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 $f_2$ (...
- 2,467
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 ...
- 7,125
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 ...
- 10.4k
4
votes
Accepted
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 ...
- 198
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 ...
- 7,125
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 ...
- 766
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First of all, these bands are not obsolete, there are many uses that might seem outdated, but won't go away easily. ...
- 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 ...
- 5,312
4
votes
Accepted
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 ...
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 ...
- 6,975
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 ...
- 12.5k
3
votes
Accepted
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 ...
- 11.4k
3
votes
signal-to-interference-plus-noise ratio (SINR) and others calculation
First, you should link in a reference to the Hata and Ericsson models. I haven't heard of them, and a quick search on Google didn't give anything.
Path loss and received signal strength are typically ...
- 131
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 ...
- 10.4k
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 ...
- 8,124
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 ...
- 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 ...
- 206
2
votes
Accepted
What kind of signal is the signum function? A power signal or an energy signal?
First point is that signum is not continuous with the jump at $t=0$.
Second because of the absolute value in the integral it has the same $E$ and $P$ as a constant signal $1$.
This means that $E_{...
- 5,751
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 ...
- 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.
- 6,112
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 ...
- 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 ...
- 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. ...
- 7,125
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 ...
- 10.4k
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 ...
- 6,544
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 ‘...
- 5,312
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; ...
- 175
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 ...
- 9,642
Only top scored, non community-wiki answers of a minimum length are eligible