You will (re)discover that reflection and absorption of radio waves by nearby objects and the relative orientation of transmitting and receiving antennas have dramatic effects on the RSSI; far larger effects than the distance between the transmitter and receiver.
To visualize these effects on the signal from a WiFi router within an apartment, an app has been developed for Android phones. Take a look at this blog, describing the results.
But by all means, get a couple of XBees and try it out yourself. It will be an interesting educational experience.
Tnx for the blog article, i enjoyed reading it but i don't think that this should concern me, yet. The final test of the project will be in so called "lab conditions", the body of water that the robot will operate on has a year-round calm water surface and the plane of operation will be free from obstacles, so the receiver will have a clear line of sight to the transmitter. But this is just the first stage of the project (about 2.5 months until presentation) where i'll try to demonstrate the basic concept of work.
But as i said tnx a lot for the info, and i'll keep it mined for further use.
By the way im not really sure for what the Xbee are used for, and what can i do with them to elp me with my project?
You could try two 2.4Ghz vertical aerials (as on a Wifi modem), spaced 1.5wavelength apart (187.5mm).
BOTH connected to the input of ONE 2.4Ghz receiver, with EQUAL LENGTS of (x wavelength) coax*.
*signal in coax does not travel at lightspeed.
The AGC/signal strength output of the receiver will indicate max signal if the aerials are 90 degrees to the transmitter source, because the signals of the two aerials are in phase.
And, more important, the signal will NULL if the aerials are INLINE with the source.
A second set of aerials and a second receiver can be used, so you don't have to "scan".
e.g. four aerials mounted in a square. One set in oposite corners.
From what you've written here, i'm guessing that you know a thing or two in RF communication, so if you don't mind i have some questions.
-If i use 2 of the antennas, i have to mount them upright so they'll create a vertical plane, right?
-If i use 2 antennas i'll have to mount them on a 180 degree panning platform so that they can scan, or can they be stationary and the robot will steer itself to a position that the signal will be the strongest?
-If i use 4 antennas, do they have to be mounted horizontally or vertically?
-If i understand it right, if the signal will NULL it means that i lost the signal completely from the robots point of view, and it'll have to correct its heading ti find it again?
-How can i create the signal for the robot to lock on, and can i configure a specific wavelength for the robot to lock on?