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RF Bridge in an Original Size FLEXI-BOX



RF Bridge 3 MHz to 300 MHz
Insertion Loss 0.5 dB  ± 0.4 dB
Directivity > 30 dB
Coupling 16.5 dB ± 1.0 dB
Return Loss > 20 dB
Impedance 50 Ohms
Power Handling +30 dBm
 Box Dimensions
63.5 mm x 50 mm x 30.5 mm
From GBP £37.56 + Connectors
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  A RF Bridge with selectable BNC, N, SMA or TNC 50 Ohms connectors and built in an original size FLEXI-BOX screened enclosure


    [Photograph of RF Bridge Box showing connectors]



  The price of the RF Bridge FLEXI-BOX is dependant on the connectors required. To find the price for your connector preference or to make a purchase, select your connector requirements in the boxes beside the photograph above and then select "Add to Cart".

[Insertion Loss and Coupling Factor Graph v Frequency]

[Return Loss v Frequency Graph]


  The RF Bridge is built in an Original size FLEXI-BOX on a dedicated PCB. The connectors can be selected from BNC, N, SMA and TNC. The bridge is a 50Ω device and has an Input, Output and a Coupled Output. The bridge is intended as a measurement aid and is also part of the "Standing Wave Kit". We can build and test these at Chemandy with an insertion loss of 0.5 dB ± 0.4 dB, coupling 16.5 dB ± 1.0 dB and directivity better than 30 dB from 3 MHz to 300 MHz. See figures 1&2.

Bridge Principal

  The RF Bridge uses two transformers which can be wound on two separate toroidal ferrite cores or one binocular ferrite. These can be connected with phase relationships as per Figure 3 and this gives a 1800 coupler. By altering the phase of the windings, a 00 coupler can be configured. The bridge measures power with the (top, in Figure 3) transformer inserted in the line detecting current and the lower transformer detecting voltage. This device is sometimes called a Tandem Bridge and often called a coupler.

  If a signal is passed from the Input to the Output, it will also appear on the Coupled output, but at a lower level. The difference in input level and the level at the Coupled output is the Coupling. A signal passing from the Output to the Input will appear on the Coupled output but at a very low level and a perfect bridge would have no output in this direction. The difference in level at the Coupled output between a signal applied to the Input and a signal applied to the Output is the Directivity. The value of the termination determines the impedance of the bridge and in some designs, this is can be provided by an external load. The use of an internal load allows the circuit to be adjusted for optimum performance, mainly directivity.

Figure 3

[Bridge circuit]

  A more detailed description can be found at Understanding Coaxial RF Transmission Lines by Measurement and Calculation Appendix B1. There is also a very good article on these devices at