Questions tagged [am]

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 would a modulated and demodulated signal differ in FM and PM? Simulink Simulation

I am trying to observe the differences of phase and frequency modulation. On the figure below, the left scope shows a frequency modulation and demodulation whereas the right scope shows a phase ...
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Mechanical buzzer heard on AM radio

If I connect this little mechanical buzzer to a 3V supply, then hold my AM radio close to it with the radio tuned so I can't hear any stations, I can hear the buzzer on the radio. If I turn up the ...
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Is AM radio louder the closer you are to the transmitter?

Following on from this question, does the volume of the receiver increase the closer it is to the transmitter because it's receiving more of the radio signal? This question specifically is for a ...
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Why is the voltage the same before and after the diode in LTspice?

In LTspice, I setup a circuit with a voltage generator giving a 160 kHz signal AM modulated with a 440 Hz signal and I'm trying to amplify this signal with a differential op amp. Why is the voltage ...
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Simple analog AM radio generating noise throughout circuit [closed]

I'm building a simple AM radio circuit for one of my classes. It works insofar as that anywhere from 400 Hz - 4 kHz we get a nice AM radioey tone. But when the outputs are connected to an oscilloscope,...
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My AM radio receiver using TA7642 IC is not working

A very simple question I’m sure but I’m struggling with making an AM radio using the TA7642 AM radio IC. I’ve looped maybe 200 coils of 0.25mm enamelled copper wire around a 1cm ferrite rod and made ...
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Request for circuit review: varactor-tuned AM radio receiver

I apologize if this is not the place for newbie questions or circuit review requests, but I was hoping for some wisdom on an AM receiver circuit I have sketched out. From left to right it is intended ...
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2 answers
213 views

Tuning problem for an AM radio receiver

After some months I went back to try to make my AM radio work. This is the schematic: ANT is a 16 meters long straight copper wire (insulated). R1 and C2 gives a time costant \$ \tau = 114 \, \mu s\$ ...
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How to switch an AC signal

I have two AC signals, and I want to control their flow (either allow them to pass or open the circuit), therefore, I can imagine that the solution to my problem could be the same for both of these ...
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Envelope detector followed by a low pass filter

What are the advantages of adding an RC low pass filter after an envelope detector? I am asking this because I often notice (in multiple studies) that this type of circuit logic (in the figure below) ...
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why do i have to add a capacitor to observe AM output

so our TA asked us to simulate this modulator in lTspice but told us to add a capacitor that has a value of 0.1 uF at the output and record the result and confirm the envelope shape from message ...
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Find min and max of magnitude ltspice

I am doing a amplitude modulator simulation in ltspice, I am trying to find the minimum and maximum amplitude of the modulated signal using .meas, I found some ...
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Measure current of 51 kHz signal and ideas for increasing range of AM signal

I have built the following circuit: I got it from http://www.discovercircuits.com/PDF-FILES/PIPEFINDER1.pdf It works Ok and generates around 520 kHz in the wire, but I have some questions. I measured ...
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1 answer
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How to calculate C for an AM demodulator?

I have read this equation from Savant's book that is used to calculate the capacitor for a demodulator: I've tried to calculate my circuit with this equation, but it didn't work. Then I tried to ...
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Amplitude Modulation

Hello, I'm new to this topic as it is my school works, I try to simulate the diagram below by using Proteus which I follow accordingly with the labsheet given from my school. The problem is the ...
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How to implement "burst" functionality for bare-bones function generator

Some fancy function generators have a burst feature which gives precise control over on-time and periodicity of the desired waveform. Ex: For my application, I have a 25 MHz sin wave (2.5 Vpp) and, in ...
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What does it mean for a "baseband" signal to be a signal near zero frequency range?

