71
votes
Accepted
Are audio cassettes FM or AM?
Neither, there is no modulation involved. The magnetization on the media is directly (and hopefully fairly linearly) related to the waveform amplitude.
There is a high frequency bias signal added to ...
- 5,609
41
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 ...
- 171k
29
votes
Are audio cassettes FM or AM?
It is neither, the signal is recorded as a magnetized pattern without any form of modulation. This can give an impression of how that works:
I got that from here.
See, no modulation needed, the ...
- 80.5k
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 ...
- 170k
20
votes
Why do FM radio signals occupy greater bandwidth than AM?
They need not, narrowband FM occupies the same bandwidth as AM, for the same audio bandwidth. Transmitted AM bandwidth is fixed at twice the audio bandwidth.
However, wide deviation FM provides ...
- 162k
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 '...
- 40.8k
12
votes
Are audio cassettes FM or AM?
Analog tape recording for audio cassette doesnt require modulation. But since magnetization ability of the particles on the tape does not have linear response at low signal levels of the audio to be ...
- 1,695
10
votes
Accepted
simplest FM radio receiver?
For a totally passive FM set you can use something like a resonant circuit that is tuned somewhat off the carrier frequency so variations in carrier frequency result in changes in output voltage from ...
- 384k
8
votes
Accepted
My FM transmitter never works, Why?
Forget building this on a breadboard. The oscillator can't work on a breadboard.
Breadboards have capacitance between the pin rows that's about the size of the capacitors in the oscillator.
...
- 69.1k
6
votes
Building an fm transmitter broadcasting simultaneously to all fm frequencies
In days long ago, this was done by transmitting a strong signal at the IF frequency of 10.7 MHz. Most radios in that era did not have sufficient shielding in the IF section and this signal was ...
- 23.6k
6
votes
I supplied 220 volts to 120 volts FM radio receiver?
Excuse me for this slightly sarcastic comment, but:
No, you cannot revive your radio parrot:
Well, you connected something to a voltage supply twice as high as it was meant to be used with. If you'...
- 90.5k
6
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.
There's more than two, depending entirely on how you perceive/analyze it, and what else is going on, on ...
6
votes
Accepted
Why can't we divide the electromagnetic spectrum into arbitrarily many radio frequency bands?
Signals don't exist at a single frequency. They have a bandwidth that spreads across spectrum. The radio station at 101.7MHz takes up the spectrum from 101.6-101.8MHz.
- 206
6
votes
Accepted
Does satellite radio use AM or FM or both?
Neither. Satellite radio such as Sirius transmits the digital data with COFDM-DQPSK modulation.
- 137k
6
votes
Accepted
Broadcast FM: Where is the pre-emphasis applied?
The recommendation how it should be done is stated in ITU-R BS.450-4, "Transmission standards for FM sound broadcasting at VHF". I know I've seen a better document with block diagrams but it ...
- 137k
5
votes
Accepted
Why do EM waves with longer wavelengths propagate longer distances?
The answer is diffraction, and the fact that it takes larger objects to block the longer wavelengths.
1 MHz, which is in the middle of the commercial AM band, has a wavelength of 300 m. In contrast, ...
- 312k
5
votes
Select Phase Detector Cutoff Frequency? Phase Locked Loop FM Demodulation
When building a phase locked loop, the purpose of the low pass filter is poorly understood.
When you wrap a phase feedback loop around a VCO, the integration of frequency to phase causes a 20dB per ...
- 162k
5
votes
How exactly does AM/FM carry both pitch and loudness of voice?
In a simple AM system, the transmitted signal is something like
$$x(t) = A\left(1+m(t)\right) \sin\omega_c t$$
and \$m(t)\$ is called the message signal.
In an AM radio, the message signal ...
- 128k
5
votes
Broadcast range of an FM radio station with given transmit power
OK lets provide a line-of-sight non-multi-path (no reflected energy that may cause peaking and nulling, as airplanes may do, or large drones may cause) link analysis.
Assume:
you want good FM audio, ...
- 33.8k
5
votes
Accepted
FM broadcasting text
It is implemented using the so called Radio Data System (RDS). Which transmits the channel name, current song and more on a 57 kHz subcarrier.
Source: https://en.m.wikipedia.org/wiki/...
- 1,542
5
votes
Accepted
Why can FM be demodulated non-coherently while PM cannot be demodulated non-coherently?
The phase of a signal is only defined with respect to a reference. If the reference cannot be communicated, then the phase is meaningless.
Often when phase modulation is used, it's treated as ...
- 162k
4
votes
Strange op-amp circuit FM radio
The opamp outputs are connected as a 'bridge'.
The caps cause a 180 degree phase change in the inputs, and the outputs are therefore 180 degrees out of phase as well.
You can therefore get double ...
- 861
4
votes
Can a filter circuit be built for the FM broadcast range to only pass the frequencies not bearing a broadcast stream?
Of course it can. What you need to do is to perform a band scan and look at signal strengths. If you plot it, you would get something like this:
If the signal is above a certain threshold, some ...
- 7,865
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