I’ve got a pair of Xbee Pro XCS modules that I’m trying to use for long-range data communication. One is attached to a Win7 PC, and the other is mobile (inside a car) on an Arduino Uno with an Xbee shield. I’ve done a lot of tweaking (especially on the Sparkfun Xbee shield) and successfully tested them and get a range of about 1.25 miles (semi-obstructed) which I am very happy with.
However, lately, I’ve been seeing max ranges of only a few hundred feet. When I take a closer look to debug the issue, the range goes back up to the expected distance. I’ve been thinking that it might be a power-save mode on the PC, so I’ve been fiddling with all the power settings I can find (Using High Performance Power setting, with no hybrid or normal sleep modes active, unchecked the box on the Device Manger USB devices entries to prevent them from sleeping, I’ve adjusted the BIOS to disable sleep modes, etc.). Nothing seems to work. I’ve also checked the Xbees and confrmed that the SM (Sleep Mode) function is disabled.
I know the weather can have an impact on range, but during last few days, we’ve had consistently good weather. I also know that other RF interference can have an impact on range, and I don’t have the equipment to determine what, if any, interference exists.
Any thoughts about why the Xbee range would be so inconsistent? Thanks in advance.
915 MHz band isn’t affected by weather.
The cause would seem to me to be changes in the antenna orientation, changing obstructions in the path, change of path length, or interference.
Since you’ve disabled sleeping, the following might not apply, but…
Sleep mode can cause problems in time-synchronized rendezvous. This means that the sender and receiver have to have some way to agree when to be powered-up / awake at the same instant. In practice, the receiver wakes up just before a time window when the sender might send. A time-slot if you will. The two nodes have to synchronize their timers now and then to avoid drifting time windows.
I don’t recall about the XSC, but in No. America, many 900MHz ISM band devices either (a) must limit transmissions to a low duty cycle, or (b) must use frequency hopping to reduce interference to other systems. This can complicate things, since the hopping sequences have to be kept in time synch and channel # synch (hopping sequence).
I just wanted to thank stevech for the response - lots of great ideas that sent me in all kinds of good directions. I certainly learned a lot!
I did discover the root cause of my issue (in case anyone else has a similar issue) - it was my Anti-Virus software performing real-time scans that was slowing my machine and ultimately impacting the responsiveness of the Xbee. Once I disabled real-time scans, I got consistently good performance. Certainly not ideal to keep the Anti-Virus disabled, so I’ll have to strongly consider the security/performance trade-off.