Week Two: Tags, and Bases, and RSSI, oh my!

Base Station on 3 meter pole with Megan Heier. 

Calibration. Our dear friend Wikipedia offers this explanation: Calibration is the process of finding a relationship between two quantities that are unknown (when the measurable quantities are not given a particular value for the amount considered or found a standard for the quantity). 

I am using Encounternet radio frequency identification tags on Spiny-Tailed Iguanas. When the iguanas are within a certain physical distance of each other, the tags will log their encounters. What needs to be calibrated is the relationship between distance and Radio Signal Strength Indicators (RSSI).

If the RSSI between two tags (soon to be attached to actual iguanas) is -11, how close are they to each other? What about when they are +7 RSSI?

How close does an iguana with a tag need to be to a base station to ensure a power-efficient download of physical proximity logs? 

What height of the base station ensures the above, 3 or 1.5 meters?

When the antennas go in the same vs. opposite vs. perpendicular directions from each other, what does that do to RSSI?

Where should the base stations be mounted?

When should we log tag interactions (wake up call) and when should we stop (bedtime)?

Which iguana sub-group would be useful to test the calibration on real animals? (This is not a trivial consideration -- it would be good to have different personalities, sexes, and perhaps not too many animals that climb 20 meter trees....)

So, we've attached base stations to different height PVC poles, marched tags up and down a measuring tape in the hot sun, taking numerous pages of data. And as explained, RSSI is stronger when off the ground (lizards with jet packs, anyone?), away from concrete and piles of rebar,  and best if antennas are parallel and facing each other.

We have mostly learned how to set controls in the system software, have a good idea of which iguanas will get tags, and are almost ready for a real run.

Rusty, a large male who patrols the open area in the above photo, has more than 8 females in his territory. He also has several second-rank males that he has to address, running them off as needed. The females are bold and shy which should also help test the system and begin to answer the question, why do these non-cooperative animals have the social structure they exhibit?