Zener Noise (was: 1N4007 varactors)

[RST Engineering]

Roy ...

I've been playing around (ahem, excuse me, heuristically engineering) with
zener noise sources for a while using the same spectrum analyzer trick and
as yet I haven't been able to make the noise as "flat" across the passband
as I'd like. I've tried varying the bias, the voltage, and a few other
tricks, but as yet, no joy.

Can you shed some light on what you've found to make the noise power/voltage
fairly level across the band?

Jim

 

[Roy Lewallen]

Roy ...

I've been playing around (ahem, excuse me, heuristically engineering) with
zener noise sources for a while using the same spectrum analyzer trick and
as yet I haven't been able to make the noise as "flat" across the passband
as I'd like. I've tried varying the bias, the voltage, and a few other
tricks, but as yet, no joy.

Can you shed some light on what you've found to make the noise power/voltage
fairly level across the band?

It's not particularly flat over the whole band, and I haven't attempted
to make it be. My interest has been mostly in relatively narrow band
filters, or the shape of a main filter rolloff. The noise is adequately
flat over the bandwidths I've been interested in. It's been a while
since I've fooled with it, but as I recall, the shape of the noise
spectral distribution changed all over the map as I changed the diode
bias. I imagine that it changes with temperature and with individual
diodes, too. So any circuit used to flatten it would only work for a
particular diode, current, and probably temperature. The bottom line is
that it's probably a lousy way to try to generate a flat broadband noise
spectrum.

Roy Lewallen, W7EL

 

[Winfield Hill]

RST Engineering wrote...

Roy ...

I've been playing around (ahem, excuse me, heuristically engineering) with
zener noise sources for a while using the same spectrum analyzer trick and
as yet I haven't been able to make the noise as "flat" across the passband
as I'd like. I've tried varying the bias, the voltage, and a few other
tricks, but as yet, no joy.

Can you shed some light on what you've found to make the noise power/voltage
fairly level across the band?

Good zener noise sources are carefully bred and tested, they
do _not_ come naturally from garden-variety zener diodes. I
suggest you go read the hundred or so messages in the famous
zener oscillation thread a few years back here on s.e.d. In
this you'll learn of my substantial investigations into the
topic, some physics - and, very important, learn what a zener
microplasma is. You'll see my ASCII waveform plots of actual
bench measurements showing exactly what's going on. After all
this you may decide to avoid using zener diodes for calibrated
noise sources. Sorry about that!

 

[Sjouke Burry]

Roy ...

I've been playing around (ahem, excuse me, heuristically engineering) with
zener noise sources for a while using the same spectrum analyzer trick and
as yet I haven't been able to make the noise as "flat" across the passband
as I'd like. I've tried varying the bias, the voltage, and a few other
tricks, but as yet, no joy.

Can you shed some light on what you've found to make the noise power/voltage
fairly level across the band?

Jim

What I did for some project which needed equal amplitude
uncorrelated noise,is amplify the zener noise with a wide
band video opamp,with high pass and lowpass filtering.
Used the low pass as input for a zero cross detector,
delayed the zerocrossing 10 microseconds,and used that
for clock to a circulating bit in a shift register.
each parallel output of that register controlled a
sample/hold opamp,sampling the highpass signal.
Voila!! 8 audio frequency, non-correlated noise sources.
The zerocrossing clock was made this way,to avoid detectable
clock tones int the output.(2 to 20 microsec between
crossings)
the 10 microsecond delay was used to get a voltage at
the sample and hold opamp which was not correlated to the
zerocrossing.
If you need only one signal ,leave out the shift register,
and just use a 10 and a 1 microsec. oneshot for the s/h
opamp clock.
The application? A wind and engine noise generator for a
car simulator.

 

[John Larkin]

Roy ...

I've been playing around (ahem, excuse me, heuristically engineering) with
zener noise sources for a while using the same spectrum analyzer trick and
as yet I haven't been able to make the noise as "flat" across the passband
as I'd like. I've tried varying the bias, the voltage, and a few other
tricks, but as yet, no joy.

Can you shed some light on what you've found to make the noise power/voltage
fairly level across the band?

Jim

These folks will sell you serious noise diodes...

http://www.noisecom.com/NC/default.htm

John

 

[JeffM]

...the famous zener oscillation thread a few years back

...my ASCII waveform plots of actual bench measurements
showing exactly what's going on.
Winfield Hill

http://groups.google.com/group/sci....2a79d11?q=microplasma+zener+Oscillation&fwc=1

 

[Winfield Hill]

JeffM wrote...

http://groups.google.com/group/sci....2a79d11?q=microplasma+zener+Oscillation&fwc=1

That's one thread, perhaps the first in a series. That thread
doesn't have the waveforms I was referring to (although there
are some waveforms in posts 51 and 66). Tony, Bill, Roy and I,
and some others here wasted masses of time on this subject over
a period of a few months, eight and a half years ago. We took
bench measurements, did calculations, found the scientific
literature (it was a subject that occupied physicists in the
late 50s, see posts 72-76), and we did plenty of speculation.

