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44 kHz Doppler radar air speed meterr phase shift in wind tunnel

On a sunny day (Fri, 06 Dec 2013 19:15:29 -0500) it happened Joe Gwinn wrote in :

Yes, of course Doppler in air (as medium) is classical.

To refer to M&M (not the candy) and speed of light breaks open a big can of worms. Better not stir that too much here, sci.physics is full of people with let's say a different view.

Yesterday there was a repeat of a TV program by some professor in a big hall in Amsterdam, where he went from the Greek 'atom;' to QM. when approaching QM (in this popular discourse, in 45 minutes on top of that), he went straight into the usual nonsense of the Copenhagen interpretation, and really, not only did it sound like nonsense, but presented as such a matter of fact way that I was really worried that any one in that audience would even be able to really get some understanding. So I switched it off in disgust (he of course also said Einstein was wrong etc), but that was about that Bell thing. Anyways, try watching this:

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it may just expend your horizon, I have pity on the state physics is in these days with that Copenhagen interpretation, dead end road would be a very mild thing to say. History repeats itself. In Germany the masses are getting the nuclear power plants dismantled, even the new ones, start burning coal, of shore wind power never went online so much (they forgot the cables). We are past the era of science, next scientists will be burned (as witches), and really, I cannot blame anyone for doing that with the current 'theories' (dark matter, dark force, Darth Vader, wormholes, graffiti waves, etc). If we do not go way of dinosaurs then maybe a few thousand years,,,,, a renaissance.

Reply to
Jan Panteltje
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Perhaps not.. we've extracted much of the easy-to-get raw material from the earth, so a primitive society in a few thousand years will have much greater difficulties than we did bootstrapping themselves up on a large scale.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Reply to
Spehro Pefhany

Well for fossil energy this is true. But for other materials our landfills will be the pits of the future. Event today some have a larger percentage of valuable materials and precious metals than natural ore.

--
Reinhardt Behm 
rb@rbehm.de
Reply to
Reinhardt Behm

Skolnik's RADAR Handbook?

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

On a sunny day (Fri, 24 Jan 2014 11:57:44 -0500) it happened "Michael A. Terrell" wrote in :

Dunno, thick book it was, soft cover.

Reply to
Jan Panteltje

Op zondag 1 december 2013 11:12:29 UTC+1 schreef Jan Panteltje:

:
5883.67
,

even

this setup,

s of the total degrees.

/ 5883 = 0.061193, say 6 % .

r hour, or 71.2 km/h.

be less effect of the air speed

do with Doppler only will increase.

istance to say be able to still measure up to 200 km/h

only works over short distances for high speed.

or

g.

ings a lot easier.

d :-)

ltiply by sine (angle of beam)..

ne with the air flow,

Jan,

i tried to follow this thread and it left me wondering: if one wants to bui ld an ultrasonic anemometer using the phase shift between the received sign al and the local oscillator would there be a way to deal with the aliasing effect of the phase becoming > 360 degrees, hence the limit of about 70 km/ h?

I tried the usual time of flight approach but things get very messy due to the pulsed nature of the signal. A continuous wave approach using the fas e shift seems much more doable.

I considered some techniques borrowed from CWFM radar but I'm not sure the doppler effect applies to changes in windspeed, as merely the propagation s peed of the medium changes resulting in only a phase shift but not in a dop pler (frequency) shift.

Also I am not yet sure wether the use of a frequency sweep (chirp) would en hance the detection boundaries beyond the 360 degrees of 1 cycle.

Any thoughts?

Regards,

Bert

Reply to
bhthaken

On a sunny day (Tue, 13 May 2014 12:45:31 -0700 (PDT)) it happened snipped-for-privacy@kabelfoon.nl wrote in :

I went to time of flight for further experiments, but for sure am not finished, my 'wind tunnel' is still on the table, been a bit busy. I made a system that creates ionized air (using sparks), and then detects those charged particles further down the tube, pure time of flight of pure air. It is not public at this moment, and I think US should not have access to it considering recent CIA actions in Ukraine.

There is nothing against using a lower frequency (audible sound, so no longer ultra sound), or modulated ultrasound, or 2 or more frequencies. Small speakers can make many frequecies in turn, IIRC there is a Dutch patent on that somewhere,

Many thoughts.. I am working on some other projects that have higher priority due to world politics, but given time and opportunity this will be worked on further.

