When you look at a cell tower site from a distance, a few things can jump out at you. Naturally, the first thing you notice will be the tall tower structure itself. In fact, the tower is more than likely the reason you will notice a cell site to begin with. But what if you had a chance to get closer to the cell tower? If you take a closer look towards the bottom of the tower, you will see the carrier equipment on some sort of pad or platform, or maybe a small shelter that houses the base station equipment. You may have also seen the cabling that stretches from each carrier’s ground equipment all the way up the tower. Now, take it a step further – what if you could climb to the top of the tower to view the equipment at the antenna level? What most people don’t have the opportunity to get a good vantage point on are the antenna RAD centers, where the carrier antennas sit atop the tower. You may be able to see the antennas from the ground, but there is more than meets the eye from way below. I’d like to focus on some of the unsung heroes that help the antennas function efficiently and powerfully – the antenna level equipment.
Common examples of antenna level equipment can include Diplexers, Tower Mounted Amplifiers (TMAs), and Remote Radio Heads (RRHs). All of this equipment serves an important purpose and works together to allow cell sites to function in a more advanced manner. This equipment is typically mounted to antenna mount frames or mount pipes as close to the corresponding antennas as possible. Below I will introduce you to some of this equipment and explain the purpose and role they play in the telecommunications industry today.
Diplexers
Diplexers are electronic devices with two ports on one end and one port on the other that allow for frequencies on two coax cables to be combined into one coax and later split back out to two. This can be very helpful when running coax cables on a tower with limited available structural capacity. Using diplexers can reduce the total number of cables, and therefore the subsequent weight, to assist with keeping tower loading under the allowable structural capacity. In many cases, diplexers will exist near the ground equipment to reduce the cables before they run up to the top of the tower, where antenna level diplexers split the frequencies back out to two cables. In some instances, multiplexers are used to reduce more than just two cables down to one single coax.
Tower Mounted Amplifiers (TMAs)
Tower Mounted Amplifiers are low noise amplifiers that can benefit cell sites by making transmitting antennas stronger and receiving antennas more sensitive. By strengthening the signals on transmitting antennas, TMAs allow antenna signals to reach further. When TMAs are used to increase sensitivity for a receiving antenna, a weaker signal from a more distant target can be received by the antenna. Long story short, these TMAs work hard to expand the coverage area of a cell site.
Remote Radio Heads (RRHs)
Remote Radio Heads are commonly used at cell sites across the country. They are generally relatively small in size – no larger than two feet by one foot by six inches. The purpose of these units is to move the majority of the base station equipment that feeds the antenna to an enclosed unit at the antenna level. The RRHs are connected to the main base station of the site by a fiber optic connection. By placing the units close to the antennas, we can reduce the coaxial feed line losses that come from long runs, increase system efficiency, and provide some flexibility in site development.
Hopefully this view from the top has helped you gain some insight to the efficiencies and advantages of the tower mounted equipment that continue to push the evolution of our telecommunications industry.
About James Marooney, PE
James Marooney, PE, is a Regional Leader for Wireless Services in Washington D.C. at Foresite Group. He graduated from University of Maryland with his Bachelor’s degree in Civil Engineering and a minor in Project Management. James enjoys working with a communicative team in order to get the job done on time. He has a special interest in working with a variety of carriers, especially learning how each carrier implements their systems and methods to complete a job.