Comprehensive Study Of FM Multipath With Repeatable Results

Multipath is an unknown variable in FM broadcasting, and quite possibly the largest annoyance for listeners. Due to momentary changes in FM signal propagation, multipath is extremely difficult to measure in a repeatable manner. On account of this, it becomes difficult to rely on captured measurements to confirm or deny the effects of multipath, when evaluating FM coverage. Additionally, signal processing can affect, or aggravate multipath in a negative manner.

Today, there are software tools available which are capable to simulating the FM signal path, as well as generating multipath. Due to the controlled environment the software system provides, creating repetitive propagation profiles, as well as synchronized signal content profiles, enables the ability to generate, transmit, and measure FM multipath situations. The testbed provides results which are repeatable, as well as confidence in the data that was acquired.

This paper will detail and illustrate work that was done using MatLab as a testbed, in this study of multipath. Employing good engineering practice, it will also provide audible examples of the effects on multipath as caused by various signal processing methods such Single Sideband Suppressed Carrier (SSBSC), and dynamic limiter functions of the FM-Stereo system. This is no ad-hoc drive up a coastal highway!

Frank Foti | Telos Alliance | Cleveland, Ohio USA