Capital Radio 604 used to broadcast to listeners in South Africa from transmitters located in the Transkei.
The station actually operated on 603 kHz (and 585 kHz) medium wave, but promoted a frequency to which the jingles would rhyme.
Capital Radio 604 began transmitting on 26 December 1979 and was shut down in 1996.The station was an almost carbon copy of Capital Radio 194 (1548 kHz) in London. The Capital 194 logo was slightly modified by changing the bird to a seagull and obviously changing the number to 604.
An interesting archive web site http://www.capital604.com/ contains photographs, video, jingles and recent interviews with ex-604 personal.