Help for negative resistance oscillator

In article <c72p7j02qd7@drn.newsguy.com>,
Winfield Hill <Winfield_member@newsguy.com> wrote:

Tony, I think by "piece of junk," Fred was referring
to Robert Baer's inductor, not your circuit. :>)
Click to expand...
Oh, ok.

Still, had something to do on a grey day........

--
Tony Williams.
 
Robert Baer wrote:

It would be nice if it could oscillate in the tens of KHz region, but
the large inductance probably would not support that.
The internal resistance is so high that i have not found a way to
determine the "self-resonant" frequency (exciting with a zener in
negative resistance mode was of no help).
Click to expand...
Have you seen the negative resistance oscillator used in this digital
LC meter (the schematic is way down at the bottom)? I never invent
what I can copy.
http://www.aade.com/LCinst/lcm2b.htm
--
John Popelish
 
In article <40958DC8.9903A643@rica.net>, jpopelish@rica.net
says...
Robert Baer wrote:

It would be nice if it could oscillate in the tens of KHz region, but
the large inductance probably would not support that.
The internal resistance is so high that i have not found a way to
determine the "self-resonant" frequency (exciting with a zener in
negative resistance mode was of no help).

Have you seen the negative resistance oscillator used in this digital
LC meter (the schematic is way down at the bottom)? I never invent
what I can copy.
http://www.aade.com/LCinst/lcm2b.htm

Ok, I've been following this thread for a while and am indeed
Click to expand...
confused. Just what is a "negative resistance oscillator"? All
oscillators are "negative resistance" (kinda required to
oscillate, me thinks). Indeed that's one way we analyzed them in
college. Even the classic cross-coupled multivibrator is
negative-resistance if you look at the coupling nodes.

--
Keith
 
Robert Baer wrote...
Fred Bloggs wrote:

Robert Baer wrote:

It seems the Q of the inductor is much less than one.

It's a PoS- better to think "door stop" ....

It is sure heavy enough!
Click to expand...
What is it anyway? Tell us more.


Thanks,
- Win

whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)
 
"KR Williams" <krw@att.biz> wrote in message
news:MPG.1aff60039e27b84a9897ed@news1.news.adelphia.net...
Ok, I've been following this thread for a while and am indeed
confused. Just what is a "negative resistance oscillator"? All
oscillators are "negative resistance" (kinda required to
oscillate, me thinks). Indeed that's one way we analyzed them in
college. Even the classic cross-coupled multivibrator is
negative-resistance if you look at the coupling nodes.

--
Keith
Click to expand...
Generally refers to an oscillator with only two terminals to the tuned
element; no tapped L as in Hartley, no tapped C as in Colpitts, no feedback
winding as in Armstrong.
 
In article <4ZudnV3eNfj5PAjdRVn-hQ@giganews.com>,
BFoelsch@comcast.ditch.this.net says...
"KR Williams" <krw@att.biz> wrote in message
news:MPG.1aff60039e27b84a9897ed@news1.news.adelphia.net...
Ok, I've been following this thread for a while and am indeed
confused. Just what is a "negative resistance oscillator"? All
oscillators are "negative resistance" (kinda required to
oscillate, me thinks). Indeed that's one way we analyzed them in
college. Even the classic cross-coupled multivibrator is
negative-resistance if you look at the coupling nodes.

--
Keith

Generally refers to an oscillator with only two terminals to the tuned
element; no tapped L as in Hartley, no tapped C as in Colpitts, no feedback
winding as in Armstrong.
Click to expand...
SO you're saying that it's an oscillator with only one reactive
element? ...or not one with two reactive elements separated by
an amplifier?

Someone suggested a Zener used in the "negative resistance"
region. That confused the hell outta me too. Uni-junction,
sure. Thyristor (Diac, SCR,...), sure. But a Zener?

I'm still confused with the terminology. Thanks for your help
though.

--
Keith
 
Robert Baer wrote:
What i have: an inductor of unknown value, but most likely in the
henry region, with resistance from 4K to 10K.
Click to expand...
Sounds very like a guitar pickup. Self-capacitance means this isn't
much like an inductor at very many frequencies, but a low-Q tuned
circuit. Measuring the inductive component is a bit pointless, you
need a network analyser or some other impedance device that plots
the complex impedance and phase over an audio sweep. Out of that,
you'll easily pick the primary self-resonance.

