Questions tagged [modulation]

Generic term for coding information onto another carrier signal

335 questions
184 views

What to use as an external 100 Hz modulation source for an RF Signal Generator?

I've got an old-school HP 8656B Signal Generator, for a 433MHz RF project. Typically, I've used the internal 400Hz or 1kHz modulation but for the receiver in question I need a signal source that is ...
279 views

Phase Modulator with JFET

At the university we have seen this circuit as a Phase Modulator: simulate this circuit – Schematic created using CircuitLab where $m(t)$ is the message at audio frequency and $v_p(t)$ is ...
47 views

OFDM demodulation time

How much time does it take to demodulate one OFDM symbol? In 802.11a standard the Symbol Interval Time is 4us. Does this mean that each symbol is demodulated within this period or there is pipelining ...
5k views

Relation between Signal to Noise Ratio (SNR) and Transmission Bandwidth for FM signal

I was encountered by the below question :: ...
3k views

difference between linear modulation and non-linear modulation scheme?

As shown in title: what's the difference between linear modulation and non-linear modulation scheme? I can not find the formal definition of this. And there is a different determination for the FSK ...
672 views

Is FM index affected by frequency multiplication?

I came across this question which goes An FM signal with modulation index mf is passed through a frequency tripler. What will be the modulation index at the output of the tripler? and according to ...
89 views

Output of a PSD fed a square wave

This is the question given in one of my papers. Input is a square wave, if phase shift was zero it would be just flat positive line, if phase is pi it would be flat negative line. Here the phase ...
1k views

How is it decided what modulation is used during an 802.11 communication?

I understand, that 802.11x protocolls can use different type of modulations. BPSK, QPSK, 16-QAM, 64-QAM... I also understand that the used modulation depends on the quality of the channel, I guess on ...
1k views

Spectrum of FM signal [closed]

I've been given a question like Draw the spectrum of FM signal with modulation index beta = 0, 1 ,2,2.5. I know that it is something related to finding bessels values of the given beta but I don't ...
2k views

Why it is preferred to have local oscillator frequency larger than carrier frequency in superheterodyne receiver?

So to obtain intermediate frequency Fif, why it is preferred to use Flo > fc So we use this equation Fif = Flo - Fc Instead of Fif = Fc - Flo
424 views

Is it true that frequency deviation over 2*pi is the phase deviation of an FM/PM signal?

for ∆f frequency deviation if for FM only and PM has Phase deviation. and Kf= ∆f (Hz) of FM? Kf = ∆f (rad/s) for PM? and for th rules: ∆f=(kfmp)/(2p) for FM where mp = mp max-mp min ∆f=(kfmp)/(2p) ...
80 views

Why isn't this a right expression for FM?

Like AM that can be represented as: $$\bigl(A_c+Km(t)\bigr)cos\bigl(2\pi f_ct\bigr)$$ Here, simply the amplitude is being varied by a sinusoid. Therefore similarly, why can't FM be written as: ...
2k views

Modulation scheme for simple signal generator

As part of a vintage radio restoration project, I decided to build a simple signal generator for alignment. The idea was straightforward, a short distance AM transmitter with a variable carrier ...
628 views

Phase shift between pole voltage and line-to-line voltage (3 phase)

I understand that the pole voltage phase shift is 120degrees for 3 phase and the line to line voltage is equal to the difference in 2 pole voltages. However, how do I work out the phase shift between ...
697 views

Balanced demodulator [closed]

I came upon this expression "Balanced demodulator" while reading about signal modulation, but didn't find anything that explain what is a balanced demodulator, can anyone explain this or give me any ...
325 views

Laser driver current and temperature management

For a project I need to make a custom laser driver for a dot green laser module. Below and here 1 you can find my design, the laser I've using now is a PLT5 510 OSRAM, the VSYS is 3,7 V DC from a Li-...
185 views

what is wideband phase shifter in modulator?

in these days I have been studying communication systems. and I want to know the role of wideband phase shifter in the picture above.
1k views

Baud to bit mapping for the UART?

Before starting the question, a reminder of the difference between on how a baud rate and a bit rate relate. Two people are standing 1km apart and they want to exchange a 8 bits of data. ...
207 views

Conceptually, what is the Message frequencies affect on the FM signals rest frequency

Context: Frequency modulation via a Voltage Controlled Oscillator (VCO) If I take a message signal of frequency $F_{mes}$ and use it to generate a FM signal with a VCO, which has a rest frequency ...
668 views

AM Demodulation with Envelope Detector

I have to project an AM demodulator using an Envelope Demodulator. To which kinds of AM (DSB, DSB-SC, VSB, SSD) is it applicable to? Thanks
984 views

Power of AM signal [closed]

I need to calculate the power of the sidebands and the carrier. The carrier is 10*cos(2pi10⁶t) [V] and the modulating is 3*cos(2pi10³t) [V]. The modulated signal is 10*cos($w_0$t)+$\frac{3}{2}$*...
144 views

Differential encoder output of PSK modulation input

I am a bit confused to the answer given for the following question. The question reads as follows: If the input to a binary differential PSK modulation system is 01100101000111 tabulate The ...
78 views

How does QAM retain the phase of the signals?

