What does the diversity antenna do?

[CyNiC]

Ive searched all over the forums and seen this antenna referenced many times and many people ask this question but never get an answer.
I just noticed that i dont think mine has been plugged in for nearly a year and I have not noticed any difference.
Any insight would be great.
Thanks,
Jerry

[AudiA4b6US]

Your car has up to 4 FM antennas and the diversity module switches between those antennas based on a signal it receives from the head unit. The HF signal is the main antenna signal coming from the diversity module going to the head unit, the ZF signal is the diversity signal coming from the head unit going to the diversity module. If the ZF wire is not connected you may not always get the best FM signal, that's all.

[CyNiC]

gotcha. thanks.
and thanks for all ur help today. how do u know so much about these nav units.