Doppler radar experiment at 44kHz

On a sunny day (Wed, 27 Nov 2013 11:11:55 GMT) it happened Jan Panteltje wrote in :

Build a wind tunnel, old PC processor fan, cardboard tube:

With the transducers in the holes in the tube, I see mainly noise from the fan motor (vibration).

So looks like I need 'time of flight' for air speed measurements.

So now to key this thing and detect the rx delay with a PIC... RS232 out. Have to sleep on that one. Wonder how fast I can key it, high Q, will die out slowly, gotta try that now.

Hey, but I have a real wind tunnel!

Welcome, but it's a bit of standard radar technology, invented long ago.

The most widely used classic intro-to-radar text is Skolnick: .

Don't let the price deflect you. Used copies of prior editions can be had quite cheaply, and many libraries have multiple copies.

Joe Gwinn

On a sunny day (Thu, 28 Nov 2013 13:50:55 GMT) it happened Jan Panteltje wrote in :

Start is immediate (within half a period) Decay is

There was a Circuit Cellar article describing an anemometer using 4 acoustical T/R sensors a few years ago. I think it may have been in an article describing an almost complete weather station.

I thought small animals would be sensitive to those freqs?

Jamie

On a sunny day (Thu, 28 Nov 2013 13:42:12 -0500) it happened "Maynard A. Philbrook Jr." wrote in :

Well, I have not heard of any people dying from it yet... ;-) I have heard somebody claim some song bird dying from 15625 line frequency whistle from TV.

Yes. Rats can hear at least to 50 KHz*, probably much higher: .

This was a proof-of-principle prototype. Had I gone farther, new (and expensive) MHz? transducers would have been required.

Joe Gwinn

• Male rats sing a boast at 50 KHz just after scoring. One assumes that the rodent population can hear this song; otherwise, why bother?

If it scares bats away that's an advantage :)

--
For a good time: install ntp 

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I had a friend who could hear to 32kHz. I didn't believe him so tested him - just about drove him nuts! ;-) He wasn't young, at the time, either (about 30). The Navy had tested his hearing to be "off-the-charts", too.

It does happen. I can (well, could many years ago) *sense* 26 KHz, feeling it as a pressure versus hearing it as a tone. It turns out to be common. For one Halloween Party, I set up an ultrasonic speaker driven by a lab oscillator (vacuum tube type, lots of power) to set the mood while ghost stories were told.

Joe Gwinn

(and

Wow that is really out there

When i was about 30 i could still hear to about 23 kHz and sense much higher than that. I remember as a kid having pain from ultrasonics on a department store, i am pretty sure it was well over 30 kHz and it seemed very loud.

?-)

The ear bones are not very linear at high audio volumes.

In the presence of at least one ultrasonic tone and other environment noise, there are going to be a lot of intermodulation products, some of which fall into the normal hearing frequency range. This might explain why you could _sense_ the presence/absence of an ultrasonic tone, even if you are not able to hear it alone.

It is. I didn't believe him at first. There was no doubt after I was done, though.

I could hear to about 20kHz. I could easily hear TV horizontal oscillators in houses, from the street. I can't hear anything like that now but even if I could, I couldn't hear it over the tinnitus. ;-(

the

a

seemed

The levels were not all that high in any absolute sense (maybe 80 to 90 dBA). It was just the fact that i could sense them, i did not get any kind of a "pitch" in the sense of hearing a frequency, just knew that it was there above any pitch i could hear and painfully loud.

Using pitch here to distinguish hearing this or that octave on a piano / organ / synth / sine generator.

?-)

I have a similar story. It was in Baltimore in the late 1970s, when I was in my 20s, when a girlfriend complained that it was oppressive in the local CVS store, and she suspected that she was sensing/hearing the burglar alarm, so I went to that store. Turns out she was correct, and I could feel it too.

I talked to the store manager, who was surprised that I could tell that the alarm was in standby (versus off). I pointed out that leaving the alarm in standby was likely driving customers away. She argued with me, but the next time I was in the store, the alarm was off.

In the US in those days, there were only two frequencies commonly used,

41 KHz and 26 KHz (controlled by the availability of inexpensive transducers), so it had to be 26 KHz.

Joe Gwinn