On Wednesday, November 16, 2016 at 9:03:00 PM UTC-5, wrote:
If the Flarm B antenna is "receive only" and same for the ADSB antenna, is there any issue mounting those two antennas next to each other, or very nearly so?

From the CORE manual -
5.3.8.2 ADS-B/SSR antenna (SMA connector, BLUE marking)
PowerFLARM Core ADS-B has one ADS-B/SSR receiver operating on 1090 MHz.
Ensure that the antenna cable is properly and fully screwed into the device. Never swap the FLARM and the ADS-B/SSR antennas. Use only little force when
inserting and tightening (1 Nm max).
This antenna should be placed at least 30cm/1 ft away from the FLARM antennas.
The FLARM antennas have priority over this antenna for best placement.

In addition, in 5.3.9 - GPS Antenna, at the end:

If more than one GPS antenna is present in the aircraft, it is recommended that
they are at least 30cm/1ft apart; the same holds for separation from all other
antennas connected to PowerFLARM Core.