Tunipole™ Folded Unipole Antenna Applications in Medium Frequency Broadcasting – Application 10

A new antenna concept, the LBA Technology, Inc. Tunipole™ folded unipole antenna, is being implemented by medium-wave (AM) broadcasters throughout the world.

The Tunipole™ is a specialized implementation of the folded unipole. It consists of a cage of wires along with appropriate resonating or coupling devices that attach to the station’s tower.

The base of the tower has no insulator, but is tied directly to the station ground system. The Tunipole™ cage wires attach to the tower at the top and to the antenna tuning unit at the bottom. Tuning elements, as required, are integral to the cage-wire assembly.

Transmitter energy travels from the tuning unit into the fold wires, up to the top of the tower, into the tower, and down to the base—where it completes its circuit into the ground system. In doing so, the antenna system radiates a high-efficiency, broadband signal.

Electrically, the Tunipole™ is equivalent to a familiar folded dipole antenna cut in half and stood upright on a ground system. It exhibits the radiation pattern characteristics of a series-fed monopole antenna, with the fold wires functioning as impedance transformation and control elements.

Unlike the series-fed antenna, the Tunipole™ folded unipole is fully adjustable in base impedance, which facilitates tuning and long-term stability. For measurement and verification, consider using an RF impedance analyzer.

Product Bulletin: Tunipole™ – Folded Unipole Antennas

For specifications, configurations, and key performance benefits, download the Tunipole™ product sheet:

? Tunipole™ – Folded Unipole Antennas (Product Sheet PDF)

• Retrofit kits and new-construction solutions for AM towers
• Grounded base improves lightning survivability and simplifies site integration
• Adjustable base impedance for easier matching and improved operational stability
• Broadband performance—especially beneficial for shorter towers
• Supports co-location of FM/TV/two-way antennas and transmission lines

How You Can Utilize the Tunipole™ Folded Unipole

Major advantages are inherent in grounding a series-fed MF broadcast tower and feeding it as a Tunipole™. One of the first advantages is that lightning energy is directed into the ground system—helping protect the antenna tuning unit and transmitter from damage.

Also, with the Tunipole™ folded unipole, special isolation precautions are generally not required to mount other antennas on the tower. Transmission lines to FM, TV, and two-way antennas can route across the base of the tower without the need for isocouplers or quarter-wave isolation stubs. Properly installed, these additional antennas and lines typically have little or no effect on MF station operation. The adjustable impedance of the Tunipole™ can also reduce ongoing maintenance effort.

Compared with a conventional series-fed MF tower, a tower equipped with a Tunipole™ tends to exhibit significantly better bandwidth. In general, the shorter a series-fed MF antenna is, the poorer its bandwidth becomes—and the more difficult it becomes to transmit “clean” audio through it. This is a concern where tower heights are limited.

In new construction, shorter towers can reduce material and construction costs. In many cases, the Tunipole™ folded unipole allows a shorter tower to be used without sacrificing broadcast quality and will often enhance transmission quality on existing short series-fed towers.

The Tunipole™ folded unipole also has the ability to improve efficiency for many MF installations. While theoretically producing the same radiated field as a series-fed antenna over a perfect ground system, the Tunipole™ often produces greater field intensity over poor, short, or otherwise compromised ground systems.

Where stations have been installed with limited ground systems, Tunipole™-equipped installations have in many cases performed comparably to those with complete ground systems. This can be an important consideration in new construction where land is limited, or when a station changes from a higher frequency to a lower frequency and seeks to continue using the same tower and ground system—potentially saving significant land and construction costs.

Another application of great significance is sharing a single antenna tower between two or more transmitters on different MF frequencies. Historically, series-fed tower sharing was constrained by limited impedance selection options, complex isolation/tuning networks, limited control over electrical height and vertical pattern characteristics, and reduced suitability for ancillary services such as FM, TV, or two-way antennas.

With uniquely designed Tunipole™ folded unipole configurations, these limitations can be overcome by permitting independent control over impedance characteristics at each operating frequency. Optimum impedances can be presented at desired and undesired frequencies to facilitate combined network design—often reducing network complexity and cost while improving bandwidth performance.

Installation of a Tunipole™ folded unipole antenna system is straightforward. A typical system for a series-fed tower is fabricated with field-adjustable hardware and fits many popular tower types without cutting, drilling, or welding. Installation time is often less than one day.

Tuning does require experienced engineering assistance and proper instruments to optimize performance. LBA Technology, Inc. provides complete field application and adjustment assistance, drawing upon its sister consulting engineering firm with over 35 years of experience in AM antenna systems.

Download the Tunipole™ Product Sheet:
? Tunipole™ – Folded Unipole Antennas (Product Sheet PDF)