What is the output of these doppler radar modules - Page 1
Forum section: electronics / projects

author: Bud
author_rank: Super Contributor
timestamp: December 07, 2016, 03:45:20 pm
content: Do you guys know what type of output signal these ebay doppler radar produce on RX side?http://m.ebay.ca/itm/5V-Radar-Microwave-Sensor-Module-Body-Detection-Sensor-Module-5-8GHz-10m-/182256411520?hash=item2a6f542380%3Ag%3AgzEAAOSwQaJXSBv%7E&_trkparms=pageci%253A063c8a00-bc8d-11e6-9825-74dbd1800e94%257Cparentrq%253Ad9c722ac1580a606414f366dffe0db92%257Ciid%253A23

author: 2N3055
author_rank: Super Contributor
timestamp: December 07, 2016, 04:50:24 pm
content: They output Doppler signal.. basically they mix reflected signal with LO, and give you beat frequency difference between LO and reflection, proportional to Doppler shift, which is proportional to velocity of object that gave reflection, relative to radar antenna...Simply you will detect movement in front of antenna..Simplest detectors are using analog filters, and comparators, to detect slow movement.. Or you can sample and DSP... You can connect it to audio card on a PC (it is in audio range) and make analysis there..It can be sensitive enough to detect breathing and heart beat...

author: LaserSteve
author_rank: Super Contributor
timestamp: December 07, 2016, 05:16:36 pm
content: There are two types on the market... Some give a raw DC-100 Mhz IF signal, others have some signal processing. Most of the ones I see on Ebay now have some simple IF processing circuits added.Here is the data for the common HB100 Series...http://www.limpkin.fr/public/HB100/HB100_Microwave_Sensor_Application_Note.pdfThe "5.8 Ghz " model is new, I have not seen it yet. If its truly 5.8 Ghz,.... There are a few Youtube videos claiming otherwise.Have you tried contacting the vendor for a data sheet?The one that your showing is not very directional, that short pin antenna makes it device with a roughly hemispherical pattern...Steve

author: Bud
author_rank: Super Contributor
timestamp: December 07, 2016, 05:29:15 pm
content: I guess there are many that act just as an on-off switch, which is not very useful for experimentation.So for those outputting IF, is it pulse modulated ? I'd imagine the radar would emit pulses, not CW

author: 2N3055
author_rank: Super Contributor
timestamp: December 07, 2016, 05:33:00 pm
content: Simplest ones actually are CW... And just output Doppler frequency..Those are used as "microwave motion detector" in alarm industry... With a bit of postprocessing..

author: LaserSteve
author_rank: Super Contributor
timestamp: December 07, 2016, 05:33:14 pm
content: , Most of them are crude CW radars, which mix a bit of the transmitted RF with a tiny diode for a "Zero IF" receive, the output of the diode mixer contains the Doppler shifted frequency plus some DC bias... These modules return presence and velocity only. They do not rely on time of flight like your classic search radar for air or sea. They only way you could get them to return range data is to modify them to sweep their frequency, and then you would have a FMCW radar that would return range data after processing. That would require a well equipped RF bench.Some of them are pulsed in commercial applications at 2 to 4 KHz to reduce their duty cycle for regulatory reasons. Ie To lower their contribution to RF background levels in cities... Really they just gate the whole assembly on or off at 4% duty cycle.Attached drawing is a snip from the HB100 data sheet showing the math...The newer 24 Ghz ones use a dedicated chip with onboard VCO which synthesizes the 24 Ghz, and has a signal processor on board. Those are not very hackable for Ham Radio, etc... Most of those just have a TTL output.Steve

author: Bud
author_rank: Super Contributor
timestamp: December 07, 2016, 05:42:23 pm
content: So how do simple CW radars not overload their receiver by the tramsmitting signal ?

author: coppice
author_rank: Super Contributor
timestamp: December 07, 2016, 05:54:11 pm
content: Quote from: Bud on December 07, 2016, 05:42:23 pmThe radar is short range. The returned signal.is not weak enough to make that a problem.

