785 FM Notch Filters

The ERI Model 785 is a compact FM Notch Filter rated to handle up to 35 kW. It is available as a single cavity or multiple cavities can be combined for higher suppression of a single frequency or rejection of multiple FM channels.


ERI filters and combiners have served the broadcast industry for over 40 years. The basic building block of ERI’s combiner and multiplexers system is a unique filter cavity. Only ERI offers an all copper and brass cylindrical cavity and all internal components in the RF path are silver plated. The result is an extremely efficient (low loss) and stable filter. ERI filters include a unique temperature compensation assembly which maintains the filters performance from a cold start to normal operating temperature without causing high transmitter VSWR.

With good antenna sites scarce and tower costs staggering, radio stations tend to operate their antennas in close proximity to one another. With close frequency spacing possible, radiation coupling between antennas is unavoidable and can be quite high. Ideally, a radio station transmitter would transmit power on just its assigned channel. Unfortunately, due to undesired coupling, a product frequency may be radiated as well. This product frequency or emission may actually compete with a station existing on or near its frequency. The FCC regulates these emissions and they must be suppressed. ERI 785 Notch Filter may be arranged in a series to achieve reduction of multiple frequencies and/or greater attenuation of any frequency.

Features and Benefits

  • High stability temperature compensated cavities
  • Copper/ brass construction with stainless steel hardware (critical components are silver plated)
  • Easily assembled floor standing units (hardware for ceiling suspension available on request)
  • Minor adjustment of cavity resonant frequency can be made during full power operation of the filter
  • Filters may be arranged in series to achieve reduction of multiple frequencies and/or greater attenuation of any single frequency
  • Each filter includes a built in temperature indicator
  • Factory tuned to customer’s specified channel, yet can be easily field converted to any FM channel
  • 785 Notch Filters are ideally suited to isolate radio station transmitters and reduce product emission to acceptable levels.


  • Band:
  • Frequency Range:
    88 to 108 MHz
  • Number of Cavities:
    1, 2, 3, 4, or 5
  • Cooling Method:
    Convection cooled
  • Notch Frequency Suppression:
    -25 dB, 0.8 to 1 MHz separation
  • -40 dB, greater than 1 MHz separation
  • 785 Power Handling:
    20 kW, 0.8 to 1 MHz separation
  • 35 kW, greater than 1 MHz separation
  • Insertion Loss:
    < 0.05 dB, 0.8 to 1 MHz separation
  • < 0.03 dB, greater than 1 MHz separation
  • VSWR (typical):
    1.07:1 ±100kHz, 0.8 to 1 MHz separation
  • 1.05:1 ±150kHz, greater than 1 MHz separation
  • Input and Output Connectors
    1-5/8-inch or 3-1/8-inch EIA Flange, captivated male

Product Brochure

785 Series FM Notch Filter Brochure

Download File