ABSTRACT -- This paper presents radio frequency modulator and demodulator for high speed data communication on Hybrid Fiber Coaxial cable television network. Modulation and demodulation uses quadrature phase shift keying, which have changes in carrier phase by multiple of 90 degree. The modulator consists of : digital signal processor, carrier signal processor, signal multiplier and signal summation. The demodulator consists of : QPSK amplifier, clock generator, carrier recovery signal generator, signal multiplier and digital processor. The resultant modem operates at 10 MHz carrier frequency with data rate 1.28 Mbps/S.

KEYWORDS -- QPSK , Cable Modem