42 votes

How exactly does AM/FM carry both pitch and loudness of voice?

Voice has both pitch, i.e. frequency, and loudness, which are two separate analog data streams. No. Voice is transmitted initially as one analog 'stream' of sound pressure waves in which the air ...
Transistor's user avatar
  • 176k
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
26 votes

How exactly does AM/FM carry both pitch and loudness of voice?

Forget about radio — how do you think voice is transmitted over a wire, which only has "voltage" — again, a single variable? The point is, "pitch" and "amplitude" are abstract parameters ...
Dave Tweed's user avatar
  • 173k
24 votes
Accepted

Why is amplitude-modulated radio broadcast (AM) still active?

In a nutshell: One antenna will give you a usable radius of 100...1000 km, depending on the power used. In Germany, for the example of my favored news station Deutschlandfunk, we used to have two ...
zebonaut's user avatar
  • 18.4k
23 votes
Accepted

How is power line communication (PLC) possible without screwing up the line as a viable power source?

The data signal is superimposed on the mains voltage. The mains voltage will typically be 120 V, 60 Hz or 230 V, 50 Hz and the data signal might be 1 V, 2 MHz. Figure 1. Graph of \$ 100sin t + 10sin(...
Transistor's user avatar
  • 176k
22 votes

What could this signal at 119.9 MHz be?

This signal is an extremely inefficient use of bandwidth, as you can see because there is an essentially unused area between the center and ±125 kHz. Therefore, I expect that it is almost certainly ...
Kevin Reid's user avatar
  • 7,524
22 votes

How much data could be stored on a standard compact cassette using modern encoding?

Have there been any projects trying to explore that? Ben North attempted to play video from a standard audio cassette tape using QAM modulation. First he tested the signal through a loopback cable. ...
Bruce Abbott's user avatar
  • 56.4k
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
  • 46.2k
17 votes

Why FM stereo uses DSB-SC instead of VSB?

The downside would be that the receiver would be more complicated. At the time that FM stereo was introduced, receivers were built entirely from discrete electronic components, and costs were directly ...
Dave Tweed's user avatar
  • 173k
13 votes

What does "shift keying" mean in the context of digital modulation?

It's not (phase) (shift keying), for example. It's (phase shift) (keying). Another answer has explained why the word keying is used --- it dates to the days when modulation was controlled by a human ...
The Photon's user avatar
  • 130k
12 votes
Accepted

Why do spectrum analyzers use envelope detectors?

After mixing and passing through the IF filter what remains is largely one small part of the spectrum that your SA is scanning through. If there's a signal present in this part of the spectrum, it'll ...
Andy aka's user avatar
  • 457k
12 votes

How exactly does AM/FM carry both pitch and loudness of voice?

Sound is just a single-dimensional time-varying signal. Microphones essentially continuously track variations in air pressure. At any point in time, this is a single value. This value is what gets '...
alex.forencich'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
10 votes
Accepted

Why are the resistors in an AM modulator necessary?

The concept here is that you are adding the signal currents before feeding the sum to the diode; the resistors are there to convert the voltage sources "NF" and "HF" to current sources. You'd get ...
Dave Tweed's user avatar
  • 173k
10 votes

How much data could be stored on a standard compact cassette using modern encoding?

Given an analog medium of known signal to noise ratio and frequency response, how can one even calculate (or approximate) the maximum digital data rate that can be written to it? Yes. The field of ...
TimWescott's user avatar
  • 46.2k
9 votes

Why is amplitude-modulated radio broadcast (AM) still active?

Besides that also in Germany you can very well listen to AM stations, although the transmissions may not be as crisp clear as wide FM stations. There are several reasons that come to my mind why they ...
PlasmaHH's user avatar
  • 6,528
9 votes

Is antenna length for a baseband signal infinity?

Sort of. Certainly antenna length is proportional to wavelength, so if you take the limit going to DC then you'll need an infinitely long antenna. However, even if you make an antenna infinitely long, ...
alex.forencich's user avatar
9 votes

How to improve the sine wave coming in to reduce the power bill?

Not really. Most of those scammy things (Where they do anything at all) amount to a half assed attempt at power factor improvement, which can (But they are always sized wrong) reduce apparent power ...
Dan Mills's user avatar
  • 17.5k
8 votes
Accepted

How does a microwave oven modulate its output power?

It's really simple. They have one fixed power level, and turn it on and off. You can hear it when it is on low power. It'll hum louder for a few seconds, then have a longer period when it is a ...
JRE's user avatar
  • 71.4k
8 votes

Do DSL / ADSL modems have an ADC with ~ 2 MHz sampling rate?

They have a much faster ADCs. Also, ADSL2+ has its downlink up to maybe 2.2 MHz, so you'd need at least 4.4 MS/s to do that. In reality, single-digit MHz ADCs are "old tech" and relatively ...
Marcus Müller's user avatar
8 votes

Are these low frequency FFT components due to insufficient op-amp slew rates?

This would be expected. Your Corona discharges are not random, they occur near the positive and negative peaks of the sine, and they always add to the amplitude. So, the Corona pulses have a 150 Hz ...
Mattman944's user avatar
7 votes

Why, where and how we use envelope detector in AM demodulation?

I don't understand how you could have studied AM demodulation and not understand the purpose of an envelope detector. Something is lacking in your studies. In any case, in AM (the M stands for ...
Barry's user avatar
  • 16k
7 votes
Accepted

Benifit of Delta Sigma DACs

A \$\Sigma\Delta\$-ADC basically works deliberately adding "noise" (not real noise though) to the input signal. By doing so, the ADC can average out signals that are between two quantization levels. ...
Sven B's user avatar
  • 5,167
7 votes

Why do spectrum analyzers use envelope detectors?

This block diagram is for an old-style CRT-based spectrum analyzer. The horizontal sweep represents the frequency being measured at a given time (like a sawtooth wrt time), and the vertical amplitude ...
Spehro Pefhany's user avatar
7 votes

What's the name of signal encoding used by WS2812 LEDs?

AFAIK it doesn't have a fixed name, apart from 'the WS2812 protocol'. As described, it is a fixed-cell pulse-width encoding. FYI: in practice, it isn't fixed-cell at all: provided that the pauses (...
Wouter van Ooijen's user avatar
7 votes
Accepted

Why is BER higher for binary modulation compared to quaternary?

Put simply, for the same average energy per bit, the modulation scheme with more bits per symbol must have less distance between the points on its constellation diagram. Therefore a smaller noise ...
The Photon's user avatar
  • 130k
7 votes
Accepted

Why do sidebands appear after Amplitude Modulation?

AM means that the amplitude of the carrier is multiplied by the payload signal plus some offset. The multiplication theorem for sine says \$\sin(a) \cdot \sin(b) = \frac{1}{2} ( \cos(a-b) - \cos(a+b)...
Curd's user avatar
  • 16.3k
7 votes

Why the triangle reference wave is used in PWM for sine modulation?

You don't need to have a triangle-wave or a PWM for that matter to generate a sine wave. You could use hysteresis modulation which does not require a PWM. However, the switching frequency is variable ...
Ben's user avatar
  • 677

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