Hi Jean-Paul, Sorry for taking so long to reply, for some reason Gmail sends the majority of your emails from piclist into my spam box. 1) Is it necessary to do I/Q demodulation in order to make simple speed measurements? 2) I was under the impression that with Doppler systems, the only information gained by having two mixers is the direction of the object being tracked. And, that single mixer systems are capable of measuring (just) the speed of an object. 2) On a related note, I intend to try to measure distance by sweeping the frequency of the Gunnplexer. According an ARRL publication [1] simply modulating the supply voltage will produce a fairly linear sweep. Would this type of measurement be affected by the lack of a second mixer? The figure quoted in the publication is ~10MHz/Volt, my design is slated to sweep 5MHz by varying the voltage between 5.1 and 4.6 volts. [1] http://www.arrl.org/files/file/Technology/microwave/0203096.pdf On Sun, Apr 17, 2016 at 5:19 PM, Jean-Paul Louis wrote: > Jason, > > After looking at the data sheet in your email, the device shown > seems to have only one receive diode, so I/Q is not feasible. > This one is one of the cheapo door openers, not the one used for price > radars. > the one I used had 4 pins, as they had two receive diodes for I/Q mixer. > > Jean-Paul > N1JPL > > > On Apr 17, 2016, at 5:10 PM, Jean-Paul Louis wrote: > > > > Jason, > > These gunplexer from Macom have been used for a long time to make > doppler radars. > > Even know that they were originally intended to be use for door openers= , > some companies > > in the police radar business used them as the base device in their rada= r > guns. > > > > I hope that you took serious care of avoiding ESD because these devices > are VERY sensitive. > > Not the gunn diode, but the two schotky that are the receiver part. > > > > It is a self mixer, when you power the gunn diode, some of the transmit > signal is used as the > > LO for the receiver, so you get only the frequency difference (doppler) > > > > Then you can use a DSP processor to calculate the speed. > > > > I hope you did not turn the screw as you might have already killed the > receive diodes. > > There are two of them that provide I/Q signal > > > > My $0.02, > > Jean-Paul > > N1JPL > > > > I worked in one of those police radar companies a long while ago. > > > > > > > > > > > >> On Apr 16, 2016, at 2:34 PM, Jason White < > whitewaterssoftwareinfo@gmail.com> wrote: > >> > >> Hello, Recently I saw a video demonstrating how Gunnplexers are used i= n > >> "Radar Guns" (speed measuring). I bought a 24Ghz gunplexer [1] so that= I > >> could make my own radar gun. Now that I have see one up close I have > some > >> questions about how they work and what some of the tuning screws do. I > have > >> attached a photograph to make things easier to explain. > >> > >> [Question 1]: There are two tuning screws a large brass one and a smal= l > >> silver one. What is the function of the silver tuning scew? > >> > >> The brass one is labeled as the frequency adjust screw, presumably it > >> sticks down into some sort of cavity resonator. The second screw, the > >> silver one, goes through the case and comes out directly in front of a > >> small aperture (hole) coupling the oscillator's output into the > waveguide. > >> Right next to this screw is the mixer diode for the Doppler output. Th= e > >> screw came adjusted so that it is even with the lower edge of the > >> oscillator aperture. Could this screw have something to do with the > amount > >> of coupling between the oscillator's output and the mixer diode? > >> > >> [Question 2]: The oscillator is coupled to the waveguide through a > ~1.5mm > >> eliptical hole that is much smaller that the wavelength for 24Ghz > (12mm). > >> How can the 24GHz from the oscillator pass through such a small hole? > >> > >> Thanks, > >> Jason White > >> > >> > >> [1] M/A-COM: MACS-007801-0M1R10 "24.125 GHz Mono Doppler Transceiver" > >> Datasheet: http://cdn.macom.com/datasheets/MACS-007801-0M1R10.pdf > >> > >> -- > >> Jason White > >> <180.jpg>-- > >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > >> View/change your membership options at > >> http://mailman.mit.edu/mailman/listinfo/piclist > > > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 Jason White --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .