Optelecom Inc., Germantown, Md., has released the 9641 series of TTL and RS422 signal optical transmission cards. The cards were developed to provide optical transmission of TTL and RS422 signals over optical fiber. The units operate at rates from near DC to 20 Mbps. Models include the 9641TT and 9641R cards, and support one-to-one TTL or RS422 transmission, respectively.