The APF button enables diversity mode on the PCR2500 receiver and selects the best antenna for the frequency. Antenna 1 are a Diamond F23 and antenna 2 are a Diamond X510. Diversity only works in FM and NFM mode and other modes will only use antenna 1.
I sometimes alternate between antennas with a TV antenna 80-700MHz AV-860B and a Diamond F23 VHF @155MHz and a Diamond X510 dualband 144/433MHz modified for scanner use and also a 13dBi 420-460MHz InnovAntennas 17-element yagi. If directional the antennas point west into Stockholm city.
My antennas have amplifiers and splitters to support other scanners. I sometimes have a FM trapfilter inline that makes FM broadcast more difficult to monitor, but almost all of them are broadcasting on the internet.
https://streema.com/radios/Stockholm
The antennas are at 25 meters above sea level in a valley surrounded by 50 meter high hills so it is a terrible qth for monitoring the radio waves.
The frequency list for my area are at
https://www.frekvenslista.se/lista.php?city=®ion=1&Submit=Uppdatera