But what can we make of the signals?
...very poor. In fact, it is almost impossible to get to zero emissions. Electromagnetic fields are like water - they always seem to find a way of leaking in and out.
Another fact is that just about all our electronic devices radiate - they are not designed to be transmitters as such, but they radiate all the same.
My final example is a fairly typical modern working environment in which mobile individuals operate in offices in and around a conventional building. What's most striking about this environment is the sporadic nature of connectivity and the bursts of activity between individuals, groups and those remote from the site.
This graph highlights a few interesting aspects of the modern IT environment in almost all companies. First, there is the security nightmare of knowing who is online and what they are doing. Secondly, the capacity limitations and potential for interference and contention always present with wireless communication are clearly illustrated.
Perhaps I should point out that these pictures are just static shots of the dynamic spectra that appear on my screen. It's interesting to watch that information as it changes because it imparts an enhanced impression of what's actually happening.
What might we conclude here? It's certainly possible to identify different communities in a society and their most likely activities at any given time. You can see where money is being generated, important information is held, and where commercially sensitive activities are being undertaken.
Perhaps more importantly, you can see where the bright young minds of the future are being shaped and tested by the latest technology. These youngsters are going to arrive in the workplace all trained, fired up, ready to go, and with different attitudes and expectations.
The really telling experiment in another decade will be to see if the spectrum shown in Figure 4 has mutated to something looking far more like Figure 2.