Have you done any real experiments yet? Regards Jan

Reply to
Jan Panteltje

Op woensdag 14 mei 2014 08:35:04 UTC+2 schreef Jan Panteltje:

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ign=

ng =

km/=

ished,

it considering recent CIA

to =

fas=

nger ultra sound),

he =

n s=

dop=

en=

d politics,

Jan,

yes I am playing around with some transducers and a pic32mx development boa rd. It took some time to generate a strong enough signal to get some noise out of the transducers, these closed front transducers are very inefficient .

The majority of the (commercial) ultrasonic transducers seem to work with a pulsed excitation signal which results in a messy signal at the receive en d due to electrical en mechanical feedback and the fact that these transduc ers do not like square waves.

They start to ring like a doorbell so you have to go through some trouble t o filter out the noise and artifacts and still have a hard time determining where the echo actually begins. I am not generating the excitation signal with a transformer and a tuned circuit but with a power opamp (40Vpp).

During the process I noticed that a continuous excitation signal (a sine wa ve generated by the PIC) results in a much clearer signal at the receive en d (almost a proper sine wave instead of a magnitude 6 earth quake readout f rom a seismograph) and also the Xmit transducer seems a lot more efficient.

The traditional time of flight calculation does not work here and as is dis cussed in this thread you can try to work with the phase difference between the received signal and the local oscillator. However the max phase differ ence for a period corresponds with a max wind speed that can be measured of about 70 km/h, which is not enough for my purposes.

Reading the comments the idea struck me it should be possible to measure th e total phase shift for the complete distance between the transducers, abou t 35 cycles for 30 centimeters, in a given time period and compare this to the number of transmitted cycles in the same (short) time interval. The PIC is more than fast enough to count a fixed number of incoming periods and c alculate the windspeed from there.

Why don't we sometimes see the obvious? I am not sure yet this idea works h owever. I wonder if there are posters here with more practical experience r egarding continuous wave ultrasonic anemometers.

Regards,

Bert

Reply to
bhthaken 

--
Well, that certainly narrows it down...
Reply to
John Fields

On a sunny day (Thu, 15 May 2014 13:21:11 -0700 (PDT)) it happened snipped-for-privacy@kabelfoon.nl wrote in :

That requires the transmitter to be keyed or AM modulated, so you know where the start is? Since you drive with a power amp anyways, what is against using lower frequency for higher speeds? This gives less periods (phase) between receiver and transmitter. You can then use different tones to get all info. It is not exactly sweeping, but the same idea.

Long time ago I used piezo speakers (array of 4, 5 Euro a piece from conrad.nl), yes I blew them all up), on my power amp:

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That chip will go way up there in the ultrasound. You can, that way, send any signal you want. Electret -, or small dynamic -, or even a piezo mike should be able to detect it. But it is very big, take out the transducers, small ceramic disks... makes it much smaller. Scares away rodents too :-)

Yes piezos are used in resonance, normally, but if you drive those with a low Zout power amp it is damped, but costs power that way.

Reply to
Jan Panteltje

On a sunny day (Thu, 15 May 2014 19:53:24 -0500) it happened John Fields wrote in :

Must be some ego thing to always want to know who wrote it, better remember what was teached. I mean your great wisdom will always be remembered, but not that it was sprayed on us by J.F. This is the reason J.L. adds his signature to every posting :-) It wont work:-)

Reply to
Jan Panteltje

to bui=

received sign=

aliasing =

70 km/=

finished,

to it considering recent CIA

due to =

the fas=

longer ultra sound),

sure the =

propagation s=

a dop=

would en=

world politics,

board. It took some time to generate a strong enough signal to get some noise out of the transducers, these closed front transducers are very inefficient.

with a pulsed excitation signal which results in a messy signal at the receive end due to electrical en mechanical feedback and the fact that these transducers do not like square waves.

trouble to filter out the noise and artifacts and still have a hard time determining where the echo actually begins. I am not generating the excitation signal with a transformer and a tuned circuit but with a power opamp (40Vpp).

wave generated by the PIC) results in a much clearer signal at the receive end (almost a proper sine wave instead of a magnitude 6 earth quake readout from a seismograph) and also the Xmit transducer seems a lot more efficient.

discussed in this thread you can try to work with the phase difference between the received signal and the local oscillator. However the max phase difference for a period corresponds with a max wind speed that can be measured of about 70 km/h, which is not enough for my purposes.

the total phase shift for the complete distance between the transducers, about 35 cycles for 30 centimeters, in a given time period and compare this to the number of transmitted cycles in the same (short) time interval. The PIC is more than fast enough to count a fixed number of incoming periods and calculate the windspeed from there.

works however. I wonder if there are posters here with more practical experience regarding continuous wave ultrasonic anemometers.

Well one way to get more information is to use 30% fsk at f/20 modulation rate.

?-)

Reply to
josephkk

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