Need help with basic Oscillator design

J

jalbers@bsu.edu

Guest
I have some electronics theory questions and some electronics
simulator questions pertaining to an Armstrong oscillator. I have
done some reading and have tried to come up with a design on my own.
Most books just show a general diagram with no specific values. I am
trying to simulate my design in LTSpice:

https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Armstrong1.asc

Plotting voltages at points A and B, the circuit will work for up to
13 seconds (.tran 13) but does something strange after 14 seconds? I
speculate that L2 is going to keep adding more and more energy to the
tank circuit until things get out of control. I don’t think that this
has happened quite yet though?

What do I need to add to the circuit to build the voltage at point A
to a maximum altitude and keep it there?

Any help would be greatly appreciated. Thanks
 
On 24 Nov, 15:28, "jalb...@bsu.edu" <jalb...@bsu.edu> wrote:
I have some electronics theory questions and some electronics
simulator questions pertaining to an Armstrong oscillator. I have
done some reading and have tried to come up with a design on my own.
Most books just show a general diagram with no specific values. I am
trying to simulate my design in LTSpice:

https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Armstrong1.asc

Plotting voltages at points A and B, the circuit will work for up to
13 seconds (.tran 13) but does something strange after 14 seconds? I
speculate that L2 is going to keep adding more and more energy to the
tank circuit until things get out of control. I don’t think that this
has happened quite yet though?

What do I need to add to the circuit to build the voltage at point A
to a maximum altitude and keep it there?

Any help would be greatly appreciated. Thanks
Click to expand...
Right-click the .tran directive and tick the check box "start external
DC supply voltages at 0V"

The changes the directive to ".tran 13 startup"

This is often necessary for oscillator simulations to run properly.
 
On Nov 24, 11:01 am, Andrew Holme <ajho...@hotmail.com> wrote:
On 24 Nov, 15:28, "jalb...@bsu.edu" <jalb...@bsu.edu> wrote:





I have some electronics theory questions and some electronics
simulator questions pertaining to an Armstrong oscillator.  I have
done some reading and have tried to come up with a design on my own.
Most books just show a general diagram with no specific values.  I am
trying to simulate my design in LTSpice:

https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Armstrong1.asc

Plotting voltages at points A and B, the circuit will work for up to
13 seconds (.tran 13) but does something strange after 14 seconds?  I
speculate that L2 is going to keep adding more and more energy to the
tank circuit until things get out of control. I don’t think that this
has happened quite yet though?

What do I need to add to the circuit to build the voltage at point A
to a maximum altitude and keep it there?

Any help would be greatly appreciated.  Thanks

Right-click the .tran directive and tick the check box "start external
DC supply voltages at 0V"

The changes the directive to ".tran 13 startup"

This is often necessary for oscillator simulations to run properly.- Hide quoted text -

- Show quoted text -
Click to expand...
Thanks
That seems to help with the simulator part. I still have the same
theory questions along with some new ones.

The output of the amplifier (node B) is 180 degrees out of phase with
the input of the amplifier (node B) . It seems to me that the
connection to the tickler coil should be reversed but when I do this
in the simulator it does not seem to help.

I believe that the voltage gain of the amplifier comparing node A to
node B is around 240 which mease that the voltage at node A can't
exceed more than about 25 mv before the amplifier starts clipping. Is
this correct? How do keep the tank circuit under 25mv or is it
desirable to have the clipping in the circuit?

I also think that my turns ratio L2:L1 is all messed up but I don't
know what it should be either. After some thought, it would seem to
me that the overall gain (transistor amp + tickler) should be slightly
more than 1 to handle any losses in the tank circuit. Is this true?

I would like to know what values would make the circuit oscillate at
159Hz and why they are the correct values.
Can anyone help? Thanks
 
On Mon, 24 Nov 2008 11:45:57 -0800, jalbers@bsu.edu wrote:

On Nov 24, 11:01 am, Andrew Holme <ajho...@hotmail.com> wrote:
On 24 Nov, 15:28, "jalb...@bsu.edu" <jalb...@bsu.edu> wrote:





I have some electronics theory questions and some electronics
simulator questions pertaining to an Armstrong oscillator.  I have
done some reading and have tried to come up with a design on my own.
Most books just show a general diagram with no specific values.  I am
trying to simulate my design in LTSpice:

https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Armstrong1.asc

Plotting voltages at points A and B, the circuit will work for up to
13 seconds (.tran 13) but does something strange after 14 seconds?  I
speculate that L2 is going to keep adding more and more energy to the
tank circuit until things get out of control. I don’t think that this
has happened quite yet though?

What do I need to add to the circuit to build the voltage at point A
to a maximum altitude and keep it there?

