How do I calculate the time delay through a length of coaxial cable?
Cable Delay Calculation
Every length of coaxial cable introduces a time delay because the signal travels at less than the speed of light through the dielectric medium. This delay is constant with frequency for TEM-mode cables (coax below the TE11 cutoff) and is proportional to the cable length.
| Parameter | Semi-Rigid | Conformable | Flexible |
|---|---|---|---|
| Loss (dB/m at 10 GHz) | 0.8-2.5 | 1.0-3.0 | 1.5-5.0 |
| Phase Stability | Excellent | Good | Fair |
| Bend Radius | Fixed after forming | Hand-formable | Continuous flex OK |
| Shielding (dB) | >120 | >90 | >60-90 |
| Cost (relative) | 2-5x | 1.5-3x | 1x |
Frequently Asked Questions
Is the delay frequency-dependent?
No, for coaxial cable operating below the TE11 cutoff. TEM-mode propagation is non-dispersive in a homogeneous dielectric. Above the cutoff frequency, waveguide-like dispersion makes the delay frequency-dependent. This is one reason to keep below the cable's rated frequency.
Can I use cable as a delay line?
Yes. Coaxial cable delay lines are used in radar, signal processing, and test equipment. For precise delays, use phase-stable cable with accurately known velocity factor. Temperature stability matters: a 1-meter PTFE cable changes delay by approximately 8 ps per degree C.
Does cable loss affect the delay?
No. Loss attenuates the signal amplitude but does not change the propagation velocity or delay. A lossy cable has the same delay as a lossless cable of the same length and dielectric. The signal arrives at the same time, just with lower amplitude.