On Wednesday, June 14, 2017 at 2:20:49 PM UTC-4, Dan Marotta wrote:
Unfortunately, the lower receive-only antenna may have nothing to
receive if the upper transmit-receive antenna is blocked by the fuselage
and does not ping the approaching aircraft behind/below.

On 6/13/2017 6:34 PM, waremark wrote:
In my Arcus I have the receive and transmit aerial where fitted by the factory on top of the rear glare shield, and the receive only aerial on the belly in front of the main wheel.

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Dan, 5J

Hi Dan. The flarm doesn't work as an interrogator/response system like a transponder. From flarm.com : "Each FLARM system determines its position and altitude with a sensitive GPS receiver. Based on speed, acceleration, track, turn radius, wind, altitude, vertical speed, aircraft type, and other parameters, a precise projected flight path can be calculated. The flight path, together with additional information such as a unique identification number, is encoded before being broadcast over an encrypted radio channel twice per second."

So the lower antenna doesn't "ping" the other flarm - it receives the signal which is transmitted twice per second by any flarm within its view.

Another Dan