TECHNOLOGY AREAS: Materials/Processes, Electronics

ACQUISITION PROGRAM: PMW 770 Submarine Communications Program ACAT II

OBJECTIVE: The objective is to develop for a 1500 foot tower a lighting system that will replace an electrical lighting system whose components have proven troublesome and incur significant costs in replacement and in downtime of the overall system. . The new system would need to provide lighting that is functionally equivalent to that presently in use but incurs no downtime for the antenna broadcast system, safe for maintenance teams to replace and are economical in nature, and would need to be approved by aviation safety authorities. The system would need to be robust in high RF electric fields and weather, including sun, heat, cold, and lightning.

DESCRIPTION: The desired tower lighting system will provide light in accordance with standard FAA and FCC guidance. Red light systems have alternating levels of flashing and non-flashing light. Systems producing white strobe light meeting aviation safety requirements may be considered. Existing systems are based on incandescent lights or on light-emitting diodes (LED).
Towers can be classified as grounded or base insulated.

Grounded towers serve to support one or more antennas that are small compared to the tower. Lighting systems on grounded towers are wired as on any other structure exposed to the elements. Wiring consists of conduit with wire, or armored cable, with junction boxes and fixtures, all chosen for weather resistance. Problems encountered, mainly corrosion, are not unique to towers. A base insulated tower is the antenna. Wiring and lighting is now constructed the same as for grounded towers. In addition, to get power on to the tower, a special tower lighting isolation transformer is installed next to the base. This type of transformer is made by only one manufacturer. One alternative system that has been used is a motor generator set with a long insulating (fiberglass) shaft.

RF current flows along the height of a base insulated tower. The RF voltage relative to ground varies along the height of the tower. Recent measurements have confirmed that significant RF voltage exists between the conduit and the lighting system wires inside.

High RF field exists at the outer surface of the tower, particularly at the top. Electric light fixtures are installed at several levels of the tower, in accordance with FAA/FCC and international guidelines. The light fixtures have traditionally contained incandescent lights, but many recent installations use LED lights. The LED lights consume less energy than the incandescent lights, and require less maintenance, but have not been trouble-free, particularly for the Navy�s very high powered transmitting stations. The radio-frequency signal from the transmitter interferes with the lights, particularly LED lights, in ways we are only beginning to understand. The service is looking for innovation in either replacing existing lights systems or in delivering lights remotely. The new processes or hardware should allow maintenance teams to operate safely around and about the large antenna systems without shutting them down.

Fiber-optic distribution is seen as one possibility.

Fiber optic distribution is used for communications. The fiber is thin glass. Fiber communications use low power, the cable is low loss, and signals can go several kilometers in "single mode" (narrow bandwidth) or shorter distances in "multi mode" (wider bandwidth) cable. Since the purpose is communications, not power transfer, losses of ten or twenty decibels (factors of 10 to 100) could be acceptable. Such losses are not acceptable when efficiency of power transfer is a consideration. Fiber optic distribution is also used in lighting. The fiber may be plastic. Distances achieved are a few meters for white (broad bandwidth) light.

Fiber optic distribution for tower lighting could be possible if fiber combining long distance (low loss) and wide bandwidth could be developed. Such fiber is not known to exist. Other approaches have been tried, and might be worth exploring. At least one tower built prior to WW2 used lights on the ground and mirror assemblies at the tower�s top. Maintaining alignment of such a system is but one challenge.

Isolated lights with photovoltaic arrays and batteries could be built. Challenges include cost, complexity, battery life vs. available light, and susceptibility to environmental damage. All the critical components would be on the tower, beyond easy reach.

The challenges seen for this project are (1) high electric field, on the order of 100 kV per meter at the base insulator, (2) attenuation in the fiber optics, and (3) weather ( sunshine, heat, cold, ice, wind, rains and frequent fogs and mist, lightning, salt air, and in some locations sulfur gasses of volcanic origin).

PHASE I: Develop an innovative concept for producing light, conveying the light to the various levels of the 1500 foot towers, and permitting emitting light in a way that will meet the standard FAA requirements for tower beacons and obstruction lights. Propose specific methods for dealing with the known high electric field at the base insulator, weather and radio frequency signal disturbances to existing light fixtures. Solution ideas need not be limited to concepts described in the description above.

PHASE II: Develop and fabricate a small-scale prototype lighting system. Test the prototype in the laboratory with respect to the performance parameters identified in the Phase I study. Identify new issues with new prototype system such as material degradation, sensitivity to tower flexibility, environmental attenuation, etc. Propose specific methods for dealing with these new issues.

PHASE III: Build a full-scale prototype lighting system, install it on a Navy communications tower, and field test with respect to the performance parameters identified in the Phase I and the new issues identified in Phase II. Assess the reliability of the new prototype system. Goal is to outperform the current system by a fiscal factor of at least 10.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Commercial business for tower lighting systems is potentially large, given the large number of telecommunications towers in use worldwide, particularly those in the medium-frequency (MF) broadcasting business. Since the telecommunications industry does not have the specific problems associated with the Navy�s FSBS, then this industry will only adopt this new lighting technology only if it can be broadly cost-beneficial compared with existing electrical lighting systems. The lighting propagation techniques developed here could be applicable in the much broader lighting industry.

REFERENCES:
1. FCC Advisory Circular AC 70/7460-1K, Obstruction Marking and Lighting, 2007

2. FAA Advisory Circular AC 150/5345-43F, Specification for Obstruction Lighting Equipment, 2006

3. FAA Advisory Circular AC150/5345-53C, Airport Lighting Equipment Certification Program, 2005

4. FAA Engineering Brief No. 67B, Light Sources Other than Incandescent and Xenon for Airport and Obstruction Lighting Fixtures

KEYWORDS: Tower Lighting; Fiber Optic Lighting

** TOPIC AUTHOR (TPOC) **

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