Microdyne Corp. of Alexandria announced yesterday that it will acquire four affiliated technology companies for an undisclosed sum in an effort to broaden its communications technology base.

The telemetry and remote monitoring company said it plans to acquire Apcom Inc., a Gaithersburg-based maker of signal intelligence products; Celerity Systems Inc., a maker of data acquisition and storage products based in Cupertino, Calif.; Acceleration Systems Inc., a Bowie-based designer of high-speed processing engines; and Digital Telecom Inc. of Damascus, which handles marketing for Apcom and CSI.

The four privately held companies will become part of Microdyne Communication Technologies Inc., a Microdyne subsidiary based in Ocala, Fla., though they will keep their existing management and headquarters, said David Dragics, Microdyne's director of investor relations.

Microdyne shares rose 50 cents yesterday to close at $4.25 on the Nasdaq Stock Market.

Dragics said the acquisitions will give the company access to a new customer base. The four companies serve a $500 million segment of the signal intelligence industry and $1 billion test and measurement marketplace, he said.

Based on last year's fiscal revenue, the acquisitions would have increased Microdyne Technologies' revenue by more than 60 percent, Microdyne officials said in a statement.

Analysts said the acquisitions, to be made in cash, should prove profitable for the company.

"I think it is a superb move for Microdyne," said Paul M. Harbolick, research director at Ryan, Lee & Co., a McLean investment banking firm. "It is going to bring money to the bottom line because they are not paying any stock for it."

The acquisition must be approved by regulators as well as the boards of directors and principal stockholders of the companies involved. Microdyne officials expect the deal to be completed by the end of July.