Bird Technologies - Everyone Needs Good Connections

Our thanks to Bird Technologies for allowing us to reprint the following article.
By Lynn Strube, Bird Technologies Group Applications Engineer


Connectors are a 21st century fact of life. If cables couldn't be connected, but were spliced, system specs would be better, but repair would be more expensive and complicated. Too many times, we think of connectors as something different from feed lines, but the same laws of physics apply. The ratio of the outer diameter of the inner conductor to the inner diameter of the outer conductor determines the impedance of the connector. Any changes in these measurements will result in a change in impedance and will cause reflected power or VSWR.

IMPEDANCE is a function of the diameters of the center conductor to the outer conductor.

Zo = 138/ve log10 (D/d)

  • Where Zo = Impedance
  • e = the dielectric constant of the insulating material
  • D = outer conductor diameter
  • d = inner conductor diameter

VSWR is the ratio of maximum and minimum voltages on a transmission line caused by the combination of a forward and reflected wave.

VSWR = [1+ Sqrt (Pr / Pf)] / [1 - Sqrt (Pr / Pf)]

  • Pr = Reflected Power (Watts)
  • Pf = Forward Power (Watts)

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