FM HD Radio™ transmission, whether pure digital or hybrid (FM+HD), requires the use of a linearized transmitter to minimize the generation of intermodulation products during amplification of the HD signal. Even these transmitters have limitations to their linearity so to further reduce spectral regrowth, pre-correction techniques at the exciter level have been employed. With the hardware now available in these modern exciters coupled with their linear transmitter, it is also possible to add corrections for amplitude and phase variances introduced by the transmission system.
The objective of this paper is to demonstrate improvements that can be achieved to the FM broadcast signal, both analog and digital, by the use of pre-equalization at the exciter stage.
Improvements FM IBOC Signal Quality Pre-Equalization by Mike Woods