A convolver based spread spectrum data communication system

An experimental data transmission system was designed for the control of moving machinery in electromagnetically polluted buildings, especially steel mills. Its operation is reported. The direct sequence spread spectrum system employs two surface acoustic wave convolvers as matched filters for the binary phase shift keying (BPSK) RF modulation with nearly orthogonal PN codes. Coherence bandwidths in steel mills range between 1 MHz and more than 20 MHz. The chip rate of the spread spectrum signal is 48 MHz, providing inherent diversity and reducing the multipath fading. Analog matched filtering by means of the convolvers offers the same flexibility and correlation gain as digital matched filter systems. The author's receiver is far less sensitive to narrowband or square-wave deterministic interference. Synchronization is fast and works without a preamble. A simple equal gain echo combiner is implemented.