SC-FDE (Single-Carrier with Frequency-Domain Equalization) block transmission technique can have excellent performance in severely time-dispersive channels provided that accurate channel estimates are available at the receiver. In this paper we consider joint detection and channel estimation for SC-FDE schemes where a coarse channel estimate is obtained with the help of a training sequence and we employ iterative receivers where for each iteration the data estimates are used to improve the channel estimates. However, since the frequency-domain data blocks can have large envelope fluctuations, a decision-directed channel estimation might have significant noise enhancement effects. To overcome this problem, we combine channel estimates based on the training sequence with decision-directed channel estimates. Our performance results show that these techniques allow good performances without requiring high-power pilots or training blocks.