does doppler systems work only for unmodulated continous wave signals?
 

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?

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?

Yes

does doppler systems work only for unmodulated continous wave signals?
 

Wes Stewart wrote:
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?

Yes

does doppler systems work only for unmodulated continous wave signals?
 

just wanna confirm.
u were saying we can still get a reliable doppler shift from a
modulated signal be it analog or digital?
thank u so much

does doppler systems work only for unmodulated continous wavesignals?
 

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?

does doppler systems work only for unmodulated continous wave signals?
 

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 6 Mar 2006 06:09:02 -0800, "mazerom"
wrote:
just wanna confirm.
u were saying we can still get a reliable doppler shift from a
modulated signal be it analog or digital?
thank u so much
yes

does doppler systems work only for unmodulated continous wave signals?
 

yes, any em wave will be shifted in frequency/wavelength when there is a
relative velocity between the tx and rx.

doppler shift is NOT 'a tone frequency'. it may be heard as a tone in a
receiver if you beat it against a fixed local oscillator. But the doppler
shift does not modulate the wave or change the type of modulation that may
already be imposed on the wave by the transmitter.

now if you are talking about a doppler direction finder system... those work
best with unmodulated signals, but will work with modulated signals but may
have difficulty getting reliable directions, especially if the modulation
frequency is near the rotational frequency of the array.


"mazerom" wrote in message
oups.com...
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?

does doppler systems work only for unmodulated continous wave signals?
 

On 6 Mar 2006 06:09:02 -0800, "mazerom"
wrote:

just wanna confirm.
u were saying we can still get a reliable doppler shift from a
modulated signal be it analog or digital?
thank u so much

Yes.

The Doppler frequency equals the rate of change of the distance
expressed in wavelengths. Thus the Doppler shift is a function of
carrier frequency and relative speed difference. It doesn't matter one
bit (no pun intended) what the modulation, if any, is.

Many tactical Radars for instance use pulse/Doppler to determine both
range and rate of closure. An example that I'm most familiar with was
in the Phoenix Missile. The early variant used a pulsed klystron PA
and all analog signal processing. The pulse repetition frequency
(prf) and duty cycle were fixed and I suppose are still classified,
although the missiles are now retired (sob).

http://www.fas.org/man/dod-101/sys/missile/aim-54.htm

The Doppler is typically determined by having a bank of Doppler
filters (at i-f) and looking in each one for the returned signal.
Either the transmitter TO or the receiver LO, but not both, is then
adjusted to put the returned signal in the center filter. In the old
analog system, the VCO(s) were linearized so that the tuning voltage
was an indicator of the Doppler.

With pulse modulation this can get more complicated because there are
modulation sidebands spaced at the prf above and below the nominal
carrier frequency. If the Doppler is greater than the prf then it's
possible for a carrier sideband +/- Doppler to fall into the Doppler
filter bank and it takes some more manipulation to sort this out.

With the digital processor in the later variants the Doppler filters
were realized in software.

Now, aren't you sorry you asked? :-)

does doppler systems work only for unmodulated continous wave signals?
 

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