The Tunipole is a specialized implementation of the folded monopole antenna. It consists of a cage of cables together with appropriate resonance or coupling devices that connect to the station tower.
The main difference between the Tunipole and folded monopole antennas is that the base of the tower has no insulation, but is connected directly to the station ground system. The Tunipole cage cables connect to the tower at the top and to the antenna tuner unit at the bottom. Adjustment items, as required, are an integral part of the cage cable assembly.
The transmitter energy travels from the tuning unit to the folding cables, to the top of the tower, to the tower and to the base, where it completes its circuit in the ground system. In doing so, the antenna system radiates a highly efficient broadband signal.
Electrically speaking, the Tunipole is equivalent to the well-known folded dipole antenna, cut in half and placed upright on a ground system. It has the radiation pattern characteristics of a series-fed monopole antenna, with the folded cables functioning as control elements and impedance transformation.
Unlike the series-fed antenna, the Tunipole is fully adjustable in base impedance, making it easy to fine-tune the unit’s setting.
The main advantages are inherent in grounding a series-fed MF transmission tower and powering it as a Tunipole. One of the first advantages is that the rays go directly to the ground system, avoiding damage to the antenna tuning unit and the transmitter.
Also with the Tunipole, it is not necessary to take special isolation precautions to mount other antennas on the tower. Transmission lines to FM, TV and two-way antennas pass directly through the base of the tower without the need for isocouplers or quarter-wave isolation terminals. If installed correctly, these additional antennas and lines have little or no effect on the operation of the MF station. However, the adjustable impedance of the Tunipole will contribute to continued maintenance savings.
Compared to a conventional series-fed MF tower, the tower equipped with a Tunipole tends to exhibit significantly better bandwidth. In general, the shorter the height of a series-fed MF antenna, the poorer its bandwidth becomes and the more difficult it becomes to transmit “clean” audio signals through it. This is a concern where tower heights are limited. In new construction, shorter towers will save materials and construction costs. In many cases, the Tunipole is a short tower that will be used without sacrificing transmission quality, and will almost always improve the transmission quality of the existing series-fed short tower.
The Tunipole has the unique ability to increase the efficiency of many MF station installations. While theoretically producing the same radiated field as a series fed antenna over a perfect ground system, the Tunipole typically produces a higher field strength in short or poor ground systems.
In cases where stations with limited ground systems have been installed, the performance of Tunipole-equipped stations has been comparable to that of stations with full ground systems. This is an important consideration when planning a new station construction where terrain is limited, or when a station is switching from a higher frequency to a lower frequency and wishes to continue using the same tower and ground system. A station can save thousands of dollars in land and construction costs this way.
Another very important Tunipole application is sharing a single antenna tower between two or more transmitters on different MF frequencies. In the past, series-fed tower sharing was limited by several factors, including a lack of operational impedance selection options, complex isolation and tuning networks, lack of control over electrical height / vertical radiation pattern, and the impossibility of using the tower for auxiliary services such as FM, TV or bidirectional antennas. However, with uniquely designed Tunipole configurations, these limitations can be overcome, allowing independent control over the impedance characteristics of the Tunipole at each frequency of use and presenting optimal impedances at the desired and unwanted frequencies to facilitate the design of combined networks. This can significantly decrease the complexity and cost of these networks, as well as improve your bandwidth performance.
Installing a Tunipole antenna system is not difficult. A typical system for a series-fed tower is manufactured with field-adjustable hardware, which adjusts to the most popular tower types without cutting, drilling, or welding. Installation time is usually less than one day.