White Noise Source

of

Then I

om

ttle

to

aving

p lead.)

Thanks Ben, I've heard that, but never tried it.

George H.

Phil Hobbs Inscribed thus:

Seems most of the photos are missing !

--
Best Regards:
                          Baron.

I've only used that kind of noise source when i'm aligning VHF and UHF preamps. The zener breakthrough is at around 6V for ordinary transistors as the 2N2222. You have to test a handful to find the best noise source ;)

/Ben - SM0KBW

Right! Thanks. Fixed now.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

Phil Hobbs Inscribed thus:

Looks fine now. Thanks.

--
Best Regards:
                          Baron.

=A0Seems

me

e l e a

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as good as I thought it was. (I'll have to do some testing, when I have time.) I was tweaking the gain of my zener noise source and turned on the overhead lamp to get some more light for soldering. The noise dropped by a factor of ten or more.... and this is with black electrical tape wrapped around the zeners! Putting my hand over the zeners to shade them... noise went back up.

I've perhaps made an anvalanche photodiode out of my zener?

George H.

Seems

It's well known that black vinyl tape is translucent to some light.

--
You can't have a sense of humor, if you have no sense.

Seems

Yup. Many black-looking things are coloured with organic dyes, which become transparent in the near IR. Silicon doesn't really cut off till about 1100 nm, so there's frequently a detectable leak.

Novolac epoxy (used for chip packages) is opaque at all wavelengths from the mid-IR to soft X-rays, so it's not an issue with plastic-packaged chips.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

Seems

the

external

some

I saw several reels of optical sensors on Ebay this morning, but probaly nothing of interest to you. I did win a reel of 3,000 UHF transistors last night, though. I see the seller posted another reel: "Reel of 3000 UHF 9GHz NPN Transistors Philips/NXP"

Now, to see what trouble I get into with them. ;-)

--
You can't have a sense of humor, if you have no sense.

Try using some heat-shrink tubing, then pinch the ends closed while still hot.

Seems

Carbon paint is pretty good, e.g. ultraflat black Krylon. It's somewhat electrically conductive, though, so you have to be careful with it.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

und? =A0Seems

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, or

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Thanks Phil, Time to order some more parts. Say can you buy Novolac epoxy? (for less than a bottle of good Scotch.)

I figured it might be something out past ~800nm. I've mostly looked at how the tape blocks the Rb D line's (780 and 795 nm)

I've got a bit of time today and will do a few measurments. I've got this old Jarrel Ash spectrometer and PAR 1205 multichannel analyzer. (I'm not sure what the detector is...)

George H.

? =A0Seems

use

some

the

rnal

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some

ith a

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OK I can look at that too.

George H.

nd? =A0Seems

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ng some

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I use to paint Aquadag on the radiation baffles in the pumping lines of low temperature probes.

George H.

Seems

So use black paint for white noise? Eric

Seems

because

some

the

external

some

a

Hmm, interesting, I'd have thought you'd get a lot of outgassing even from dried DAG, just on account of all that surface area.

And you weren't worried about flakes of DAG getting into the turbo? Or was it diffusion-pumped?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

Seems

the

external

some

Absolutely. Use it and like it. ;)

Cheers

Phil Hobbs

:

around? =A0Seems

t because

ying

trying some

alized the

cased

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ing, or

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. =A0With a

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s

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t -

No this was in the big ass pumping lines.... Mechanical pumps. going down into a He4 pot. Some piece of low temperature lore said to use aquadag.. and I just followed that advice, no idea how much it reduced the heat load. If at all.

George H.

? =A0Seems

use

some

the

rnal

r

some

ith a

the

Black electrical tape.

3M Scotch Super 33+ Vinyl electrical tape made in USA (2007)

I=92m also posting this on sci.optics too. (So a bit of a recap)

So I was testing a noise source made with some glass encapsulated Zener diodes (1N5250). The Zeners are wrapped in the above electrical tape to keep out the light. I found that light was still leaking in. (The noise amplitude goes down dramatically when exposed to light.)

I tried to measure the transmission of the above tape with a Si PIN photodiode. I first used a diode laser at 780 nm. The laser was producing a bit more than 10mW of power (8mA of photo current) and I could see no signal leaking through one layer of tape (PD gain =3D 10Meg ohm, DC offset =3D 0.1 mV.. no change at 10uV level.)

I then put the same photodiode under a 60 Watt incandescent lamp. Which when stuck right in front of the PD produced about 2.5mA of photo-current. Again with the tape, at the highest gain setting I could see no change at the 10uV level.

10uV/ 10 M ohm, about 1pA of current vs a few mA=92s. Attenuation of at least10^9!

I=92m stuck wondering what the heck is going on? Is the Zener also a =91very=92 sensitive photodetector? Or does it respond to some longer wavelength photons than the Si photodiode that is leaking through the tape?

The PD is a square about 0.25=94 on a side (0.0625 sq. in area). It=92s a bit hard to know the zener active area. Looking under a microscope there=92s gap about 0.01=94 (inches) between copper colored electrodes. Maybe 0.06=94 wide, so an area of maybe 6x10^-4 sq in.

George (confused again) Herold