If one of the smarter engineers here cares to suggest or point to a
test circuit, perhaps to connect to a PC sound card, I'd like to test
the unusual pickups I've been building. My proposal would be to pump
audio in (sound card out) via a resistor while measuring both the
feed voltage and the terminal voltage (stereo full-duplex sound card
required), to get I and V waveforms at each frequency. Any suggestions
on how to improve this method? Would it work ok?

Clifford Heath.
 
Nope. Picture an ordinary parallel LC circuit with a "negative resistance"
element that prevents the tank from using up its stored energy, thereby
letting it "ring" forever. A parallel LC tank with a (properly biased)
tunnel diode and voltage source in series across it is perhaps the "purest"
implementation, but many other implementations are of course possible.

The terminology "negative resistance oscillator" is very old. The concept
was a novelty in the 1930's and 1940's. That was of course the vacuum tube
era, and the challenge was to use as few tubes and parts as possible.

Given that a single amplifying device (tube or transistor) in the
conventional configuration has a phase shift of 180 degrees, an oscillator
that used only one active device needed another 180 degree shift to make it
oscillate. This was usually accomplished by either center tapping the L of
an LC circuit, resulting in a Hartley oscillator, or center tapping the C,
resulting in a Colpitts oscillator. Unfortunately, these expedients made the
tank circuits 3 terminal devices, posing some nasty but not insurmountable
problems. Of course the Armstrong oscillator had an additional winding on
the L, which was even worse.

The negative resistance concept permitted the use of 2 terminal tank
circuits by removing the necessity for the tank circuit to provide a 180
degree phase shift at resonance. The first real examples were the Dynatron
oscillator, which utilized the negative resistance characteristic peculiar
to certain vacuum tubes called tetrodes. Later, multi-device amplifiers were
devised that accomplished the same thing with standard components. The
tunnel diode example discussed above is perhaps the simplest possible LC
oscillator.

"KR Williams" <krw@att.biz> wrote in message
news:MPG.1aff73b0eea2f2159897f4@news1.news.adelphia.net...
In article <4ZudnV3eNfj5PAjdRVn-hQ@giganews.com>,
BFoelsch@comcast.ditch.this.net says...

"KR Williams" <krw@att.biz> wrote in message
news:MPG.1aff60039e27b84a9897ed@news1.news.adelphia.net...
Ok, I've been following this thread for a while and am indeed
confused. Just what is a "negative resistance oscillator"? All
oscillators are "negative resistance" (kinda required to
oscillate, me thinks). Indeed that's one way we analyzed them in
college. Even the classic cross-coupled multivibrator is
negative-resistance if you look at the coupling nodes.

--
Keith

Generally refers to an oscillator with only two terminals to the tuned
element; no tapped L as in Hartley, no tapped C as in Colpitts, no
feedback
winding as in Armstrong.

SO you're saying that it's an oscillator with only one reactive
element? ...or not one with two reactive elements separated by
an amplifier?

Someone suggested a Zener used in the "negative resistance"
region. That confused the hell outta me too. Uni-junction,
sure. Thyristor (Diac, SCR,...), sure. But a Zener?

I'm still confused with the terminology. Thanks for your help
though.

--
Keith
Click to expand...
 
John Popelish wrote:
Robert Baer wrote:

It would be nice if it could oscillate in the tens of KHz region, but
the large inductance probably would not support that.
The internal resistance is so high that i have not found a way to
determine the "self-resonant" frequency (exciting with a zener in
negative resistance mode was of no help).

Have you seen the negative resistance oscillator used in this digital
LC meter (the schematic is way down at the bottom)? I never invent
what I can copy.
http://www.aade.com/LCinst/lcm2b.htm
--
John Popelish
Click to expand...
Have not seen that one; seems to be a slight variant of the "chaos"
oscillator mentioned.
Gotta get off my rump and build one to see if it will do the job.
 
