The Wonder of Radio Waves and Yagi’s

I have a great interest in radio waves, and I did my PhD on the analysis of radio waves using a time-domain method. It amazes me that the radio waves from a GPS satellite can reach my mobile phone, even when it is in my car (and surrounded by metal).

I thus marvel at antennas, and while others might pass-by a road side antenna without a thought, I imagine the spread of the signals. A few years ago I was working on a research project in a hospital, and I discovered that the power levels on an antenna was emitting radio waves that were a great risk to those who went through the door. When I did the calculations, I found that it was focusing a beam on a small area, and which amplified the signal.

In radio, we don’t really talk about Watts, we normally talk about milliWatts (mWs — which are one-thousands of a Watt). The typical power output for the wi-fi access point in your home is around 100mW. Overall, we use dBm as a measure of the power, and where a 3dB is the drop in power when we half the power (-3dB). So if we go from a signal strength of -50dBm to -53dBm, we have halved the power. Here’s a quick presentation on this: