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Antenna diversity on MKW21D512

Question asked by Lix N. Paulian on Mar 12, 2015
Latest reply on Apr 8, 2015 by Lix N. Paulian



We are trying to activate the antenna diversity feature (FAD) on a radio we designed with the MKW21D512 (we use the Skyworks SE2436L Front End that includes also the antenna switch). Problem is, it doesn't operate properly: the antenna switch shows as it would "hunt" for a preamble all the time, even then when a frame is received. It switches back and forth with the specified 28us interval, but never decides to stop on a specific antenna (the better one). We've done a setup where one of the antenna input delivers a better signals than the other, but due to this permanent switching, the resulting LQI is jumpy.


There is unfortunately no application note from Freescale showing how are the involved registers to be set. There is also at least one undocumented register, FAD_THR (0x50, probably FAD threshold), but there is no reference to what this register is supposed to do. In our application we activated FAD by setting bit 0 in the ANT_AGC_CTRL register (0x51). We played around with the FAD_THR, and it clearly makes a difference, but we couldn't see that the FAD feature works. Is it anything else required to do?


After googling the Internet on this issue and finding almost nothing (there is only this post on this forum: KW24D512 antenna diversity which doesn't say anything about the register configuration; and the APIs referenced in the post are nowhere to find!), we start to believe that this feature simply doesn't work (silicon bug?). Did anyone managed to use the Fast Antenna Diversity feature on these chips?