60 votes
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Is it possible to receive information if the received power is below the noise floor?

Short answer: yes, possible. GPS does that (nearly) all of the time. Long answer: The SNR your receiver system needs depends on the type of signal you're considering. For example, good old analog ...
Marcus Müller's user avatar
36 votes
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Why do microwave ovens use magnetrons?

Magnetrons are cheap, reliable, pretty efficient (65% or so- and they tolerate high temperatures so heat sinking is easy) and made with mature technology. They are also reasonably tolerant of VSWR ...
Spehro Pefhany's user avatar
22 votes

Is it possible to receive information if the received power is below the noise floor?

Fundamentaly, we have the Shannon-Hartley formula for the communication capacity of a channel: $$C = B \log_2\left(1+{\rm SNR}\right).$$ \$C\$ is the error-free channel capacity in bits per second ...
The Photon's user avatar
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20 votes

Are TV coaxial cables compatible with WiFi antennas?

So you want to transport that 2.5 GHz (or even 5 GHz ?) Wifi signal over TV COAX cable ? Indeed to the non-RF people you'd just think that would work. And it does BUT there will be almost no signal ...
Bimpelrekkie's user avatar
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19 votes
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Is Gaussian noise equal to white noise?

No, they are completely orthogonal concepts. The probability distribution says nothing about the frequency content, and the power distribution across frequency says nothing about the sample ...
Dave Tweed's user avatar
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15 votes

Through-Glass WiFi Antenna

Parallel capacitor plates of 25 mm by 25 mm seperated by 4mm of glass with a relative permittivity of 4 would give a coupling capacitance of about 5 pF. That capacitance is in series with an antenna ...
Andy aka's user avatar
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15 votes
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Is there any relationship between frequency of signal and distance it travels?

In general, yes, higher frequencies attenuate more the further distance they travel. There are two effects that are responsible for this. First, higher frequency radio waves tend to be absorbed more ...
Synchrondyne's user avatar
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12 votes

Why do microwave ovens use magnetrons?

The domestic microwave oven needs high power to cook the meal and high frequency to excite the water molecules. What is not needed is high stability because the water energy absorption spectrum is ...
Autistic's user avatar
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12 votes
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Why is power of a signal equal to square of that signal?

If the signal is represented as a voltage \$v(t)\$ or a current \$i(t)\$ and it is connected to a (1 ohm) resistor, the power dissipated in the resistor is proportional to \$v^2(t)\$ or \$i^2(t)\$. ...
AJN's user avatar
  • 3,796
11 votes

Through-Glass WiFi Antenna

I never fully understood how or why it worked Well, it's not magic ;-) Actually it can either be done magnetically using coupled inductors. This is like a transformer without a magnetic core. ...
Bimpelrekkie's user avatar
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10 votes

Is it possible to receive information if the received power is below the noise floor?

What I would really like to know is that is it possible to establish a communication channel (sending information) if the received power level of the signal, received by the receiver antenna is ...
Andy aka's user avatar
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10 votes
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Do I need to maintain source of a signal till it reaches the destination?

Years ago I designed a video system that sent a composite video signal down a coax cable from the video controller to the display CRT. This system used monochrome video with a 20MHz dot clock to ...
Michael Karas's user avatar
9 votes

Why can't all data be sent across 4 wires?

Serial buses are widely used for high speed transfer. This diagram shows the available data transfer / clocking rate of a number of serial and parallel buses. In addition, it is common to implement ...
Russell McMahon's user avatar
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8 votes

Are TV coaxial cables compatible with WiFi antennas?

You must use coaxial cable of the proper impedance. The most common impedance for coax cable is 50 ohms or 75 ohms. If the cable you want to use matches the impedance of the interface AND the antenna,...
Richard Crowley's user avatar
8 votes

Do I need to maintain source of a signal till it reaches the destination?

