View Full Version : Wireless transmisson over a wide area

01-01-2006, 02:47 PM
Hi people I want to control an UAV from a remote control station, for that I need a setup which can transmit data with very wide range like half kilometer or more.

Can anyone suggest me some method of making a compact wireless Tx-Rx for this purpose.

I need nice Bandwidth too, but initially lesser bandwidths will do too.

01-02-2006, 04:10 AM
Try Zigbee Modules from maxstream.net

They cost 1000-1500Rs each ,good enough for your range and if your projects funded

The pro modules have a range of 1mile( 1.6Km)...where as the cheaper module has a range of 300m

01-03-2006, 06:13 AM
Hi folks,
ISM modules may not be suitable for UAV appln. Though they are excellent in their performance, the freq range is not.
802.11 wlan and GSM freq are good for static applications. Besides, finding a clear freq for UAV control/data is virtually impossible on these widely used( and misused!!) bands.
Also they are too damn 'line of sight' for a moving receiver.
Any Flight control tx/rx combo would fare better in the lower freq, preferably HF.
A reliable 1km Tx will be
500mw @800mhz.
200mw @ 2.5Ghz
2W @ HF 27Mhz
5W <27mhz
These are pretty hefty transmitters!
To eliminate line of sight blind spots, Doppler shifts and Cross polarisation effects, the effective lo power land to air frq of operation should be below 70Mhz. The Bandwiths are narrow and data reliability will be 1:16 (minimum). This is enough time to crash the UAV.

I would suggest using Futaba et al RC remotes: those may guarantee safe 'flying'....to some extent.
Radios for better performance cost Ks of dollars and are not permitted to be imported by individuals.

01-07-2006, 05:47 PM
If i want to replace the remote controller by a Computer or a uC then tell me something which I can use ?

01-08-2006, 01:32 AM
hi Devpriya,
--before you read, THIS is NOT to discourage you or uthers--
Replacing the remote control is easy.
The communication is not.
A Flying machine works via wireless signals that control servo motors or actuators. These 'end controls' or elctro-mecxhanical switches will move the rudder, alerons etc of the plane for flight etc., This is done by a Micro at the remote controller and another at the receiver on-board the plane.
There are many types of signals that do this for Proportional and/or positional control.: PCM- Pulse Code Modulation, PPM-Pulse Position Modulation, PWM (You know this!) etc.
Servos can accurately position mechanical parts and hold position till changed. Actuators are just 'Relay Levers" that go back to a neutral position- no proportional control.
All this is Software and DIGITAL; can be easily fine-tuned/ debugged.
Now These control signals have to reach the receiver, which is up above somewhere and moving around. This means Wireless signals.
...And this, is the problem!
Why? Because it is a blind science- you cannot 'see' the signals without very expensive 'eyes'. It does all kinds of things without your knowledge.
Understanding this is not everybody's piece of cake. There are plenty of wireless (RF) signals all around Mane made, sun made, machine made, atmosphere, water........
These will try to take control of YOUR signals, modify them, interefere with and generally create havoc. This will lead to either erratic behaviour or utter failure- the plane will simply DIVE to destruction.
The solution is eleborate SW and design techniques to minimise them. One of this is Failure Control, Auto-Pilot, Failure algorithms etc.,
Most R/C remotes have this built in and can be user Programmed. (via PC)
RF transmitters are power devices drawing substantial current. This is the enemy No. ! : heat.
Fading of signals due to movement especially Fast movement: doppler effect.
Loss of signal + loss of Control.....and loss of the AUV! Crash recovery( autonomous) will be at the receiver, but then result in an unreliable behaviour and unsuccessful mission.
An airplane flies with the most delicate balance of various forces. Any instantaneous change will upset this balance, irreversibly. Every thing happens very fast. So any 1 in 8 reads, 1 in 16 reads for data integrity will be too late.
I suggested futaba because they have spent millions and years on research. They still fail, on occasion, to bring back the plane safely home.
Buit they're the best bet, and bring MOST of the planes safely home.
Thats why they are EXPENSIVE! 12k for an 8ch proportional control.
The servos( which some people gleefully "spoil" to use it just as a motor) are also expensive because of there rugged, quality and precision.
This are my views through my own experience (and losses!).
Murphy's Law: if anything can fail, it will.
When NASA can fail.....
Dev let me know what you have in mind and we'll see what can be done.
A Computer? You can't. It generates all kinds of junk signals from DC to infinity. It will crash the plane, 100 %.
Micro? I said easy. Software? Also easy. Transmitter? Well, Why are there plenty of receiver makers and very few transmitter manufacturers??

( I know, Too long and should be an article, not a reply. But I want no misconceptions about discouraging. This is the challenge one should take. Success will be Expensive but the achievement is great. The returns? NIL) )