This master thesis is for my exam in Master of Science in Electrical Engineering with emphasis on Telecommunications/Signal Processing at the university of Karlskrona / Ronneby. It was carried out at Flextronics International in Karlskrona and this report is a follow-up to my bachelor thesis made at the same premises. My assignment was to develop and implement an interface unit so that two different test instruments could communicate with each other. The instruments are used in the production of DECT (Digital Enhanced Cordless Telecommunications) based products. This report deals with the theory, design, construction and test of how to build this interface unit. Result: This report shows that it is possible to build a fully functional interface unit with few parts and that the quality of the interface box is as expected.