KR Williams wrote:
In article <4ZudnV3eNfj5PAjdRVn-hQ@giganews.com>,
BFoelsch@comcast.ditch.this.net says...

"KR Williams" <krw@att.biz> wrote in message
news:MPG.1aff60039e27b84a9897ed@news1.news.adelphia.net...
Ok, I've been following this thread for a while and am indeed
confused. Just what is a "negative resistance oscillator"? All
oscillators are "negative resistance" (kinda required to
oscillate, me thinks). Indeed that's one way we analyzed them in
college. Even the classic cross-coupled multivibrator is
negative-resistance if you look at the coupling nodes.

--
Keith

Generally refers to an oscillator with only two terminals to the tuned
element; no tapped L as in Hartley, no tapped C as in Colpitts, no feedback
winding as in Armstrong.

SO you're saying that it's an oscillator with only one reactive
element? ...or not one with two reactive elements separated by
an amplifier?

Someone suggested a Zener used in the "negative resistance"
region. That confused the hell outta me too. Uni-junction,
sure. Thyristor (Diac, SCR,...), sure. But a Zener?

I'm still confused with the terminology. Thanks for your help
though.

--
Keith
Click to expand...
I am the nut that mentioned the zener diode.
All zener diodes greater than about 5.6V have a negative resistance
region from roughly 0.1uA to 100uA (highly variable range depending on
make and voltage rating).
It is due to the avalange mode that the zeners operate in.
At currents from about 10% of Izt and up, one sees them as having a
low and positive resistance.
But at "low" currents, they are rather noisy, and a curve tracer can
usually show a peak voltage before breakdown, and a decidedly lower
"sustaining" voltage after breakdown.
 
Winfield Hill wrote:
Robert Baer wrote...

Fred Bloggs wrote:

Robert Baer wrote:

It seems the Q of the inductor is much less than one.

It's a PoS- better to think "door stop" ....

It is sure heavy enough!

What is it anyway? Tell us more.

Thanks,
- Win

whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)
Click to expand...
The inductor is in a monel (i think) case about 9 inches long by about
1.75 inch diameter.
It is wound on a (monel?) "bobbin" about 1.5 inch diameter and about 6
inches long; ten thousand minimum turns; perhaps 80 thousand maximum
turns (wire size unknown).
It is part of a device used in oil wells called a collar locator
("CCL" in their parlance).
They use a funky amplifier circuit to convert the dV/dT output of the
coil to a current (pulse) on the 120VDC power line.
The coil has a rather powerful Alnico magnet on each end, magnetized
so that both north (or south) poles point inward - making it a variation
of a variable reluctance detector.
As the assemble passes (inside) from one (connected) pipe to the next,
the thicker "collar" which connects the pipes together had a different
permeability.
The movement past this distorts the hyperbolic magnetic field, and so
generates the dV/dT mentioned.

I was thinking that "maybe" one could turn the inductor into an
oscillator and thereby get rid of the expensive magnets.
Now you know my "secret".
 
Winfield Hill wrote:
Tony Williams wrote...

Fred Bloggs wrote:

Tony Williams wrote...

[ snip interesting circuit ]

I am fairly certain that it is impossible to make a
stored energy oscillator out of this piece of junk ...

Oh-oh! Time for a breadboard maybe............

[ snip ]

Well, it oscillated quite nicely, and ...

Tony, I think by "piece of junk," Fred was referring
to Robert Baer's inductor, not your circuit. :>)

Thanks,
- Win

whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)
Click to expand...
I, also suspect that to be the case.
 
Clifford Heath wrote:
Robert Baer wrote:
What i have: an inductor of unknown value, but most likely in the
henry region, with resistance from 4K to 10K.

Sounds very like a guitar pickup. Self-capacitance means this isn't
much like an inductor at very many frequencies, but a low-Q tuned
circuit. Measuring the inductive component is a bit pointless, you
need a network analyser or some other impedance device that plots
the complex impedance and phase over an audio sweep. Out of that,
you'll easily pick the primary self-resonance.

