Questions tagged [demodulation]

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BPSK demodulation on scilab

I have a csv file which contains the time and magnitude of the BPSK modulated waveform. I now want to demodulate this. Its bitrate is fc/128 (~106 kbit/s) and the carrier frequency is fc/16 (~847 kHz)....
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260 views

Analog television: What is the difference between the first IF and second (demodulated) IF?

I am trying to understand what kind of changes occur to a signal in the chips which sit between the tuner and, for example the FM audio demodulator. Take the attached example - the TDA2546A. It takes ...
126 views

What is the relation between a signal and its generated audio?

Assume we have a simple AM signal, which is a mix of the carrier wave and upper/lower bands. If I were to plot its time domain graph, I would get a graph with Y being its amplitude and X as time, ...
• 235
184 views

Cost-efficient mixers and/or demodulators for low frequencies

I am working on a circuit project where I need an in-phase/quadrature mixer for acoustic signals in the range of 200 kHz. I have seen that there are a lot of ICs for radio frequencies that implement a ...
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1 vote
99 views

Choose optocoupler diode current limiting resistor

I've designed following circuit: But let's completely forget the MOSFET and only focus on the optocoupler. The signal provided to the input of the optocoupler (yellow) has following characteristics: ...
• 139
155 views

Removing DC offset in MATLAB

My teacher has a demodulated signal and he removed the DC offset with this one line of code in MATLAB: y_dc = y - mean(y) Can someone please explain how this line ...
1 vote
87 views

How does a phase shift keying receiver detect when a new incoming modulated signal is at the input?

This is not a math question. What I want to know is the physical implementation of the receiver where phase modulated signal is coming to the receiver. How does the receiver decide when the phase ...
43 views

Apsk modulation in lt spice

Greetings according to the schedule, help to do APSK modulation in LTspice. I built oscillators and the ideal AM modulator but whow make variations for amplitude and phase become 16-apsk is my biggest ...
933 views

Half wave rectifier query

This is an ASK asynchronous demodulator In the circuit, we can see 3 differentiated parts: One half-wave rectifier, one envelop detector and a comparator. The circuit receives SIG which is a ASK ...
37 views

How decreasing the effective load impedance in the secondary of a transformer heavily dampens it?

I am reading the operation of the ratio detector for FM demodulation. It works on the principle of diode variable damping (please see the figure here). The capacitor C9 restricts the changes in the ...
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96 views

Differences between phase locked loop on PCB and on breadboard

I have a question with regard to the differences between a PLL on a PCB and on a breadboard. In this test, I have connected the output of the amplifier (LMH6503) to both the PLL on the PCB and the PLL ...
• 93
170 views

Hearing the radio by touching a jack plug

Here is what happened to me a few days ago: I own an amplified speaker with a jack plug. Usually, when I touch the jack plug with my finger I hear a "hum" sound. On this specific day, on a ...
• 103
41 views

What is the value of voltage controlled switch to demodulate the PAM circuit

What is the possible value of V3 (voltage controlled switch) and the command to demodulate PAM signal?
1 vote
69 views

Minimum value of A to be able to use envelope detector in amplitude demodulation when m(t) includes an exponential

This is one of the exam questions I have come across with. My approach was, To be able to get detected by the envelope detector, $$A\geq |\max(m(t))|$$ Max value of m(t) is 1 right? When t = 0 we get,...
37 views

LPF based Differential demodulator design

I am designing LPF based differential demodulator(LPF_DDM) to retrieve differentially modulated signals, which are on-chip capacitive isolated [shown]. LPF_DDM includes a differential amplifier, LPF, ...
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1 vote
59 views

MUX Pulldown resistor Questions

I have a precision application where I am demodulating two sine waves using an analog mux (ADG613) and then Low pass filter to measure it's amplitude. The ADG613 is a 1:4 MUX made into a DPDT (chosen ...
• 509
52 views

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 ...
87 views

Charge injection Compensation for Demodulation

I have a precision application where I am trying to limit the charge injection on an analog mux that is demodulating a sine wave from 0deg and 180deg components (with a trigger signal from a ...
• 509
63 views

Frequency de-modulation question [closed]

Why is in some cases that the messaged received from the demodulation process has slightly more amplitude then the original message?
94 views

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 ...
63 views

Problem with demodulation system, LTspice

First of all, I'm sorry if my English isn't perfect, that's not my natural language. I'm trying to simulate an electronic system for my project and I want to demodulate a sinusoidal signal. To do that,...
46 views

op amp random pulsing to ground

I have simple circuit with ada4891 op amp. I am using it to demodulate ASK modulated signal. But sometimes op amp is pulsing to ground for no reason. These pulses are short (about 1 us). I have ...
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111 views

Why does a phase shift happen in the demodulated AM signal using envelope detection?

