1N4007 varactors
 

Asimov wrote:

I never tested a zener when used as varactor but I think these have a
much greater reverse saturation current (even far below breakdown
threshold) and it is this that might cause comparatively more noise
than a conventional diode with a tiny leakage current. Well, at least
that is what the junction noise equations would seem to indicate.

They also have a whale of a lot more capacitance than a conventional
diode. So I don't think it's a fair comparison.

Roy Lewallen, W7EL

Zener Noise
 

On 11 Jan 2006 17:52:16 -0800, Winfield Hill
wrote:

Jim Thompson wrote...

I watched the money-making portable test division in Phoenix
get trashed by the ****-heads in Massachusetts... now you know
_part_ of the source of my animosity toward Massa2****s ;-)

That's an amazing extension. Plenty of healthy Massachusetts
companies have been sucked dry by their out-of-state owners.
Obviously the ability to mis-manage a company from a distance
is not notably a Massachusetts sin, unless you're obsessed with
the Harvard Business School's modest influence on the issue.

It is sadly true that many of the old-line Rt 128 companies are
gone... DEC, Data General, GR, Sensitive Instruments, Clevite,
Transitron, probably others. Have others popped up to take their
place? Analog Devices, for sure.

John

1N4007 varactors
 

Roy Lewallen wrote:
Asimov wrote:


I never tested a zener when used as varactor but I think these have a
much greater reverse saturation current (even far below breakdown
threshold) and it is this that might cause comparatively more noise
than a conventional diode with a tiny leakage current. Well, at least
that is what the junction noise equations would seem to indicate.


They also have a whale of a lot more capacitance than a conventional
diode. So I don't think it's a fair comparison.

Okay, if we are discussing strange and high capacitance varactors,
what would you think of using a PIN photo diode as a varactor? They
have more chip area per dollar and per package size and capacitance
than many rectifier diodes, and that are made to have low leakage
current and often have low inductance packaging.
For example:
http://rocky.digikey.com/WebLib/Osra...pw34fa_fas.pdf
looks like a nice 15 to 70 pF capacitor.

I guess you would have to keep them in the dark, unless you wanted to
tune them (biased by a high resistance to a fixed voltage) with a
variable intensity light beam.

Zener Noise (was: 1N4007 varactors)
 

Just ask for samples, I got five of them a few years ago.


"RST Engineering" wrote in message
.. .
I've used noisecom for some years, but they are hard to buy in
onesie-twosies and are rather expensive in quantity when you only need
one.

They USED to sell seconds that didn't meet spec, but I don't see that
offer on their current website.

Jim



"Clark" wrote in message
...
Try this
http://www.noisecom.com/

1N4007 varactors
 

"Highland Ham" bravely wrote to "All" (11 Jan 06 09:47:40)
--- on the heady topic of " 1N4007 varactors"

HH From: Highland Ham
HH Xref: core-easynews rec.radio.amateur.homebrew:90890

HH Zener diodes are often used as wide band 'noise generators'for use in
HH an impedance bridge used in conjunction with a receiver.

I understand to generate the noise that the zener diodes are operated
within their normal breakdown current range. However, as a varactor it
isn't desirable to have a breakdown current flow. The only tiny
current that flows is a saturation current which is related to
setting up the P-N junction boundaries within the semiconductor.

M*i*k*e

Zener Noise
 

RST Engineering wrote:

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



"Winfield Hill" wrote in message
...


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.



Wouldn't a zener running in (or near) the (easily seen on curve
tracer) negative resistance mode have lots of noise?

Zener Noise
 

In article et,
Robert Baer wrote:
[...]
Wouldn't a zener running in (or near) the (easily seen on curve
tracer) negative resistance mode have lots of noise?


There's noise and then there's noise. Any signal we don't want we call
noise. A noise source for instumentation needs to have a flat spectrum.
The noise on a zener is a good example of the former and poor example of
the latter.

--
--
forging knowledge

Zener Noise
 

John Larkin wrote:
On Wed, 11 Jan 2006 14:10:32 -0500, Phil Hobbs
wrote:


John Larkin wrote:

On Wed, 11 Jan 2006 10:08:19 -0800, "RST Engineering"
wrote:

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



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


You use one of the circular-gap plugs, run it to a HV supply via a 10M
resistor, and just discharge the capacitance of the plug--you get a nice
irregular relaxation oscillation. It isn't the absolute most beautiful
pulse, but (a) it's easy to shield so you get rid of the pickup, (b)
it's surprisingly bright, and (c) the rising edge is way under 1 ns,
which should be fine for the VHF to low UHF range. I might stick one on
my sampling scope sometime and find out more about its actual
performance, but this is a pretty common trick.

There are femtosecond lasers around here--my fastest one is about 20 ps,
but it's continuously tunable from 420 nm to 10 microns, when it's working.

Cheers,

Phil Hobbs

Zener Noise
 

John Larkin wrote...

Winfield Hill wrote:

Jim Thompson wrote...

I watched the money-making portable test division in Phoenix
get trashed by the ****-heads in Massachusetts... now you know
_part_ of the source of my animosity toward Massa2****s ;-)

That's an amazing extension. Plenty of healthy Massachusetts
companies have been sucked dry by their out-of-state owners.
Obviously the ability to mis-manage a company from a distance
is not notably a Massachusetts sin, unless you're obsessed with
the Harvard Business School's modest influence on the issue.

It is sadly true that many of the old-line Rt 128 companies are
gone... DEC, Data General, GR, Sensitive Instruments, Clevite,
Transitron, probably others. Have others popped up to take their
place? Analog Devices, for sure.

We have scads of large wealthy "newer" high-tech companies
headquartered here, that you may not often hear of, like
Thermo Electron, Bruker, Summit Technology, EMC, etc., and
others you do know, with a substantial presence, like Agilent.

Many software and Internet companies are headquartered in MA,
like Peoplesoft, Novell, etc., and many others have a large
presence, like Sun, Red Hat, IBM, Microsoft, etc.

We all know scores of top-tier biotech companies with their
headquarters in MA, who have massive high-tech employment here.


--
Thanks,
- Win

Zener Noise
 

On Wed, 11 Jan 2006 19:20:09 -0800, John Larkin wrote:

It is sadly true that many of the old-line Rt 128 companies are
gone... DEC, Data General, GR, Sensitive Instruments, Clevite,
Transitron, probably others.

Have others popped up to take their place?

Why sure. Can you red Chinese tech manuals?