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16 votes
Accepted

Why do we not use AM and FM at the same time to transmit more information?

QAM modulates both the phase (= frequency) and amplitude of the signal.
Mike Playle's user avatar
14 votes

Why do we not use AM and FM at the same time to transmit more information?

It turns out that we DO simultaneously use frequency and amplitude modulation: our everyday term for this is "single sideband." As described on Wikipedia, single-sideband is a special case of ...
Brian K1LI's user avatar
  • 7,878
7 votes

MW AM reception improvements?

That's a lot of questions! Would there be any SNR advantage if each sideband was detected separately? Would the correlation of the LSB and the USB be useful because the noise in general is not ...
Dave Tweed N3AOA's user avatar
7 votes
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AM Radio Envelope Dectector

The capacitor and resistor make a low-pass RC filter, with a frequency cutoff around $\frac{1}{2\pi RC}$ (in hertz). Do keep in mind $R$ is not just the value of the resistor, but rather the entire ...
Phil Frost - W8II's user avatar
7 votes
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Broadcast signal deviating with time

Since you said you're using an RTLSDR, it's very likely that you aren't receiving a station on 22,695 kHz, but rather one on 6,105 kHz. NHK World Radio does broadcast on that frequency (according to ...
hobbs - KC2G's user avatar
  • 12.5k
6 votes
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Is FM modulation still more resistant to noise when given the same bandwidth as an AM signal?

FM modulated radio is much more resistant to noise and can deliver better sound quality than AM radio. Under certain conditions, that is! Namely, additive noise, and a fading channel. or is this ...
Marcus Müller's user avatar
6 votes

Transmitting as SW AM station, not ham

What if I wanted to run a radio broadcast station on a commercial SW band? Say, I am on a boat in international waters. What you're suggesting is known as pirate radio. That Wikipedia page provides ...
Caleb's user avatar
  • 238
5 votes
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Building a crystal radio with my brother. How does this circuit work?

I'll try to address your concerns a bit! I'll be simplifying here and there, but I think you'll notice where I'm doing that. I'll be doing my best to explain to him how this works. I understand ...
Marcus Müller's user avatar
5 votes

Radio Waves propagation (Intuitive Understanding of Wave propagation)

Radio waves (such as broadcast AM and FM) can travel through a vacuum (thus do not require air). They are electro-magnetic (or EM) waves, the same as light waves (from the sun and stars, etc.), that ...
hotpaw2's user avatar
  • 13.5k
4 votes
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Why are FM radio waves less susceptible to interference than AM?

The waves (to be correct: the signals) are exactly as suspectable to noise for both modulations! What's different is the receiver: As the name suggests, Amplitude Modulation (AM) works by taking the ...
Marcus Müller's user avatar
4 votes

How does this circuit work? Why is the antenna connected to the output of the amplification stage?

EDIT to be more specific about the input circuit per Phil's comment: The antenna (aerial) is connected to the the oscillator of the first transistor stage formed by VC, L and the self capacitance of ...
Glenn W9IQ's user avatar
  • 18.6k
4 votes
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Peak envelope power should be 2:1 or 4:1 on meter?

Say the unmodulated carrier amplitude (voltage) is 1. At 100% modulation, the envelope will vary between amplitude 0 and 2. So at peak, the amplitude is twice an unmodulated carrier, but because power ...
Phil Frost - W8II's user avatar
4 votes
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Is there any way in which elevation *does* affect medium frequency (AM radio) transmissions?

Groundwave field intensities in the MW broadcast band depend almost entirely on radiated power, frequency, and Earth conductivity. Below is a map of the 0.5 mV/m groundwave contour of radio station ...
Richard Fry's user avatar
  • 2,922
4 votes

Improve AM reception on an old Walkman that has no external antenna

The genuine Sony Walkman, and most of the Walkman-style radios from other makers, did indeed use the headphone cable for their antenna. My experience (with an early 1980s Sony model) was very good on ...
Zeiss Ikon's user avatar
  • 4,107
4 votes
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How can AM radio work differently when approaching the true frequency from different directions?

I can tell you of how your radio is built: It's got an integrated radio IC that does everything, from preselection to mixing (if any) to digitization to digital filtering, audio demodulation, audio ...
Marcus Müller's user avatar
4 votes
Accepted

Effect of using wrong injected frequency when tuning IF cans in an AM radio?

