If a DAC with a clock rate fc generates a signal with a frequency fc/3, the image will be at the frequency 2fc/3 and the anti-image filter must have a very sharp cut-off, making it complex and expensive, and also involving excessive phase-shifts. The obvious solution is to use a higher clock frequency Kfc. K does not need to be very large - values of 2, 4 or 8 are more than enough in most very high frequency (VHF) applications. But the major problem with a higher clock frequency is that data must be sent to the DAC at the new higher rate, which may put unacceptable demands on the system processor.