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In this paper, implementation of a FPGAbased and VHDL coded reconfigurable frequency shift keying (FSK) modulator for nano-satellite communication systems is presented. Reconfigurable FSK modulator includes 2-FSK and 4-FSK modulators. The system is compatible with AX.25 data link layer protocol for general amateur radio communication which is popular in micro/nano satellite communication. ROM based direct digital synthesizer (DDS) generates a sinusoidal wave at the output with a specified frequency and phase.Keywords -frequency shift keying, software defined radio, AX.25 protocol, FPGA, nano/micro satellites.