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Questions tagged [amplitude-modulation]

Amplitude Modulation (AM) modulates a signal by varying the amplitude of the carrier. The ease with which it can be demodulated made AM radio broadcasting popular before FM demodulation was cost effective.

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How exactly does RF to IF conversion work in an AM radio?

I am currently researching AM radio detection circuits. From my understanding, RF is received, amplified and converted to an IF(455khz for AM) before being converted into an audible frequency for ...
lemon's user avatar
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Why does this simple op amp create an AM modulated envelope over its carrier?

The circuit below is an ideal op amp (requires no power, can produce any output voltage) in LTSpice: LTSpice shows it amplifying the 159.155 kHZ input, as expected. But it also shows a 2500 kHz AM ...
SRobertJames's user avatar
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Receiver tracking problems

The medium wave band, in which AM is still dominant, has a very high ratio of Fmax to Fmin, unlike most other radio bands. The exact edges vary from country but compare 510-1650 kHz to say 144 to 148 ...
Autistic's user avatar
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Why do we need a diode in an AM demodulation circuit?

The incoming signal is a modulated carrier wave, right? If we only apply a low-pass filter to it, we will get an AC signal that can be passed to a speaker directly, right? Using a diode, we end up ...
Coykto's user avatar
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Recommendation for sine wave of 100kHz with 1ppm stable amplitude

I need to design a 100 kHz sine wave with 1 ppm stable amplitude. I mean the noise of the amplitude should be lower than 1 ppm RMS and also the thermal stability should be < 1 pmm/K. I was thinking ...
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Amplitude modulation problems

I am trying to do amplitude modulation using a diode, but my circuit will not work. This is the circuit I am using: simulate this circuit – Schematic created using CircuitLab I don't know why ...
Marcus Marchese's user avatar
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Why 8051 is not detecting logic from circuit's voltage?

I am working on a ASK modulator and demodulator circuit which I wish to interface with a 8051 microcontroller to read serial data from demodulator circuit. The mod/demod circuit is developed and ...
Akshat Panda's user avatar
4 votes
3 answers
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Do sidebands exist physically?

This is a concept that has puzzled me for a long time: from the Wikipedia: "In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency" My ...
ribosoma's user avatar
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How to minimize modulated signal clipping in an amplifier circuit with improper Q1 biasing?

I'm currently working on two amplifier circuits designed to process modulated signals. While the circuit on the right operates as expected, both theoretically and practically, I'm facing an issue with ...
Kaspars's user avatar
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7 answers
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Why does this AM radio circuit not work?

I have been trying to make an AM radio over the last couple days and am very confused as to why this circuit is not working. I found the circuit on this website and I saw this video on this design. I ...
Marcus Marchese's user avatar
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Why do loopsticks and chokes receive RFs equally well?

In response to answers from my previous question, I compared the ability of a tank circuit to receive signals when the inductor was a loopstick vs a choke. The inductor was either a) a choke with Lc=0....
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Equidistant PAM-n symbols

Why do we choose PAM-n symbols to be equidistant ? What will happen if it's not so? Any references are welcomed !
Isha's user avatar
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Frequency meter (counter)

I am currently working on designing a circuit that should be able to measure the frequency of an input signal by giving off a value directly proportional to the frequency at the input. The circuit ...
David Ab's user avatar
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2 answers
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Ferrite Loopstick Antenna Grounding

I've built a simple tuned frequency radio based a description in Ronald Quan's book. I have two questions about the tuning part of the circuit. The radio has a ferrite core antenna with two separate ...
M. Enns's user avatar
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Why is there a DC component in the output spectrum from an op-amp adder?

I'm experimenting with a DSB-SC circuit using TINA simulation tool. As input I'm using two sinusoids with frequencies of 500 and 1000 Hz, i.e. 0.05sin(2π500t) and 0.1sin(2π1000t) which are guided into ...
Pavlos Papanikolaou's user avatar
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2 answers
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How does this metal detector circuit work with an AM receiver?

I do not understand how this circuit works. From Fun Electronics Projects for the Experimenter by Newton C. Braga. It is described as using the beat-frequency method to detect an object. The ...
Maro2058's user avatar
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AM Demodulation code error MatLAB

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MattCG's user avatar
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I need help understanding the envelope detector part

I started reading "Build Your Own Transistor Radios" by Ronald Quan and I don't get how the envelope detector works in his TRF radio. I know that a "classic" envelope detector ...
Vlad Balmos's user avatar
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1 answer
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AM-Receiver circuit, problems with saturation?

