The MIL-STD-188-110A Single Tone high frequency modem is used by the United States military everyday as a beyond line-of-sight radio. Typically, beyond line-of-sight military radios use satellites for reflection. Satellite time is in high demand, and since there are a finite number of satellites in orbit, it makes over-the-air time expensive. The Single Tone high frequency modem offers a reliable alternative by using the ionosphere, rather than a satellite, for reflection. The ionosphere adds unique channel effects, causing the signal processing software to be more complex and harder to debug than radios which use satellites.

Before being placed into production, the MIL-STD-188-110A Single Tone high frequency modem is placed under comprehensive performance tests. These tests are meant to fully verify all aspects of the software and to impose all possible channel effects such as additive white Gaussian noise, doppler shift, terminal clock differences, frequency and time dispersion. When a test fails, debugging the software can be tedious and time consuming. The two major steps to quick and successful debugging are understanding and isolation. The engineer must understand the channel model and receive path in order to correlate a test failure with a specific section of software. After the channel model and receive path are understood, timing patterns of bit errors and test failures caused by individual channel effects help the engineer isolate the software defect. This thesis compiles the necessary information to understand a generalized receive path and provides a framework for isolating a software defect.