Calculation Result
Advanced Cable Calculator
Example Data Table
| Frequency | Cable Type | Velocity Factor | Mode | Approx Length | Use Case |
|---|---|---|---|---|---|
| 145 MHz | LMR-400 | 0.82 | Quarter wave | 0.424 m | VHF matching stub |
| 433 MHz | RG-58 | 0.66 | Half wave | 0.229 m | UHF test lead |
| 27 MHz | RG-8X | 0.78 | Full wave | 8.661 m | Radio feeder estimate |
Formula Used
The free-space wavelength is calculated with:
λ = c / f
Here, c is the speed of light, about
299,792,458 m/s. The value f is frequency in hertz.
The wavelength inside a coaxial cable is shorter because signal speed is reduced:
λcable = λ × VF
Cable length by electrical angle is:
L = λcable × degrees / 360
One-way delay is:
Delay = L / (c × VF)
Estimated cable loss is scaled from the reference loss:
Loss = loss100ft × (f / fref)^n × lengthft / 100 + connector loss
How to Use This Calculator
- Enter the operating frequency and select the correct unit.
- Choose a cable type or select custom velocity factor.
- Select full wave, half wave, quarter wave, degrees, or target length.
- Enter loss data if you want an attenuation estimate.
- Press the calculate button to view results above the form.
- Use CSV or PDF buttons to save the calculation.
Coaxial Cable Length Planning
Why Length Matters
Coaxial cable length is important in many Physics and radio systems. A cable does not only carry energy. It also adds delay, phase shift, and attenuation. These effects can change measurements. They can also change matching networks, antenna stubs, and timing lines. A small length error may matter at high frequency. It becomes more serious as wavelength becomes shorter.
Velocity Factor
Signals inside coaxial cable travel slower than light in free space. The velocity factor shows this speed ratio. A solid polyethylene cable may have a lower factor. Foam dielectric cable usually has a higher factor. The calculator multiplies free-space wavelength by this factor. This gives the wavelength inside the cable.
Electrical Length
Electrical length describes cable length as part of a wave cycle. A quarter-wave section is 90 degrees. A half-wave section is 180 degrees. A full-wave section is 360 degrees. This idea is useful for impedance transformation, phasing lines, and tuned stubs. It is also helpful when comparing test leads at the same frequency.
Loss and Delay
Cable loss rises with frequency and length. The tool estimates this loss from a reference value. It also adds connector loss. The delay result shows how long the signal takes to travel one way. Round-trip delay helps with reflected signals and time-domain testing.
Practical Notes
Real cable data varies by brand, age, temperature, and installation. Bends, moisture, poor connectors, and adapters can add extra loss. For precise laboratory work, measure the cable with proper equipment. For general design, this calculator gives a fast and organized starting point. Always cut long first, then trim carefully during final tuning.
FAQs
What is coaxial cable length?
It is the physical length of cable used between devices. In high frequency work, it may also mean electrical length, which depends on frequency and velocity factor.
What is velocity factor?
Velocity factor is the signal speed inside cable compared with light speed in free space. A value of 0.82 means the signal travels at 82 percent of light speed.
Why is cable wavelength shorter than free-space wavelength?
The dielectric material inside the cable slows the signal. This reduces wavelength inside the cable. The calculator applies the velocity factor to adjust the result.
When should I use quarter-wave mode?
Use quarter-wave mode for matching stubs, impedance transformers, and resonant sections. It represents 90 degrees of electrical length at the chosen frequency.
Can this calculator estimate cable loss?
Yes. It estimates loss from reference attenuation, frequency scaling, length, and connector loss. Use manufacturer data for more accurate professional results.
What does electrical degrees mean?
Electrical degrees express cable length as part of one signal cycle. A full wavelength is 360 degrees. Half wavelength is 180 degrees.
Why does frequency change the cable length?
Higher frequency creates a shorter wavelength. Since tuned cable sections depend on wavelength, the required cable length becomes shorter as frequency increases.
Should I cut cable exactly to the calculated length?
For tuned work, cut slightly longer first. Then measure and trim carefully. Connectors, adapters, and real cable tolerances can shift the final result.