# Velocity Factor

1. Sep 4, 2004

### edieber

is the Velocity Factor is a factor to caculate the length wave(gama) or its only connected to the type of the cabe

2. Sep 4, 2004

### Integral

Staff Emeritus
Could you try rephrasing the question? Perhaps there are others on the board who speak your native language who will help you translate.

3. Sep 4, 2004

### edieber

I just want to know the meaning of Velocity Factor and if it influence the calculation of the length wave? :uhh:

4. Sep 4, 2004

### jcsd

Your going to have to be alot clearer and give the context as what you are using is from what I gather the 'velocity factor' is engineering terminlogy referring to the speed of propagation of a signal as a fraction of c, though I could be wrong (and I think you mean wavelength not 'length wave').

5. Sep 4, 2004

### edieber

do you know if it influence the wavelength?

6. Sep 4, 2004

### Tide

Yes, the relative speed of the source and the detector influences the observed wavelength.

7. Sep 4, 2004

### edieber

what is formula to calculate the wavelength if Velocity Factor is 0.66
and Er=1.2 for example

8. Sep 4, 2004

### jcsd

ou have to be clearer 'cos I'm not exactly sure what you're talking about: what exactly are we delaing with? are we dealing with an electrical signal through a wire?

9. Sep 4, 2004

### edieber

yes! electrical signal through a wire

10. Sep 4, 2004

### jcsd

You'd do a lot, lot better to post this on the engineering forum, but:

wavelength = velocity factor*(the speed of light in a vacuum/frequency)

11. Sep 4, 2004

### edieber

where do you take under consideration the Er ?

12. Sep 4, 2004

### jcsd

What is 'Er'?

13. Sep 4, 2004

### edieber

Code (Text):
$$\epsilon_r$$
dialectrical coefficient

14. Sep 4, 2004

### jcsd

I'll have to say I don't know how you'd go about calcualting or even if you can calculate it from the velcoity factor and the dialectric cooefficient ,though I think your not after the wavelength but the reflection coefficient.

15. Sep 4, 2004

### Tide

$$\lambda_{observed} = \lambda_{source} \sqrt { \frac {1-\frac {v}{c}}{1+\frac {v}{c}}$$

16. Sep 5, 2004

### edieber

why you don't take under consideration $$\epsilon_r$$
the dialectrical element

17. Sep 5, 2004

### Tide

Because I don't fully understand your question. If you are talking about a transmitter and a receiver that are in relative motion with respect to each other then I presume the signal is propagating through empty space or possibly air whose dielectric constant is very close to 1. It doesn't make sense to me that one end of a cable would be moving relative to the other if that's the medium you are talking about.

18. Sep 5, 2004

### pervect

Staff Emeritus
I think he's talking about the velocity of signal transmission along a coaxial cable, or possibly a transmission line.

as in for instance

http://www.nr6ca.org/vf.html [Broken]

If so, the velocity factor should be approximately c/sqrt(Er), where Er is the permitivity of the dielectric material relative to the permitivitty of free space.

Last edited by a moderator: May 1, 2017
19. Sep 5, 2004

### Tide

Oh, okay! I've never heard it called a "velocity factor."

Last edited by a moderator: May 1, 2017
20. Sep 5, 2004

### edieber

how come if Er=1.24 put it in the formula c/sqrt(Er) it never will be vf=0.666 for example

Last edited by a moderator: May 1, 2017