XBee with 80km range?

[Hein du Plessis]

Hi all

A friend of mine, an electrical engineer, referred me to this product:

http://www.digi.com/products/wireless-wired-embedded-solutions/zigb...

It's a XBee Pro on 868mhz, with a high power output capable of reaching 80km LoS.

Are these modules interchangeable, should I be able to follow the same configuration procedure as with the classing Xbee Pro 900mhz?

Who needs 3G :)

[Gary Mortimer]

Yes point to point but not on a UAS its like pointing a pencil at the target at range, best I can manage with 50mw and correct antennas is 8km.

If you want to go further make the frequency lower and keep an eye on the WRC meetings. They will rule soon on what frequencies are permitted for UAS worldwide.

[Hein du Plessis]

Hi Gary

From what I understand, the above module is 300mW, which should give you 24km without using a high gain. Do you think it can easily be implemented?

Regards,

Hein

[Mike Pursifull]

like http://fjallfoss.fcc.gov/ecfs/document/view?id=7020919969

[Hein du Plessis]

Sorry I don't follow :)

[Mike Pursifull]

While you might be able to adapt and modify the systems to use this Xbee module, it is not a simple drop-in replacement.

XBee Pro 900 supports 156kbps (according to the docs, but we configure for less; 56Kbps on the Serial side, and your bandwidth achieved depends on many factors; I find 48Kbps a pretty solid link, when I can get it) RF

XBee Pro 868 supports 24Kbps RF and is limited to 10% duty cycle

In practice, my use of Xbee for APM telemetry suggests that you need more bandwidth than 24Kbps typically around 38Kbps

[Mike Pursifull]

But ask or read in forum Wireless. You might get more information. 

[Hein du Plessis]

Ah I see, thank you.

Still, 50mW seems very underpowered, is there any version out there that keeps everything the same, except run at 500mW etc?

I'm involved with the FPV community and a 1 Watt transmitter is quite common. Antenna trackers are also cheap off-the shelf. Can't we build on that technology? Sorry I'm mentally challenged when it comes to RS232...

[DaveyWaveyBunsenBurner]

Hein,

Xbee 868s have been covered to death on this site. Search is in the top right corner :)

1. 1watt is illegal in just about everywhere I can think of.
2. Legally you can only transmit for 6 mins per hour on 868.

Without breaking the law either on power or duty cycle, 868s are usless.

[Mike Pursifull]

Hein,

Part of what you are running into is regulatory, part is product market. 

See http://www.digi.com/pdf/chart_xbee_rf_features.pdf

I think you might find that the "best" module fit, that is, the longest range with sufficient bandwidth, is not for EU. That is not a technical issue, it is regulatory and market driven. And even the "best" module will not give you (reliable) communication in the 80Km range, even with some great directional antennas. But under the right conditions, you can get some very surprising ranges, if you have line of sight and good antennas. There are some blogs and discussions here on the site listing tests folks have performed, double digit distances....

[Mike Pursifull]

For examples, see 

http://diydrones.com/profiles/blogs/what-is-the-maximum-range-of-an...

http://diydrones.com/forum/topics/xbee-pro-900-range

Unfortunately, these are both for 900Mhz, but they are good examples of the discussions and blogs you should be reading :)

[Hein du Plessis]

Thanks Mike I've seen those posts, studied them in detail.

[Mike Pursifull]

re: 1watt being illegal - I regularly transmit at a great deal more than 1watt. But then I am an amateur radio guy. I have not combined much of my UAV and HAM hobbies, but I expect to do so in the future, following all the rules, of course. I would encourage any UAV/UAS persons interested in exploring radio in more depth to get their HAM license and spend time talking to other HAM radio folks. There is a wealth of engineering experience in that community...