Hopefully, this picture should explain: - Picture taken from here. The spring represents the media in which a signal can travel. The signal can be a voltage/current or an electromagnetic field or, ...
Andy aka's user avatar
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8 votes

Is Gaussian noise equal to white noise?

As Dave (and Brian) said: two totally different concepts. One doesn't imply the other. This is homework, and you should research it well! Getting the difference between (auto)correlation/PSD and ...
Marcus Müller's user avatar
8 votes

Why is power of a signal equal to square of that signal?

$$ P = \frac{V^2} R $$ If you're driving a constant resistance then the power is proportional to the square of the voltage. You can rewrite the equation substituting, from Ohm's Law, \$ V = IR \$: $$ ...
Transistor's user avatar
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8 votes
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What is the term for a code that has duplicate or redundant/equivalent symbols?

In the specific use case of balancing out a DC bias on a signal, this is referred to as a paired-disparity code. Such a code chooses between synonymous codewords in order to keep the average voltage ...
Hearth's user avatar
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7 votes

Are oscillators always non linear?

A practical oscillator has to be designed taking into account component tolerances. In your example the ratio of RG to RF needs to be such that the gain round the loop is unity. Because of the ...
Kevin White's user avatar
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7 votes

Sampling Theorem and reconstruction

You can think of any perfectly bandlimited signal as the superposition of a set of \$\frac{\sin(t)}{t} = \text{sinc}(t)\$ curves, with their peaks positioned uniformly along the time axis. Their ...
Dave Tweed's user avatar
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6 votes

Is it possible to receive information if the received power is below the noise floor?

As a practical adjunct to Marcus Müller's excellent answer... Ham radio has a number of digital modes suitable for successful signal reception below the noise floor. These numbers have a caveat, ...
Eric Towers's user avatar
6 votes

Is it possible to receive information if the received power is below the noise floor?

the power received by the antenna in dBW has to be higher than the noise floor in dBW "noise floor" as most people would understand it is not measured in dBW, or any other unit of power. Rather, the ...
Phil Frost's user avatar
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6 votes
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Why frequency of a DC signal is chosen as zero? If the period can be anything, isn't it same for frequency?

If you want to treat this signal as a periodic one, then you can take its Fourier series. Unlike most other periodic signals, you have free choice of what frequency to consider as its fundamental ...
The Photon's user avatar
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6 votes

Can signals pass through a single wire in both directions simultaneously?

Conventional telephone service wiring sends signals in both directions simultaneously using a 'hybrid'. Wikipedia - Telephone Hybrid
Kevin White's user avatar
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6 votes

Intuitive explanation for RMS voltage of discontinous sinewave

If I were to run this AC sinewave through a resistor it would be the same power dissipated as running 230V DC through it. Indeed: that is both the definition and the intuitive explanation mentioned ...
devnull's user avatar
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5 votes
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Steady State Error: why we use a negative feedback rather than a single gain to reduce the error?

It's the stability that's impractical in the real world. Mathematically, numbers look very stable, and yes, of course we can tweak a coefficient here and get the answer we want. In the real world, ...
Neil_UK's user avatar
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5 votes
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Is the Signal-to-Noise ratio arbitrary?

At first I wondered what to do with your question, because there was a lot of misunderstanding in it, but finally, let's just answer the core question: It looks to me that the Signal-to-Noise ratio ...
Marcus Müller's user avatar
5 votes

Are oscillators always non linear?

Usually clipping limits the amplitude, but if you want to build a low-distortion oscillator, then every component must stay in its linear range. Clipping is not allowed. Which means we have a problem: ...
bobflux's user avatar
  • 74.6k
5 votes

Why the resultant period of two signals is the LCM of the individual period of that signal?

Take two sine waves of periods \$T_1 = 2s\$ and \$T_2 = 3s\$. Suppose they both start at time = 0s. Then their "end of the cycle" points coincide only at the multiples of \$LCM(T_1,T_2) = LCM(2,3) =...
Meenie Leis's user avatar
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