RF Transistor Noise Source

Unfavourable for climate control purposes, anyway. Great for beach purposes.

Never did like them.

Gotcha. My son Simon is going to make some dough by insulating the attic. I wanted to use vermiculite but you basically can't get it any more--which is a pity. You have to use a bit more, but you don't wind up with red eyes and itchy skin the way you do with rock wool or fibreglass.

I'm a warm-blooded sort of cove, actually--I nearly melted down in Costa Rica a couple of weeks ago.

Cheers

Phil Hobbs

"There is no bad weather, there are only wrong clothes."

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

On Tue, 29 Dec 2009 16:57:23 -0500, Phil Hobbs wrote: [snip]

[snip]

That IS a shame. Best insulated house I ever owned had vermiculite filled walls.

Only problem was if I cut a hole to add, for instance, another electrical outlet... it poured out on the floor.

So I'd catch it in a bucket, do my wire pulling, put the box in place, and seal it. Then go up in the attic and re-pour the vermiculite ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
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Avalanche breakdown results in amplification of shot noise. A true 'Zener' (like Claude Zener described) diode is a good approximation of low-voltage breakdown (under 5V) and doesn't have that amplification effect.

So, better noise production will occur with higher voltage diodes (I'd try 20V or so), than with a B-E breakdown. The B-E area of any suitable transistor will be large, and limit your high frequency output due to capacitance; maybe a small-signal junction diode will do better. Best, actually, might be a Ne lamp (same avalanche breakdown, very low shunt capacitance), but that'll take some high voltage to strike, and has magnetic field sensitivity.

I've seen microwave noise sources that had a discharge lamp inside a waveguide.

Point-contact diodes or Schottky will have age degradation issues, because the junction is near the surface. Probably. They aren't really tested or specified for that kind of bias, so you can't assume the right precautions are in place (field rings, surface passivation) to stabilize operation in this reverse-conduction condition.

Wow! When we lived in VT we had the set-back thermostat set to 59F at night and 64F during the day, with a spike to 68F early morning (with weekends having a different definition of "early"). At night we'd boost it up when we got too cold. Now we keep it at a pretty constant

67F. The heat pump doesn't like being set back. The recovery time sucks.

That's too warm for the winter.

We're set at 68ºF ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
                    Help save the environment!
             Please dispose of socialism responsibly!

They make loose cellulose insulation. My (new) house has it, bit it's a PITA, IMO. It doesn't itch (been working in it this week), but

*does* compress.

That too. I still haven't replaced it in the wall above the sub-panel I put in. I'm finishing that room so the insulation won't be needed.

Umm, walls aren't supposed to be open at the top, for *many* reasons.

Some of us are clever enough to pour it thru the wire hole ;-)

(Vermiculite is about the size of rice.) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
                    Help save the environment!
             Please dispose of socialism responsibly!

he attic and re-pour the vermiculite ;-)

This stuff is more like small croutons. The really little stuff is mostly used in potting soil.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

I thought kitty litter was almost pure vermiculite.

Jim

Clay, usually. Vermiculite is a kind of mica that unfolds like an accordion when you heat it. It isn't like anything else.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

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Interesting thanks, I=E2=80=99ve used the LM399=E2=80=99s that come with a= nice plastic cover and heater circuit. They run right about 6.95 Volts, which I=E2=80=99ve always thought was the =E2=80=98magic=E2=80=99 balance p= oint between =E2=80=98tunneling=E2=80=99 zener current and =E2=80=98avalanche=E2=80=99 z= ener current, (but maybe there=E2=80=99s another diode in series?).

For a noise source I think the avalanche zeners above 7 V will be much better than tunneling zeners. I think (though I=E2=80=99m half talking out= of my a$$ since I haven=E2=80=99t made the measurements.) that tunneling zener= s should show about the same noise as forward biased diodes. (At least if you measure the current noise.) This assumes that the only noise source is shot noise.

Say do zenered pnp=E2=80=99s show more noise than zenered npn=E2=80=99s?

(I=E2=80=99ve never measured the zener voltage of a transistor.)

George H.

Cool, do you do anything with the base? Seems a shame to just leave it hanging.

George H.

The insulation I've seen is more like popcorn or pea gravel. Even wire holes are supposed to be sealed, though I suppose it's less important on exterior walls.

I have no experience with those diodes, but would guess they would have the same problem.

7mA; usually the minimum current which most zeners and reverse-biased E-B junctions exhibit stability (ie: no negative resistance and noise).

Name a few NPNs.

What level of a dope do you think i am, anyway??

You have already demonstrated that ;-)

Just kidding! Just kidding! Just kidding! ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
                    Help save the environment!
             Please dispose of socialism responsibly!

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Hello Robert,

Today I tested reverse current effects for a 1N4448 that I will use in a small 12V to 300V converter. I will put several in series and would like to know the effects of spread in reverse recovery time. I supplied 14C of charge (7mAp, 1.3mA average, 130 kHz PRF) to the diode. The differences in avalanche voltage, avalanche impedance and reverse leakage were too small to detect in my simple setup (two devices tested).

In the product's lifetime, the diodes will be subjected to very low overall reverse breakdown charge, so I think I will use the series circuit of 1N4448.

Probably one can do this for RF schottky diodes also (like BAT15). As these have low capacitance and low break down voltage, they can be used for a noise source.

Best regards and good 2010,

Wim PA3DJS

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