Coax Cable Delay Calculator
Calculate one-way propagation delay, round-trip delay, propagation velocity, wavelength in the cable, electrical length, and RF phase shift for a coaxial cable.
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Math
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Enter parameters and click Calculate to view results
Formula & Theory
Velocity = c × VF, Delay = Length / (c × VF), Phase = 360° × f × Delay, λc = (c × VF) / fThis formula is used to calculate antenna parameters for coax cable delay calculator.
Overview
The Coax Cable Delay Calculator computes one-way and round-trip propagation delay (nanoseconds), guided signal velocity, wavelength in cable ($lambda_c$), electrical length ($lambda$), and RF phase shift for coaxial transmission lines. Essential for phased array feed networks, antenna phasing harnesses, and high-speed digital clock alignment.
Input Guide
Enter Cable Length, Velocity Factor, Frequency exactly in the units shown by this coax cable delay. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Cable Length — use m.
- Velocity Factor.
- Frequency — use MHz.
Output Guide
The results describe the calculated coax cable delay values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The Coax Cable Delay uses Velocity = c × VF, Delay = Length / (c × VF), Phase = 360° × f × Delay, λc = (c × VF) / f. Supply Cable Length (m), Velocity Factor, Frequency (MHz) in the displayed units, then use the calculated values as the first engineering target for this transmission lines design or analysis.
Design Notes
RF signals travel slower through coaxial cables than through free space due to the relative dielectric constant ($epsilon_r$) of the insulating material ($VF = 1 / sqrt{epsilon_r}$). Solid polyethylene (PE) dielectrics yield a velocity factor of $VF approx 0.66$ ($approx 5.06 ext{ ns/m}$ delay), foam polyethylene achieves $VF approx 0.80 ext{--}0.85$ ($approx 3.9 ext{--}4.1 ext{ ns/m}$ delay), and PTFE (Teflon) ranges between $0.69 ext{ and }0.88$. Accurate delay matching is critical in phased arrays and TDR (Time Domain Reflectometry) cable fault detection.
Build and Tuning Notes
When building phase-matched cable pairs or delay lines, measure actual velocity factor ($VF$) using a Vector Network Analyzer (VNA) or Time-Domain Reflectometer (TDR) rather than relying solely on manufacturer nominal datasheet values. Cable temperature fluctuations and mechanical bending radii alter physical cable propagation delay and phase stability.
Frequently Asked Questions
How is coaxial cable propagation delay calculated?
Propagation delay ($ au$) is calculated using cable length ($L$), speed of light ($c$), and dielectric velocity factor ($VF$): $ au = L / (c cdot VF)$. In nanoseconds per meter, delay is approximately $ au_{ ext{ns/m}} = 3.335 / VF$.
What is Velocity Factor (VF) in coaxial cables?
Velocity Factor is the ratio of signal propagation speed inside a cable to the speed of light in vacuum. It depends directly on the relative dielectric constant ($epsilon_r$) of the insulating dielectric: $VF = 1 / sqrt{epsilon_r}$.
Why is Round-Trip Delay important in RF testing and TDR?
Time Domain Reflectometers (TDR) measure the time taken for an RF pulse to travel down a cable and bounce back from a fault or mismatch. The distance to the fault is calculated as $ ext{Distance} = ( ext{Round-Trip Delay} cdot c cdot VF) / 2$.
How does coaxial cable length introduce RF phase shift?
Signal propagation delay translates directly to phase shift ($Deltaphi$) at a given frequency ($f$): $Deltaphi = 360^{circ} cdot f cdot au$. Phase-matched cables ensure signals arrive perfectly in phase across multi-element antenna arrays.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.