Sunday, April 5, 2009

Long Range XBee PRO

Digi recently released a new series of XBee wireless long range transmitters which I have been very excited to play with. The XBee-PRO 900 series has up to a 6 mile range using a high gain antenna! Some other features from the XBee site:
  • Fast 156 Kbps RF data rate
  • Point-to-multipoint networking ideal for low-latency applications
  • Support for large, dense networks
  • 128-bit AES encryption
Jim cam over this past weekend to help me perform some basic ranging tests with these modules to see what type of distance can be achieved in an urban area. The plan was to set up a base station and send messages out to a mobile XBee PRO as a repeater and see how far away we can get without dropping any packets.

The base station is simply an XBee PRO linked to my bench machine through it's serial port via a MAX232.

The mobile module is simply an XBee PRO with it's TX and RX lines wired together forming a basic echo repeater. Lithium polymer batteries are being used through a 3.3v regulator. This is simply in basic mode as well, no API mode.

Using Digis' useful X-CTU application for range testing, we were able to get some impressive results. We were not able to get anywhere near a 6 mile range, but with the fact that we were using only the on board whip antenna on these modules instead of a high gain antenna, it was expected. Our testing environment significantly limited the range as well because of the amount of concrete structures in the area. With all of this we were still able to reach a range of several thousand feet before packet loss. A standard XBee would never reach this range.

Range was very limited to line-of-sight. If there was a building in between the source XBee and repeater XBee, packet loss would occur in a very predictable manner. This was all happening from the source transmitter being on my bench inside my home, so there was already an initial structure blocking it's signal path.

Our next tests will occur in a more open area which will allow more line-of-sight testing. I am confident that we will reach several miles in this scenario and will report our findings.

1 comment:

  1. We only got 800m on the 2.4GHz version: substantially less then the 1.5 miles claimed; And that was a pure open area site. To get full range, I think it would have to be raised several metres from the ground.