need help identifing this diode,radar unit

[05blackduramax]

Iam working one a decatur electronics radar head. I need help identifing this yellow diode. the diode has three sets of numbers on it , 475k, +20 k , 0803. The flat end of the diode is hooked up to the - power and the other end has a small tapper to it and its hooked up to the + side. This unit is 12 volt.

 

[davenn]

hi welcome to the forums

if its really connected directly between the + and - power input to the board, then its a reverse protection diode
I would have to assume there is a fuse in the positive power lead ?

not having a pic of the board ... you may like top upload one
you could use a 1N4007 or similar

cheers
Dave

 

[05blackduramax]

I have a good pic but it says its too big.

 

[davenn]

I have a good pic but it says its too big.

yeah, you cant just upload a pic out of a camera
its too big in 2 ways
1) its height and width pixel count you need to resize it to ~ 800 x 600 pixels
2) is kb size .... it could be huge depending on your camera 1mb to 20+ mb
you need to compress it to bring it below 100 kb

you can use a program like Irfanview .... its free for download off the net

Dave

 

[05blackduramax]

I think I got the pic to upload.

 

[05blackduramax]

Is this a
Schottky diode?

 

[davenn]

I don't see a diode in that pic

if you are referring to the yellow component ... its a capacitor that is across the 5V supply to the GUNN Oscillator

 

[KrisBlueNZ]

475k, +20 k , 0803.

If it's a capacitor, "475K" means 0.47 µF ±10%. The "+20" may be a polarity indication and a 20V rating. If it's polarised it's probably a tantalum capacitor.

Here's a 25V-rated one from Kemet: http://www.digikey.com/product-detail/en/T322A474K025AT/399-4580-ND/946598

 

[davenn]

not sure why the OP thinks it may be faulty ??

 

[KrisBlueNZ]

not sure why the OP thinks it may be faulty ??

<shrug> People sometimes think strange things

 

[davenn]

indeed


That brass block with the MO9205-01 and 5V ... that's 24GHz GUNN Oscillator
in front of it ( the aluminium block) is the cavity with the mixer diode in it, the signal comes out on
that screened lead to the right of it

You may already know that ? haha I have played with quite a few of them and ones for 10GHz
with my amateur radio experiments

Dave

 

[05blackduramax]

When I send the antennas out they always replace the diode. I would like to learn how to replace the diode. I've already learned a lot. So is the diode in the aluminum block replaceable or is it all one part? Thanks

 

[05blackduramax]

I tore into the aluminum block the only thing I see that even looks close to a diode it is very very small with gold ends and the center is white. Its about the size of the end of a tooth pic.

 

[05blackduramax]

I took a couple pics.

 

[davenn]

I tore into the aluminium block the only thing I see that even looks close to a diode it is very, very small with gold ends and the centre is white. Its about the size of the end of a tooth pic.

Yup, that's the GUNN Diode. Not sure how readily available 24 GHz GUNN diodes are ??
All the ones I have procured have come out of used equip
You don't want to go touching a good one with out anti-static mat and wrist strap, they can be zapped in a heartbeat

When I send the antennas out they always replace the diode.

this on different units ? or are you always killing the diode on the same unit ?

if on the same unit, it begs the question as to what you are doing that is killing the diode ?

Dave

 

[05blackduramax]

Its on different units I send them out it takes almost a month to get them back.As to why they go bad I have no idea. The radars get used every day so there is a lot of hours on them.

 

[05blackduramax]

Well I ordered some schottly diodes and they came with little nubs on both ends I need ones that are flat. I would also like to know is there a diode in the brass block? Thanks

 

[davenn]

Well I ordered some schottly diodes and they came with little nubs on both ends I need ones that are flat. I would also like to know is there a diode in the brass block? Thanks

ummm you should have been getting 24GHz GUNN diodes. Did you really get Gunn diodes or did you get Schottky diodes ?


Dave

 

[davenn]

OK there's some confusion here .....

lets back up a minute .....
in your first pic .....




the brass section refers to this I said earlier ....

That brass block with the MO9205-01 and 5V ... that's 24GHz GUNN Oscillator

in your 2nd and 3rd pics .....




this is the receive mixer stage and output and refers to this I quoted earlier....

in front of it ( the aluminium block) is the cavity with the mixer diode in it, the signal comes out on
that screened lead to the right of it

That is the Schottky mixer diode

But your opening question was about the yellow thing on the outside .... The capacitor
so that ID was sorted out

So.... what part is the part that gets replaced each time ?

the cap?,
the Gunn diode in the brass block ?
or the mixer diode in the aluminium block ?

The Gunn diode would be the most likely to fail, as it has continuous voltage on it
The mixer diode doesn't, it just picks up a little of the Gunn diode signal and mixes it with incoming reflected signal from the object

In post #12 you said ....

When I send the antennas out they always replace the diode. I would like to learn how to replace the diode

But you thought the capacitor was a diode .... so you MUST find out and clarify exactly what was being replaced

I also need you to clarify .....
1) is this a radar motion detector ... like used for auto door openers or
2) is it a radar detector for detecting police speedtrap radars ?

this is very important, as system 1 is active and system 2 is passive


Dave

 

[05blackduramax]

Schottky mixer diode is what my paper work says they replace. This is radar out of police cars.