Optical emission spectroscopy (OES) was used to study plasmas generated by a novel plasma-enhanced linear antennas microwave chemical vapor deposition system for nanocrystalline diamond (NCD) growth in gas mixtures of H2 + CH4 + CO2. Atomic hydrogen intensities were investigated for pulsed plasmas and continuous wave (CW) mode plasmas. OES was used to study the effect of pressure (0.38–2 mbar), microwave pulse frequency (3.8–25 kHz), and total gas flow (125–1000 sccm). By using the Boltzmann plot for atomic hydrogen line intensities, plasma electron temperatures for pulsed and CW plasmas were calculated. During experiments, NCD films were deposited, which were investigated by secondary electron microscopy and Raman spectroscopy in terms of surface crystalline morphology and nondiamond carbon content. NCD films produced in high pulse frequency plasmas show low sp2 content (less than 5%) and homogenous crystalline structure with only a small amount of crystalline defects.