If one of the smarter engineers here cares to suggest or point to a
test circuit, perhaps to connect to a PC sound card, I'd like to test
the unusual pickups I've been building. My proposal would be to pump
audio in (sound card out) via a resistor while measuring both the
feed voltage and the terminal voltage (stereo full-duplex sound card
required), to get I and V waveforms at each frequency. Any suggestions
on how to improve this method? Would it work ok?

Clifford Heath.
Click to expand...
Nope; swept it from 0.01Hz to 10MHz. Had to get into the 100KHz and
above region before i could see phase shifting.
No amplitude variance, except at the very low end; had to use "Lazy
Joe" for the phase variations..
 
Robert Baer wrote...
Nope; swept it from 0.01Hz to 10MHz. Had to get into the 100KHz
and above region before i could see phase shifting. No amplitude
variance, except at the very low end; had to use "Lazy Joe" for
the phase variations..
Click to expand...
Swept with what source impedance? 50 ohms? Try feeding the
coil with 10k or 100k (i.e. a current source) and monitoring
its response with a 10M scope probe when you sweep it.


Thanks,
- Win

whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)
 
Robert Baer wrote:

As the assemble passes (inside) from one (connected) pipe to the next,
the thicker "collar" which connects the pipes together had a different
permeability.
The movement past this distorts the hyperbolic magnetic field, and so
generates the dV/dT mentioned.

I was thinking that "maybe" one could turn the inductor into an
oscillator and thereby get rid of the expensive magnets.
Now you know my "secret".
Click to expand...
You should have said that from the start. I was wondering why anyone
would want to fool around with an inductor of such poor Q, other than
some kind of perverted fetish for obscure junk.

That gadget was probably designed, 'tuned', to the velocity it passes
through pipe permeability transitions.

Now what is your purpose today? Same application, just different mode of
operation by sensing FM rather than amplitude?

I can't see that reluctance sensor in that application functioning
better in an FM mode. Eddy currents will reduce the sensor
effectiveness. It needs to oscillate at a low frequency to be sensitive,
so it would have to move slowly through the pipe.

But just using a current amplifier would allow it to move through the
pipe faster to sense transitions. It wouldn't function well at low speeds.

--
Scott

**********************************

DIY Piezo-Gyro, PCB Drill Bot & More Soon!

http://home.comcast.net/~scottxs/

**********************************
 
On 1 May 2004 16:33:26 -0700, Winfield Hill
<Winfield_member@newsguy.com> wrote:

Jim Thompson wrote...

Winfield Hill wrote:

OK, I see where you're coming from. I've been using
this for comparators, a vertical line at the output,
__
--|- |\
| | >--
--|+_|/


Win, I think the vertical line is "standard" notation.

That would be nice, I've been using it for over 30 years,
but I don't recall seeing it on other people's drawings
(this could be my forgetfullness). For example, do you
use it yourself? Can you give us a reference or guidance
for its being a standard notation? Also, can we safely
mention it in our book's next edition?


Thanks,
- Win

whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)
Click to expand...
I just took a look through IEEE Std 315 and 31A. There is no
dedicated comparator symbol that I could find. The closest thing is
the generic amplifier symbol (the triangle), and this is what you see
in comparator data sheets. The symbol above looks similar to IEEE
symbols for integrator and electronic function generator, so I would
say that it should not be used to designate a comparator (unless you
want to argue that a comparator is better described as a function
generator than an amplifier).


================================

Greg Neff
VP Engineering
*Microsym* Computers Inc.
greg@guesswhichwordgoeshere.com
 
In article <XKWdndMDqI7LJwjdRVn-uQ@giganews.com>,
BFoelsch@comcast.ditch.this.net says...

I thank you for you explanation and I *think* I understand the
semantics of the "negative resistance" part (though I think it's
a rather lousy term). I read it at work today, but haven't fully
digested it all. I'll have to do some more research to fully
understand. As you've likely guessed, oscillators aren't "my
thing". ;-)

Again, I appreciate the education! ...but need more.

--
Keith

Nope. Picture an ordinary parallel LC circuit with a "negative resistance"
element that prevents the tank from using up its stored energy, thereby
letting it "ring" forever. A parallel LC tank with a (properly biased)
tunnel diode and voltage source in series across it is perhaps the "purest"
implementation, but many other implementations are of course possible.

