CRITICAL FREQUENCY

1. In radio propagation by way of the ionosphere , the limiting frequency at or below which a wave component is reflected by, and above which it penetrates through, an ionospheric layer . ( 188 ) 2. At vertical incidence, the limiting frequency at or below which incidence, the wave component is reflected by, and above which it penetrates through, an ionospheric layer. ( 188 ) Note: The existence of the critical frequency is the result of electron limitation, i.e., the inadequacy of the existing number of free electrons to support reflection at higher frequencies.