Analog single-carrier transmission with frequency-domain equalization (called analog SC-FDE) was recently proposed in order to improve performance of analog signal transmission. Analog SC-FDE signal spectrum has a complex conjugate relation between lower sideband (LSB) and upper sideband (USB) since analog signal is real-valued. Exploiting this property, the received LSB and USB subcarriers can be combined to obtain an additional frequency diversity gain. In this paper, a subcarrier combining method is proposed to improve the performance of analog SC-FDE. A theoretical analysis of normalized mean square error (NMSE) performance is presented to evaluate the effect of subcarrier combining and is confirmed by computer simulation. It is shown that subcarrier combining improves effectively the NMSE performance in multipath fading channel.