![]() Like a tiny organ pipe, the tone is set by the shape and size of the material. The ceramic disk (usually made from Barium Titanate Ba 2Ti 9O 20) acts as a resonant chamber for RF energy. This is actually a Dielectric Resonance Oscillator. I even broke it open slightly to check it didn’t have wiring inside, but it was solid ceramic. A major component was clearly the white disk that I thought was a potted inductor, because the adjustment screw in the case changed its distance slightly to this disk, (and then set with thread-lock but otherwise wasn’t physically touching) so I assumed (wrongly) it was altering the magnetic flux of a coil.īut on closer inspection, the white disk didn’t have any leads and wasn’t electrically connected to anything. Those are RF filter capacitors.Īt first, I couldn’t figure out how the local oscillator worked. Note the weird “quarter circles” which form part of the tuned oscillator. +5V power comes in from the top right through the resistor. #DOPPLER 10 RADAR PATCH#Not only for the patch antennas but also several RF filters, the local oscillator, and the mixer are all largely made from peculiarly-shaped PCB tracks.Īpart from the PCB, there are only five “components" on the board.įive passive components to implement a Doppler radar module. I don’t know who designed this, but they were a master of the black art of Radio Frequency waveguide engineering. I wasn’t expecting much, but I got far less. So, what’s inside? Everything is under a metal shield, which comes off easily enough.įrankly, I was rather shocked by what I found. Which is the perfect time to tear something apart! Teardown That will kill it dead and trip your DC supply protection to boot. However, the HB100 isn’t immune to 5v on the IF pin, I discovered. It’s also the case that the exact emitted frequency can drift quite a bit and yet the mixer results barely change, making the modules immune to most temperature and power supply variations. Since low-frequency signals are much easier to preserve and amplify than RF and the frequency difference so great, in practice that means we can hear very faint Doppler signals next to our relatively powerful carrier signal. Now, most mixers are imperfect, which means we’ll still have a good amount of the original 10Ghz signals in there too… but since we’re really only interested in the low-end frequencies coming out of the mixer, we can just scythe off everything above a few hundred kilohertz (by using NON-microwave-rated components like common audio amplifiers) and all we’re left with is the ‘doppler’ signal we wanted. When using the HB100 for “movement sensor” applications, the output just goes to an appropriate frequency filter for the range of movement you’re looking for (like a person walking) and that can flip a light switch or open an automatic door What would cause our return signal to be a different frequency from the one we emitted? Doppler shift! Anything moving towards or away from our antenna will introduce a shift (and therefore beat note) proportional to object speed and your carrier frequency. So if we’re emitting a 10Ghz wave and getting back a 10.0001Ghz wave, the result of mixing those will be 20.0001Ghz and 100Hz signals. More technically, a good linear RF mixer will generate two sidelobes at the sum and difference of the two frequencies. The left pair is the TX and the right pair the RX. The copper squares around the edge are patch antennas. Instead, these modules constantly emit a low-level radio beam and then mix the return signal with the original to generate heterodyne “beat notes” which occur if one frequency has been shifted slightly. That requires precise speed-of-light calculations and expensive components, in order to emit pulses of radio energy and count how many nanoseconds they take to echo back. The basic idea of Doppler radar is that we’re not doing “distance” pulse ranging. It needs some support components for most uses (like a post-amplifier for the “couple of millivolts” signal it outputs) but does its part of the job well enough. The HB100 Doppler Radar module costs about $5 from the usual online suspects, which is down at the “insanely cheap” end of the spectrum when you’re talking about 10Ghz radio gear.ĭoes it work? Surprisingly, yes. #DOPPLER 10 RADAR CRACK#In this special edition of Teardown Tuesday, we crack open an HB100 Doppler radar module and delve into the mysteries of RF component design. ![]()
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