This research examined the theory and application of using discrete multi-tone (DMT) frequency-domain equalization (FEQ) with communications systems that inherently posses null-tones in their respective transmission frequencies. DMT-FEQ relies on null-tones to equalize a non-ideal channel. A Hadamard encoded code division multiple access (CDMA) communications system with up to 32 synchronous users nd a transform domain communications system TDCS) with one user were investigated. Both communications systems were stimulated while operating with real channel data corrupted by noise. Simulation results showed that the Hadamard encoded CDMA system worked well with DMT-FEQ only when the transmission signal obeyed DMT-FEQ null-tone conditions in conjuction with a vector estimation method. Simulation results also showed that modifications to TDCS with a conjugate-symmetric phase component in conjunction with a modified spectral mask with consecutive null-tones and forced null-tones provided acceptable results when equalizing with DMT-FEQ.