Any help would be greatly appreciated.  Thanks

Right-click the .tran directive and tick the check box "start external
DC supply voltages at 0V"

The changes the directive to ".tran 13 startup"

This is often necessary for oscillator simulations to run properly.-
Hide quoted text -

- Show quoted text -

Thanks
That seems to help with the simulator part. I still have the same
theory questions along with some new ones.

The output of the amplifier (node B) is 180 degrees out of phase with
the input of the amplifier (node B) . It seems to me that the
connection to the tickler coil should be reversed but when I do this in
the simulator it does not seem to help.

I believe that the voltage gain of the amplifier comparing node A to
node B is around 240 which mease that the voltage at node A can't exceed
more than about 25 mv before the amplifier starts clipping. Is this
correct? How do keep the tank circuit under 25mv or is it desirable to
have the clipping in the circuit?

I also think that my turns ratio L2:L1 is all messed up but I don't know
what it should be either. After some thought, it would seem to me that
the overall gain (transistor amp + tickler) should be slightly more than
1 to handle any losses in the tank circuit. Is this true?

I would like to know what values would make the circuit oscillate at
159Hz and why they are the correct values. Can anyone help? Thanks
Click to expand...
Usually the tickler coil has a lot fewer turns (lower inductance) than
the tank coil, to avoid saturating the transistor. Also, you usually
want to capacitively couple to the base, to allow for high standing
voltages on the tank without too much loading (I can't see your circuit
right now, I'm on the wrong computer).

I'd go for a turns ratio of about 10:1 from tank to tickler (IIRC you
have 1:10).

Normally for a standing current of 1mA or so I'd choose a tank coil and
cap that have a reactance of 200 ohms or so at the design frequency. But
-- 159Hz?? For that frequency this just isn't the right oscillator,
unless you're doing something very special. 159kHz would start to be
reasonable, but at 159Hz you'll use more space, weight and money for the
tank coil than would be taken up by a nice solid digital sine wave
generator.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
 
On Nov 24, 4:13 pm, Tim Wescott <t...@justseemywebsite.com> wrote:
On Mon, 24 Nov 2008 11:45:57 -0800, jalb...@bsu.edu wrote:
On Nov 24, 11:01 am, Andrew Holme <ajho...@hotmail.com> wrote:
On 24 Nov, 15:28, "jalb...@bsu.edu" <jalb...@bsu.edu> wrote:

I have some electronics theory questions and some electronics
simulator questions pertaining to an Armstrong oscillator.  I have
done some reading and have tried to come up with a design on my own.
Most books just show a general diagram with no specific values.  I am
trying to simulate my design in LTSpice:

https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Armstrong1.asc

Plotting voltages at points A and B, the circuit will work for up to
13 seconds (.tran 13) but does something strange after 14 seconds?  I
speculate that L2 is going to keep adding more and more energy to the
tank circuit until things get out of control. I don’t think that this
has happened quite yet though?

What do I need to add to the circuit to build the voltage at point A
to a maximum altitude and keep it there?

Any help would be greatly appreciated.  Thanks

Right-click the .tran directive and tick the check box "start external
DC supply voltages at 0V"

The changes the directive to ".tran 13 startup"

This is often necessary for oscillator simulations to run properly.-
Hide quoted text -

- Show quoted text -

Thanks
That seems to help with the simulator part.  I still have the same
theory questions along with some new ones.

The output of the amplifier (node B) is 180 degrees out of phase with
the input of the amplifier (node B) .  It seems to me that the
connection to the tickler coil should be reversed but when I do this in
the simulator it does not seem to help.

I believe that the voltage gain of the amplifier comparing node A to
node B is around 240 which mease that the voltage at node A can't exceed
more than about 25 mv before the amplifier starts clipping.  Is this
correct?  How do keep the tank circuit under 25mv or is it desirable to
have the clipping in the circuit?

I also think that my turns ratio L2:L1 is all messed up but I don't know
what it should be either.  After some thought, it would seem to me that
the overall gain (transistor amp + tickler) should be slightly more than
1 to handle any losses in the tank circuit.  Is this true?

I would like to know what values would make the circuit oscillate at
159Hz and why they are the correct values. Can anyone help?  Thanks

Usually the tickler coil has a lot fewer turns (lower inductance) than
the tank coil, to avoid saturating the transistor.  Also, you usually
want to capacitively couple to the base, to allow for high standing
voltages on the tank without too much loading (I can't see your circuit
right now, I'm on the wrong computer).

I'd go for a turns ratio of about 10:1 from tank to tickler (IIRC you
have 1:10).

