View source for ASN9 - 3rd Harmonic & QSD

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'''Third Harmonic Sampling'''


The cosine series is made up of a infintie sum of harmonics 

<math>
\sum_{n=1}^{\infty} \frac{1}{n} cos(n \omega t) = cos(\omega t) + \frac{1}{2}cos(2\omega t) + \frac{1}{3}cos(3\omega t) + \frac{1}{4}cos(4\omega t) + \cdots </math>

The third harmonic is the third term 

<math> \frac{1}{3}cos(3\omega t)</math>.

The benefit of using the third harmonic for sampling in a circuit rather than than the first harmonic is that it creates an oscillation that is three times as fast. SoftRock -40 software defined radio for example uses third harmonic sampling as a technique to obtain faster oscillation. In addition, third harmonic sampling is that it is cheaper to buy a low frequency oscillator and the parts driven by one. The disadvantage is that it results in power loss of -9.54dB.See how Softrock uses Third Harmonic Sampling[http://www.groups.yahoo.com/group/softrock40 Soft Rock]


'''Quadrature Sampling'''


A Quadrature is output signal that is a phase off from the output signal. For example, in a software define radio two signals that are generated from two mixers are phase shifted 90 degrees. One signal is the desired signal and the second is the quadrature signal that is used for quadrature sampling.

Further information on Quadrature Sampling 

[http://www.flex-radio.com/News.aspx?topic=publications SDR-1000 QEX]