My current 12" Longwave FSL antenna is a slightly more sensitive version of the 2015 model 12" Longwave FSL, the design photo for which is attached.
The ferrite rods, frame components and size of variable cap are all the same, although the 660/46 Litz wire has been replaced by 1162/46 Litz wire, which provided a sensitivity boost. Because the 1162/46 Litz wire has a larger diameter than 660/46 wire, though, I was not able to fit enough coil turns on the ferrite sleeve in order to get the start frequency down to 153 kHz. This didn't bother me, though, since the start frequency is now around 195 kHz, which is fine for chasing long range South Pacific and Asian NDB's during a DXpedition.
The variable cap has also been replaced with the razor-sharp tuning "384P" type from Oren Elliot Products, which improved the overall performance of all of the FSL antennas used during the recent Rockwork Cliff DXpedition. That type of variable cap is also now the tuner for the "Frequent Flyer" FSL antennas, three of which we plan to use this November in Poipu, Hawaii.
73, Gary DeBock (in Puyallup, WA, USA)