The terminology "negative resistance oscillator" is very old. The concept
was a novelty in the 1930's and 1940's. That was of course the vacuum tube
era, and the challenge was to use as few tubes and parts as possible.

Given that a single amplifying device (tube or transistor) in the
conventional configuration has a phase shift of 180 degrees, an oscillator
that used only one active device needed another 180 degree shift to make it
oscillate. This was usually accomplished by either center tapping the L of
an LC circuit, resulting in a Hartley oscillator, or center tapping the C,
resulting in a Colpitts oscillator. Unfortunately, these expedients made the
tank circuits 3 terminal devices, posing some nasty but not insurmountable
problems. Of course the Armstrong oscillator had an additional winding on
the L, which was even worse.

The negative resistance concept permitted the use of 2 terminal tank
circuits by removing the necessity for the tank circuit to provide a 180
degree phase shift at resonance. The first real examples were the Dynatron
oscillator, which utilized the negative resistance characteristic peculiar
to certain vacuum tubes called tetrodes. Later, multi-device amplifiers were
devised that accomplished the same thing with standard components. The
tunnel diode example discussed above is perhaps the simplest possible LC
oscillator.

"KR Williams" <krw@att.biz> wrote in message
news:MPG.1aff73b0eea2f2159897f4@news1.news.adelphia.net...
In article <4ZudnV3eNfj5PAjdRVn-hQ@giganews.com>,
BFoelsch@comcast.ditch.this.net says...

"KR Williams" <krw@att.biz> wrote in message
news:MPG.1aff60039e27b84a9897ed@news1.news.adelphia.net...
Ok, I've been following this thread for a while and am indeed
confused. Just what is a "negative resistance oscillator"? All
oscillators are "negative resistance" (kinda required to
oscillate, me thinks). Indeed that's one way we analyzed them in
college. Even the classic cross-coupled multivibrator is
negative-resistance if you look at the coupling nodes.

--
Keith

Generally refers to an oscillator with only two terminals to the tuned
element; no tapped L as in Hartley, no tapped C as in Colpitts, no
feedback
winding as in Armstrong.

SO you're saying that it's an oscillator with only one reactive
element? ...or not one with two reactive elements separated by
an amplifier?

Someone suggested a Zener used in the "negative resistance"
region. That confused the hell outta me too. Uni-junction,
sure. Thyristor (Diac, SCR,...), sure. But a Zener?

I'm still confused with the terminology. Thanks for your help
though.

--
Keith
Click to expand...
 
In article <4095EB90.B34C3013@earthlink.net>,
robertbaer@earthlink.net says...
KR Williams wrote:

In article <4ZudnV3eNfj5PAjdRVn-hQ@giganews.com>,
BFoelsch@comcast.ditch.this.net says...

"KR Williams" <krw@att.biz> wrote in message
news:MPG.1aff60039e27b84a9897ed@news1.news.adelphia.net...
Ok, I've been following this thread for a while and am indeed
confused. Just what is a "negative resistance oscillator"? All
oscillators are "negative resistance" (kinda required to
oscillate, me thinks). Indeed that's one way we analyzed them in
college. Even the classic cross-coupled multivibrator is
negative-resistance if you look at the coupling nodes.

--
Keith

Generally refers to an oscillator with only two terminals to the tuned
element; no tapped L as in Hartley, no tapped C as in Colpitts, no feedback
winding as in Armstrong.

SO you're saying that it's an oscillator with only one reactive
element? ...or not one with two reactive elements separated by
an amplifier?

Someone suggested a Zener used in the "negative resistance"
region. That confused the hell outta me too. Uni-junction,
sure. Thyristor (Diac, SCR,...), sure. But a Zener?

I'm still confused with the terminology. Thanks for your help
though.

--
Keith

I am the nut that mentioned the zener diode.
Click to expand...
LOL! It's been a long time since I used avalanche diodes (or
anything close to that voltage). But your twit to my ribs brings
back much memory. Is the negative resistance region of a zener
really usable? It's gotta be small, but specified?

All zener diodes greater than about 5.6V have a negative resistance
region from roughly 0.1uA to 100uA (highly variable range depending on
make and voltage rating).
Click to expand...
Usable?

