Weak DigiMesh connections only go one way?

Question

Hi,

I have a network of XBee-PRO 900HP S3B modules with DigiMesh 200Kbps firmware ver. 8074. For part of this network, I have a module seated in a tree (u.FL version connected to a dipole antenna) that communicates with a module seated on the side of a railway track (wire antenna) a hundred metres away. For the past few weeks, these radios have been communicating without issue---when I examine the network using XCTU's network working mode, strong or moderate two-way connections are consistently established between these two radios. I have removed and replaced the radios for battery changes, and the connections remained as strong before.

Recently, I removed the modules again to change batteries and replaced the modules in the same positions and orientations as before. However, XCTU's network working mode showed that only one-way connections could be established: The radio on the railway track reported a -83 dBm connection to the radio in the tree, but even after several scans, the radio in the tree reported only "?" for its connection with the radio on the track. Confirming this behaviour, a broadcast transmitted from the tree radio was not received by the track radio.

What does it mean when one radio can "see" another, but that other cannot "see" the first? And why might the connectivity of the radios change, even though I placed them back in the same locations with the same orientations?

Any ideas or suggestions would be appreciated.

Thank you,

Jon

Answer 1

Sounds like the power level was reduced on one of them. You may need to query the PL command to make sure it is correct. You may also need to replace the antenna depending on what kind of connection it is using (RPSMA and U.FL are NOT out door rated connections.)

Comments

Hi mvut,

Thanks very much for your response. I was able to check PL and it is set to 4 (Highest) on all of my radios.

The radios with u.FL connections are using the 6" Digi-branded u.FL to RP-SMA adapters. The radio and adapter are enclosed in a weather-proof plastic tube, with the RP-SMA connector poking out of the enclosure and attached to the Digi-branded 900 MHz dipole antenna. I recognize this is a vulnerable point, so I made sure to wrap the connection in self-sealing tape. This doesn't make it water-proof, perhaps, but it's been pretty cold and dry here all winter. (Temperature swings anywhere between -35 C and +5 C.)

Are you thinking that just exposure to temperature swings or occasional moisture could degrade the antenna performance, even though it still seems to work when tested?

Any other possible reasons for these one-way connections?

Thank you very much again---I really appreciate your insight.

Jon

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Jon,

The plastic antennas that Digi offers are only rated down to about -20c if that. You really need to use an outdoor rated product for that kind of environment.