I have a question about this specific circuit. I marked the potential-point I have "problems" with. I think there will be saturation in this point at some time. This point doesn't look to be ...
javagreenhorn's user avatar
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Please help me understand this amplitude modulation LC oscillator

I have a problem understanding the circuit below where the LC oscillator is used to produce the negative cycle wave for the amplitude modulation. I am having a difficulty in grasping the fact that the ...
kam1212's user avatar
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1 answer
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Designing amplitude modulator for class [closed]

I am required to design an amplitude modulator for a class. The baseband signal is an audio signal x(t). The carrier frequency should be generated using a dielectric resonator oscillator with an ...
JustSnapple's user avatar
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2 answers
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Understanding an op-amp modulator circuit

I'm trying to understand an op-amp modulator circuit I came across in a book. The circuit uses switches. According to the book, switches S1 and S4 are on during the positive half cycle of the carrier ...
Urthona26's user avatar
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AM Radio Transmitter

I have been trying to make an AM transmitter and I found this schematic from a persons college project. I understand what is circled in red but the rest I am struggling with. The part circled in red ...
Marcus Marchese's user avatar
8 votes
3 answers
486 views

Can Bandwidth be Traded Off with SNR in Analog Modulation?

With typical linear digital modulation schemes, we can, for a given bit rate, make a trade-off between modulation bandwidth and modulation order (effectively, how close the constellation points are). ...
LetterSized's user avatar
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9 votes
8 answers
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How does an emitter follower work as an AM detector?

Can someone explain how an emitter follower used as an AM detector (shown below) actually works? I don't get how a (theoretically) linear system like an emitter follower would work as a detector when ...
kene02's user avatar
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Solving an exercise of superheterodyne receiver with high IF frequency

I've been struggling with this problem for several hours. I have a high IF superheterodyne receiver. The input frequency can vary from 9kHz to 3GHz. I need to calculate the minimum intermediate ...
neil_huygens's user avatar
3 votes
2 answers
424 views

Advice for an AM detector using a BJT

I'm designing an AM detector that uses a 2N3904 transistor in common collector configuration. Pardon me if my design's silly because I'm still quite a novice with using BJT transistors as amplifiers, ...
kene02's user avatar
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1 answer
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How can I only let a specific frequency pass in an AM receiver?

I wanted to create an AM receiver and I know partly how to demodulate the signal. I know I need to use a low pass filter to get the low frequency audio signal, but I don't know how to only get data ...
RadoslavL's user avatar
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4 answers
555 views

AM Receiver Antenna Coil

In almost all the radio receivers whether FM or AM, custom wire-wound coils are used that are wrapped on a ferrite core usually (not always) of 100 mm x 10 mm dimensions. Is it possible to use fixed ...
Awais Mushtaq's user avatar
2 votes
1 answer
582 views

Why does the frequency deviation of a FM wave have different definitions?

Source 1 defines the modulation index in the expression for FM as follows: As per the expression for frequency modulated wave, isn't the frequency deviation same as Modulation index 'M'? "The ...
Dynamic_equilibrium's user avatar
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1 answer
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VHDL: Testbench for ASK modulator

I've been trying to learn VHDL recently and came across the following tutorial for an ASK modulator: https://surf-vhdl.com/implement-digital-ask-modulator-vhdl/ I tried writing a testbench for this ...
user1397215's user avatar
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1 answer
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Anyone know what this capacitor is for in a BJT audio amplifier?

I'm wondering what C46 is for?
mrbean's user avatar
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1 answer
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Where and how are the carrier and message signal multiplied in this circuit?

