thingy91 GPS matching network

[okw]

I am looking at the GPS matching network from Nordic thingy91 (development kit based on nRF9160).
What function does L4/C87 have? And do they only have purpose when used with external active antenna (C13 not assembled)? I.e. if external isn't needed, L4/C87 can also be eliminated from the design?
How would I calculate their values?

If this same circuit was to be used, but redrawn without external antenna (remove parts J2/L3/L4/C11/C87). Would I replace the DC block C12/C13 with one 20pF, 39pF or even 82pF? Or does two identical (or differently sized) capacitors block wider/better? Like decading the bypass capacitor values to spread out the noise suppression frequencies.

Is is common practice to use capacitor C13 like this, to disconnect the radio from the on-board antenna like this, instead of a 0R resistor?

[nali]

Have you looked at Nordic's Infocenter? Their example shows the LNA directly connected to the GPS pin

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fnwp_033%2FWP%2Fnwp_033%2Fnwp_033_gps_lna_ex.html&anchor=nwp_033_gps_lna_ex__fig_jtl_sgx_43b



The whole bias network on the thingy seems just to allow an active antenna on J2 as it's fed 3v3 via L3.

[okw]

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.

[nali]

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?

To be fair you asked several questions... My guess about L4/C87 maybe a 2.4G notch filter? Without values it's just a guess.