MACXLine® Rigid Coaxial Transmission Line

Made with heavy wall extruded copper inner and outer conductors, MACXLine® Rigid Line with Bellows Inner Connector is designed for exceptional reliability and long life. Six sizes, ranging from 3-1/8-inch through 8-3/16-inch, are available in original MACXLine®. ERI offers solutions optimized to meet your needs. ERI’s field proven bellows expansion compensator accommodates the differential expansion between the inner and outer conductor and vertical and horizontal spring hangers are designed to support the system and compensate for differential expansion between the tower and vertical and horizontal runs. All the required system components and installation accessories can also be purchased from ERI.


  • No planned replacement cycles
  • Bullets never slide once put into service — eliminate the shavings that can cause arching at the flange and insulator areas
  • No need for a redundant/backup run
  • Disk insulators ensure minimum VSWR and maximum power transfer to your antenna — fully utilize your transmitted power even at high ambient temperatures

Product Description

During broadcasting, RF heating of the inner and outer connectors causes differential expansion between them. With original design rigid transmission line, this expansion is compensated for with sliding metal bullets. Eventually this produces wear, hot spots—and burnout. Experienced broadcast consultants recommend replacing these bullets every seven years to avoid sudden failure.

The solution to eliminating sliding-contact wear is to eliminate the sliding. All expansion of the ERI, patented, MACXLine® inner connector is taken up with a flexible, built-in bellows; once put into service. Burnout and bullet replacement are eliminated. This advantage comes with no VSWR penalty or significant cost premium.

MACXLine® is manufactured by ERI from high conductivity copper tubing, outer conductors. Extra strength, custom PTFE dielectric disk insulators maintain precise mechanical alignment. Each section comes complete with a bullet/bellows assembly, stainless steel flange hardware and pressure sealing O ring gasket.

WIDELine™ Broadband Rigid Coaxial Transmission Line

ERI’s MACXLine® is also available configured as a WIDELine™ that allows multiplex DTV television signals and minimize VSWR spikes, while extending the life of their transmission line. WIDELine™ wideband transmission line is made up of different length sections to minimize the addition of reflections. The result is excellent VSWR performance of a maximum of 1.1:1 over all UHF-TV channels in the U.S. FCC core spectrum.

For example, a 1,480-foot run of WIDELine™ transmission line (8-3/16-inch, 75-ohm) was calculated to have a maximum VSWR of slightly more than 1.08. Actual field results may vary, but VSWR will not exceed 1.1:1 for any UHF-TV channel 14 through 51.

ERI WIDELine™ transmission line also protects your investment by eliminating problems caused by sliding bullet-type connections found in conventional rigid transmission line. Conventional rigid line is capable of accepting future changes in frequency assignments, with acceptable VSWR performance, however, its service life is limited by the rubbing of its connection points, which can ultimately lead to bullet burnout or arc-over. WIDELine™ transmission line incorporates a unique, patented bellows section into each inner conductor that compensates for differential expansion between the inner and outer conductors. Mechanical wear from sliding contacts is thus eliminated. The result is extremely long life. Since 1984, more than 200 broadcasters have selected transmission line using this technology, without a single failure due to bullet burnout. WIDELine™ is available in 3-1/8-inch,4-1/16-inch, 6-1/8-inch, 7-3/16-inch and 8-3/16-inch sizes.

DUALine™ Custom-Length, Dual-Channel, Rigid Transmission Line

If full wideband performance is not required, ERI will calculate the optimum rigid line section length to minimize VSWR, by using a proprietary computer program. Sections would normally be 20 feet long, or somewhat shorter and would all be the same length to simplify installation. This solution is ideal for applications where the DTV and NTSC signals are combined in a single line, as it typically results in outstanding VSWR performance (depending on which channels are combined).

Inners Only™ Inner Conductors Replacement System

MACXLine® transmission lines are available as Inners Only™ replacements. Since MACXLine® lengths are identical to those of standard rigid line, it is an excellent choice for any application.

Conventional rigid transmission line systems require maintenance after just ten years to avoid premature burnout of bullet-style connectors. By upgrading with ERI Inners Only™ before your existing transmission line fails, you avoid the disaster of dead air.

MACXLine® Inners Only™ replacements provide the ultimate in operational dependability at about half the cost of a new installation. You swap your worn-out, failure-prone bullets and inner conductors for the most dependable components in the industry while reusing your expensive outer conductors, which are normally good for many more years of service.

Related Publications

ERI Rigid Transmission Line Catalog

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Attenuation and Power Handling Tables for ERI Rigid Transmission Line

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