RigExpert AA-35 ZOOM - Page 15

RigExpert AA-35 ZOOM
Velocity factor measurement
For a known resonant frequency and physical length of a cable, the actual value of the
velocity factor can be easily measured:
3. Calculate the physical length of the
cable by dividing the above speed by
the resonant frequency (in Hz) and
multiplying the result by the number
which corresponds to the location of this
resonant frequency (1/4, 1/2, 3/4, 1, 5/4,
etc.)
197,863,022 / 4,100,000 × (1/4) =
12.06 meters
- or -
649,156,897 / 4,100,000
× (1/4) =
39.58 feet
3. Finally, find the velocity factor .
Just divide the above speed by the
electromagnetic constant.
Example:
5 meters (16.4 feet) of open-circuited
cable. Resonant frequency is 9400 kHz
at the 1/4-wave point.
2. Calculate the speed of electromagnetic
wave in this cable. Divide the length
by 1/4, 1/2, 3/4, etc. (depending on the
location of the resonant frequency), then
multiply by the resonant frequency (in
Hz).
5 / (1/4) × 9,400,000 =
188,000,000 meters per second
- or -
16.4 / (1/4)
× 9,400,000 =
616,640,000 feet per second
1. Locate a resonant frequency as
described above.
188,000,000 / 299,792,458 = 0.63
- or -
616,640,000 / 983,571,056 = 0.63
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