Hi, I'm Thomas and in today's Inside Wireless episode we'll talk about the Frenelzones. Frenelzones is a pill-shaped box between a transmitting and receiving antenna. It was named after the 19th century French physicist, Augustine Jean-Franel. The number of Frenelzones is in finite. But for the practical use we only care about the first few ones. For a good operation of an R-erflink, the line of sight should be clear and at least 60% of the first Frenelzones should be free of obstructions. If an object is at the border of the first Frenelzones, it can cause a decrease of the received signal level, also known as fading. Let's take a vertically polarized antenna system first. So when vertically polarized wave reflects from a horizontal surface, it flips its face. Additionally, compared to the line of sight wave, the wave reflected from the first Frenelzone border is half a wavelength delay. Where the wavelength is the distance over which a wave repeats its shape. So the total shift at the receiver antenna equals to one whole wavelength. The direct and the reflected waves are in phase at the receiver antenna and the total received signal is therefore stronger. When the wave reflects from the second Frenelzone border, the situation is quite a deal-positive. The total received signal is weakened. So if a vertically polarized antenna system, the resulting signal is stronger when the wave reflects from the odd Frenelzones and weaker when it reflects from the even Frenelzones. For a horizontal polarized system, the situation is a positive. The odd Frenelzones reflections weaken the signal and even once strengthen it. In practice, you can see the influence of the reflections from the Frenelzones is changing signal level with the changing position of the antennas. Or when you switch the polarizations, you can see a significant change in the signal level even if the antennas have balanced chains. While figuring out why a link might not perform well, maybe a complex task, the knowledge of the Frenelzone influence might help you rule out some of the possible problems. Try to move the position of an antenna on one side of the link up and down to see if the signal improves. Since Earth waves reflect from all kinds of surfaces, such as lakes, roofs, or Earth surface, as well as the walls of the buildings, the general rule of thumb is to be aware that the longer the length distance, the bigger the Frenelzone becomes, potentially making the link more sensitive to the vertical antenna position adjustment.