[SOLVED] I need help for CXY11 gunn diode

[9a3daa]

Hi!

I bought 25 gunn diode from eBay 2 years ago.

**broken link removed**

It is possible that all of 25 dont work? Yesterday I put one in gunnplexer and dont work. I put another one and change polarity and nothing.
Model is CXY11C and they work on 7V and 140mA datasheet say, but in datasheet is cathode is ring on end

**broken link removed**

On this site say that anode is ring on end

https://www.radiomuseum.org/tubes/tube_cxy11.html

I am not sure of polarity. Maybe power supply must be negative voltage?
Diodes come in plastic bag like in picture from eBay. Is possible that static destroy them?
(But I worked with lot of MA COM gunn diodes also they was in plastic bag, and touching with bare hands and static didnt destroy them.)

Any advice schematic or datasheet would be helpful
73, 9A3DAA

 

[betwixt]

I would trust the Mullard data sheet, they made them.

I have several here and they all have a stud on both ends, the Radio Museum link seems to show a different package with a flange at one end.

Warning: don't slowly ramp up the voltage to them, the negative resistance characteristic can burn them out if the voltage is too LOW. Always apply 7V +/- 1V with short rise time. I think the 140mA current is measured in an oscillating state.

Brian.

 

[9a3daa]

I would trust the Mullard data sheet, they made them.
Brian.

So is like this in picture?

Thanks!

 

[betwixt]

I just looked down a waveguide (not powered!) and the flange on mine is mounted into the wall with an insulated stub going to a positive input tab so I would say your picture is correct. Bear in mind that you can't check Gunn diodes in the same way as normal diodes, in fact a DVM may indicate they are almost a short in both directions depending on the voltage it applies across it's probes.

Brian.

 

[9a3daa]

So I made this setup. Not professional, but I have WR90 detector with movable short and attached gunnplexer. I put all of 25 pieces of CXY11C gunn diode in it like picture from datasheet say that flanged side is chatode or negative from power supply, and only 2 of 25 oscillate. I dont know why other don t work (except one I destroyed by rewersing polarity)..
So what can be that other dont oscillate?

P.S. Thanks Brian for looking for your gunn..

 

[betwixt]

It's difficult to see exact sizes from the photograph but at a glance, the cavity seems a little small for a CXY11. Is it possible that you are trying to make it oscillate at higher frequency than the diode can manage? I've never used one higher than about 11GHz so my experience is somewhat limited.

You might be able to detect the negative resistance region if you plot the current vs voltage from about 5V to 8V without it being in a cavity but clamped to dissipate heat. Do not go outside that voltage range and ideally limit the current to about 150mA.

Brian.

 

[9a3daa]

Cavity is from original gunnplexer Microwave Associates model MA86656D
operating frequency 10.525 GHz
Mullard datasheet say that CXY11 operate from 8 to 12 GHz
I dont see why they shuldnt operate in this cavity... BUT I saw this shematic:

http://www.microwave-museum.org/exhibits/mwm-033.htm

CXY11 in WR90 waveguide dimensions...
Maybe when I find a little longer WR90 waveguide with flange (for attaching horn antenna) I will build like this schematic and see will they oscilate on 10 GHz

 

[betwixt]

Or you could try this one:
http://www.atv-projects.com/Gunn_Diode_Controller.html
which works for me.

Brian.

 

[9a3daa]

Do I need put this capacitor or it's just 33 ohms resistor parallel with gunn enough?

 

[betwixt]

The capacitor just stops you wasting DC current so it is better to leave it in place. Some Gunn diodes exhibit strange characteristics as you change the voltage across them, their impedance changes and it can upset the circuit driving them. All the resistor and capacitor do is help to keep the impedance more constant.

I see you are using an ERA-3 MMIC as an output amplifier. Remember that the output from the mixer diode is the difference between Gunn frequency and a signal arriving from outside the waveguide so the frequency is generally quite low. When used for proximity detection using the Doppler shift, the frequency is usually no more than a few Hz. If you are using this as a transceiver, the frequency will be the difference between your Gunn oscillation and the frequency from the transmitter sending to you so it's likely to be no more than a few MHz. For example, if your oscillator is at 10.525GHz and the other source is at 10.550GHz, the output frequency will only be 25MHz.

Brian.

 

[9a3daa]

Today I am making small gunn oscillator with WR90 flange by GM8BKE design. I don't have waveguide.. so I am making one just with parts from I found. It is finished, and work!

 

[9a3daa]

I got another 25 CXY11C gunn diodes. They behave very strange (probably because they are old) Datashet say that working voltage is 7V dc, but they oscilate on 5V. So I checked them all and I probably destroyed 8 diodes before I figured out they work on 5V dc and NOT ON 7V Dc like datasheet say. They are old and they probably have weakened or changed their characteristics.
So anyone that have CXY11 gunn diodes, put 5V on diode FIRST, and if they not oscilate on 5V must slowly raise the voltage (very little cca from 4.5V to 5.5V) some of diode oscilate on 7V like datasheet say BUT I vould not put 7V on first turning on.
So In my first post I say that they dont work, but before I didn t apply lower voltage and I listen datasheet that say 7V and probably I destroy them all.
Now I have 30+ pieces that dont work, but when I figured out that is bad series or bad caracteristic by aging, I have 16 pieces that WORK!
Thanks to seller!
so is a little gunn diode (case style 30) on the market..
There are a lot of Russian gunn diodes on eBay, but the gunn diode is much bigger dimension than my diodes.

 

[Electronican]

I have the same oscillator on my laboratory excercises on studies. It was my first applications of gunn diode that i saw i was testing it. About gunn diodes, on my laboratories they were changed like once per month even if they weren't used soo much time. So if you have old one this is true that it will have not so good characteristics.

 

[betwixt]

I have Gunn diodes 20+ years old that have had hundreds of hours of use and they still work perfectly. I can't see the need for changing them unless they have failed.

Brian.