1. Aug 8, 2007

### mixy

first HI to everyone!

I have a question:

is there a (simple) way to reduce radio wave speed at it's source - transmitor (e.g. to 100 or 1000x less then the speed of light)?

2. Aug 8, 2007

### ZapperZ

Staff Emeritus
Unless you are transmitting it in an ordinary dispersive medium, or a waveguide, no.

Zz.

3. Aug 8, 2007

### mixy

sorry but I have only basic phsycs knowledge. So ... what is an ordinary dispersive medium?

thx

4. Aug 8, 2007

### ZapperZ

Staff Emeritus
Example: water, glass, etc.

Zz.

5. Aug 8, 2007

### Mentz114

There's no simple way to this, but physicists are trying. Have a look at this -

www.hno.harvard.edu/gazette/1999/02.18/light.html [Broken]

physicsworld.com/cws/article/news/17870

Last edited by a moderator: May 3, 2017
6. Aug 8, 2007

### ZapperZ

Staff Emeritus
But again, those require a medium. The NEC experiment from a few years ago requires an "anomalous" dispersive medium. Things will still go back to normal if the signal goes back into air/vacuum.

So unless one is willing to live in water or in those medium, there's nothing one can do to change the speed of light.

Zz.

7. Aug 8, 2007

### Danger

Hi, Mixy.
I don't suppose that simply introducing a delay circuit into the transmitter would simulate the effect enough for your purposes? What I mean is, do you actually want the signal to go slower, or just get there later?

8. Aug 9, 2007

### mixy

Thx for the help.

Danger: no, just interested in actually slowing it down (travelling thru air)

9. Aug 9, 2007

### chroot

Staff Emeritus
You can design a signalling standard based on phase velocity instead of group velocity. Then you can accomplish arbitrarily slow transmission of information, even though the actual signals propagate at c.

- Warren

10. Aug 14, 2007

### mixy

Is there an estimation on how much velocity is reduced (average) in using radio waves in cities or populated regions (trees, hills, houses, etc.) ?

Is this frequency dependent?

thx
Miha

11. Aug 14, 2007

### Staff: Mentor

Sending radio through a city is still just sending it through air. A building can block or reflect radio, but won't slow it down.

12. Aug 14, 2007

### mixy

so, a radio wave would travel the distance from point A to point B in constant time T, no matter what stands between this two points (buildings, trees ...) ?

13. Aug 14, 2007

### Integral

Staff Emeritus
Pretty much, yes. You can get reflections which can mean that the same signal can take different paths to reach the same point, but the speed is the same.

14. Aug 14, 2007

### mixy

but wouldn't it take longer then - if the signal takes different paths (consider measuring time T in nano or piko seconds)?

15. Aug 14, 2007

### K.J.Healey

Takes longer because the path length is longer, the speed stays the same.

16. Aug 14, 2007

### Staff: Mentor

In analog television received over the air with an antenna, this is what causes "ghosts:" faint secondary images that are shifted slightly to one side of the main image on the TV screen. Reflected signals from a large nearby object (building, water tower, etc.) take slightly longer to reach the antenna because they have to travel a longer path.