# Tag Info

## New answers tagged modulation

0

I tend to group the advantages of using I/Q into two main categories. These can however be combined depending on the system being implemented: Exploiting the properties of I/Q for spectral efficiency. This is all about having two signals independently "ride" on their respective in-phase (I) and quadrature (Q) channels. It is possible to transmit ...

1

As I understand it, I/Q data is the complex representation of any waveform. Yes and no. I/Q data is the result of demodulating an RF signal (i.e. a signal riding on a carrier) with a pair of local oscillator signals that are 90 degrees out of phase. I think you're assuming that I/Q data must be represented as a stream of complex values -- this isn't ...

3

The main motivation for using quadrature (I/Q) signals is spectral efficiency. Most signals are naturally baseband: they have no carrier, their energy is concentrated around DC, and they are limited to bandwidth $B$. An example would be an audio signal, which has bandwidth of roughly 20 kilohertz. To transmit such a signal, often it must be modulated (or &...

0

the main advantage of using I and Q data is that you can receive and transmit every kind of analog or digital modulation simply changing amplitude of the I and Q components. Take a look to the Phasor theory to better understand the whole matter. A signal can be seen as a moving vector in the IQ plane from the origin. When the amplitude of the signal I and Q ...

1

For a signal that rides at VSS/2, goes down to 0V and up to VSS, just use a pair of GPIO pins, each with a $10\mathrm{k\Omega}$ resistor, with the far ends connected together. When both pins are high you'll get VSS, when both are low you'll get 0V, when one is high and the other low you'll get VSS/2. Then sequence the pins to get the pattern you want. If ...

1

Analogue passband means high frequency radio waves. Analogue baseband means the signal does not modulate a high frequency radio wave. So basically, keying is for radio wave transmissions while line coding is for transmission over bounded media (transmission lines) like coaxial cables, Ethernet cables etc.

1

Keep in mind, QPSK has the same bit error rate as BPSK when both schemes are used to transmit underlying data at the same rate. If you are trying to use QPSK to double your data rate, then you get half as much power per bit, hence half as much Eb/N0, hence a higher bit error rate. So you have to choose: maintain your data rate and keep your BER, or use QPSK ...

1

Another reason to encode to $3$ level is that the occupied bandwidth is less. This is often driven by an emission mask constraint for transmitter certification. To satisfy this constraint, the tradeoff is made on symbol distance. It is however a costly tradeoff affecting receiver sensitivity because the multi level scheme is done post detection where ...

6

High-capacity tape formats use helical scanning. Here I look at why that gives a higher capacity than linear recording with four tracks (one stereo track on each side) like in a compact cassette (C-cassette). Figure 1. Stereo C-cassette player/recorder linear head (left) and a helical scanning head from a data drive (right), same scale. There is a too-short-...

1

In my workplace, with huge datasets, tapes are still in use for long term backup. Namely, one often uses Data8, a 8 mm Backup Format pionnered by Exabyte corporation. Some history on tape formats: Much Ado About Exabyte/8mm Tape Drives.

4

You have already selected your answer, but I would like to put a few more lines. First of all, objecting to Marcus, I think that your first assumption is correct! We can store one hour of almost CD quality (14-16-bits, 44100Hz, stereo) analog audio into these commercial music casettes; i.e magnetic reels. So on a very rough basis you have almost a 600 MB (...

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Typical cheap cassette tape recorders and players in the 1970's used audio circuitry that did not have a completely flat frequency response and added a lot of phase distortion (mostly inaudible to most consumers). In addition, the computers did not use high sample rate low quantization DACS and ADCs (which cost a fortune back then), sometimes only a simple ...

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I had heard that tape is still the best medium for storing large amounts of data. well, "best" is always a reduction to a single set of optimization parameters (e.g. cost per bit, durability, ...) and isn't ever "universally true". I can see, for example, that "large" is already a relative term, and for a small office, the ...

3

Conventional AM and narrowband PM signals look quite similar: $$x_{AM}(t) = A \cos(\omega_c t) + m(t) \cos(\omega_c t)$$ $$x_{NBPM}(t) = A \cos(\omega_c t) - A k_p m(t) \sin(\omega_c t)$$ And based on this, their spectrum also look quite similar. However, there's an important distinction between them: AM modulation changes (modulates) the amplitude of the ...

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Actually, in theory and error performance there is no difference. But in practice, OQPSK decrases the maximum phase alteriation from 180 to 90 degrees which is better for RF power amplifiers.

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