A transmitter-combining broadcast system and method is provided that allows IBOC-compatible broadcast with simple analog-to-IBOC upgradeability with high efficiency. At full power, a standard analog signal and an IBOC-compatible digital signal are transmitted by combining the output of a wide-band transmitter...http://www.google.com/patents/US7254374?utm_source=gb-gplus-sharePatent US7254374 - Switchable multi-transmitter combiner and method
