# The Wonder of Radio Waves and Yagi’s

I have a great wonder for 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 marvel at antennas, while others might pass-by a road side antenna, 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 risk to those who went through the door. When I did the calculations, 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 milliWatt (mWs — which are one-thousands of a Watt). The typical power output for the wi-fi access point in your home is 100mW. Overall we use dBm as a measure of the power, and where -3dB is the drop in power when we half the power. So if we go from a signal strength of -50dBm to -53dBm, we have halved the power. Here’s a quick presentation on this:

Would you know how long the wavelength is for 2.4GHz? Well it is around 12.5cm, and that’s the reason that dipole antennas are around 6.25cm (as our antennas are a half a wavelength long). If you want, you can now go and take a test on dBms here:

and a calculator here:

My favouriate antenna is the Yagi:

I even created a Cisco Aironet simulator here:

#### Conclusions

I think we take wi-fi for granted. It is an amazing technology and has broken our link with physical cables. For future world will be created from wi-fi, and 5G will bring about one of the most amazing changes in the whole of human kind.