I've been searching for a way to use rf signal strength for location discovery. I've tried searching the forums and the consensus is that it is not possible, then i came across this: Intelligent Tracking Robot System Based on Radio Frequency Passive Location - YouTube
Anyone have any idea how this guy might be doing this?
With several antennas you can estimate the direction to a radio transmitter. The robot appears to have four, but only two are required.
Google radio fox hunt to learn how the radio amateurs do that.
mwawrzyniec:
I've been searching for a way to use rf signal strength for location discovery. I've tried searching the forums and the consensus is that it is not possible
It is not really, and mostly people assume that you can use signal strength as an accurate measure of distance and thus from two such receivers can calculate a location. That can work outdoors in large flat open spaces but not otherwise.
What can be used to estimate direction is a TDOA system which can be as simple as two antennas and a NE555 timer circuit and a radio. These have been used for decades in amateur radio.
The robot in the video has 4 antennas, so perhaps two TDOA systems which would probably allow you to work out direction.
But TDOA systems are not using RSSI...........
And even if the video example was not using TDOA, there is a significant difference between having a moveable directional antenna and moving it to point at the source of maximum signal versus using RSSI to attempt to calculate location, or direction, from two fixed location non-directional antennas.
The 4 antenna idea is simply an electrically rotatable antenna, which uses 4 pin diodes to sequentially switch each vertical antenna to the input of a receiver at a rapid rate, and the output of the receiver then produces an AM signal which has a peak in the direction from where the signal is coming from.
It only shows direction , not distance, and gives a fairly poor indication of the direction, and is also fooled by multipath.
Its effectively the equivalent of having a small yagi antenna on a motor which rapidly rotates around in a circle.