LONDON, Dec 12 (Reuters) - Broadcom shares dropped 4.7% in Frankfurt on Friday a day after the company projected first-quarter revenue above Wall Street estimates, but said margins would fall due to a higher mix of AI revenue. That fall was broadly in line with its U.S. after-hours move. Broadcom has jumped into the AI chip business, which has investors nervous about the profitability and costs of enormous investments. The company has a backlog of $73 billion that it anticipates shipping over the next 18 months, CEO Hock Tan said on a post-earnings call, but his lieutenant said profit margins could drop. (Reporting by Alun John; Editing by Amanda Cooper ) (The article has been published through a syndicated feed. Except for the headline, the content has been published verbatim. Liability lies with original publisher.)