Yes the oscillator transistor is also the receiver/mixer. Kinda like a grid dip oscillator or the front end of a WW2 proximity fuze.
As motion detectors they also respond to drapery or foliage movement unlike PIR which only react to moving thermal emitters, that can make those microwave motion detectors useless in some applications.
piglet
I believe it's the same approach that used to be used by the 10GHz automatic door detectors that used to trigger automotive radar detectors. Oscillator and mixer in one device, pick out the audio Doppler signal.
CH
I gathered that much, yes. I was more interested in a discussion of the PCB traces and how they work together to make an oscillator and antenna.
I'm trying to guess the signs of the reactances between the terminals of Q1 at 3GHz. The trouble is that everything is coupled to everything else and I'm at a loss to tell what is dominant. Every damn bit of trace around Q1 looks like a resonator that could be either capacitive or inductive at
3GHz!At least I'm convinced that none of the actual /components/ on the schematic are involved in determining this oscillator. (Except for Q1, of course.) It's all in the PCB traces.
Jeroen Belleman
As a solution purely to generate a sinewave between 70 - 8kHz, in a "drop in" strategy, I would consider either
It sounds like the product is not very cost-sensitive.
There are pretty cheap DDS chips these days (AD9837 $2), which might solve the problem of generating the waveform well.
Something like the AD5933, AD5934 could also measure the impedance of the transducer and a micro could use this for adjusting the tuning. This is what I would do.
I suspect that the technological impedance mismatch might be a bit of an issue--the previous version used an XR2206!
(Nice part though.)
Cheers
Phil Hobbs
If the resonant load has a reasonable Q, you could drive it with a square wave in a self-oscillating circuit. One simple IC and a few passives might do it.
A "modifed sine wave" would be almost as simple and would get rid of the third harmonic component. The OP didn't like that idea ether.
His actuator produces a optical scan, and he'd prefer that it generated a smooth scan, but he's not up to specifying how smooth a scan he might need, and he clearly isn't up to monitoring how smooth it might be.
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