Techniques for described for combining fragmented carriers. An example method can include processing, using a first local oscillator (LO), a first analog signal and a second analog signal that are separated by a frequency offset, an output of the first LO used to generate a first digital signal and a second digital signal. The method can further include downshifting the first digital signal based on the center frequency to generate a downshifted digital signal. The method can further include upshifting the second digital signal based on the center frequency to generate an upshifted digital signal. The method can further include combining the downshifted signal and the upshifted signal to generate a combined digital signal, wherein the downshifted digital signal is orthogonal to the upshifted digital signal, and wherein a second total bandwidth of the combined digital signal is less than the threshold bandwidth.

A high frequency (HF) cellular system includes base stations and HF terminals that initiate calls in the HF cellular system. The base stations perform sounding operations of transmitting sounding transmissions from the base stations to the HF terminals. A controller within the HF cellular system manages the sounding operations by having the base stations sound at different time intervals at specified frequencies.