ASN9 - 3rd Harmonic & QSD

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Explain Third Harmonic and Quadrature Sampling

Third Harmonic Sampling The cosine series is made up of a infintie sum of harmonics as shown $\sum _{n=1}^{\infty }{\frac {1}{n}}cos(n\omega t)=cos(\omega t)+{\frac {1}{2}}cos(2\omega t)+{\frac {1}{3}}cos(3\omega t)+{\frac {1}{4}}cos(4\omega t)+\cdots$

The third harmonic is the third term ${\frac {1}{3}}cos(3\omega t)$ is better to use in circuit designs rather than the first harmonic because it is three times as fast. An device that uses third harmonic sampling is SoftRock -40 software defined radio. One benefit of using thrid harmonic smapling is that it is cheaper to buy a low frequncy oscillator and the parts driven by one. The disadvantage is that the loss is -9.54dB.

Further information on Third Harmonic Sampling Soft Rock

Quadrature Sampling

A Quadrature is output signal that is of phased off the desired signal. For example, in a software define radio 2 signals 90 degrees phase shifted are generated from two mixers. One of those signal outputed will be the desired signal and the other for quadurature sampling. Further information on Quadrature Sampling SDR-1000 QEX