# A question related to “quadrature carrier multiplexing”

While studying 'Qaudrature carrier multiplexing', I came across these statements in my text material:

"Precisely varying the phase of a high-frequency carrier sine wave in a hardware circuit according to an input message signal is difficult. A hardware signal modulator that manipulates the amplitude and phase of a carrier sine wave is expensive and difficult to design and build, and, as it turns out, not as flexible as a circuit that uses I and Q waveforms."

Thus practical hardware design concerns make I and Q data the better choice. This way we can avoid manipulating the phase of an RF carrier directly.

Why manipulating the phase directly is not a good choice?

## migrated from dsp.stackexchange.comMay 18 '15 at 11:36

This question came from our site for practitioners of the art and science of signal, image and video processing.

• What part of the two sentences that you quote do you fail to understand? – Dilip Sarwate May 17 '15 at 16:07
• @DilipSarwate:Sir, I am unable to understand that why/how it is difficult to precisely vary the phase of a high-frequency carrier sine wave in a hardware circuit according to an input message signal. Is this the same reason for which we prefer non-coherent detection over coherent detection? – a.s. May 17 '15 at 16:49
• The why is a question for electronics.SE or engineering.SE, not dsp.SE. – Dilip Sarwate May 17 '15 at 17:08
• How do I migrate my question to electronics.SE? – a.s. May 18 '15 at 1:20
• Click on the flag link and you can send a request to the moderators to migrate the question to electronics.SE – Dilip Sarwate May 18 '15 at 3:31