dBc is the log scale measurement of the ratio between a signal level its respective carrier. This figure is most commonly used when measureing harmonic distortion of a signal. For example one may test the purity of a 100MHz Sine signal by first measuring the power at 100MHz = Po (through 50ohms termination), then measure the power of the first harmonic at 200 MHz=P1 both of these measurements could be taken in dBm. The power of the 1st harmonic in dBc would then be Po-P1.
Triad has extensive engineering expertise in the analysis and verification of signals and systems and employs relevant analysis when appropriate.