IIRC (I have a Polo '01 and I think it uses the same antenna) the
antenna is a powered one which needs (well, I use a JVC head for tapes
and radio, and it seems to get the stations around here well enough
without it) a special adapter that feeds power to the antenna.

Not that I listen very much to the radio... (think it was three
months ago, last time :-)

Also, beware of VW's habit of swithing pin 4 & 7 in the ISO connector
(constant and keyed +12V)

/Michael