Quadrature modulation for FM and AM

1. What is quadrature frequency modulation?
2. How is QAM different from AM?
3. Where is 256 QAM used?
4. Is QAM and QPSK same?

What is quadrature frequency modulation?

The carrier signals are of the same frequency but differ in phase by 90 degrees. Since the carriers are in phase quadrature, the modulation scheme described is referred to as, 'Quadrature frequency modulation'.

How is QAM different from AM?

QAM (quadrature amplitude modulation) is a method of combining two amplitude modulation (AM) signals into a single channel. This approach helps double its effective bandwidth. QAM is also used with pulse AM (PAM) in digital systems, like wireless applications.

Where is 256 QAM used?

64-QAM and 256-QAM are often used in digital cable television and cable modem applications. In the United States, 64-QAM and 256-QAM are the mandated modulation schemes for digital cable (see QAM tuner) as standardised by the SCTE in the standard ANSI/SCTE 07 2013.

Is QAM and QPSK same?

Yes, QPSK and 4-QAM are effectively the same. Higher order PSK and QAM would be different, but they reduce to the same thing if you only have 4 constellation points.