I'm trying to understand the intuition and math of "baseband." Wiki says it is a signal near zero frequency range. Don't all signals of any type need a frequency otherwise they are not a ...
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Troubleshoot DIY AM radio

I need help troubleshooting my DIY radio. I am following the schematic this link. See pictures below for a diagram of how the components are wired and the actual wiring. The design I made is different ...
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Amplitude modulation with JFET

I have found a circuit that does AM modulation with a JFET transistor (2N5485). I modified it slightly and ended up with the circuit below. A sample output is also given. I used Microcap 12 for the ...
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PWM/PPM with external carrier

I want to generate PWM/PPM signal with external supplied carrier e.g. for 'outphasing' AM transmitter (for educational purposes). Convetional methods of PWM generation implies that carier signal has ...
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1 answer
89 views

Watt output of radio station

I was wondering how many watts an AM radio station outputs, and if I can calculate the watts on a tuned antenna by this equation: Where Win = the watts input for the antenna, Wout = the watts output ...
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1 vote
1 answer
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AM modulator's negative peak saturation issue

I am working on AM modulator. I am using NMOS as a voltage controlled resistance, and opamp in inverting aplifier configuration to get carrier signal multiplied by input signal. I created a simulation ...
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Hearing only noise and ticking sound with simple AM radio - The art of electronics

I've tried to build the simple AM radio that is proposed at page 56-The Art of Electronics (3rd). The idea is to tune my radio on a frequency of 657 kHz (I'm sure there's a station at that frequency)....
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1 answer
107 views

Do AM radio broadcasters pick frequencies that are picked up as interference on purpose? [closed]

This is not meant to be a political question, rather a historical one, USA based. Every place I have lived, if I have an amplifier with a long enough input wire, I will start picking up AM radio if I ...
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Envelope detector RC values [closed]

I have understood how the envelope detector works, but I am unable to find the formula for R and C appropriate values. The closest I have found is this link: Explain The Square Law Demodulation and ...
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3 answers
228 views

Use opamp for demodulation and amplification

For small frequencies (20-20000Hz) the opamp has output more than -3dB If we make a low frequency AM receiver , can we use an opamp for demodulation instead of a diode and for amplifications instead ...
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3 votes
1 answer
83 views

SIMULINK: The spectrum of the modulated signal remains unchanged despite modification of the modulation index

I try to implement a frequency modulator. From what I know, the more I vary the modulation index (which is set by the gain block here,) the more the spectral lines should increase in number. When I ...
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1 answer
108 views

Does satellite radio use AM or FM or both? [closed]

Somehow, I cannot find an answer anywhere... I am guessing both... Several actual satellites had FM in their names, so perhaps that is a clue, but I want to know for sure...
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2 votes
2 answers
159 views

AM radio antenna optimization

I am an RF noob and am trying to understand if optimizing an AM crystal radio antenna (maximizing the signal transmission from the antenna to the LC tank) is practical, or even makes sense. Here is a ...
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Ring modulator with matlab [duplicate]

I'm a bit newbie in DSP. I'm trying to modulate two signals and create DSB-SC am signal. I choose ring modulator for it. So can anyone show me any working ring modulator circuit?
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2 answers
275 views

Gaussian signal generation circuit

I was studying op amp application and saw the square wave, triangular wave, sine wave. I was wondering if it is possible to generate Gaussian shape wave with op amp. I am basically trying to modulate ...
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1 answer
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AM circuit LTspice

I have to analyze the following circuit and understand its function. As far as I understand the top part is the simple phase-shift oscillator generating output sine wave at circa 145kHz. The NE555 is ...
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MC1496 can be used as a DSB SC and AM IC, but their circuits on the datasheet are the exact same. What is the difference between the two?

I am looking at the MC1496 IC datasheet provided by ON here. Figures 1 and 3 show that you can make an AM or DSB-SC signal using this circuit. However, the two test circuits listed on the datasheet ...
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1 answer
1k views

FM demodulator LTspice

I am now designing an FM demodulator circuit. And the first step is turning FM into AM, so I could use envelope detector afterwards. Modulator circuit is designed using Colpitts topology. So frequency ...
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1 answer
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Unable to generate AM wave using opamp log antiog multiplier

I was trying to make a op amp based AM modulator. I used a log anti-log multiplier to generate the below waveform. This is the output I am getting as from this circuit What I intended to generate
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4 answers
433 views

Different antenna lengths for different frequencies?

