I have recently been pushing the limits of the XBee Pro to see how far it can go.
Unfortunately my current plane (SkyFun) only has a 38 minute duration and a maximum travel distance of 20km, this means the furtherst I have been able to go is 10Km (a 20Km return trip).
I have a 14dB patch antenna which has still shown signal of 85%+ out at this distance.

I wanted to find out how far the XBee could really go.
This meant planning a one way mission.

I spent about a week looking for the perfect start and destination, plotting the course and arranging access to the landing location with a local farmer.

The start point was my normal local park and the landing location was a farm paddock 16Km away.
The flight was over sparsely populated farm land and at a constant incline meaning I could increase altitude during the flight in order to get greater range.

My plan was to launch and monitor the flight from the launch location until I lost contact with the plane via Telemetry. After this I would drive to the landing location where the plane would be circling and manually land.

I calculated that even if I maintained contact with my plane during the flight and it made it all the way that I would still have time to make the 12 minute drive without running out of battery power.
With a tail wind, the plane would average 60Km/h at 45% throttle.

With everything planned and 45 test flights already in the bag with this airframe I was ready.

I launched and the plane took off to the waypoint as planned.
I was hoping for at least 12Km as this was ideal conditions.
The point on the map above shows the point I lost contact which is 10.6Km from the launch location.
The XBee maintained a very strong signal up until the last Km and then it began to drop off very rapidly.
It begins to be unusable below about 40%.

I packed up the ground station and drove to the destination which took just 11 minutes.
The plane was circling perfectly as expected and I put it in FBWA and landed without incident (apart from the slightly startled flock of sheep).

It turns out that the 10Km I had been flying to is around the maximum range of an XBee.

I am working on a much bigger aircraft that will have a 1 hour plus duration at a higher speed so I am going to have to look into more long range options for telemetry. GPRS / cell is preferable as we have excellent coverage here and fully routable and cheap internet plans. However, for experimentation I have been surprised at the distances that can be achieved with an XBee with a cheap patch antenna added on.

Here are a couple of tips for people wanting to achieve maximum range..

 - Minimize antenna cable length. My XBee is mounted on the back of my patch antenna and I run a long USB to my laptop. This maximizes gain and reduces lost signal.
 - I use either the ground or my car to enhance the ground plane effect. Putting the antenna in front of my car door or right beside my car makes a big difference to the distance. Also keeping it as close to the ground as possible.
 - Altitude is king, the higher you can fly the greater the achievable distance. Due to the fact my destination was on an incline, my end waypoint was 400m high relative to my starting point.
- Fly long straight missions so you can line up your antenna properly, I am building an antenna tracker that removes the need for this but Ardustation2 is currently broken since the last Mavlink updates.

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  • Heheh, you right. But the power drain is still exists... I think it's need more energy than xbee modules...

  • Best result has been 30cm off the ground.
    As close to my car door as I could possibly get around 4cm from the panel.

    Janos, no not free but relatively inexpensive on a prepay plan.
  • By the way, has anyone found a decently priced 900MHz booster out there?

  • Toby, how close to your car door and to the ground are you talking about?

    If close to the ground, I imagine the antenna would have to be pointed at a decent up angle compared to ground in order not to have the ground interfere with the Fresnel zone, right?


  • Hmm. But GPRS communication is not free, and drain the battery. No?

  • 900RF
    I believe they are around 65mW.
    Data rate 57600 bps until dropout at about 40% signal strength.
    Got some updates on the steen down to about 25% but at a much reduced frequency.
    I consider dropout the point where it becomes flakey and I could not reliably send instructions to the plane so around 40%.

    Maybe GPRS is an option for you (droncell). I'd still like to see this as a long range telemetry option.
  • Great test!

    I have some question:

    • it's XBee-Pro 900 RF?
    • workink power (50mW?)
    • the data transfer rate is almost constant before you lost the signal? If no, can you create a test? (distance vs power maybe...)
    • It's power from the main power? not drain too much?

    I'm try to find a long range xbee, but in EU the 900Mhz freq. is reserved. (The XBee 868 is long range but it's max data rate is only 24Kbps (and limited to 10% duty cycle).


    (sry, english is not my native language)


  • 3300 3S
  • Moderator

    what battery r u using on ur skyfun?

  • Plane was 300m above my altitude when I lost contact zo well above the horizon.
    I could go higher but its well out of site and I might start tangling with other air traffic. I think this establishes the maximum practical range.

    Im running the latest arduplane code, I compiled the ardustation with the older arducopter mavlink libraries but no joy. I assumed it was a mavlink incompatibility.
    I only want antenna tracking really, the get and set features of the ardustation are not required as I always take a laptop.
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