One thing bugs me about building oscillators and that's the
possibility that they may not start in the first place, or else start
fine then somewhere down the line just flip into an overtone or
sub-harmonic for no apparent reason. If only one could physically prod
the circuit around to induce instability but of course that's unlikely
to show up any potential problem. What's needed is some method of
instigating instability to try to show up any latent tendency for any
particular osc to go tits-up and I can only think of one practical way
of precipitating it: varying the power supply voltage.
If one can vary the supply over a fairly wide range and the oscillator
only responds by very small changes in output frequency and doesn't
jerk into another frequency/output mode altogether, is this a
sufficient test on its own of that oscillator's likely stability in
the field?
p.
--

The BBC: Licensed at public expense to spread lies.

Paul Burridge wrote:
One thing bugs me about building oscillators and that's the
possibility that they may not start in the first place, or else start
fine then somewhere down the line just flip into an overtone or
sub-harmonic for no apparent reason. If only one could physically prod
the circuit around to induce instability but of course that's unlikely
to show up any potential problem. What's needed is some method of
instigating instability to try to show up any latent tendency for any
particular osc to go tits-up and I can only think of one practical way
of precipitating it: varying the power supply voltage.
If one can vary the supply over a fairly wide range and the oscillator
only responds by very small changes in output frequency and doesn't
jerk into another frequency/output mode altogether, is this a
sufficient test on its own of that oscillator's likely stability in
the field?
p.

I don't know, but if you know the frequency of the overtones, try
injecting that frequency. Use a really strong signal so that it
dominates, then switch it off and see if your oscillator snaps back
to the correct frequency.

--
local optimization seldom leads to global optimization

my e-mail address is: my first name my last name AT mmm DOT com

Paul Burridge wrote:
One thing bugs me about building oscillators and that's the
possibility that they may not start in the first place, or else start
fine then somewhere down the line just flip into an overtone or
sub-harmonic for no apparent reason. If only one could physically prod
the circuit around to induce instability but of course that's unlikely
to show up any potential problem. What's needed is some method of
instigating instability to try to show up any latent tendency for any
particular osc to go tits-up and I can only think of one practical way
of precipitating it: varying the power supply voltage.
If one can vary the supply over a fairly wide range and the oscillator
only responds by very small changes in output frequency and doesn't
jerk into another frequency/output mode altogether, is this a
sufficient test on its own of that oscillator's likely stability in
the field?
p.

I don't know, but if you know the frequency of the overtones, try
injecting that frequency. Use a really strong signal so that it
dominates, then switch it off and see if your oscillator snaps back
to the correct frequency.

--
local optimization seldom leads to global optimization

my e-mail address is: my first name my last name AT mmm DOT com

Paul Burridge wrote:
One thing bugs me about building oscillators and that's the
possibility that they may not start in the first place, or else start
fine then somewhere down the line just flip into an overtone or
sub-harmonic for no apparent reason.

Yes. This area is all about limit cycles, attracters, and such like, in
non-linear equations.

If only one could physically prod
the circuit around to induce instability but of course that's unlikely
to show up any potential problem. What's needed is some method of
instigating instability to try to show up any latent tendency for any
particular osc to go tits-up and I can only think of one practical way
of precipitating it: varying the power supply voltage.

There is no general solution to non-linear equations. One can only use
experience and brute force by trying the usual suspects.

If one can vary the supply over a fairly wide range and the oscillator
only responds by very small changes in output frequency and doesn't
jerk into another frequency/output mode altogether, is this a
sufficient test on its own of that oscillator's likely stability in
the field?

One tries varying components and the PS and hopes for the best:-)

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"That which is mostly observed, is that which replicates the most"
http://www.anasoft.co.uk/replicators/index.html

"quotes with no meaning, are meaningless" - Kevin Aylward.

Paul Burridge wrote:
One thing bugs me about building oscillators and that's the
possibility that they may not start in the first place, or else start
fine then somewhere down the line just flip into an overtone or
sub-harmonic for no apparent reason.

Yes. This area is all about limit cycles, attracters, and such like, in
non-linear equations.

If only one could physically prod
the circuit around to induce instability but of course that's unlikely
to show up any potential problem. What's needed is some method of
instigating instability to try to show up any latent tendency for any
particular osc to go tits-up and I can only think of one practical way
of precipitating it: varying the power supply voltage.

There is no general solution to non-linear equations. One can only use
experience and brute force by trying the usual suspects.

If one can vary the supply over a fairly wide range and the oscillator
only responds by very small changes in output frequency and doesn't
jerk into another frequency/output mode altogether, is this a
sufficient test on its own of that oscillator's likely stability in
the field?

One tries varying components and the PS and hopes for the best:-)

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"That which is mostly observed, is that which replicates the most"
http://www.anasoft.co.uk/replicators/index.html

"quotes with no meaning, are meaningless" - Kevin Aylward.

In article , Paul Burridge
writes:

If one can vary the supply over a fairly wide range and the oscillator
only responds by very small changes in output frequency and doesn't
jerk into another frequency/output mode altogether, is this a
sufficient test on its own of that oscillator's likely stability in
the field?

