I was really surprised to see this in the PowerFLARM Core manual:

'CORE has two separate FLARM radio transceivers FLARM A and FLARM B. FLARM A is used to receive and transmit and must always be connected to an antenna. FLARM B is only used to receive, an optional antenna may be used for better reception performance. Usage of FLARM B requires purchase of the respective feature licence.'

Feature licence? Turns out it's a 44EUR charge http://www.air-avionics.com/support/...rflarm_lic.pdf to enable this feature. My understanding is that this fee is just a software activation; the hardware (antenna and cables) seems to be extra.

Later in the manual:

'The primary antenna (FLARM A) should have good view into the direction of flight. FLARM B (if used) should be placed to complement the field of view of FLARM A.'

... So, if you're following the recommended install, the secondary FLARM B antenna should be configured solely to reduce your radio reception blind spot.