When realizing a high-quality land mobile radio transmission system, one of the most important and difficult problems is how to mitigate the multipath fading effect which degrades the signal transmission performance severely. Transmitter diversity without any feedback signal transmission link is the most effective technique, because mobile radio units can be simply implemented. This paper proposes a new transmitter diversity suitable for digital land mobile radio transmission systems using MSK with differential detection. More than two MSK signals carrying the same information are transmitted simultaneously from separate antennas, received combiningly by a single receiver antenna, and demodulated by the conventional differential detector. After describing the diversity principle, bit-error-rate (BER) performance improvement effect is theoretically analyzed and experimentally confirmed by the laboratory simulation tests.