Electronics > Projects, Designs, and Technical Stuff

Gunn diode Oscillator doppler Radar Transceiver


Hello EEVblogers!

Lately I have been toying with a low power Doppler Radar detector from a police radar detector (Cobra model: ESD-9110) http://cobra.com/downloads/manuals/ESD9110_manual.pdf 

Which is a gunn diode oscillator with a waveguide. A gunn diode is an interesting device being that it is constructed of only n-doped silicon. Two heavily n-doped regions at either terminal and a thin layer of material as the middle layer.

As electricity is applied, the conductive properties of the middle layer become altered, increasing resistance and preventing conduction as current falls. These diodes are used as oscillators to generate microwaves which can then be tuned with a waveguide. A relaxation oscillator is made by applying a dc voltage to bias the negative resistance, which then creates a zero resistance circuit and then it begins to oscillate. the frequency of the oscillations is determined by the middle layer, and a resonator, such as a waveguide. These are very low power devices, making them suitable for low power applications such as radar detectors.When a high enough voltage is applied, the charge carrier along the cathode becomes unstable which develop slices of low conductivity and high field strength  which move from cathode to anode. as voltage is increased more slices are made.   http://academic.cankaya.edu.tr/~basdemir/downloads/ECE358Exp1.pdf

I would love to hear your feedback on this topic any Knowledge of this device and its applications is greatly appreciated!

    Image references below
explanatory veiw

MY gunn oscilltor

and another

Yep, Gunn diode modules are fun to play with.

About 10 years ago you could pick up old X-band gunn diode doppler modules for a song -- they used to be commonly used for automatic door openers and even burglar alarms.

The design of most of these "movement detection" modules however, wasn't suited to long-range stuff like making your own radar speed gun because the mixer diode would be saturated by the oscillator.  I significantly increased the sensitivity of these modules by moving the mixer diode to a separate waveguide and antenna which meant you could make a really good radar gun for beans.    Although they're only 8-10mW it's pretty easy to build some *very* high gain antennas at this frequency so a little power goes a *long* way.

I think there were some pretty impressive point-to-point microwave links build by HAM enthusiasts using these modules too.  With a decent dish they got massive line-of-sight distances out of them.

Thanks for the reply RCMR
I might have to give that a try, I've been wanting to do a cool project with this. Seemed too good to just leave in my junk box. This gunn module seems to be purpose-built for this detector, being that on the side it has a 360 degree laser/LIDAR detector module. The mounting metal also acts as a heatsink for a nearby MOSFET.


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