoid overvoltages! Obvious reasons are not obvious to everybody. I assume ...
MAB's user avatar
  • 352
4 votes

Why can't the orthogonal PN codes help in the near-far effect?

Well, the clue is in the last sentence. The receiver has to reliably detect the number of received signals (e.g. 1's in the code sequence), since they add up on the receiver end. If there are two ...
JvO's user avatar
  • 620
4 votes

Does a poor mobile network signal cause faster battery drain?

Quite a simple question actually, does a poor mobile network signal cause faster battery drain? Yes, the problem is three fold: The phone needs to use more CPU and radio resources to establish a ...
Voltage Spike's user avatar
  • 84.1k
4 votes

Why doesn't higher frequency mean higher data rate?

10 MHz of bandwidth contains the same amount of information, regardless of whether it's centered at 900MHz or 2600MHz, or any other center frequency. This is easy to show -- the center frequency of a ...
Matt Timmermans's user avatar
4 votes
Accepted

3G, 4G, 5G and 6G simple differences

Seems like a simple question but I've searched and not found good answers. This is really not much of a simple question. You're basically asking about "what happened in ca 23 years of rapid ...
Marcus Müller's user avatar
3 votes

voltage output on double USB chargers

If there is a single label, it indicates the output of the whole charger. Hi-power chargers usually also specify max current per port because a USB connector has its own limit. 4.8 A may be too much ...
A.K.'s user avatar
  • 352
3 votes

Powering multiple cellphones with a DC power supply

Do you need to transmit? Used to do this at work, and I made several fake batteries and battery charge/discharge emulators at my old work. Powering all phones can work as you say can work fine as ...
Vince Patron's user avatar
  • 3,606
3 votes
Accepted

Why do mobiles phones have non removable batteries at all?

Technically, the battery is removable. I've replaced batteries on iPods and iPhones. All you have to do is pry in the right places to open the case. (Be sure to use the right tools if you care about ...
Adam Haun's user avatar
  • 22k
3 votes

Why do mobiles phones have non removable batteries at all?

Cost... and you sell more phones since the life is now limited. But in reality there is a significant cost involved in making the case such that you can remove the battery. The manufacturer also ...
Trevor_G's user avatar
  • 46.8k
3 votes
Accepted

What Voltage/Current Levels Can I Send Into the Microphone Input on a Mobile Phone?

Microphone inputs on phones are designed to be compatible with electret microphones which produce very small ac voltages. A signal at about 5mV peak to peak should work. The phone may be looking for ...
PaulB's user avatar
  • 409
3 votes

Is it possible to move an internal SD card from a Samsung Galaxy S3 into another phone (Galaxy S2) to retrieve the information from the card?

Internal memory is soldered to the motherboard and is not physically a removable SD card. So the short answer is no. Obviously the IC could be desoldered if you have the equipment and skills, but it ...
user3190797's user avatar
3 votes

Power old Nokia phone from Bench Power Supply

I know the question is not very recent, but: Yes, you can power the phone up using a pull down resistor from bsi to gnd (82K). Connect VCC and Gnd to 3,9 volt powersupply. Without a working sim you'...
Erik Harkema's user avatar

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