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57 votes

If a square wave has infinite bandwidth, how can we see it on an oscilloscope?

We can't. We see a bandlimited version. That's obvious for two reasons: perfect square signals cannot physically exist, for changing a voltage within 0 time would require an infinite amount of power ...
Marcus Müller's user avatar
43 votes
Accepted

Why does 1/4 wavelength have a ground plane and 1/2 wavelength needs none?

I can't understand why we need to use a ground plane at 1/4 wavelength and 1/2 wavelength not needed. A 1/2 \$\lambda\$ dipole has voltage and current waves like this: - Picture from Wikipedia. ...
Andy aka's user avatar
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26 votes

If a square wave has infinite bandwidth, how can we see it on an oscilloscope?

You are correct that an ideal square wave needs an infinite bandwidth as it contains frequencies up to infinite frequencies. But this is theory, ideal square waves do not exist in the real world as ...
Bimpelrekkie's user avatar
23 votes

How can a DC spark create EM waves?

The spark, unless it is a continuous steady arc, will fluctuate in intensity. This means it will have an AC component even if the current never goes in reverse. In practice sparks are very noisy and ...
Transistor's user avatar
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22 votes
Accepted

Why is "wavelength" used as a unit for the length of an antenna?

Antennas are designed for operation at a specific frequency, and the physical dimensions of an antenna scale with the design frequency. In the case of a dipole antenna, things like the antenna gain ...
alex.forencich's user avatar
19 votes
Accepted

Is there something as common frequency?

The interval of repetition will be the LCM (least common multiple) of the periods of the sinusoids. This is also the inverse of the GCD (greatest common divisor) of the frequencies. The periods of ...
Elliot Alderson's user avatar
18 votes

If a square wave has infinite bandwidth, how can we see it on an oscilloscope?

The 'scope won't show a perfect squarewave and if you zoom in on the timebase you should be able to see the rising and falling edges with some slope on them. This will be most obvious on an analogue ...
Transistor's user avatar
  • 176k
13 votes

Why does 1/4 wavelength have a ground plane and 1/2 wavelength needs none?

A quarter wave monopole antenna doesn't have to have a ground plane... unless you want it to radiate EM energy with a certain efficiency and pattern. EM radiation requires accelerating electrical ...
hotpaw2's user avatar
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13 votes

Circuit that converts sine wave to RMS voltage

Maybe use a chip such as the AD636. True rms-to-dc conversion 200 mV full scale Laser-trimmed to high accuracy 0.5% maximum error (AD636K) 1.0% maximum error (AD636J) Wide response capability ...
Spehro Pefhany's user avatar
12 votes

What size of hole do microwaves eventually pass through?

Wah! WAH! Ok, you're putting yourself and your friend in deadly danger. First of all, your 29$ device is not a substitute for proper RF qualification. It simply isn't. You might be able to find a ...
Marcus Müller's user avatar
12 votes

Are radio waves naturally polarized like light or is that a function of how they are produced?

Radio waves and light are both electromagnetic waves. The only difference between them is the wavelength. The polarization is initially determined by the way they are produced FM Broadcast radio is ...
SDsolar's user avatar
  • 1,744
11 votes
Accepted

What is the best way to get a sine wave from a square wave?

Is there any other better way to get a pure sine wave from square wave without this voltage drop? Take your square wave and use a phase lock loop to generate a frequency that is maybe 50 times ...
Andy aka's user avatar
  • 460k
11 votes
Accepted

Are radio waves naturally polarized like light or is that a function of how they are produced?

Radio waves emitted by an antenna have a specific polarization, and receiving antennas are generally sensitive only to a specific polarization. So in principle if the transmit antenna were strictly ...
user2475529's user avatar
10 votes

How can a DC spark create EM waves?

It is not the DC part itself. It is the raising edge. The spark creates a square-like waveform which actually consists of infinitely many sine waves. That is explained by the Fourier transformation. ...
tomas789's user avatar
  • 201
10 votes

Precise square wave generator 32768 Hz

You have basically two choices- buy a crystal and make an oscillator or buy an oscillator. If you buy an oscillator it should meet the specifications on the datasheet and if those match or exceed your ...
Spehro Pefhany's user avatar
10 votes

Circuit that converts sine wave to RMS voltage

You could try Linear Tech's (now ADI's) frequency independent RMS detector: ∆Σ Breakthrough: LTC1966 True RMS-to-DC Converter Uses No Diodes, Heaters or Logarithms. A typical application circuit, ...
a concerned citizen's user avatar
10 votes

Why does this inverter use two bridges?

