Antenna Installation & Setup

 A Yagi antenna uses several elements to form a directional array. A single driven element, typically a dipole, propagates RF energy; elements placed immediately in front of and behind the driven element re-radiate RF energy in phase and out of phase, enhancing and retarding the signal, respectively. The elements are called parasitic elements; the element behind the driven element is called the reflector, while the elements in front of the driven element are called directors. Yagi antennas have beam widths in the range of 30 to 80 degrees and can provide well in excess of 10 dBi passive gain.

Antenna Installation & Positioning

Proper antenna installation and positioning is important and will allow you to achieve maximum performance and distance between your transmitter and receiver unit. This will reduce the possibility of a lost connection during operation. Antenna Basics When installing your transmitter and receiver it is important to install both units in such a way as to optimize the position of both antennas within what’s known as the “Fresnel Zone”. A Fresnel Zone can be thought of as a football shaped invisible tunnel between two antennas that provides an optimum path for the RF signals between your transmitter and receiver.

The Fresnel Zone

Fresnel created a calculation on how out of phase the wave would be between the transmitter and the receiver. The Fresnel zone is a 3-D cylindrical ellipse shape (like a football) and is made up of multiple zones, Zone 1 being the strongest area for signal strength, Zone 2 being the weaker, Zone 3 being weaker still and so on. There are many Fresnel zones, but only the first 3 have the any major effects on signal strength. Phase cancelling effect in even numbered zones have the maximum effect, while in zones with odd numbers can have a positive effect to signal strength.

So, to maximize the signal strength at the receiver, you want to minimize the any out of phase signals from reaching the receiving end by making sure the strongest signals do not bump into any obstacles. The general rule of thumb is that the 1st Fresnel zone must be 60% clear of obstruction from the center line of sight to the outer boundary of the 1st Fresnel zone to maintain a good connection. To achieve maximum distance, the path in which the RF signals travel must be free of all obstructions. Obstacles in the path will decrease the transmit/receive distance. Also, if the antennas are mounted too low to the ground, most of the Fresnel zone ends up being obstructed by the earth resulting in significant reduction in transmit/receive distance. Your antennas should be mounted as high off the ground as possible. A minimum of at least 8-9 feet is recommended. It is important to understand that your application environment may change over time due to new equipment, buildings or other RF equipment being installed. There can also be change within your building such as new construction, etc. If new obstacles are added between your switch transmitter and relay receiver you may need to move and re position your antennas.