Hello,
I am working on a UAV project, and was wondering which wireless system to use. It will mainly be used to transmit data, but I need it to be able to switch into direct flight control for emergencies.
The modem modules look really appealing.
What bps should I look for?
Are you in the US and thus under FCC rules?
As to speed/bps - you need to determine data volume and bursty-ness. And if you need two-way medium, and what extent of error detection and correction is needed. And what line of sight and/or non-line-of-sight conditions will exist.
I’ll take a guess - You’re in No. America, need reliable two-way with error correction, modest data volume, and at least a mile’s range line of sight.
A good choice, IMO, would be the unlicensed 902-928MHz band, in preference to 2.4GHz.
Thus
http://www.sparkfun.com/commerce/produc … ts_id=9087
A strategy for sleeping for battery life preservation may be needed, or perhaps not, if the UAV has a hefty battery.
I am in the US, the same state as sparkfun (colorado)
That module actually does look great, but I need to see if its worth the cost.
How do I connect one to a computer? Do I have to get the explorer module?
How does 433MHz fall under FCC?
As to cost, if you want a mile or more range, reliably, with the UAV end having a small/low gain antenna, then it isn't going to be a $10 item.rp181:
I am in the US, the same state as sparkfun (colorado)That module actually does look great, but I need to see if its worth the cost.
How do I connect one to a computer? Do I have to get the explorer module?
How does 433MHz fall under FCC?[/quote]
The XBee can connect to a computer via (1) serial RS232 or (2) USB. There are many boards available that accept a plug-in XBee and produce RS232 or USB. SFE sells some of these but not all.
433MHz is legal for FCC but it’s applicable to your UAV project only if you have a a tiny few bytes to send infrequently. So it depends on your needs. Most 300/400MHz RF modules have little or no air link protocol and you have to do a lot of low level coding yourself. The XBee and Jennic and other 802.15.4 modules take care of all of this for you.
Ok, 2 more questions:
Does the XBee the type that provides the same output as input on another module without any coding? Eg. data in module 1 Tx, same data comes out other module Rx.
I dont need 15 mile range, would this work well? http://www.sparkfun.com/commerce/produc … ts_id=9099
thanks!
Yes.
I dont need 15 mile range, would this work well? http://www.sparkfun.com/commerce/produc … ts_id=9099
thanks!
I just realized a Ethernet bridge could be used as the board has Ethernet compatibility. Can anyone suggest a bridge? All the ones I find or either for in home use and 40 mile+ tower mounted ones.
The 50mW radiosI dont need 15 mile range, would this work well? http://www.sparkfun.com/commerce/produc … ts_id=9099
thanks!
http://www.sparkfun.com/commerce/produc … ts_id=9099
will probably work. Depends on antennas and your expectations.
A little simple math will let you predict the line of sight range you can expect.
A learning experience.
Would you like to crunch the numbers? If so, I’ll guide you.
Sure, Thanks.
The platform is large enough to allow me to use this antenna:
http://www.sparkfun.com/commerce/produc … ts_id=9143
I can use the same antenna at the ground station.
Never done anything with radio before, just a warning 
~Rp181
what range to you need?rp181:
Sure, Thanks.The platform is large enough to allow me to use this antenna:
http://www.sparkfun.com/commerce/produc … ts_id=9143
I can use the same antenna at the ground station.
Never done anything with radio before, just a warning
~Rp181
Let’s do a line of sight RF link budget. In doing this, you state the transmitter power and receiver sensitivity which are product specific. Then give the frequency (within a few MHz) and the antenna gain and losses due to coax cables/connectors. The rest is laws of physics, for the range/distance from transmitter to receiver.
Go to this web site to just plug in numbers and let a spreadsheet do the simple math…
http://www.afar.net/rf-link-budget-calculator/
Some input numbers
Mode: fade margin
freq: 900MHz
antenna gain, both ends: 0dBi (rubber ducky at 900MHz might even be -3dBi or so)
coax/cable losses: 0
transmitter power: 17dBm (equiv. to 50mWatt)
receiver sensitivity: -100dBm or so
You choose range (line of sight). If non-line-of-sight, here’s where experience and intuition comes in to play.
You want 10dB of fade margin or more. The more the better!
Try it for 900MHz, 50mW and for 2400MHz with 2Mw (XBee 2.4GHz) and 50mW (XBee Pro 2.4GHz). For 2.4GHz, change receiver sensitivity to -90dBm because of the wider channel used; higher speed too.
Watts to dBm converter