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

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

does doppler systems work only for unmodulated continous wave signals?
 

Richard,

Doppler DF systems like mazerom is thinking about work by rotating a
virtual antenna in a circle -- by successively selecting one antenna at
a time from a set of antennas around a circle. (He finally got around
to saying that in the other thread...) The effect is to ADD an FM
modulation to whatever signal you're receiving. If the signal happens
to be a continuous carrier, then you end up receiving a signal with
just your antenna's FM modulation. If the transmitted signal was FM to
begin with, your FM adds in. If it was an AM signal with carrier,
you're still good to go. But if the signal looks like random
noise--does FM modulated random noise not still look like random noise?

If you have reasonably clean FM to demodulate, then you just need to
calibrate out the (audio) phase shifts of your detector, including
whatever filtering you use to extract just the modulation your antenna
put on the signal. Then you compare the phase of that detected
modulation with the phase of the antenna effective rotation to get
bearing. This is similar, in a sense, to how VOR works to give a
_receiver_ in an airplane the bearing that receiver is from the VOR
transmitter: the VOR effectively rotates a directional antenna very
quickly so that the receiver sees an AM signal: max envelope when the
directional transmission "points at" that receiver. But the VOR
transmitter ALSO is FM modulated. So all receivers tuned to that VOR
get the same FM phase reference, but the phase of the AM is different
at each receiver depending on its bearing relative to the transmitter.
In the Doppler DF, the reference phase is the antenna rotation, which
you are controlling, and then the FM phase relative to that depends on
the bearing of the arriving signal. In your receiver system, you'll
want to use a very narrow filter to reject other modulation, and the
trick then is to make the phase shift in that filter be very constant
at the frequency of interest. A switched-capacitor
(commutating-capacitor) filter will do that, if the commutation is
driven synchronously with the antenna switching. But you can also do
it with a digital filter which samples at a rate that's synchronous
with the antenna switching.

There's an article in QST -- for May, 1978 if I'm remembering correctly
-- that describes it, along with plans for constructing such a beast
for 2 meters. Anyone want mine? I tried to give it away a couple
years ago, but no takers. Worked OK last time I used it.

Cheers,
Tom

does doppler systems work only for unmodulated continous wave signals?
 

On 8 Mar 2006 16:33:17 -0800, "K7ITM" wrote:

Doppler DF systems like mazerom is thinking about work by rotating a
virtual antenna in a circle -- by successively selecting one antenna at
a time from a set of antennas around a circle. (He finally got around
to saying that in the other thread...)

Hi Tom,

Finally indeed.

Yes, commutating antennas. I am also familiar with VOR, I used to
calibrate those systems (and other flight systems) years ago.

73's
Richard Clark, KB7QHC

does doppler systems work only for unmodulated continous wave signals?
 

"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

Amazingly they used to accomplish this with vaccum tubes.

Doppler direction finders work better on a steady CW source, but they usually also work fine on "reasonably" modulated signals. The principle of operation is normally not exactly what you wrote; in other words, nobody actually wiggles an antenna physically -- it is typically done electronically by switching on one antenna at a time in a horizontal array spaced 1/4 wave apart. That results in a tone superimposed on the received signal resulting from the simulated Doppler effect of "moving" and antenna, and the bearing to the signal source is related to the phase of the tone relative to the switching tone as a reference.

The only time I have trouble using my Ramsey Electronics DDF-1 is when the signal has lots of spectral spikes drifting through the audio passband of my FM receiver, e.g. when I was hunting for the source of interference in an apartment complex where someone had a sick router box leaking out RF in and around the 2m band.

Andy KR6DD