I was studying AM signal demodulation using envelope detection with the circuit shown below. In the book it says the low pass filter part is called a post-detection filter and that this filter causes ...
108 views

433 MHz Transceiver - understanding OOK demodulator parameter 'OokFixedThreshold'

I would appreciate some help to understand a parameter for this device https://www.semtech.com/products/wireless-rf/fsk-transceivers/sx1231h. I'm far from an expert at RF matters and this question has ...
108 views

Is this a demodulated signal?

1st attempt I have a problem. I built the FM demodulator circuit, but i am not sure if this signal is demodulated. This was my first attempt which following an answer, resulted in a 2nd attempt ...
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76 views

How do you find the phase lag of the current in this FM demodulation "discriminator" circuit?

I need some help understanding this discriminator circuit for FM demodulation. (L1, C1) is the primary LC tank which resonates with the carrier frequency, whose FM signal is applied at V12. As the FM ...
298 views

Envelope detector and distortions

I am attempting to design an envelope detector, however, I'm having problems with regards to diagonal clipping and negative peak clipping of a certain input. While trying to follow this video's ...
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99 views

Is it true that FPGAs and DSPs are widely used for modulation and demodulation of signals? [closed]

I have to write a thesis about digital communications, and I don't want to write something stupid in it. I also wrote that "most of the digital modulations and signal processing nowadays are done ...
1 vote
29 views

General approach of signal detection after demodulation of BPSK

I'm very new to electrical engineering. I'm trying to understand the basic approaches/options to detect symbols after demodulation of BPSK. I found some articles mentioning Maximum Likelihood ...
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1 vote
552 views

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 ...
169 views

Why can FM be demodulated non-coherently while PM cannot be demodulated non-coherently?

I have read that frequency modulation has the advantage that it can be demodulated non-coherently while phase modulation can only be demodulated coherently. I don't find any reason to support this ...
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85 views

Why is transformer coupling used in a simple slope detector? Can't the FM signal be applied directly in parallel to a tuned circuit?

This is what I mean by simple slope detector: Why can't it be like:
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66 views

communication via ultrasound

I want to communicate simple requests and ids over ultrasound. To do this I need to modulate a message onto a 40kHz carrier to drive a ultrasound transducer. Here you can find a simulation of what I ...
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1 vote
188 views

How to avoid false detection when using IR object detection circuit?

I have a circuit to demodulate 2KHz Infrared pulsed light which is generated by 555 timer IC and its output drives an IR transmitter circuit, which is received by IR receiver located 10 cm apart which ...
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90 views

Can I debug this simple circuit without VNA and proper RF equipment?

I am debugging a very simple circuit (existing PCB, not designed by me) that downconverts an AM modulated signal at 900 MHz: The problem: What I measure at "Vo" does not match my LTspice ...
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1 vote
98 views

N-stage rectifier as AM demodulator?

I want to downconvert a simple 100kbit/s NRZ OOK/ASK signal from 900 MHz. In a previous design I found two options: Option 1: simulate this circuit – Schematic created using CircuitLab Option 2:...
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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 vote
117 views

How can picked up FM noise be demodulated?

I have a set of cheap computer speakers, which happens to use a TDA2822M. Its circuit is almost identical to the example circuit from TDA2822M's datasheet. It's USB powered and has no shielding. I ...
• 13
158 views

Coherent and non-coherent detection

Let's say I am simulating something as simple as BFSK. It has two symbols, one entirely on the real plane, and one entirely on the complex plane for representing let's say zero. That is how the ...
216 views

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106 views

Filtering a demodulated signal

I've created a simulation on Matlab of amplitude modulation. After demodulating the signal I need to add a low-pass filter to remove the high frequency components. I'm confused as to why this is? I ...
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350 views

How is dc restorer circuit used for PWM demodulation/detection?

In the Microelectronics Circuits textbook by Sedra & Smith, it is said that: As an application, consider a pulse signal being transmitted through a capacitively coupled or ac-coupled system. ...
135 views

Synchronous detector question [closed]

The author explains it as a synchronous demodulator. Here we can see that two multipliers which multiply both the inverted and non inverted signals. Can I do the same with only one switch for non ...
• 799
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What does division order mean in Rayleigh Fading?

So I'm just beginning to understand how Rayleigh Fading works and I'm trying to model some different modulation schemes with Rayleigh fading channels. I'm doing this on MATLAB where one of the ...
1 vote
198 views

How does this demodulator exactly work?

I have the following circuit which is an AM demodulator (I think). RF input is between the diodes left: Plotting the bode plots for the negative and positive input of the comparator, I get a lousy ...
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2k views

Can someone explain how this Ratio detector circuit works?

I understand how a Foster Seeley discriminator works, but in this Ratio detector, which is a modified version of the former, I don't understand the purpose of having three transformer windings, or ...
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1 vote
665 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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1 vote
227 views

Foster - Seeley FM Demodulator Explanation

Consider this Foster Seeley Demodulator If I have correctly understood, its basic working principle is the fact that at the secondary coils (L2) of the Balun there will be two signals equal and ...
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1 vote