Unexpected power consumption


I have been attempting to diagnose a problem were XBee end devices are occassionally leaving and rejoining the network for no apparent reason.

To that end, I have been looking at the power consumption (supply current) of several XBeePROs using a CRO (using a 1 ohm resistor on the unregulated side of the power supply).

What I have observed is that the RPSMA (XBP24-Z7SIT-004) version is drawing around 270mA during transmission (expected), while the UFL (XBP24-Z7UIT-004) version is only drawing about 110mA (very low). In both cases the receive current is the same, at around 45mA. I assume the reuced power consumption translates to reduced range. Can anyone explain this behavior?

I have tried the following:

  • only 2x64 firmware
  • several units of each type , with dates ranging from 2008-2010
  • router and end device firmware
  • factory settings
  • digi RS232 interface board (to eliminate my hardware)
  • same RPSMA antenna (the UFL uses a short adapter cable)
  • no antenna at all

I thought perhaps the UFL device was lowering power output due to the coordinator being in easy reach. But even with no coordinator, the PAN scan still operates with reduced power.

Any ideas would be appreciated.


Hi again,

Further to my previous post, I have realised that the RPSMA units are actually XBP24-BSIT-004 (not Z7SIT). I have been able to compare a Z7UIT with a BUIT (both UFL) and they exhibit this power consumption disparity.

So it appears that the newer Z7xxx modules are amazingly more efficient than the older Bxxx hardware. This seems rather unlikely, and contradicts the datasheet which indicates 205mA. So I’m observing around 90mA lower than expected.

I assume the XBeePRO has automatic/dynamic transmit power control (there is no manual control). So this could account for it. But why then wouldn’t the device transmit at full power when searching for a PAN (and failing)?