Precision and Shively Partner on Vertical Polarization for VHF DTV
Precision Communications, Inc. is partnering with Shively Labs® in developing a supplemental vertically polarized antenna which can be added to existing horizontally polarized main antennas broadcasting on CH7-CH13.
“We saw the need for, and developed this product in conjunction with Shively because we identified that broadcasters need help with their DTV signal penetration,” said Troy Kyman, President of Precision Communications. “We approached Shively because of their long track record with high quality FM antennas, and their ability to respond quickly to new requirements. It was not difficult for Shively to design a vertically polarized antenna for TV based upon one of their new, full-size FM products.”
“We are excited about partnering with Precision Communications on this application and being able to be a small part of the DTV revolution,” said Martyn Gregory, Vice President of Shively Labs. “The criteria provided to us were that the antennas had to be of rugged design, easily installed and have a very low impact upon the existing tower structure. This requires very low wind load and a straightforward, readily repeatable mechanical design. We ultimately provided a stainless steel, pressurized antenna array which can be sized for channels 7 13 to suit the gain and coverage needs of the individual TV station. We had originally developed a very similar system for an international customer and it was a natural fit for this application.”
Precision Communications recruited WGEM CH10 in Quincy, IL for the field testing of the new antenna array to verify signal penetration improvement. WGEM contracted independent signal strength studies throughout their geographical coverage area to establish a baseline of performance with their existing horizontally polarized antenna configuration. Precision Communications specified a 6-bay directional antenna with a broad cardioid pattern and installed it 100’ below WGEM’s current top mount 12-bay batwing antenna on their 6’ face tower. Precision reconfigured the existing transmission lines in the tower to provide RF power to the new array yielding vertical signal that is 85% of the horizontal power.
The results surpassed initial expectations; signal received over the air at the studio increased from 48.1µV to 80µV, which did include a small amount of gain from the minor repositioning of the receive antenna. Feeding both the existing horizontal antenna and the new vertical array required a transmitter output power increase of 65% but yielded a gain in signal strength of 66%. So preliminary results just at the studio show that signal penetration gain is both substantial and highly efficient.
“We’re honored to work with professionals like PCI on this project to improve VHF Highband reception and encouraged by the initial data,” according to Brady Dreasler, Director of Engineering for Quincy Newspapers Inc., corporate owner of WGEM.
“We are very pleased with the initial results of the testing,” stated Mr. Kyman. “We are going to follow up with signal strength measurements in the same locations as our previous measurements and these results should be available in the next few weeks.”
The results of the test case and specifications of the antenna are in the PDF file available for download above.
These links provide additional information about vertical polarization and its benefits to coverage and penetration: