Spectrum Digital Corp., a Herndon telecommunications company, has announced that Jay T. Pisula will become its president and chief operating officer, easing the company's transition from the developmental to the manufacturing stage.

Pisula joins Spectrum after 20 years of management experience in the telecommunications industry. He was previously vice president and general manager of the Data Communication Group at Penril Corp., where he was responsible for the manufacturing and marketing of a line of modems, statistical multiplexers and data PBX systems.

Pisula was also vice president of sales and marketing at Timeplex Inc., a company that manufactures a product much like Spectrum's networking T-1 multiplexer.

The T-1 allows users to share a single communications line using voice, computer-data and video-communications functions. In his new position, Pisula will oversee the financing, marketing and manufacturing of the T-1 and of Spectrum's digital microwave products.

"It's a unique opportunity when you come across a business with all the key elements for success -- adequate funding, high market growth and a state-of-the-art product," said Pisula. "I'm excited about joining a company with such potential."

Spectrum has not delivered its first product, but has signed five contracts with data-communications companies that will sell the T-1 multiplexer in the United States and international markets. Paradyne Corp., one of these companies, placed its first purchase order, valued at $1.2 million, last week.

Spectrum was formed in 1984 by a group of executives from MCI Communications Corp. to develop and manufacture the sophisticated telecommunications equipment, including the T-1 and microwave telecommunications devices.

Pisula will succeed John B. Mann, a cofounder, who will become senior vice president of corporate development and vice chairman of the board. Robert P. Bernardi, the other cofounder, will remain chairman and chief executive officer.