does doppler systems work only for unmodulated continous wave signals?
 

On 6 Mar 2006 04:26:05 -0800, "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?

Back around '57 or so, the beep-beeping of the Sputnik satellite was
used to track its orbit by measuring the Doppler effect.

bob
k5qwg

does doppler systems work only for unmodulated continous wavesignals?
 

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??

does doppler systems work only for unmodulated continous wave signals?
 

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

does doppler systems work only for unmodulated continous wave signals?
 

yes sir.thanks for this

does doppler systems work only for unmodulated continous wave signals?
 

yes sir.thanks for this

does doppler systems work only for unmodulated continous wave signals?
 

the answer is... it depends. most cheap ham style doppler direction finders
with electrically rotated arrays may have trouble locking on to the doppler
shift if it is modulated in some ways. modulation frequencies that cause
phase shifts near the simulated rotatation frequency will be worst as they
will likely be detected by the simple audio phase detector as the doppler
signal and throw it off. if you use a better demodulator that is matched to
the type of signal you are tracking and still can produce an output that is
locked to the phase of the rotating array then it will work. this means if
it is a wideband digital signal you will have to lock on to the base signal
and still differentiate the rotation caused phase shift on top of it... not
always an easy job.

"mazerom" wrote in message
ups.com...
thanks for your comprehensive knowledge.
i intend to make my signal source stationary and would like to emply a
rotating/switching antenna to produce the doppler shift..based on your
explanation,it wont matter what type of signal my source is whether
digital or pure CW signal.assuming a GFSK signal or spread
spectrum(FH), a "reliable" doppler shift will be measured...any
objection or comment sir?

thanks

does doppler systems work only for unmodulated continous wave signals?
 

hello dave,

same thought here..i wish to use 2.4ghz as my carrier and a doppler
shift in the kHz range.
any recommendation on good FM receivers in this frequency?
thanks

does doppler systems work only for unmodulated continous wave signals?
 

On 7 Mar 2006 17:52:39 -0800, "mazerom"
wrote:

hello dave,

same thought here..i wish to use 2.4ghz as my carrier and a doppler
shift in the kHz range.
any recommendation on good FM receivers in this frequency?
thanks

To give you 10% resolution will require it have its local oscillator
accurate (and stable) to one part in 100 Billion (of course, same goes
for the source). Hmm, maybe Bang & Olufson....

Laser interferometry would be simpler, and probably cheaper too.

73's
Richard Clark, KB7QHC

does doppler systems work only for unmodulated continous wave signals?
 

what are you mumbling about richard? doppler direction finders operate at
audio frequencies and since the detector and switching system operate from
the same clock they are perfectly accurate... at least as well as you can
calibrate the phase reference between the demodulator and clock.

"Richard Clark" wrote in message
...
On 7 Mar 2006 17:52:39 -0800, "mazerom"
wrote:

hello dave,

same thought here..i wish to use 2.4ghz as my carrier and a doppler
shift in the kHz range.
any recommendation on good FM receivers in this frequency?
thanks

To give you 10% resolution will require it have its local oscillator
accurate (and stable) to one part in 100 Billion (of course, same goes
for the source). Hmm, maybe Bang & Olufson....

Laser interferometry would be simpler, and probably cheaper too.

73's
Richard Clark, KB7QHC

does doppler systems work only for unmodulated continous wave signals?
 

On Wed, 8 Mar 2006 23:19:10 -0000, "Dave" wrote:

what are you mumbling about richard? doppler direction finders operate at
audio frequencies and since the detector and switching system operate from
the same clock they are perfectly accurate... at least as well as you can
calibrate the phase reference between the demodulator and clock.

Hi Dave,

Look at the question again asking for an "FM" receiver. This would
require the action of the discriminator which operates relative to the
LO. Any frequency offset would be a bias, not an audio frequency.
There are two sources in this question, the doppler transmitter, and
the doppler detector. This requires coherence. The magnitude of the
doppler shift has been described all over the map without a strict
correlation to the speeds (or applications) involved. When discussion
devolves to FM detection of a base frequency of 2.5GHz shifting KHz (6
orders of magnitude), the necessary components (for coherence of the
whole system) demand a rather strict requirement for stability and
accuracy for any suitable resolution.

And, of course, some doppler applications can do it with far better
economy - but that wasn't asked for.

73's
Richard Clark, KB7QHC