Why isn't a single full bridge used before the transformer, that generates a 25kHz or 50kHz carrier square wave and modulates a 60Hz sine wave on top of it (as a pwm duty), and do away with the ...
Andy aka's user avatar
  • 460k
9 votes

How to shift down a square wave at 0 - 5 V?

One way is what's known as a data slicer. A simple one, as shown below, requires the average value to be near the middle between the two levels. That is true for a square wave. Since the input ...
Olin Lathrop's user avatar
9 votes
Accepted

How can a DC spark create EM waves?

We usually use the math of sine waves ("AC") to analyze electromagnetic radiation, and there are good reasons for this. However, the first treatment of how charge generates radiation that my ...
John Doty's user avatar
  • 4,482
8 votes
Accepted

What wavelength will achieve higher speed in optical fiber?

First, when you talk about the "speed" of a signal in optical fiber, that's ambiguous. You should be clear about whether you're interested in the latency (the time it takes a signal to travel from one ...
The Photon's user avatar
  • 130k
8 votes
Accepted

How to shift down a square wave at 0 - 5 V?

@Olin's answer is a good one if you can live within the limitations which are: High voltage supply for the comparator (or special comparator) Duty cycle of input close to 50% Some pulses will be ...
Spehro Pefhany's user avatar
8 votes

What would cause a square wave to become rounded?

What you are seeing are several harmonics of the square wave being attenuated. As you know, a square wave can be represented by an infinite series of sine waves whose frequencies are multiples of the ...
Los Frijoles's user avatar
  • 2,252
8 votes
Accepted

Standing waves in Dipole antennas

I am the creator of the dipole animation above. There have been some excellent points made above. I think the reason there is still confusion over the question is that there is some missing ...
Chetvorno's user avatar
8 votes
Accepted

What is a guided mode?

A mode is a configuration of the electromagnetic field that is stable as the system evolves in time according to Maxwell's equations. Mathematically, it's an eigenstate of the differential equations ...
The Photon's user avatar
  • 130k
8 votes

Rail to rail +12/-12 V square wave generation with microcontroller

Shoot-through current, the problem is that there is a current path through R5 and R6 in series with the two transistors (basically, diodes) whenever the Q2 collector voltage is between +11.4 and -11.4,...
AnalogKid's user avatar
  • 20.7k
7 votes
Accepted

Confusions on FFT of a square-wave in theory and in scope and simulation

Welcome to the real world! The "mathematically perfect" transform you show at the top, with the "discrete" harmonics is generated assuming that the rise and fall times of the waveform are zero, and ...
Dave Tweed's user avatar
  • 173k
7 votes

How to convert sine wave from an oscillator to TTL signal for microcontroller?

How should I do to avoid the signal drift, to convert the sine wave to TTL. You need to set DC voltage levels on both comparator inputs to (nominally) half supply rail. You can do this with a ...
Andy aka's user avatar
  • 460k
7 votes

Are radio waves naturally polarized like light or is that a function of how they are produced?

The polarization of the emitted wave is a result of the antenna design. Typically, antennas that primarily extent in vertical direction have vertical polarization. However, it's often hard to see the ...
Marcus Müller's user avatar
7 votes

Why is "wavelength" used as a unit for the length of an antenna?

Not only is it best practice to state the length in \$\lambda\$ it's also important to specify the type i.e. monopole or dipole for instance. Consider a monopole and look at the impedance it presents ...
Andy aka's user avatar
  • 460k
7 votes

How to generate a high energy electromagnetic wave? Using high voltage or high current?

If you are generating an electromagnetic wave in free space then the ratio of the E field to the H field is fixed at 377\$\Omega\$ (yes, ohms -- the units work out). You would hope that would ...
TimWescott's user avatar
  • 46.5k

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