To meet the transmission demand of radio-frequency (RF) signals, a radio-over-fiber (RoF) transmission link was designed based on an intensity-modulation/direct-detection scheme, employing high-linearity directly modulated semiconductor lasers, array waveguide gratings, and analog photodetectors. This link achieves low crosstalk, low harmonic distortion, and a variable link gain. Directly modulated semiconductors and control circuits, an analog RF transmitter, and receiver modules are designed and fabricated. Experimental results indicate that the link gain can be tuned in the range of -30-10 dB, the second harmonic suppression ratio exceeds 50 dB, the crosstalk among channels is lower than 60 dB, and the phase difference is within ±5°. For different input RF powers, the link gain can be tuned online to improve the noise figure or to reduce the nonlinear distortions of the RoF link. This design and prototype can be used for L-band RF signal transmission.