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8 votes
Accepted

How were the tones for DTMF chosen?

From: Engineers Garage Dual Tone Multi-Frequency: $f_1$ = 697Hz, 770Hz, 852Hz, 941Hz. $f_2$ = 1209Hz, 1336Hz, 1477Hz, 1633Hz. A key press on a DTMF keypad means a combination of $f_1$ and $f_2$ (...
StainlessSteelRat's user avatar
6 votes
Accepted

Why do bluetooth headsets get interference (choppy sound quality) outdoors?

As you might have already realized there is a good reason that some of Bluetooth headset are inexpensive. Poor design. High quality, well designed Bluetooth headset tend to be expensive. Also not all ...
Mahendra Gunawardena's user avatar
5 votes

Would not a telephone call (from the late 1950s) auto-disconnect if one of the parties "closes the handle"?

If you could truly indefinitely keep a line open for anyone who calls you, by simply not hanging up on your end, the potential for abuse is endless. That's the way the POTS (plain old telephone ...
Transistor's user avatar
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4 votes

What is the difference between Bluetooth Low Energy and Bluetooth BR/EDR in Park mode?

There are many factors that make BLE low power, and I have attempted to address as many of them as possible. In order to better understand the power consumption differences between Bluetooth classic ...
Mahendra Gunawardena's user avatar
4 votes
Accepted

How can I make a GPS traceable microchip?

Firstly you seem to be under the common misunderstanding that the GPS satellites somehow calculate where a GPS receiver is. They don't. The satellites are transmit only systems (ignoring the command ...
Andrew's user avatar
  • 766
4 votes
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Will the water in a gold fish bowl signficantly abosorb Bluetooth or WiFi if transciever is at bottom of bowl?

There is information out there, but probably the best way to find out is to actually try it. Grab a small Bluetooth or Wifi device and seal it in a waterproof enclosure or bag, and submerge it to the ...
Colin D Bennett's user avatar
4 votes

Why is WiFi increasing frequency?

why not scrap all the obsolete bands and reassign the 1 GHz - 6 GHz range to WiFi? First of all, these bands are not obsolete, there are many uses that might seem outdated, but won't go away easily. ...
Eirik M's user avatar
  • 141
4 votes

Why radio communication was limited to military use and did not become popular with general public like cell phones have become today?

The radio spectrum is limited. There are is only a finite range of frequencies over which we can transmit so you if have two people communicate by directly transmitting to each other over two ...
DKNguyen's user avatar
  • 5,621
4 votes
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Does anybody know what this symbol is?

This symbol means that the contact number you have called was connected via Voice over WiFi (VoWiFi) technology instead of VoLTE. Your service automatically shifts to VoWiFi whenever there is a WiFi ...
Suman Roy Ghatak's user avatar
4 votes

What are the differences between a standing wave ratio meter and a frequency counter?

The frequency of an electromagnetic wave (or any other wave form) is the number of times that the wave reaches the maximum over a specific period of time. This is common when referring to radio ...
fred_dot_u's user avatar
  • 7,132
3 votes

With the "plain old telephone system", would two neighbors be able to call each other privately?

Joe and Sue's calls would go to their exchange where the lines were terminated on an automatic exchange. There is (generally) no electronics between their wall socket and the exchange circuits so ...
Transistor's user avatar
  • 10.8k
3 votes

How is it possible that an *undertaker* invented the automatic telephone exchange? And as early as in 1888?

You may be misunderstanding what "undertakers" actually did in this time period. Even in the 1950s in the UK when I was growing up, in rural areas the local undertaker not only did the carpentry and ...
alephzero's user avatar
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3 votes
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Why only the spectrum range of radio waves can be reflected from atmospheric layers while higher ranges (Infrared-Visible Light-Ultraviolet) can't?

Different materials reflect, absorb, and scatter different wavelengths of light. The ionized layer at the edge of earth's atmosphere happens to reflect a certain range of wavelength while ...
Olin Lathrop's user avatar
  • 11.4k
3 votes

Rotary Phones vs Pushbutton -- why did we ever have rotary?

