Model 430 FM Isolation Transformer

The Model 430 is a high-power, broadband version of isolation transformer within ERI’s full line of isolation transformers.  The Model 430 was developed for use across the entire commercial FM band (92.1 MHz to 107.9 MHz), in order to allow multiplexed Master FM Antenna systems to be mounted on AM transmission towers.

Isolation transformers couple FM across the base insulator of an AM broadcast station transmitting tower, with little or no effect on the AM base impedance and no mismatch into the FM antenna feed line.  An isolation transformer is especially desirable for feeding high impedance AM radiators or towers that are part of a directional array where “bazooka” isolation systems would have adverse effects.

The transformer’s passive design is free of critically tuned resonating elements, which results in an excellent match and low insertion loss over the wide operating range.  Conservatively rated at 70 kilowatts, the Model 430 is perfectly suited for operation in multiplexed broadcasting configurations. In addition, the rugged design makes the Model 430 well-suited for harsh environmental conditions.  The Model 430 is designed to be used within pressurized systems and includes other features such as a spark gap for lightning protection, a weather shield, and an integrated support stand for ease of installation.

ERI Model 430 Broadband FM Isolation Transformer Outline Drawing

430 FM Isolation Transformer Specifications

  • FM Operating Frequency:
    Broadband over the commercial FM band 92 to 108 MHz
  • AM Peak Voltage:
    40,000 volts
  • AM Shunt Capacity:
    Approximately 150 pf
  • Continuous FM Power Rating:
    70 kW
  • FM Instertion Loss:
    0.05 dB, maximum
  • VSWR:
    <1.1:1 maximum
  • Lightning Protection:
    DC short circuit across inner and outer conductors on both input and output.
  • FM Leakage Isolation:
    Signal level measured between the outside of the coaxial output line and the transformer grounded case will be at least 30 dB down from the FM carrier level.
  • Mounting:
    Supplied with mounting stand
  • Pressurization:
    Designed for gas pass operation with a recommended pressure of 3 to 5 PSI (21 to 35 kPa) not to exceed 10 PSI (69 kPa).
  • Input Connector:
    6-1/8-inch EIA, 50 ohm, fixed male
  • Output Connector:
    6-1/8-inch EIA, 50-ohm, female, with included male to male adapter on output.
  • Weight:
    625 pounds (283.5 kilograms)
  • Length of Transformer:
    79-inches (207 mm)
  • Tank Diameter:
    26-inches (660 mm)
  • 29-inches (737 mm) at flanged end
  • Height (with mounting stand):
    58-5/8-inches (1489 mm) overall
  • 54-inches (1372-mm) to center line of input and output flanges

Ordering Information

  • Part No.
    Description
  • ITA0058
    FM Isolation Transformer Type 430, rated at 70 kW. Input is 6-1/8-inch EIA 50 ohm captive male. Broadband, 92.1 MHz to 107.9 MHz. Output is 6-1/8-inch EIA 50 ohm female, with included male to male adapter on output. Includes stand.

Information to be Specified with Order

Model 430 FM Isolation Transformer Product Brochure