Calculates Delay, Velocity Factor, Effective Dielectric Constant and Characteristic Impedance of a PCB track. This calculator can also be used for measuring coaxial cable and will then give Relative Dielectric Constant rather than Effective Dielectric Constant. The operation of this calculator can be better understood by first reading Measuring Characteristic Impedance and Effective Dielectric Constant of PCB tracks using a Vector Network Analyser
The time delay (ta) at a + 900 point is found by dividing the total phase shift at the measured + 900 point by the phase shift per second due to frequency
Where f is the frequency in Hz at + 900
rev is the number of completed revolutions of phase before the + 900 point is reached
Similarly the time delay (tb) at a - 900 point is found by dividing the total phase shift at the measured - 900 point by the phase shift per second due to frequency
The average time delay (tav) for + 900 and - 900 is then
Finding the Velocity Factor
Equivalent delay in free space for a similar distance
Where l is the length of the track in mm
c is the speed of light in free space
An average of the measurement frequencies is found
The principal of deriving the Characteristic Impedance from an OPEN and SHORT measurement is based on Transmission Lines and Networks by Walter C. Johnson, McGraw-Hill 1963 p155 Para 4.7 Measurement of the Characteristics of lines.
This calculation is combined for two adjacent measurements and so ripple (measurement error) caused by the mismatch of the VNA to the transmission line is also removed.
W J Highton Updated 4/4/2008
This calculator is provided free by Chemandy Electronics in order to promote the FLEXI-BOX
Return to Calculator Index