I just want to understand a few things which I couldn't get clarity from a lot of websites searched through google as I could see differing information. My questions : How does a single FM antenna ...
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2 votes
2 answers
295 views

When we raise a signal to a power n, does the bandwidth always gets multiplied by n?

I know that when we have a message signal $$m(t) = \cos(\omega t)$$ when it gets squared, its bandwidth gets doubled, because $$\cos^2(\omega t) = \frac{1}{2}+\frac{1}{2}\cos(2\omega t)$$ But is ...
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AM radio sound frequency

I have a radio transmitter and a radio receiver . simulate this circuit – Schematic created using CircuitLab Will the sound produced by the loudspeaker have the same frequency with the tuning ...
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4 votes
4 answers
301 views

Code transmitter question (original Forrest Mims design)

I found some old Radio Shack Electronic books from my childhood (authored by Forrest M. Mims III) and have been trying to construct a few of the circuits for fun. I've been stumped by the operation ...
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4 answers
269 views

Clarifications about up and down converting mixers

Let's look at this definition of mixers (reference): A real mixer cannot be driven by arbitrary inputs. Instead one port, the "LO" port, is driven by a Local Oscillator with a fixed amplitude ...
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2 votes
1 answer
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Night-time Shortwave radio broadcast

I recently read an article from https://www.fcc.gov/media/radio/am-stations-at-night It says: During daytime hours when ionospheric reflection does not occur to any great degree, AM signals travel ...
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1 vote
1 answer
90 views

Envelope Detector Improvements?

The classic Envelope Detector is very old and very cheap and very simple .Sure there are now better schemes like synchronous detection ,PLL etc.The circuit is responding to the peak of the Amplitude ...
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Design AM modulator circuit [closed]

I having an assignment that need to design AM Transmitter using Multisim with following specification: • Audio input (200-14000Hz) • Double Sideband Full Carrier • RF carrier frequency of 50 MHz ...
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0 votes
5 answers
641 views

How to turn on LED using RF as a catalyst?

I am trying to build a circuit that turns on a LED diode when it detects AM radio waves, in order to create a "radio wave detector". Before I explain further, please note that I am not trying to ...
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3 answers
505 views

Frequency/amplitude modulation and SNR

I read (for instance here) that FM modulation is less affected by noise than AM modulation. But I don't understand conceptually the reason for that: why is the SNR with frequency modulation higher ...
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1 vote
1 answer
620 views

Envelope detector for AM signals

How or what are the constraints for deciding factors of envelope detector for AM? As far as I know that charging time of the capacitor should be below 20T where T is periodic time of carrier and ...
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5 votes
3 answers
289 views

How does this circuit work? (AM receiver)

I do not completely understand how this circuit works: First, I do not understand how the LC filter selects the frequency. I know that it's impedance is 'infinity' at the resonant frequency, but I ...
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2 votes
2 answers
673 views

AM radio wave LED indicator

I recently learned about simple AM transmitters and receivers. Now, I'm trying to apply this and expand my understanding by trying to create an AM radio wave powered LED. I'm a very beginner ...
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2 votes
1 answer
263 views

Why only odd harmonics after signal is amplified? *Plots inside*

Why do I get only odd harmonics appearing? This not only happens at saturation of the transfer curve, but also in the linear portion of the curve. I make an input signal and the power of this will ...
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0 votes
3 answers
341 views

Why do carrier waves sound silent on radios?

I was recently reading about and building low-power AM radio transmitters, and read/noticed that when the carrier wave is not yet modulated, the radio receiver goes silent. For example, let's say my ...
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