I have this circuit diagram of an AM modulator and I am trying to understand what is going on. I know that the c(t) is taken from the collector of transistor Q1 and the multiplication of signals : m(t)...
Ashwin Singh's user avatar
1 vote
1 answer
1k views

Yet another 807 tube transmitter

I just can't seem to get away from these 807s. Although I am to the point where I might replace them with 6146s. I built this transmitter with a 6AG7 oscillator, and 2x 807 final amplifier. The ...
McMurdo's user avatar
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2 votes
2 answers
905 views

FET AM modulator

I have been meddling with a FET-based AM modulator. I implemented a basic circuit as attached here along with its output. Is the output as it should be? If not, what am I doing wrong, and how can I ...
Awais Mushtaq's user avatar
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1 answer
369 views

Peak detector circuit for AM demodulation

In Lee's Design of CMOS Radio Frequency Circuits, the leaky peak detector circuit for AM demodulation is discussed. The AM expression is: $$v(t)=(1+mf(t))cos(\omega_ct)$$ And the associated frequency ...
Halleff's user avatar
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1 answer
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Band selection circuit for SI4825 A10

Following the official schematic and guideline (AN738: Si4825/36-A Antenna, Schematic, Layout, and Design Guidelines), I am building a Si825 A10-based radio receiver. I am getting weak audio output ...
digiwizkid's user avatar
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1 answer
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Why is this resistor important in my AM radio transmitter?

I've been building an AM radio transmitter and had a few questions about my diagram. I built this using components on a breadboard. Having the resistor there is critical otherwise it doesn't work. The ...
Derpy's user avatar
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0 answers
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Amplitude shift keying using NMOS cascode transistor configuration

. I am using 50 MHz as a carrier signal and a pulse signal as the data signal. Unfortunately, I could not get my desired modulated ASK signal. I am using ADS software. Kindly guide me on how to do it. ...
Naqeeb Ullah's user avatar
6 votes
5 answers
1k views

Does an AM radio wave make use of a lower side band?

I believe my problem is I am having some confusion on the meaning of "side bands". I read the wiki but I am wondering that since an AM signal is rectified doesn't that eliminate the lower ...
Sedumjoy's user avatar
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Diode AM detector linearity

Most valve radios use a vacuum tube diode as a detector. Over the decades, I have used germanium diodes with good apparent performance. In other words, cheap equipment sounds good when the germanium ...
Autistic's user avatar
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1 vote
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What is the function of these transformers in an AM transmitter (Sender 5000 solid state AM transmitter)?

What could be the function of these transformers in the back of the Sender 5000 solid state AM transmitter?
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3 answers
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PCB8711 Rev. A of Sender 5000 solid-state AM transmitter: schematic symbol

I wonder what the symbol encircled below means, because we're repairing an AM transmitter. I think the real-life version of that schematic looks like this: I really wonder what the symbol encircled ...
Shobeh's user avatar
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0 votes
2 answers
214 views

Trying to make a quadrature amplitude modulation - Having problems in the quadrature output

Here is the transmitter circuit: This is the receiver circuit: I think everything is fine in the AM transmitter but not in the receiver circuit. In the 'in phase' part of the receiver circuit, I ...
Scipio's user avatar
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1 vote
0 answers
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Trying to recover signal in AM modulation

The circuit above is the AM transmitter and the other circuit is the AM receiver. The AM transmitter consists of: Baseband signal (source), BB amplifier and adder (MixerIn), mixer (it's a pulse/square ...
Scipio's user avatar
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2 votes
1 answer
290 views

How to buffer an AM signal?

The above shows an AM modulator circuit which sums a sine wave and a triangle wave to produce an output which will undergo resonance using RLC to produce an AM signal. The TL072 is commonly used in AM ...
jessica smith's user avatar
1 vote
1 answer
154 views

How does one test an AM antenna matching network?

I'm lost. I need to test two AM matching networks. I was not given training and I'm a newborn compared to every other guy in AM Radio out there. I do own a osciloscope with Bode plot generator but I ...
Cesar Guevara's user avatar
1 vote
1 answer
301 views

Condition for multi tone AM for proper envelope detection

Given a multi-tone amplitude modulated wave as follows : s(t) = Ac[1+2kasin(w1) + kasin(w2)] cos(wct) where wc is the carrier frequency and w1 and w2 are the modulating frequency components. My ...
MAJID AHMAD's user avatar
1 vote
1 answer
177 views

Opamp current source - Impedance matching to a laser diode - MHz range current modulation

I want to modulate the current through a laser diode with the output of a (FPGA into R2R DAC)source. I am using an opamp to do voltage to current conversion as shown in the circuit diagram. The laser ...
Ravi Pradip's user avatar
3 votes
2 answers
427 views

How does this modulation cause sidebands?

The following figure is an excerpt from this paper: Input Differential-Mode EMI of CRM BoostPFC Converter by Fei Yang. Q#1 (first highlighted sentence): How does the modulation line frequency cause ...
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