On Tuesday, September 30, 2014 8:28:46 PM UTC+1, wrote:
Having done extensive testing with both 'A' and 'B' antennas of various types in various locations and combinations I have come to the conclusion that the 'B' antenna is mostly for extending range at the limit. Very few gliders have blind spots that are so directional that a 'B' antenna will add materially to collision avoidance functionality. To the extent that they do have very specific blinds spots it is likely due to poor placement of the 'A' antenna and/or RFI in the cockpit which can be remedied without a 'B' antenna.

Can't argue with practical testing, but I can't reach the same conclusion. If there are attenuating items in the aircraft, a single antenna must have diminished performance in their direction, just as individuals lit by a single candle in the middle of a room must throw a shadow. Moving the antenna away from the attenuating items may reduce the areas affected, but there will still be specific areas of reduced performance. A second antenna should bring the coverage closer to the ideal.

As for the significance of attenuated areas / blind spots: I think I recall FLARM using the example of the steady-state collision course scenario where both aircraft maintain constant heading, speed and climb rate. In this situation there is effectively no movement of the conflicting aircraft against the background, so it's difficult to spot the conflicting traffic visually. Since the relative bearing to the conflicting aircraft will be nearly constant in this scenario, even a narrow area of attenuation can be potentially significant if it happens to lie in the right (wrong?) direction.

I conclude the 'B' antenna is mostly for pilots who want the absolute maximum range limit for better tactical situational awareness in contests or buddy flying.

I don't see how the configuration suggested in the manual would provide extra range, and I haven't seen high-gain directional antennas being marketed by FLARM or its suppliers. I have to conclude the B antenna function is intended to cover blind spots, as the documentation suggests.

As to pricing models - it's a software world where much, most, or even all of the value of products is attributable to the intellectual property that goes into a product (embodied in software), rather than means of delivering that intellectual property - including the hardware. You should expect that pricing will increasingly be based on customer value, rather than COGS (Cost of Goods Sold). Deleting ADS-B, PCAS, the 'B' antenna and other features are what allowed Flarm to dramatically reduce the price to reach new customers who don't value the full-featured version to the tune of $1500. Price elasticity of demand and market segmentation, pure and simple.

I understand the rationale behind making various features on the Core Plus chargeable, and I have no objection to the other features which have only secondary relevance to electronic conspicuity. I still find it difficult to understand why the capability of increased antenna coverage has apparently been categorised as an additional, chargeable 'feature', discouraging users from fitting a second antenna.