We're using an LMX2531 to transmit a 2.4 GHz carrier over a distance of 5 feet and measuring phase shift of the carrier as the LMX2531 is moved. The PLL is driven by an always-on 20 MHz TCXO. If the PLL is re-locked for any reason, we need the phase value to be the same when it re-locks. As long as the R divider is set to 1 (PD freq = 20 MHz) and the RF N divider is set to an integer value, this works as expected. However, if the R divider is set to anything other than 1 (and the N counter is re-adjusted appropriately) the phase value comes up with different, arbitrary values. Also, if the N counter is set to a non-integer value, the same problem occurs. Is this because the R frequency counters and fractional-N counters are not triggering from the same stage or some other phenomenon? Is there some way to get around it?
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