The whole bias network on the thingy seems just to allow an active antenna on J2 as it's fed 3v3 via L3.
Yes, I've read most of the references.
It's not really what I asked. I asked what is the purpose of L4/C87?
I have two different designs, one with onboard antenna, much like the Nordic schematics, and another with only external active antenna.
The Nordic DK has very poor GPS reception. I've compared it side to side with my own PCB, and mine gets fix after 23-25 sec (cold start), while the DK really struggles, if it even gets fix.
PS. Title was misleading. It first said thingy91, but the attached schematics it in fact nRF9160DK.