QAM is a modulation technique where amplitude modulation is performed for two signals, one sine signal and another cosine signal. Since the signals are out of phase, the information in these signals ...
92 views

Vibrato audio effect circuit

I would like to build a circuit that adds a "vibrato" audio effect to a simple sine wave input. Sample audio clip from Wikipedia: Vibrato, Sound Frequency 500Hz, Frequency Modulation 50Hz - Vibrato ...
232 views

Delta modulation (DM) signals

Trying to understand this circuit. Will this produce a representation similar to example in second image (if U_inf is the sine wave "original") ? Assuming that, I expect U_DM to look like the "...
985 views

AM Demodulation of Square wave

Good day Guys, I am working on an AM Modulator and Demodulator circuit using the diode method. My modulation signal is a 10kHz Square Wave and I have a carrier frequency of 850 kHz. My modulation ...
151 views

Modulation signal getting distored when connecting demodulator

Good day Guys, I have a question regarding output signals of a specific stage getting distorted when connecting the next stage. In my scenario, I am working on an AM modulator and demodulator of a ...
57 views

Role of Mixer post Modulation Stage

I was going through radio transmission, and looking at a handout from Analog Devices on Heterodyne structure. Here is layout from this handout. What I understand that in "MOD" (refer the layout above)...
590 views

maximizing IR range and peak current

I ordered a bunch of infrared detector diodes (aka IR diode) and infrared transmitters. luckily the detectors are blue (and don't respond to normal room light). I am planning to order a bunch of ...
49 views

Can I store all channels from the signal coming from a digital antenna? [closed]

Whatever signal comes out of a digital antenna carries many basic broadcast channels (ABC, FOX etc.) Once this signal reaches the TV, some extraction circuit extracts (or tunes to) the channel I want ...
121 views

Showing QAM constellation diagramm on signal analyzer

I've been playing with some lab equipment recently in order to learn more about digital modulation techniques. I've connected R&S signal generator SMIQ 03B with the R&S spectrum analyzer FSIQ ...
49 views

Increased current draw in data transmission circuit

Ok so here's my question. I'm fairly new to electronics research, my background is chemical engineering, but I'm attempting to improve my understanding of basic circuits and data transmission for my ...
43 views

Do we take significance of bit into account while calculating bit error rate?

The question is broadly about bit error rate, but to be concrete, I am asking it in context of 16-QAM. Consider we have a rectangular 16-QAM modulation and also assume that we have grey coding. As I ...
2k views

Why does more bandwidth guarantee high bit rate?

The definition of bandwidth is frequency range and it seems to be correct to say that higher bandwidth guarantees higher data rate. However, i do not understand why it does. Data rate depends on ...
92 views

The use of cyclic prefix in OFDM to mitigate Intercarrier Interference

I understand that a guard interval (GI) is required to eliminate ISI in OFDM-based systems. In this context, an empty GI could be used. But, why an empty GI does not remove Intercarrier Interference (...
321 views

Help designing a circuit to drive a 1550nm DFB LD and use it to modulate an RF signal

I need to modulate an RF signal (random sine wave acting as data) using the 1550nm DFB Laser Diode, I need a control circuit to drive the Laser Diode and inject the data to modulate the LD carrier ...
6k views

Why, where and how we use envelope detector in AM demodulation?

I have studied AM modulation and demodulation. But i can't understand the purpose of envelope detector in demodulation. So my question is: Why, where and how we use envelope detector in AM modulation?
910 views

Visible Light Communication Signal Transmission

Im working on a VLC project where Ill need to transmit encoded data through an LED using an Arduino board to a photodiode receiver that somehow demodulates the signal and extracts the data. Im looking ...
4k views

Amplitude Modulation Circuit Implementation

I am trying to understand AM modulation at circuit level. As per theoretical framework, we have to multiply $V_{G2}(t)$, $V_{G1}(t)$, so that frequency shifting happens at carrier frequency, i.e.,...
5k views

In this Amplitude Modulation circuit, what is the purpose of the diode load (L2)?

In this circuit i know that the diode mixes the signal. I know that after the diode it is a half-wave. I know that the capacitor reproduces the lost signal. I have a feeling L2 is maybe plays a part ...
3k views

How to convert Pulse Position Modulation (PPM) to duty cycle?

I can convert PWM to duty cycle since each frame starts with a rising edge. Then I count the on time, off time and take the ratio to find duty cycle. However, for PPM signal, there is no start of ...
64 views

PAM nonlinear amplitude compression in lower eyes

I needed some help to understand why at Rx, we observe different effective SNRs in individual eyes for higher level PAM signalling. If you need additional info, http://literature.cdn.keysight.com/...
813 views

Is antenna length for a baseband signal infinity?

I am studying RF communications and learned that antenna length is proportional to a wavelength of a signal. And many literature say that a high frequency is preferred in wireless communication ...
338 views

Output of Oscillator and Modulator is Absent

I am designing circuit of AM transmitter. This circuit I got from youtube. You can have it from here I designed the same circuit in proteus and simulate it and try to obtain different waveforms on ...
4k views

In my country (Germany) we have frequency-modulated (FM) and amplitude-modulated (AM) radio broadcasts. However, the reality is that no one ever listens to the AM since you just don't hear anything (I ...
98 views

Mach Zehnder phase change?

According to Comsol, a multiphisics simulation software company, a mach zehnder modulator "modulates" the input signal by splitting it into two parallel branches, affecting the relative phase on one ...
43 views

Two to one Analog to Digital conversion

I am measuring two DC biosignals but have only one input channel. I was wondering if some type of signaling or modular simple trick might be used to 'interleave' the signals while also digitizing them....
148 views

Does this look like amplitude modulation?

I have designed a transmitter and a receiver for amplitude modulation. Does the signal in the image looks like amplitude modulation?