A fun question to mull over. What does it mean for a receiver to be "on frequency"? First there's the tuning dial and its indicator. This usually drives both the capacitor that resonates ...
tomnexus's user avatar
  • 11.4k
3 votes

Why does the output power of some AM transmitters increase when modulated and of others decrease?

First a bit of background on AM modulation and power levels. If we start with a 100 watt carrier and no modulation, we would measure 100 watts peak and average power. They are the same due to lack of ...
Glenn W9IQ's user avatar
  • 18.6k
3 votes
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Why does a Class-C non-linear power amp distort SSB but does not distort AM?

A class C amplifier indeed distorts AM and causes widespread splatter just as it does for SSB signals. BUT if you have a class C amplifier and apply modulation to it by superimposing the modulation ...
sm5bsz's user avatar
  • 1,009
3 votes

How to make simple AM detector using an LED?

Partial answer (what's going on, but not a good recommendation for how to fix it): the LED simply turned on the whole time This circuit puts DC across the speaker terminals. You don't need to ...
Kevin Reid AG6YO's user avatar
  • 24.7k
3 votes

Daisy Chaining AM filters to help with IMD

Cascading more filters may help. Also simply adding an attenuator may help, as long as the RF noise floor is above the receiver's internal noise floor. However, spurious emissions from the station ...
Phil Frost - W8II's user avatar
3 votes

How to make simple AM detector using an LED?

Good morning F-16Falcon, Immediately i read you question, I thought about a Roimeter, and lucking in internet i found this: https://radioclubplacetas.cubava.cu/2016/11/17/medidor-de-roe-optico/ It's ...
Dardo Bagnis's user avatar
3 votes

Peak envelope power should be 2:1 or 4:1 on meter?

It depends... With a 100% steady modulated carrier, the PEP will be 4 times the unmodulated carrier power. The average power under this condition will be 1.5 times the unmodulated carrier power with ...
Glenn W9IQ's user avatar
  • 18.6k
3 votes

Transmitting as SW AM station, not ham

I don't know that commercial class HF transmitters are still being built, but it shouldn't be very difficult to put one together. You'd need the audio mixing and control equipment that goes with any ...
Zeiss Ikon's user avatar
  • 4,107
3 votes

Building an AM Radio receiver

The tuner is whatever allows the frequency to be selected. Tuners usually involve some kind of resonant circuit. For a very basic AM receiver like you describe, the tuner is probably nothing more ...
Phil Frost - W8II's user avatar
3 votes

Building an AM Radio receiver

To answer the last part of the question, the detector for an AM receiver is basically a rectifier, which rectifies the RF and the signal that it was modulated with. Once the RF has been rectified, it ...
Scott Earle's user avatar
  • 4,619
3 votes

Radio Waves propagation (Intuitive Understanding of Wave propagation)

Question 2 & 3 not fully answered... You probably actually are within line of sight of the FM transmitter. Broadcast transmitter antennas are typically placed on high towers specifically so that ...
user10489's user avatar
  • 6,485
3 votes

Broadcast signal deviating with time

As hobbs - KC2G says, there could easily be multiple stations transmitting. Also, the frequency stability of the RTLSDR is quite poor. If you are seeing the frequency drift slowly over time (and not ...
Phil Frost - W8II's user avatar
3 votes

How can AM radio work differently when approaching the true frequency from different directions?

Your radio, as do many of the inexpensive portables over the last five years or so, uses the Silicon Labs Si473x DSP chip or one of the recent Asian clones. Tuning is controlled entirely by software. ...
timetraveller's user avatar
3 votes
Accepted

Natural dipole / monopole filtering

Word has it these antennas are broadband, As far as I can tell, that word would be wrong: Broadband antennas work "well" for a contiguous band larger than 1/5 of its center frequency. (This ...
Marcus Müller's user avatar
2 votes

Would it be feasible to set up a SSB or AM 2 meter repeater?

Rotorua branch 33 of NZART 2m linear repeater is still operational and has been for more than 20 years. It is a solar powered repeater and situated on a high point overlooking Rotorua Town. Output is ...
Mike's user avatar
  • 21

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