author: Bud
author_rank: Super Contributor
timestamp: December 07, 2016, 06:14:33 pm
content: Quote from: LaserSteve on December 07, 2016, 05:33:14 pmI'd actually prefer this instead of the ones that may rectify the signal and use it to control a voltage to frequency converter or something, in which case part of information may be lost

author: LaserSteve
author_rank: Super Contributor
timestamp: December 07, 2016, 06:16:10 pm
content: With a 1 meter per second target, a 10.525 Ghz CW radar returns a ~ 70 Hz Doppler shift...., you could hook a preamp to the IF port and hear the motion.If the board is modified to add a second detector fed by the LO phase shifted 90 degrees, then you can recover direction from the phase shift between the detectors.Which is why these little radars are so beautiful.On the simple ones, you can FM modulate them by ever so slightly sweeping the PSU voltage and use them to transmit audio, using an ordinary FM radio as the IF.Steve

author: Bud
author_rank: Super Contributor
timestamp: December 07, 2016, 06:19:56 pm
content: Thanks SteveThis one is 24GHz, outputs IF and is pulsed. May be i will get one to play with.http://m.ebay.ca/itm/Microwave-Body-Induction-Module-24GHz-CDM324-Radar-Induction-Switch-Sensor-/351921499829?hash=item51f027eeb5%3Ag%3A2dMAAOSwEzxYPwvr&_trkparms=pageci%253A15859710-bca9-11e6-814b-74dbd180fe85%257Cparentrq%253Ada7f07051580a788499ac86fffdd3c23%257Ciid%253A1

author: LaserSteve
author_rank: Super Contributor
timestamp: December 07, 2016, 06:32:26 pm
content: I like 10 Ghz because the plumbing is cheaper/easier.. I've added a 10 Ghz horn to one of mine using UT-085 coax expanded to UT-141 using a few SMA connectors.Basically bypassing the patch antenna.There are plenty of horn and patch antenna designs for ham radio at 10 and 24 Ghz.While the little Chinese boards use chipsets at 24 Ghz, and Dielectric Resonator Oscillators at 10 Ghz, instead of Gunn Diodes, you might find these links interesting:http://www.n5dux.com/ham/files/pdf/Gunnplexer%20Cookbook.pdfhttp://ham-radio.com/sbms/presentations/Walt_Clark/DROplexer.pdfAny of the RSGB Microwave Handbooks are a good read, too...DROs are less sensitive to frequency pushing by changing supply voltage, but it can be done.Steve

author: Bud
author_rank: Super Contributor
timestamp: December 07, 2016, 08:44:52 pm
content: The first link resolves to a list of pdfs that is longer than life - can you double-check?

author: LaserSteve
author_rank: Super Contributor
timestamp: December 07, 2016, 10:11:34 pm
content: Easiest way is Google "Gunnplexer Cookbook", and a few download links will pop up.Steve

author: Berni
author_rank: Super Contributor
timestamp: December 08, 2016, 06:35:47 am
content: The continuous wave ones are the easiest to use. The doppler shift is simply output out of the IF where every moving object creates a sine wave tone where the frequency corresponds with the speed of movement and the amplitude with the signal strength.Put that trough a bandpass filter and a peak detector and you have a circuit that detects objects moving in a range of speeds. For tracking the speed of just one object you can just feed it in to a comparator to get a square wave and measure the frequency to get the speed. Or to track multiple objects use a sound card and do FFT on it.Do note that some radar modules cheep out on circuitry and give you the direct IF output. The problem with that is that the signal is incredibly tiny. So you need a 1000x gain low noise amp on it to get a meaningful amplitude signal out of it.Its possible to also detect static targets with doppler radar if you have some way of slightly sweeping the local oscillator up and down. In that mode the frequency of the tones you get out of it depend on the distance from the radar (Farther something is the higher frequency tone it gives off).