This test was performed using the original Purell mote as the reciever (the mote that was stationary) and a badge mote. The Purell mote was oriented vertically how is meant to be mounted inside and the badge was attached to me at about the waistline so there was a 0.3 meter height difference between the badge and the dispenser. The tests were completed with a resolution of 30 degrees and a range of -90 to 90 degrees. This range included 90 degrees to the left of dispenser (-90) to 90 degrees to the right of dispenser (90) with 0 degrees offset right in the middle. The first test was done from a distance of 0.5 meters with the badge on my front side and the data and plots can be found here:
Data, RSSI Plot, Standard Deviation Plot
From these plots you can see that the STDEV generally is larger at a lower power setting and the RSSI appears to be distributed normally. The only low point on the RSSI with this orientation is at 90 degrees to the left of the dispenser, and even this isn’t that much of a deviation from the rest of the values.
The next test was done with the mote at a distance of 0.2 meters from the Purell dispenser with the badge again on my front side, the data and plots can be found here:
Data, RSSI Plot, Standard Deviation Plot
With this test the RSSI value again appears to drop when approaching from the left, but as in the last test not by very much. Other than that the RSSI plot is pretty even from all directions with little difference elsewhere. The standard deviation plot though shows a wild jump at power level 15 that could be from bad reads, but overall the trend is that at lower power levels there is greater variance in the RSSI values seen.
The final test was done with the mote at a distance of 0.2 meters, but this time it was stapped to my backside to simulate the inteference of a person. The data and plots can be found here:
Data, RSSI Plot, Standard Deviation Plot
The plots again show a drop when approaching from the left, but this time at about a 30 degree offset. There is also a STDEV spike at this offset for all power levels except 5.
These final plots and data sheets are for the overall results of the test when at a power level of 15:
Is the angular variation entirely determined by the transmitter, or does the angle of the receiver matter equally? Did you test this in some experiments?
Comment by Ted Herman — September 25, 2009 @ 2:06 pm
Good point Ted, and one that’s been on my mind a lot last week. We don’t have great equipment to test whether these signals are polarized one way or the other or what polarities the motes are good at picking up. There may be orientation effects; they were not varied in this experiment, nor in many that we’ve been doing. We’ll add that to our list.
Comment by gthomas — September 28, 2009 @ 12:05 pm
If there are extreme “lobes” in a transmission pattern, can these lobes be attenuated by some kind of masking? I did measure different RSSI between cases of a mote and the same mote with a bit of antistatic bad (mylar) taped onto the F-antenna.
Comment by Ted Herman — September 29, 2009 @ 3:22 pm