Yes. Dunno if I'd call it reliable though grin. If you had this kind
of system on a moving vehicle for example the RX would have to be able
to follow the TX. You'll get about +-200Hz shift with a speed of 100kph.
(ie 400Hz as a vehicle goes past you)

I have been intending for ages setting up a 2m beacon on my car and
seeing if I can yield any driving location/speed etc info from the shift
and phase noise. (11Hz at 100kph)

Cheers Bob VK2YQA

mazerom wrote:

the doppler shift is fundamentally a tone frequency brought about by a
continuous wave source moving in and out. is it possible to have
reliable doppler shift when our source is spread spectrum or say some
form of digital modulation?

Bob wrote, "You'll get about +-200Hz shift with a speed of 100kph."

Ahem. Care to qualify that as to the carrier or transmitted
frequency??

You know I am not quite sure how to answer that..

Doppler shift is a relative thing. If you are travelling at 100kph the
signal/carrier whatever relative to you is unaffected. Relative to a RX
that is relatively moving either towards or away from you a shift will
be apparent.

The entire transmitted spectrum will be affected, not just the
"carrier". There will of course be a calculable difference in shift over
the bandwidth of the signal as the lower end will shift less than the
upper one more. Whether it will be a significant amount or not depends
on your application. A +- 10MHz wide signal at 2.4GHz for example
(100kph) would be close to an extra 1Hz of shift at the signal edges.

As your relaitive velocities approach the speed of light other problems
crop up. I dont quite remember Einstein's stuff on this. Since though I
doubt I'll never get to experiment with it I dont need to go through it
again!

Is that what you were looking for?

Cheers Bob VK2YQA

K7ITM wrote:

Bob wrote, "You'll get about +-200Hz shift with a speed of 100kph."

Ahem. Care to qualify that as to the carrier or transmitted
frequency??

On Tue, 07 Mar 2006 10:07:46 -0600, Bob Bob wrote:

I dont quite remember Einstein's stuff on this.

Hi Bob,

Actually it was Lorentz.

Since though I
doubt I'll never get to experiment with it I dont need to go through it
again!

Not hard to do if you think in terms of a Klystron tube. Although it
might not directly use Doppler within the stretch of its beam current,
the tube structure is quite decidedly built for speed of light and
wavelength bunching. Hop in a car with one and you got your 100 kM/h.

Walla (as the french say) you've built your own speed trap radar
beacon.

73's
Richard Clark, KB7QHC

yes sir.thanks for this

yes sir.thanks for this