The reason is simple - the timing in the evaluation of technology. The required technology to make touchtone signal possible, Dual-tone multi-frequency signaling (DTMF), wasn't developed/introduced by ...
r13's user avatar
  • 8,184
2 votes
Accepted

Why is Li-Fi faster than regular wifi?

The wave propagation speed is only relevant when you start approaching the theoretical limit of that type of wave's ability to transmit information. For an analogy, consider people having a ...
Air's user avatar
  • 3,211
2 votes

What is the thinnest possible depth of any given material required to display an image?

Let's assume that you are using OLEDs (organic light emitting diodes) which can emit a photon when charged with an electron. You could build a single molecule pixel (just nip down to the corner store ...
hildred's user avatar
  • 206
2 votes

A 40MHz oscillator in usb wifi adapter

Generally when you need to scale up a clock you use a PLL (Phase lock loop). A very crude explanation is that you have a voltage controlled oscillator at roughly the required frequency. You divide ...
Andrew's user avatar
  • 766
2 votes

Tethered Balloons vs Towers for Wireless Communication

They would be a great hazard to air traffic; The umbilical would be essentially invisible to passing aircraft. In spite of regulations not to fly here or there.
blacksmith37's user avatar
  • 6,144
2 votes

why can't remove the Image frequency using a band-pass filter?

You only know something is an "image frequency" because you know what the signal was like before you sampled it and reduced its bandwidth. Do an experiment, either with real hardware or a computer ...
alephzero's user avatar
  • 12.5k
2 votes

Would not a telephone call (from the late 1950s) auto-disconnect if one of the parties "closes the handle"?

This is still done by scammers who want to trick somebody into believing there is something wrong with the internet connection of their PC, and that some malware on their PC can disconnect their phone ...
alephzero's user avatar
  • 12.5k
2 votes

Bandwidth vs Capacity

Your understanding is correct. Here is an alternate definition from Wikipedia - Bandwidth Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies. ...
Mahendra Gunawardena's user avatar
2 votes

Ethernet extender kit claims to send data through power cables - Is this correct?

Is there any way I can prove/disprove this? Yes. Run an extension lead from your neighbour's house to power one of the devices. It should fail due to either distance or your neighbour being on a ...
Transistor's user avatar
  • 10.8k
2 votes
Accepted

Rotary Phones vs Pushbutton -- why did we ever have rotary?

Rotary phones were controlled by sending pulses down the line. These pulses were the equivalent of hanging up the phone quickly - hence what you see in old movies and TV shows when they quickly tap ...
Tiger Guy's user avatar
  • 6,901
2 votes

Why do we always use 3.8 x 10^(-3) value as Forward Error Correction (FEC) threshold?

I found this. Which states: For example, for 7% overhead HD-FEC with a NCG of 9.19 dB at a corrected BER of 10−15, the pre-FEC BER should be lower than $3.8 × 10^{−3}$ [4], which is regarded as ‘...
DKNguyen's user avatar
  • 5,621
2 votes
Accepted

Generating 10 GHz Frequencies with Reasonable Power Requirements

UPDATE From clarifying the specs in comments: the poster wants a region with a high electric field generated by as low an input power as possible. You want standing waves, not propagating waves; ...
Alex I's user avatar
  • 175
1 vote

How progressive scan televisions works in depth?

The question is still a little confused after the edits. I'm trying to understand in depth the behavior of progressive scan TV monitors (LCD/LED - Digital Television). The subject is really only ...
Transistor's user avatar
  • 10.8k
1 vote

With the "plain old telephone system", would two neighbors be able to call each other privately?

Two neighbors living in a city or major town would be able to call each other the "Plain Old Telephone System". In rural areas however they would have been able, but there would have used the ...
Fred's user avatar
  • 9,687
1 vote

Electronic symboles in datasheets

Yes! The logic gates from a RS485/422. Most likely the signal are level shifted. Below is an except form Low power RS-485/RS-422 transceiver ST485B, ST485C datasheet. Below is an another similar ...
Mahendra Gunawardena's user avatar

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