Looking at the BOM for the Core and the BOM for the Photon, I noticed that both of them use different chip antennas. Both are the same size, and both have 50Ω impedance. But the gain on both are somewhat different:
The Core uses a Johanson 2500AT44M0400E (Mouser #609-2500AT44M0400E). Peak gain is specified at 2.5dBi, average gain of -0.5dBi.
The Photon uses a Johanson 2450AT43B100E (Mouser #609-2450AT43B100E). Peak gain is specified at 1.3dBi; average gain of -0.5dBi.
Searching for the Asia part numbers, I turned up ANT8010LL04R2400A (Mouser #603-ANT8010LL04R2400). Peak gain specified at 5.36dBi.
I’m no RF engineer, but I can’t help wondering: Is a higher peak gain number better for sensitivity and transmit range?