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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2answers
98 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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1answer
38 views

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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1answer
67 views

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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1answer
82 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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1answer
61 views

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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4answers
109 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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2answers
103 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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0answers
43 views

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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4answers
131 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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4answers
76 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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1answer
124 views

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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1answer
62 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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1answer
1k views

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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5answers
250 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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3answers
147 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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1answer
118 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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2answers
149 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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2answers
301 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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1answer
147 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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3answers
194 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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0answers
62 views

Single-frequency AM Receiver?

Previously today, I tried to make an extremely simple AM receiver without a tuner. It didn't really work (I'm still trying to work on it), but I also tried to make an AM receiver that is tuned to one ...
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3answers
378 views

Simple AM receiver schematic?

I've been trying to make an extremely simple AM receiver (without even a tuner), however, it doesn't seem to be working. As shown in my schematic, what I did was connect the antenna wire to the base ...
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6answers
1k views

Why is superheterodyning better than direct conversion?

What is the advantage of having the extra stage of IF, extra local oscillator and extra filtering stage and amplification. It just seems like more work and circuitry. Surely the direct conversion to ...
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2answers
479 views

High pass filter for use in amplifier circuit

I've designed an amplifier for a small ac signal (amplitude of around 5mV, frequency 252kHz) with a BJT (2N2222.) The BJT is set up in a common emitter amplifier configuration, with the biasing ...
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1answer
132 views

can I use a choke 150uH inductor for my AM transmitter circuit?

I am trying to develop an AM transmitter but I am having problems with getting a variable capacitor and inductor (for the rf circuit) in my location. I was able to find a choke coil with an inductance ...
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2answers
856 views

Tube transmitter tuning

I am trying to tune/tweak/repair this transmitter for a friend of mine. It is oscillating, and it has rf power on the antenna, but it just doesn't seem as "strong" as it should be. The diagram says ...
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1answer
93 views

Tube transmitter plate current meter question

Can I install the mA meter in this schematic directly in the circuit? This is the high voltage plate supply and there is RF on it. The diagram doesn't specify if there is any circuitry to adapt the ...
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3answers
85 views

Wire size question

I am trying to figure out AWG from a European/German schematic. The wire is listed as 0,3mm. (That's 0 (comma) 3mm.) I can find wire for sale in this diameter, but I need a reference to AWG. Is ...
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0answers
303 views

Amplitude modulation with diode

I was studying about amplitude modulation and I found this circuit on the internet. Does anyone know why that ground is needed? Is the first part(three resistors) an adding circuit? Does the diode ...
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1answer
124 views

How to increase range of AM radio waves? [closed]

As a personal project, I made a very simple AM transmitter with an idea from an online tutorial, using a 1 MHz crystal oscillator (plus power source, antenna, breadboard, etc.). However, when using ...
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1answer
1k views

RC transmitter and receiver for Raspberry Pi possible? [closed]

I've got a pet project in which I'm trying to write/build a self learning autopilot for my rc plane. I've got a Raspberry Pi with an IMU and a pitot tube in the plane and it can now control the servos ...
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4answers
219 views

What happens if the frequency of the receiver osc does not match (exactly) the carrier frequency?

I thinking about FM and AM. Theoretically the carrier frequency is perfectly match the demodulation frequency. But what happens if there is a mismatch? I think using AM the frequency of the base-band ...
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2answers
1k views

Why are the resistors in an AM modulator necessary?

In preparation for the amateur radio exam, I have been following the preparation course material by DJ4UF. In the section about modulation it presents this diagram of a simplified AM modulator. The ...
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3answers
10k views

Are audio cassettes FM or AM?

I know that cassettes store an analog signal, but is the signal Amplitude-Modulated (AM) or Frequency Modulated (FM)?
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1answer
208 views

How is the signal Multiplied with the Carrier in AM

In wireless transmission, via Amplitude modulation, we multiply the message signal by a carrier wave to get the modulated signal $$x(t) = m(t) \times cos(\omega t)$$ Where \$m(t)\$ is the original ...
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1answer
87 views

Stereo Enhanced Mono

Medium Wave AM in most countries is monophonic. AM stereo was never universally adopted. Given a monophonic signal, how can one create a stereo output? I know there are some 'tricks' you can play on ...
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4answers
155 views

Signal Theory paradox

Very often we apply to circuits sinusoidal or constant voltages, and we study methods (like the phasors method) to analyze them. Here's a simple question to which, in many years, I have found not yet ...
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3answers
166 views

Multi-tuning AM selector

I'm thinking about the design of an AM receiver frontend that needs to select between three channels. The community suggested that I investigate manually wound loop antennas, and they seem like a nice ...
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1answer
77 views

Multi-fixed-station AM receiver

I'm in the pencil-and-paper stage of building a radio receiver that has the following characteristics: AM shortwave/HF three fixed frequencies - 3.33, 7.85 and 14.67 MHz single upper sideband with ...
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1answer
34 views

Pearmability Tuning Vs Cap tuning for MW AM

I constructed a wide band Hi Fi TRF tuner for MW AM that sounds great. It used an old 365 pF air spaced 3 gang variable capacitor that had equal sections. Selectivity was marginal at the top of the ...
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1answer
7k views

How can I modify the frequency of a simple 433mhz transmitter module?

How can I change the frequency of a simple RF transmitter? These are the transmitters in question: Background Research On this question s3c says: To change the ...
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1answer
59 views

Is possible to modulate the upper and lower sides of a carrier with two distict signals?

I would like to modulate in amplitude the upper and lower sides of a carrier with two distinct signals. Would it be possible? There is a specific name for this scheme of modulation? The detection ...
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1answer
80 views

AM radio Attenuation.

I have built the following AM radio circuit : I was able to pick several radio stations. I fixed the variable capacitor so that I can only hear the 1230 kHz station which I identified from the FCC ...
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2answers
295 views

How to create an OOK signal in ADS

I'm trying to make an OOK modulated signal in ADS. I need a random bit generator, and a block to multiply a sinusoidal signal with that random pulse. I did this in Cadence by the 'rand_bit_stream' and ...
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3answers
4k views

Full AM signal vs DSB-SC

I conducted an experiment where I constructed a Full AM signal and changed the message signals amplitude to change the modulation index of the Full AM signal. I then increased the amplitude of the ...
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1answer
381 views

Germanium Diode 455KHz AM Detector

Ge Diodes have been used for AM detection many decades before Si Diodes became cheap.They were attractive when compared to the large power hungry valve .Nowdays Si diodes are much cheaper and easier ...
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2answers
186 views

Flatness vs Frequency parameter in RF zero bias detectors

I require the measurement of RF power from a port, and I am considering using a zero-bias RF detector in order the measure the power being delivered through the port. These devices give a voltage ...
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1answer
567 views

Understanding a simple crystal oscillator transmitter

I try to understand the AM transmitter on the figure below, but I cannot figure out two essential things. The carrier frequency is created by the crystal oscillator chip. Why does it suffice to put ...
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1answer
3k views

Why do FM radio signals occupy greater bandwidth than AM?

If a 5kHz baseband signal is modulating an AM carrier wave, the sidebands will be centered around the carrier wave and the the signal will occupy 10kHz bandwidth. AM radio limits the upper modulating ...
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2answers
2k views

Demodulate a AM signal from the carrier using Matlab

So the AM signal has a bandwidth of 5kHz and the carrier signal is 100kHz. I demodulate the AM signal by multiplying it to a sin function (sin(2000000*pi), same frequency with the carrier frequency). ...