ROTOTILLER® Circularly Polarized FM Antennas


  • Product Line
  • Frequency Range
    88 - 108 MHz
  • Multiplexed Versions Available
  • Broadband Applications
  • Polarization
  • Azimuth
    ± 2 dB in free space
  • VSWR at Input:
    1.07:1 or less (with field matching)
  • 1.25:1 or less (with top pole or LAMBDA™ Mounting System)
  • 1.50:1 or less (top mounted without field matching)
  • Maximum Power Rating

ERI antennas are unchallenged in quality and dependability. ERI is the only manufacturer to use large diameter outer conductors and a completely enclosed, pressurized, internal series feed system. The result is a simple and reliable method of coupling power to the elements. Unlike competing designs, ERI series fed antennas do not require a troublesome secondary current loop for element excitation with all the resulting disadvantages. All ERI antennas include brackets for mounting on leg, pole, or face mounting (up to 42-inch uniform cross section tower); brackets for other mounting configurations are optionally available.

ERI’s original and distinctive design combines the exceptional engineering features of an internally fed, fully pressurized system with superior fabrication characterized by totally welded feed connections, rugged brass material and TIG welding. The ROTOTILLER® FM antenna’s unique design consists of two series fed, bent dipole elements which form a space phased, circularly polarized radiator. The antenna’s configuration and the large diameter of the radiating elements contribute to the excellent bandwidth of the antenna system, and also inhibits corona discharge.

The horizontally polarized horizontal plane azimuth pattern of the SHPX series antenna is omnidirectional within ±2 dB when the antenna is pole or LAMBDA™ Optimized Mounting System mounted atop a tower. Side mounting the antenna on a typical tower structure will affect the azimuth pattern. ERI offers a pattern measurement service to assist in determining the effect of the mounting structure on the antenna’s pattern. Using ERI’s pattern optimization service, the pattern’s circularity may be improved through the addition of parasitically excited elements.

  • Low VSWR, superior VSWR band width, and minimal weather r
  • Fully pressurized, internal feed and welded feed connections
  • High input power capacity
  • Modular construction facilitates easy installation and repair
  • Rugged brass construction and stainless steel support brackets and hardware – Corrosion resistant construction
  • Radomes or deicing heaters not normally required for radial ice less than 1/2-inch; however radomes or deicing heaters are available
  • Quarter Wave Stub included

Type Number Definition

a - b c d e - f - g - h
  • a
    Model: SHP | LP | MP
  • b
    Number of Bays
  • c
    Interbay Line Size: A = 3 1/8 inch | B = 4 1/16 inch | C = 6 1/8 inch
  • d
    Input Feed Configuration: E = End Fed, C = Center fed for even number of bays, off center fed for odd number of bays
  • e
    RF Input Size ("SHP A" Series Only): Blank = 3 1/8 inch | 6 = 6 1/8 inch
  • f
    Design Note 1: Blank = Omnidirectional | DA = Directional Azimuth Pattern
  • g
    Design Note 2: Blank = Full wave length bay to bay spacing | HW = Half wave length bay to bay spacing
  • h
    Design Note 3: Blank = Standard product | SP = Special Design
  • Example
  • Description
    ERI Model SHP ROTOTILLER FM Antenna, four bay, 4 1/16 inch interbay line, center fed, directional azimuth pattern, half wave length bay to bay spacing.


  • Anti-rotation brackets
  • Beam tilt (center fed antennas only)
  • First null fill (center fed antennas only)
  • Second null fill (center fed antennas only); Second null fill not available for LP antennas
  • Beam tilt and first null fill (center fed antennas only)
  • Radomes
  • Deicers (600w/220v)
  • Stem heaters (300w/220v)
  • Export packing

Mounting Information

Utilize the ERI Advantage

Combine an ERI antenna with an ERI Mounting Structure, Pattern Measurement and Installation. Assure yourself of the best antenna/tower interaction. ERI’s Pattern Measurement service will provide the crucial answers concerning the relationship between the antenna mounting orientation and antenna pattern.

ERI Mounting Sections are designed to achieve optimum antenna performance while reducing weight and wind loads. Only ERI can offer you an antenna/tower/installation package that will achieve your highest expectations in a demanding FM market. Contact Electronics Research for complete electrical and mechanical specifications.

Related Publications

ROTOTILLER® Circularly Polarized FM Radio Antenna Brochure

Download File

The original ROTOTILLER® circularly polarized FM (88 – 108 MHz) antenna combines the exceptional engineering features of an internally fed, fully pressurized system with superior fabrication characterized by totally welded feed connections, rugged brass material and TIG welding. The ROTOTILLER is available in low, medium, and super high power versions; capable for single frequency or multiplexed operations; and suitable for directional applications.