Question

Describe three different types of modulation used with modems.

Please do not copy from internet and need it typed not hand written.

Answer 1

Here are the 3 basic types of modulation used in modems:

1) FSK - Frequency Shifted Keying

2) QPSK - Quadrature Phase Shifted Keying

3) QAM - Quadrature Amplitude Modulation

1) FSK - Frequency Shifted Keying

Frequency Shift Keying (or FSK) is the frequency modulation of a carrier that represents digital intelligence. For Simplex or Half Duplex operation, a single carrier (1170 Hz) is used - communication can only be transmitted in one direction at a time. A Mark or 1 is represented by 1270 Hz, and a Space or 0 is represented by 1070 Hz.

2) QPSK - Quadrature Phase Shifted Keying

Quadrature Phase Shift Keying employs shifting the phase of the carrier at a 600 baud rate plus an encoding technique. QPSK is used in Bell 212A-compatible modems and V.22 - both are 1200 bps Full Duplex standards. The originate modem transmits at 1200 Hz, and receives on 2400 Hz. The answer modem receives on 1200 Hz, and transmits on 2400 Hz.

3) QAM - Quadrature Amplitude Modulation

Quadrature Amplitude Modulation refers to QPSK with Amplitude Modulation. Basically, it is a mix of phase modulation and amplitude modulation. QAM phase modulates the carrier and also modulates the amplitude of the carrier.