Gunn Diode

[biferi]

Here is a Photo of a Gunn diode but how do you know witch end is [-] or [+]?

I am now getting this in school.

 

[(*steve*)]

Sorry, we don't talk about Gunn's...

Just kidding.

You forgot the photo.

 

[davenn]

Here is a Photo of a Gunn diode but how do you know witch end is [-] or [+]?

I am now getting this in school.

have a look at the data sheet
what is the type number of the diode ?

 

[biferi]

Sorry here is the link to the Photo
https://upload.wikimedia.org/wikipedia/commons/3/35/Ganna_diode_3A703B.jpg

 

[(*steve*)]

Diode strictly means that it has 2 electrodes, not that it has a PN junction. A Gunn diode without an injector is symmetric. It is composed of GaAs that is all N doped, but with varying doing levels.

An injector breaks the symmetry, but they still conduct in both directions.

 

[hevans1944]

The image you uploaded is from this Wikipedia page. It is a Russian Gunn diode and may be available as surplus on eBay. It must be mounted in a tuned microwave cavity to produce microwave oscillations. Because it is a negative differential resistance device, it can self-oscillate to self-destruction at low frequencies powered by the bias circuit. These oscillations occur because of parasitic inductance and capacitance associated with its mounting. A large high-frequency by-pass capacitor can prevent these oscillations in the bias circuit as described in this article.

As @(*steve*) mentioned, it is not a diode. Some manufactures describe their Gunn diode packaging as Anode Heat Sink, meaning you solder or braze the thick stud end (anode) to the microwave cavity (which acts as a heat sink) and apply a negative DC bias to the smaller opposite end (cathode) which is insulated from the microwave cavity.

This is just about the simplest way to generate GHz microwave radiation, but they aren't very efficient and will get hot and self-destruct if not properly heat sunk when operating bias voltage is applied. Well, simple, if you are a microwave Guru like @davenn is. Us ordinary mortals can only marvel. Read the articles I have linked to above, gather about $100,000 worth of used surplus microwave equipment and wave guides, then go play with them.

Hop - AC8NS

 

[davenn]

Awesome response @hevans1944

I have used Gunn diode oscillators on 10 GHz and 24GHz, They are great for wideband FM TV transmission in the amateur bands
( I do also have narrow band gear on those freq's as well)

here's a couple of really straightforward 10 GHz transmitters using a Gunn Diodes from my experiments with circuits ......



the lower left circuit is a plain basic transmitter, there is only a Gunn diode in the cavity/waveguide -- modulation is applied to the Gunn PSU
The upper right circuit uses a cavity that also has a varactor diode in the cavity ... modulation is applied to the varactor diode whilst the DC supply
to the Gunn is kept stable. This unit also uses a mixer diode in the waveguide for receiving


Dave

 

[hevans1944]

I have been almost completely un-involved with microwaves, except for a brief stint in the Air Force learning to service and repair a Ku band (16 - 17 GHz) dual radar system, and then later (very briefly) at 70 GHz for line-of-sight propagation studies. It's a fascinating world, frequencies above 1 GHz, and more and more amateurs are becoming involved as the industry moves away from mass-market microwave sensors towards other (cheaper) solutions. Look at how laser "speed guns" have replaced Gunn diode "radar guns" or how PIR (passive infra-red) detectors have replaced microwave motion sensors, the latter mentioned by Dave in a note on his schematic post. The Government still uses microwave motion sensors to protect against unauthorized access to highly classified facilities, but the civilian market chooses low cost over higher security.

This paradigm shift probably bodes well for the dedicated experimenter, as a decline in microwave R&D and manufacturing should "free up" some sorely needed test and measurement equipment at reasonable prices. The "maker movement" has also helped with the introduction and acceptance of 3D printed parts. You can now make wave-guide components at home out of plastic and then vapor-deposit or electroless-plate metal films on them. You can even go on to electroplate thick films if necessary for higher power handling capability. Still, for really significant power, you need vacuum tube technology and, AFAIK, the usual suspects are unobtainable inexpensively. I think most magnetrons, TWTs, BWOs, and such are either re-built after failure or discarded. Good luck affording to buy a new one for amateur radio frequency bands... or maybe I am wrong there. Chime in, Dave, if you have some recent information on availability of powerful microwave components for amateur radio use.

 

[biferi]

I did not want to start a new post but I do not know how to look up past posts of my own to ad to it.

Please tell me how to do it?

Can anybody give me a photo of a Gunn diode and point out the 2. Terminals?

 

[Audioguru]

If you have the part number then you can look at its datasheet.

 

[davenn]

Can anybody give me a photo of a Gunn diode and point out the 2. Terminals?

tho this .....



is the more correct Gunn Symbol

 

[Rayregula]

I do not know how to look up past posts of my own to ad to it.

Please tell me how to do it?

With your mouse hover over your Username (top right) and click on "Your Content"