Mandatory Design Requirements and Work Flow Processes

Unless specifically agreed to in writing as an exception, this specification requires certain processes be carried out and adhered to during all phases of the work.

The service provider will employ or subcontract a registered professional engineer licensed to practice in the state or jurisdiction where any and all work is carried out.

The Passive Transmission System is a ‘‘gas tight’’ system. Preserving the condition of the surface inside the transmission line, antenna, and other parts of the system is critical to long-term stability and trouble-free operation. The Tower and Erection Services provider must contribute to preservation of positive gas pressure at all times practical during installation. The following are minimum requirements and the responsibility of the service provider on-site supervisor:

• The antenna will be under pressure when it arrives on site. The antenna input terminal will include a gas stop. The gas stop must remain in place until the antenna is safely mounted on the tower and the vertical transmission line and tower top elbow complex are ready for connection to the antenna.
• The transmission line must be assembled from the ground up. The horizontal line will be mounted in a three-point spring hanger suspension arrangement. The vertical line will be mounted with a minimum of two spring hangers attached to mounting brackets on tower members. At the end of each working day or upon work stoppage because of weather, the in-place line will have a cap provided for the purpose of sealing the transmission line. This cap is to be installed anytime work is stopped for more than 2 hours.
• Upon completion of installation of the transmission line and before connection to the tower top elbow complex, a precision terminating load will be attached to the line. The line will be purged with dry air or nitrogen whereby the termination load is not tightened gas tight so as to permit ‘‘bleeding’’ of dry air equal to three times the capacity of the line. Usually this can be done overnight or within a few hours. The Passive Transmission Systems supplier representative will make measurements on the line.
• When the tower-top elbow complex has been installed and connected to the vertical line, the precision load will be moved to the antenna side of the complex, the system pressurized again, and measurements made.
• After the measurements are complete and the antenna is in place, the gas stop will be removed and the final connection of all components made. Depending on the length of time and weather conditions, it may be necessary to purge the system again. Regardless, the system is to be pressurized to one and a half times the recommended operational pressure. The Passive Transmission System supplier representative will make one final set of measurements. If there are no issues, then the service provider will confer with the buyer’s representative as a final step before dismantling rigging and other tools.

The following paragraphs are extracted intact from the Passive Transmission System Specification and provided for reference information and guidance to the Tower and Erection Services Provider:

‘‘Any antenna designed and supplied according to this specification will incorporate a unique mounting interface to the supporting structure. The antenna manufacturer is solely responsible for designing the antenna and mounting interface. The antenna manufacturer will exchange design reference drawings and information with the tower and erection services provider. The antenna manufacturer will coordinate a mutually satisfactory mounting interface meeting all applicable EIA, SAF, and/or other applicable standards commonly used in such work by both parties. Design documents necessary to guarantee physical orientation of the vertical and horizontal radiation patterns referenced in the RFQ for each site will be provided to the buyer prior to release to manufacture of the antenna. Any work commenced, including material release, prior to approval by the buyer is at the risk of the antenna manufacturer. Approval of any drawings or other information in respect to this requirement does not relieve the antenna manufacturer/supplier of the responsibility for final orientation of the antenna on the support structure. The antenna manufacturer is encouraged to design unique mounting interface to ensure final placement is in accordance with each site’s unique radiation requirements. For example, if a particular antenna is either a tower top mount using a pole in a socket or bolted flange mount, it should have only one way in which to interface with the tower top plate or socket.

‘‘Any antenna designed to comply with this specification will incorporate one or more lifting lugs designed to be an inherent part of the structure through a welding or casting process. Drawings, pictures, illustrations, and design details showing clearly how the antenna is to be attached to lifting cable and tag lines will be provided and subjected to design analysis by third-party erection services providers and structural experts who are qualified to render opinions on safety aspects under all conditions including shipping, handling, installation, operation, or removal. Under no conceivable conditions will this requirement be waived.

‘‘Any antenna made up of panels, feed lines, and mounting bracket subassemblies (i.e. not a single mechanical assembly) will follow the same process as outlined in 2 above, except that these conditions will apply at the sub-assembly level, such as a panel and its feed lines and radiators— a power divider/splitter assembly or sub-component as assembled, tested, and shipped from the factory under pressure with gas barriers in place.

‘‘Upon completion of the assembly of an antenna will be fitted with a gas barrier, including pressure indicator and drain cock, and pressurized at its input connection to a level twice the recommended field pressure value. The pressure shall be maintained continously until disassembled in the field for connection to the tower top elbow complex after mounting on the tower. If pressure drops, the leak shall be investigated and fixed prior to further test or installation work.

‘‘Upon completion of assembly and any other tests deemed appropriate and necessary by the manufacturer, the manufacturer shall carry out pattern tests to demonstrate that the finished antenna meets or exceeds the vertical and horizontal patterns invoked in the RFQ. The manufacturer is encouraged to use scale models to reduce cost and test time. If scale models are used, the buyer must review the design process and extent to which they are used and approve or waive any part of the manufacturer’s standard full-size pattern test.

‘‘If the transmission line component of the system is greater than 300 feet in overall length or if the line will carry more than one RF signal, the line will be laid out in a single assembly and pressurized at twice the normal recommended level under operation in the field with dry air or nitrogen gas commonly used in the industry. The completed, pressurized assembly characteristic impedance will be optimized to a VSWR of 1.02:1 across an occupied bandwidth consisting of the television channel and any FM signals þ/10 Mhz above and below the bandwidth occupied by all the specified signals. The signal source and detection equipment will be described and noted with serial numbers, the name of the person making the measurements, their qualifications to do such work, and the dates the work was undertaken and completed with all interruptions in the daily routine noted. The line shall be terminated in a precision load of the same characteristic impedance as the line. The source and detection equipment and load used shall be part of the manufacturer’s normal test equipment and its calibration traceable to NBS standards commonly used for such purposes.

‘‘All tower top elbow complex units shall be built, optimized, and tested as a single unit. Upon completion of this process and prior to making ready for shipment, the manufacturer will notify the buyer of this fact and provide evidence that the unit has met or exceeded the agreed-upon specifications. The buyer will examine and approve the unit to be made ready to ship.

‘‘Factory RF Pulse and VSWR measurements must be made and recorded. These will be duplicated in the field. VSWR measurements must be made at intervals of .25 Mhz or less.’’