Normally for a standing current of 1mA or so I'd choose a tank coil and
cap that have a reactance of 200 ohms or so at the design frequency.  But
-- 159Hz??  For that frequency this just isn't the right oscillator,
unless you're doing something very special.  159kHz would start to be
reasonable, but at 159Hz you'll use more space, weight and money for the
tank coil than would be taken up by a nice solid digital sine wave
generator.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says..
See details athttp://www.wescottdesign.com/actfes/actfes.html- Hide quoted text -

- Show quoted text -
Click to expand...
Thanks

I just pulled the 159Hz out of thin air. I wanted to do some
experimenting with various types of oscillators. I have seen two
different configurations of Armstrong oscillators. One type seems to
have the tickler coil as the input to the amplifier and the other
seems to have the tank circuit as the input to the amplifier. My
design is using the tank circuit as the input to the amplifier, and
the amplifier feeds the tickler coil.
 
Windows Mail sucks...

Anyway, as Tim mentioned, make L1 be 1mH, and L2 be 10mH. It then oscillates
quite nicely at 782.6Hz. If you want a lower frequency, use proportionally
larger inductors.

Also, look into a Wein bridge, which is a better circuit for low frequency
sine waves. The parts for resonant LC circuits get a bit unwieldy at the
frequencies you are looking at.

Regards,
Bob Monsen

<jalbers@bsu.edu> wrote in message
news:d922cdc6-88c1-463b-979a-2ea4884f8ed2@t11g2000yqg.googlegroups.com...
On Nov 24, 4:13 pm, Tim Wescott <t...@justseemywebsite.com> wrote:
On Mon, 24 Nov 2008 11:45:57 -0800, jalb...@bsu.edu wrote:
On Nov 24, 11:01 am, Andrew Holme <ajho...@hotmail.com> wrote:
On 24 Nov, 15:28, "jalb...@bsu.edu" <jalb...@bsu.edu> wrote:

I have some electronics theory questions and some electronics
simulator questions pertaining to an Armstrong oscillator. I have
done some reading and have tried to come up with a design on my own.
Most books just show a general diagram with no specific values. I am
trying to simulate my design in LTSpice:

https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Armstrong1.asc

Plotting voltages at points A and B, the circuit will work for up to
13 seconds (.tran 13) but does something strange after 14 seconds? I
speculate that L2 is going to keep adding more and more energy to the
tank circuit until things get out of control. I don’t think that this
has happened quite yet though?

What do I need to add to the circuit to build the voltage at point A
to a maximum altitude and keep it there?

Any help would be greatly appreciated. Thanks

Right-click the .tran directive and tick the check box "start external
DC supply voltages at 0V"

The changes the directive to ".tran 13 startup"

This is often necessary for oscillator simulations to run properly.-
Hide quoted text -

- Show quoted text -

Thanks
That seems to help with the simulator part. I still have the same
theory questions along with some new ones.

The output of the amplifier (node B) is 180 degrees out of phase with
the input of the amplifier (node B) . It seems to me that the
connection to the tickler coil should be reversed but when I do this in
the simulator it does not seem to help.

I believe that the voltage gain of the amplifier comparing node A to
node B is around 240 which mease that the voltage at node A can't exceed
more than about 25 mv before the amplifier starts clipping. Is this
correct? How do keep the tank circuit under 25mv or is it desirable to
have the clipping in the circuit?

I also think that my turns ratio L2:L1 is all messed up but I don't know
what it should be either. After some thought, it would seem to me that
the overall gain (transistor amp + tickler) should be slightly more than
1 to handle any losses in the tank circuit. Is this true?

I would like to know what values would make the circuit oscillate at
159Hz and why they are the correct values. Can anyone help? Thanks

Usually the tickler coil has a lot fewer turns (lower inductance) than
the tank coil, to avoid saturating the transistor. Also, you usually
want to capacitively couple to the base, to allow for high standing
voltages on the tank without too much loading (I can't see your circuit
right now, I'm on the wrong computer).

I'd go for a turns ratio of about 10:1 from tank to tickler (IIRC you
have 1:10).

Normally for a standing current of 1mA or so I'd choose a tank coil and
cap that have a reactance of 200 ohms or so at the design frequency. But
-- 159Hz?? For that frequency this just isn't the right oscillator,
unless you're doing something very special. 159kHz would start to be
reasonable, but at 159Hz you'll use more space, weight and money for the
tank coil than would be taken up by a nice solid digital sine wave
generator.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details athttp://www.wescottdesign.com/actfes/actfes.html- Hide quoted
text -

- Show quoted text -
Click to expand...
Thanks

I just pulled the 159Hz out of thin air. I wanted to do some
experimenting with various types of oscillators. I have seen two
different configurations of Armstrong oscillators. One type seems to
have the tickler coil as the input to the amplifier and the other
seems to have the tank circuit as the input to the amplifier. My
design is using the tank circuit as the input to the amplifier, and
the amplifier feeds the tickler coil.
 
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