Above is the EVM measurement taken of DATV-Express using an Agilent E4406A.

It is of an unmodified board with no IQ offset applied. Some of the error is due to

a symbol rate mismatch between Express and the test gear. Express derives it's

symbol rate from a cheap xtal oscillator (the one used for the USB2 clock).

When generating the same waveform using an Agilent E4437B using a common

reference the EVM is only a couple of percent better.

The tests were done using the W-CDMA option that allows QPSK EVM

measurements to be taken provided the symbol rate is around

4 MSymbols per second.

The maths

EVM (%) = √(P

_{error}/P

_{ref}) x 100

Where P

_{error is the power of the error vector and }P

_{ref is the power of the ideal reference.}

_{}

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