Shark Fin Antenna
All,
It is my understanding that all of the MK5 "Shark Fin" antennas are for the Sat and AM/FM. On the cars that there is no Sat Radio, then they use the Rear Window antenna only. The radios are set up for a diversity antenna arrangement. What this means is that the radio can choose which signal is the strongest and the best based on the situation that the car is in. it does this automatically. There is also a signal filter and amplifier that is mounted in the rear headliner on the MK5 cars with the ”Shark Fin” antenna and this boasts the signal. The boasting of the signal is due to the short length of the antenna. The OEM “Fuba” style antenna has the boaster built into the bottom of the antenna and boasts the signal and makes the antenna appear longer than it actually is and this allows the better reception for both AM and FM signals. The MK5 antenna has this, but it is located in a different place (under the headliner) and this is the reason for your poor reception. If you were to purchase the correct items and add them to the antenna circuit ,then your issues would more than likely go away. Now interestingly enough, if you want satellite radio, this is a good antenna to have since the satellite antenna is built into this version. It would provide a very clean installation and look good too. I did a similar installation with the VW triplex antenna. I took the GPS antenna out and replaced it with an XM antenna for satellite radio reception. I also wanted the AM/FM and Cellular antenna and this was the easiest way to obtain it. I hope that this helps understand the principle of the antennas and that you sometimes cannot just replace them and expect everything to be just fine in terms of the reception and application.
Thanks,
Greg