Nanocrystalline diamond films have been prepared using a novel magnetically enhanced radio frequency assisted plasma chemical vapor deposition source. Such films show field emission at applied fields below 10 V/mu m(-1). Similar results are obtained using methane-hydrogen and methane-nitrogen gas mixtures, suggesting that the nitrogen promoted enhancement in field emission that has been observed in high quality diamond films does not occur for nanocrystalline layers. The design of the source used is easily scaled up for large area deposition, suggesting this could be a useful approach for the preparation of nanocrystalline diamond films for practical field emission purposes.