Fig. 1: The KinStar antenna final design configuration, using lumped element matching and with top and bottom of vertical radiating wires connected together. Antenna wires are insulated from ground and supports. In January the first KinStar antenna was put into service at KCST(AM) in Florence, Ore.
You may recall that our "Cool Stuff" judges gave special recognition to the design in 2003 with a "Cool Concept" Award. The antenna was conceived by Star-H Corp., particularly Dr. James Breakall, professor of electrical engineering at Penn State University, and developed for market by Kintronic Labs.
It was type-accepted by the Federal Communications Commission in late 2005 for full-time omnidirectional operation in the AM band.
Let's get low
Kintronic President Tom King says the system is timely for AM nondirectional stations.
"More and more communities and neighborhoods across America are growing tired of the proliferation of cellular telephone towers, resulting in the establishment of revised local zoning laws for new structures that reflect a lowering of the maximum allowable height."
Fig: 2: This is the feedpoint of the KCST antenna, showing three of the four insulated vertical elements with the associated commoning ring and the Kintronic Labs Model LTU-1B-1600 antenna matching unit. KCST operates on 1250 kHz with 900 watts daytime power and 37 watts at night. King said station owner Jon Thompson needed to replace his 57.89 meter tower. His contract engineer, R. Sparks Scott, recommended that he consider the low-profile KinStar.
"Following further investigation with his consulting engineer, Bob McClanathan, P.E., he decided to install at a location 1.3 miles northeast of his old tower site," King told me in a written summary of the project prepared for Radio World.
"With a local zoning height restriction of 72 feet, the KinStar at his frequency of 1250 kHz would have a maximum height above the ground of 70 feet, which eliminated any legal zoning issues." Thompson also liked that there would be no tower painting involved.
The antenna design that was licensed by the FCC as a top-loaded antenna is shown in Fig. 1. "The KCST KinStar was designed in accordance with the scaled electrical dimensions that were defined by the experimental antenna that was operated under FCC experimental license WS2XTR for operation on 1680 kHz," King continued.
Fig. 3: You've heard of tower farms; this is a phone pole farm. A view of the KCST KinStar antenna, with the center feed at the left, three of the five support poles shown, and the transmitter building on the right with the STL dish installed on the pole closest to the transmitter building. "With an electrical height of 63 feet and top loading of 134 feet, the KCST KinStar operating on 1250 kHz was installed with five 85-foot wooden utility poles and standard pole line hardware and cable in one and a half days by a utility company out of Portland."
The anchors were screw anchors buried in the soil using a hydraulically-driven auger; no concrete was required. A 120-radial quarter wave ground system was installed following the antenna installation.
A photo of the feed point at the base of the center pole of the KinStar antenna is shown in Fig. 2. An overall view of the KCST KinStar antenna is shown in Fig. 3.
"With the height of the KinStar pole supports falling below the average height of trees in the nearby forest, the antenna blends into the background, rendering it invisible to the passers by on the coastal highway," King said.
"As a result, the KinStar is clearly an environmentally friendly antenna technology." This is a theme the developers are emphasizing. Witness the title of their NAB presentation: "The Inaugural Installation of the First KinStar AM 'Green' Antenna.'"
Another advantage of the KinStar antenna, King said, is the wide audio bandwidth that it offers in comparison to the typically narrow band characteristics of electrically short AM antennas.
Fig. 4: KCST KinStar antenna drive impedance measured at the output J-plug of the antenna matching network by Bob McClanathan, P.E. He points to Fig. 4, which illustrates the small change in resistance and reactance of the KCST KinStar measured over the 1250 +/- 15 kHz band.
"The inherent audio bandwidth performance of the KinStar is evidenced by the less than 2 ohm variation in R and the less than 10 ohm variation in X over the 30 kHz bandwidth of a typical HD Radio channel," he said.
King quoted McClanathan saying he was impressed with the quality of the antenna construction and its performance.
"The impedance at 1250 kHz is Z=15.1 + j80.0 ohms and is flatter than a pancake +/- 20 kHz. Would be excellent for IBOC but fortunately KCST is not going there," McClanathan told King. "I met a neighbor near the antenna site who is very pleased with the unobtrusive and nearly invisible appearance of this antenna."
Attendees of the upcoming NAB Show can learn more about the KinStar installation in a Tuesday presentation. As usual, the folks who organize the Broadcast Engineering Conference have done an exceptional job of preparing an agenda that is well worth exploring.
The author is Editor in Chief of Radio World U.S.