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Directional 3dB Couplers
DC Series 88 - 108 MHz

  • The DC series of directional couplers are commonly used within channel combiners and in switch frames as splitters for dual input antenna systems. Also, they can be used as stand-alone transmitter combiners and splitters.
  • Flanged versions are normally used in antenna systems and are therefore designed for outdoor use where they may be pressurised. Pressurisation details are the same as those used for RFS antenna system components: test pressure is up to 100kPa and operational pressure is 14 -25 kPa. Note that all connectors of the flanged couplers are gas pass to allow air pressure to flow through the antenna feed system.
  • Crossed outputs (i.e. on same side of coupler) are standard in order to simplify equipment layout (not available in ""N"" type versions).
  • Each coupler size is defined by its ""standard"" connector size. For example: an FM 3dB coupler rated for 50kW usually has 3-1/8"" connectors, so this coupler is defined as a model DC31BU. Using RFS developed R series adaptors for connector sizes 7/8"" to 6-1/8"", all coupler ports can be adapted to any size flanged or unflanged EIA or IEC standard.
  • A coupler consists of a pair of strip lines approximately a quarter wavelength long configured in such a way to provide the required couplings.
  • If two signals of similar amplitude in phase quadrature are applied to Ports A and B (with B leading) the sum will appear at Port C. The arrangement provides good isolation between inputs with low VSWR over a wide bandwidth without adjustment.
  • If the inputs do not have the correct amplitude and/or phase relationship, an out of balance signal is dissipated in a load connected to Port D. Conversely a signal applied to Port C will split to give two outputs of equal amplitude in quadrature at Ports A and B.


3dB coupler series demonstrated showing DC31EU model with flanged and unflanged connectors

Technical features

General Specifications

Product LineComponents
Product TypeDirectional 3dB Couplers

Electrical Specifications

Frequency Range MHz88 - 108
Frequency BandVHF Band II
Power RatingkW50
Input Return LossdB30 (35 on specified channel)
Output Power SplitdB3 ± 0.15 Note 2
Output Phasedegrees90 ± 1 Note 2

Mechanical Specifications

Standard Connector Size3-1/8" EIA

External Document Links


Note 1 Power ratings are based on an ambient temperature of 40 degrees C and represent the maximum average power at any ports, at the highest operating frequency in each band.
Note 2 Across full band.