FSK外文及其翻译.doc

DIGITAL FSK/AM/PM SUB-CARRIER MODULATOR Theodore J. Hordeski ABSTRACT Aerospace Report No. TOR-0059(6110-01)-3, section 1.3.3 outlines the design and performance requirements of SGLS (Space Ground Link Subsystem) uplink services equipment. This modulation system finds application in the U.S. Air Force satellite uplink commanding system. The SGLS signal generator is specified as an FSK (Frequency Shift Keyed)/AM (Amplitude Modulation)/PM (Phase Modulation) sub-carrier modulator. GDP Space Systems has implemented, on a single 6U-VME card, a SGLS signal generator. The modulator accepts data from several possible sources and uses the data to key one of three FSK tone frequencies. This ternary FSK signal is amplitude modulated by a synchronized triangle wave running at one half the data rate. The FSK/AM signal is then used to phase modulate a tunable HF (High-Frequency) sub-carrier. A digital design approach and the availability of integrated circuits with a high level of functionality enabled the realization of a SGLS signal generator on a single VME card. An analog implementation would have required up to three rack-mounted units to generate the same signal. The digital design improve performance, economy and reliability over analog approaches. This paper describes the advantages of a digital FSK/AM/PM modulation method, as well as DDS (Direct Digital Synthesis) and digital phase-lock techniques. KEY WORDS SGLS, FSK/AM/PM, Ternary FSK, Dibit Command Data, AM Phase Delay, Digital Phase-Lock Loop, Direct Digital Synthesis, Numerically-Controlled Oscillator INTRODUCTION GDP Space Systems has developed the FSK001, a single 6U-VME card SGLS signal generator. See Figure 1 for a graphical representation of the SGLS FSK/AM waveform. Earlier analog approaches to SGLS signal generation required three separate chassis: (1) a frame synchronizer with a phase-lock loop to extract the frame-formatted dibit encoded data and generate a rate-adjusted cloc