Hi Jason, You are wright about the I/Q functionality, but for police radar it is a mu= st as the officer in the car want to select the direction of the traffic he= /she is monitoring. For a simple speed info without direction, a simple mix= er will work and that is used in sport radar guns where the direction is no= t ambiguous. You modulate the frequency of the Gunn diode, but be careful n= ot to exceed the limit of the K-Band. You can do some heavy math with the D= SP to determine the range, but it will not be very precise. You do not need a second mixer because you use the same frequency for TX/RX= , so the IF is always true. Deriving the distance from the derivative of the doppler signal is not easy= , even if the high level math is straight forward. Doppler shift =3D K * speed distance =3D d(speed) / dt The speed usually is calculated easily with a counter (frequency meter), but the derivative is a bit more convoluted. In police applications, you have multiple targets which make the problem no= n trivial and require the use of FFT to discriminate the various signals. The Gunn diode requires constant current, so the variation is not just vary= ing the voltage as at 4.6V, some diodes will not even start oscillating. Your mileage may v= ary. I would build a current generator and modulate the current to sweep the fre= quency, but stay within the limits of stable oscillation, or you will lose = precision. By the way, the ARRL article refers to a X-Band gunn-plexer (10GHz), and no= t a K-Band like the one you have (24.150GHz). So you will have to figure out the slope for the K-Band Gunn diode. Good luck on your experiment, that should be fun. Jean-Paul N1JPL > On May 7, 2016, at 8:16 PM, Jason White wrote: > > Hi Jean-Paul, > > Sorry for taking so long to reply, for some reason Gmail sends the majori= ty > 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 >> > > > > -- > Jason White > -- > 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 .