SFN (Single Frequency Network) by using OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme is an essential technology for digital terrestrial broadcasting to ensure the effective use of frequencies. Field trials were conducted to investigate the transmission characteristics in SFN using two transmitters. This paper discusses the minimum usable field strength of DQPSK-OFDM and the coverage area of the transmitters in mobile reception, and the increase in area covered by SFN compared with by a conventional network. Additionally it is shown that the manmade noise deteriorates the BER performance of OFDM signals even in the UHF bands in urban area.