Explanation: VHF-DSC (Digital Selective Calling) utilizes time diversity to enhance reliability, particularly in the presence of fading or impulse noise. To achieve this, each 10-bit character within a DSC message is transmitted twice. The interval between the start of the first transmission of a character and the start of its retransmission (the second identical character) is precisely specified by the ITU-R M.493 standard as 33-1/3 milliseconds. This specific interval is chosen to be long enough for short-term channel impairments to decorrelate, improving the likelihood that at least one of the two transmissions is received correctly. This duration is also exactly four times the duration of a single 10-bit DSC character (4 * 8-1/3 ms = 33-1/3 ms). The other options do not correspond to this standardized time diversity interval for VHF-DSC.