 

[Winfield Hill]

Winfield Hill wrote...

JeffM wrote...

That's one thread, perhaps the first in a series. That thread
doesn't have the waveforms I was referring to (although there
are some waveforms in posts 51 and 66). Tony, Bill, Roy and I,
and some others here wasted masses of time on this subject over
a period of a few months, eight and a half years ago. We took
bench measurements, did calculations, found the scientific
literature (it was a subject that occupied physicists in the
late 50s, see posts 72-76), and we did plenty of speculation.

All of which led Roy McCammon to remark (post 90), "I'd have to
say that it is the best thread this year." He said that Aug 5th,
after 3 weeks of posts, and yet the followup threads in Aug and
Sept on the same topic were just as long, and perhaps even more
interesting. Ah, those were that days!

 

[RST Engineering]

OK, then. A zener makes a poor noise source according to what I'm reading.
Noise.com used to sell off-spec diodes by the onesies for we poor peons to
play with, but for whatever reason that doesn't seem to be the case any
more.

Given that a zener (at whatever current) is a poor noise source, what is a
good source of electronic broadband noise from low HF through high UHF --
say, 5 to 500 MHz.? (No smart remarks about spark gaps.)

Jim





We took

 

[John Larkin]

OK, then. A zener makes a poor noise source according to what I'm reading.
Noise.com used to sell off-spec diodes by the onesies for we poor peons to
play with, but for whatever reason that doesn't seem to be the case any
more.

Given that a zener (at whatever current) is a poor noise source, what is a
good source of electronic broadband noise from low HF through high UHF --
say, 5 to 500 MHz.? (No smart remarks about spark gaps.)

Jim

A hot resistor.

How about a thermistor or a lamp filament that was 50 ohms at some
high temperature. You could heat it with DC, sense its
resistance/temp, and let it make noise, all in a single part.

Old vintage noise figure meters used gas tubes. And I think there was
a pencil tube that mounted in a waveguide and made shot noise.

And, of course, the old photomultiplier trick.

John

 

[Mark]

I have seen a small "gain of wheat" type light bulb used as a noise
source...

Feed it with DC through a choke and AC couple the noise out ....

and you can vary it too!!

Mark

 

[RST Engineering \(jw\)]

Immediately you say "choke" you have modified and peaked the bandwidth.
I'll buy that you can feed it with a resistor for broadband, but in my
humble opinion the construction of a grain of wheat bulb won't get up into
the UHF region with noise. Do you have any idea of the output level of this
circuit?

Jim

 

[Phil Hobbs]

A hot resistor.

How about a thermistor or a lamp filament that was 50 ohms at some
high temperature. You could heat it with DC, sense its
resistance/temp, and let it make noise, all in a single part.

Old vintage noise figure meters used gas tubes. And I think there was
a pencil tube that mounted in a waveguide and made shot noise.

And, of course, the old photomultiplier trick.

I still like the flashlight/photodiode trick. You can get a really good
calibration just from the dc, and can calibrate the frequency response
with a spark plug.

Cheers,

Phil Hobbs

 

[Bill Turner]

ORIGINAL MESSAGE:


"Phil Hobbs" <[email protected] wrote

and can calibrate the frequency response with a spark plug.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I generally use a pipe wrench, but I'll try anything once.

Bill, W6WRT

 

[Tim Williams]

Old vintage noise figure meters used gas tubes. And I think there was
a pencil tube that mounted in a waveguide and made shot noise.

I've got a gaussian noise generator, some SS in the power supply, tubes
everywhere else, found it on the curb and apparently works. Uses a pair of
6D4 thyratrons in magnetic fields for the noise.

Tim

 

[John Larkin]

I've got a gaussian noise generator, some SS in the power supply, tubes
everywhere else, found it on the curb and apparently works. Uses a pair of
6D4 thyratrons in magnetic fields for the noise.

Tim

GR?

John

 

[John Larkin]

I still like the flashlight/photodiode trick. You can get a really good
calibration just from the dc, and can calibrate the frequency response
with a spark plug.

Cheers,

Phil Hobbs

What's the light-flash waveform look like from a spark plug? What do
you drive it with?

Don't you have gobs of femtosecond lasers around your place?

John

 

[Clark]

Try this
http://www.noisecom.com/

 

[Tim Williams]

GR?

Come again?

Tim

 

[K7ITM]

Jim wrote: "...what is a good source of electronic broadband noise
from low HF through high UHF -- say, 5 to 500 MHz.?"

A linear feedback shift register. Small, repeatable. 500MHz should be
no particular problem these days. (There's an idea for some IC
manufacturer...32 bits clocked at 1G/sec repeats every 4 seconds, which
would be OK, but I'd prefer 40 or more bits. Should fit nicely into a
5 pin SOT-23: power, gnd, reset, out, ...)