Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [quadrature]

48 questions
43
votes
4 answers

Can somebody explain what IQ (quadrature) means in terms of SDR?

This is a bit of a basic question, but I am having trouble understanding why a signal needs to be broken up into I and Q components to be useful for software-defined radio (SDR). I understand that the I and Q components are the same signal, just 90…
Malvineous
  • 1,649
  • 1
  • 15
  • 27
6
votes
2 answers

What could cause a quadrature encoder to produce this output?

I'm working on a software quadrature decoder and testing with a Lego EV3 medium motor (which has an integrated quadrature encoder). The thing is, while the large motor produces perfectly normal-looking quadrature output, my medium motor produces…
sh1
  • 316
  • 1
  • 7
5
votes
3 answers

Separating the AM and QAM components in PAL signal demodulation

I'm attempting to emulate the modulation and demodulation of a PAL video frame in software, but I'm having trouble understanding how the AM (luma) and QAM (UV) components of the signal are separated during the demodulation process. Background: The…
Polynomial
  • 10,562
  • 5
  • 47
  • 88
4
votes
2 answers

FPGA encoder counter running away randomly

I am programming an Altera FPGA using Quartus II v9.0 to count encoder pulses and output that count to an external LabVIEW program (see diagram below). I was able to debug one issue with my code thanks to the StackExchange community, but now I am…
Engineero
  • 199
  • 1
  • 3
  • 10
4
votes
6 answers

Removing digital noise on quadrature encoder signals

I am using a quadrature encoder with 3 lines to track the rotary position of a shaft attached to a BLDC motor(through a planetary gearbox). When I rotate the shaft, the A, B and Z lines always have an erratic digital noise(observed using a logic…
Tarang Shah
  • 476
  • 1
  • 5
  • 12
3
votes
1 answer

design a 90 degree hybrid coupler 2-8GHZ

I designed a 90 degree hybrid coupler in hfss, in 5~6 GHZ. S₁₁ & phase difference are okay, but S₂₁ & S₃₁ don't match. What change should I make in the form to improve matching between S₂₁ & S₃₁?
Ali.kavari76
  • 25
  • 4
2
votes
2 answers

QPSK Modulation towards DAC

Modern DACs are able to accept 2 digital values (representing I and Q), multiply them internally by a Sine and Cosine waveforms and combining the result to form the output signal. When dealing with QPSK modulation textbooks show it like that: To me…
shaiko
  • 459
  • 1
  • 6
  • 15
2
votes
1 answer

How to avoid decay in quadrature oscillator?

Let's consider following quadrature oscillator below (source). It should provide two 90° out of phase sine signals with equal amplitude. It consists of two inverting integrators as well as an inverting amplifier. I added a momentary switch to…
flawr
  • 681
  • 6
  • 18
2
votes
0 answers

What is the meaning of "Demodulation in quadrature sense"?

With regard to stepped frequency radar, what does it mean when we say that the transmitted signal is "demodulated in a quadrature sense"? The property of interest in this kind of radar is the phase difference. We basically obtain a phase delayed…
anildadj
  • 25
  • 6
2
votes
1 answer

Quadrature modulation Digital to Analog

I want to use an FPGA to generate quadrature modulated signals for use with an RF transceiver (something like MAX2828 ). I am confused specifically about how the digital to analog modulation should be done. Please correct me if this is not…
ronald_s56
  • 175
  • 5
2
votes
0 answers

Offset QPSK Frame sync markers

What actual protocols exist out there that employ Offset Quadrature Phase-Shift Keying (OQPSK)? What do they use for the frame synchronization marker (or "preamble" or "sync word" or "flag")? Do they use a unique word, a unique pattern of bits? If…
robert bristow-johnson
  • 1,645
  • 1
  • 12
  • 29
2
votes
2 answers

What is the best oscillator to be used in a capacitive soil moisture sensor?

I am working on this project where I am going to make a soil moisture sensor. The principal that I'm going to use is the change of capacitance of the soil with moisture. What I'm going to do is make a capacitor that would be buried under the soil,…
slhulk
  • 143
  • 8
2
votes
3 answers

Quadrature encoder has one synced edge and one phase-shifted edge, is this a special encoding scheme?

Special encoder output scheme? I am testing an inexpensive encoder and encountered a strange but consistent output pattern. In other encoders I've used, the A signal consistently has a 90 degree or -90 degree phase shift, depending on the rotation…
Jelle van Campen
  • 145
  • 4
2
votes
1 answer

Frequency Dependent IQ imbalance

I would like to know does anyone know how to model the frequency dependent IQ imbalance. The frequency independent model is when gain and phase imbalance are just constant now assume that gain and phase are linearly changing. The independent case…
math
  • 121
  • 3
1
vote
2 answers

Encoder direction change during index pulse

I have a quadrature encoder with an index pulse, and I would like to keep track of angular position over multiple turns. The microcontroller I am using has counters that count both index pulses (revolutions) and phase edges. Each time an index pulse…
knick
  • 163
  • 5
1
2 3 4