It is due to the avalange mode that the zeners operate in.
At currents from about 10% of Izt and up, one sees them as having a
low and positive resistance.
But at "low" currents, they are rather noisy, and a curve tracer can
usually show a peak voltage before breakdown, and a decidedly lower
"sustaining" voltage after breakdown.
Click to expand...
Sheesh, a CT was once my best friend. I haven't seen one for at
least a decade. Hell, they *scrapped* my new 6GHz spectrum
analyzer and matching antennas five years ago. sob. Oh well,
all in the interest of a retirement check.

Soon...

--
Keith
 
KR Williams wrote:

In article <XKWdndMDqI7LJwjdRVn-uQ@giganews.com>,
BFoelsch@comcast.ditch.this.net says...

I thank you for you explanation and I *think* I understand the
semantics of the "negative resistance" part (though I think it's
a rather lousy term).
Click to expand...
I had trouble with the concept too.

Resistance is the ratio of voltage/current. So a negative resistance at
a circuit node is the ratio of current that a node will force back at
you for putting a voltage on it.

Imagine someone pushing you. You're not one to be pushed around, so as
they apply force to move you back, you apply more force to push them
back further than they are pushing you. And since you're not hysterical,
you apply proportional and appropriate force back.

Its hard to imagine a circuit behaving this way at DC, but for AC,
capacitors and inductors store energy and return it phase-shifted.

As you've likely guessed, oscillators aren't "my
thing". ;-)
Click to expand...
Simply amplifiers with feedback.

--
Scott

**********************************

DIY Piezo-Gyro, PCB Drill Bot & More Soon!

http://home.comcast.net/~scottxs/

**********************************
 
KR Williams wrote:
In article <4095EB90.B34C3013@earthlink.net>,
robertbaer@earthlink.net says...
KR Williams wrote:

In article <4ZudnV3eNfj5PAjdRVn-hQ@giganews.com>,
BFoelsch@comcast.ditch.this.net says...

"KR Williams" <krw@att.biz> wrote in message
news:MPG.1aff60039e27b84a9897ed@news1.news.adelphia.net...
Ok, I've been following this thread for a while and am indeed
confused. Just what is a "negative resistance oscillator"? All
oscillators are "negative resistance" (kinda required to
oscillate, me thinks). Indeed that's one way we analyzed them in
college. Even the classic cross-coupled multivibrator is
negative-resistance if you look at the coupling nodes.

--
Keith

Generally refers to an oscillator with only two terminals to the tuned
element; no tapped L as in Hartley, no tapped C as in Colpitts, no feedback
winding as in Armstrong.

SO you're saying that it's an oscillator with only one reactive
element? ...or not one with two reactive elements separated by
an amplifier?

Someone suggested a Zener used in the "negative resistance"
region. That confused the hell outta me too. Uni-junction,
sure. Thyristor (Diac, SCR,...), sure. But a Zener?

I'm still confused with the terminology. Thanks for your help
though.

--
Keith

I am the nut that mentioned the zener diode.

LOL! It's been a long time since I used avalanche diodes (or
anything close to that voltage). But your twit to my ribs brings
back much memory. Is the negative resistance region of a zener
really usable? It's gotta be small, but specified?

All zener diodes greater than about 5.6V have a negative resistance
region from roughly 0.1uA to 100uA (highly variable range depending on
make and voltage rating).

Usable?

It is due to the avalange mode that the zeners operate in.
At currents from about 10% of Izt and up, one sees them as having a
low and positive resistance.
But at "low" currents, they are rather noisy, and a curve tracer can
usually show a peak voltage before breakdown, and a decidedly lower
"sustaining" voltage after breakdown.

Sheesh, a CT was once my best friend. I haven't seen one for at
least a decade. Hell, they *scrapped* my new 6GHz spectrum
analyzer and matching antennas five years ago. sob. Oh well,
all in the interest of a retirement check.

Soon...

--
Keith
Click to expand...
The negative resistance region is useable for at least two things:
a) "truely" random noise generator
b) relaxation oscillator (similar to use of a neon bulb)
 
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