Normally...but it may not satisfy everyone in here. :-)

What should be done in oscillator design is to make the minimum
gain through the feedback path - under all environment conditions,
including variation in supply rails (filament voltage if tubes) and even
component tolerances and tolerance changes - above unity by a
fraction. Then the opposite environment conditions should be
examined and the gain through the feedback path analyzed to see if
it exceeds unity to much. Too much gain might overdrive a quartz
crystal unit or generate harmonic garbage or whatever else might
be a no-no.

Once the above is satisfied, the prototype is then subjected to
actual environment changes, again everything from temperature,
shock, vibration, supply voltage, etc., etc., while measuring the
oscillation frequency changes with each environment condition.
To go really deep into that, one might get a number of active devices
with varying tested specifications and try them...but that would only
be for large production runs of the same thing.

If the frequency stays within the desired limits, it passes! Yay! :-)

In too much hobby work, someone grabs a schematic from some
publication and copies it, but usually with some parts changes ("for
convenience") and hopes it will work. Sometimes it does.
Sometimes not. :-)

Oscillators are actually a rather complex subject and take time to
get working within all the desired specifications. Before SPICE and
the ability to model ALL the various things in a circuit, all analysis
had to be done open-loop. The loop (for feedback) could only be
closed on the bench. That work was a real #$%^&!!!!

The best text I have on oscillators is a rare, little-known NTIS-
distribution contract report, AD 460 377, "Quartz Crystal Oscillator
Circuits Design Handbook," prepared by D. Firth at Magnavox
Company, Fort Wayne, Indiana, under contract to U.S. Army
Electronics Command, Fort Monmouth. It was obtained mail-order
in 1985 from the National Technical Information Service (NTIS) from
the U.S. Department of Commerce. Cost $8.20 for 478 pp, Xeroxed
on 8 1/2 x 11 inch paper. Original contract completion date is given
as 15 March 1965. [yes, transistors were around back then...:-) ]

"D. Firth" (name sounds very familiar) covered the whole gamut of
oscillator frequencies from 1 KHz (!) on up to 200 MHz, showed the
gain-impedance analysis of the feedback loop, and working units
done for actual environmental test and the test results which
included variations in not only supply voltage but also component
tolerances of each test unit! Marvelously complete report...can be
an example of how-to-do-it for anyone, including hobbyists who are
very fussy about their oscillator circuits, especially quartz crystals.
It's also a good tutorial that goes deep into circuit theory for
oscillators.

I'm NOT saying everyone ought to get that publication. There's lots
of good information around and a lot of that free (for quartz oscillators)
at the various quartz crystal makers' sites. Basic information on
oscillators, types, etc., is in lots of places and publications. The
final word on oscillator performance is its frequency stability over a
hobbyist-designated total environment.

Accuracy of a frequency measuring device to measure that oscillator
frequency is quite another thing. :-)

Len Anderson
retired (from regular hours) electronic engineer person

In article , Paul Burridge
writes:

If one can vary the supply over a fairly wide range and the oscillator
only responds by very small changes in output frequency and doesn't
jerk into another frequency/output mode altogether, is this a
sufficient test on its own of that oscillator's likely stability in
the field?

Normally...but it may not satisfy everyone in here. :-)

What should be done in oscillator design is to make the minimum
gain through the feedback path - under all environment conditions,
including variation in supply rails (filament voltage if tubes) and even
component tolerances and tolerance changes - above unity by a
fraction. Then the opposite environment conditions should be
examined and the gain through the feedback path analyzed to see if
it exceeds unity to much. Too much gain might overdrive a quartz
crystal unit or generate harmonic garbage or whatever else might
be a no-no.

Once the above is satisfied, the prototype is then subjected to
actual environment changes, again everything from temperature,
shock, vibration, supply voltage, etc., etc., while measuring the
oscillation frequency changes with each environment condition.
To go really deep into that, one might get a number of active devices
with varying tested specifications and try them...but that would only
be for large production runs of the same thing.

If the frequency stays within the desired limits, it passes! Yay! :-)

In too much hobby work, someone grabs a schematic from some
publication and copies it, but usually with some parts changes ("for
convenience") and hopes it will work. Sometimes it does.
Sometimes not. :-)

Oscillators are actually a rather complex subject and take time to
get working within all the desired specifications. Before SPICE and
the ability to model ALL the various things in a circuit, all analysis
had to be done open-loop. The loop (for feedback) could only be
closed on the bench. That work was a real #$%^&!!!!

The best text I have on oscillators is a rare, little-known NTIS-
distribution contract report, AD 460 377, "Quartz Crystal Oscillator
Circuits Design Handbook," prepared by D. Firth at Magnavox
Company, Fort Wayne, Indiana, under contract to U.S. Army
Electronics Command, Fort Monmouth. It was obtained mail-order
in 1985 from the National Technical Information Service (NTIS) from
the U.S. Department of Commerce. Cost $8.20 for 478 pp, Xeroxed
on 8 1/2 x 11 inch paper. Original contract completion date is given
as 15 March 1965. [yes, transistors were around back then...:-) ]

"D. Firth" (name sounds very familiar) covered the whole gamut of
oscillator frequencies from 1 KHz (!) on up to 200 MHz, showed the
gain-impedance analysis of the feedback loop, and working units
done for actual environmental test and the test results which
included variations in not only supply voltage but also component
tolerances of each test unit! Marvelously complete report...can be
an example of how-to-do-it for anyone, including hobbyists who are
very fussy about their oscillator circuits, especially quartz crystals.
It's also a good tutorial that goes deep into circuit theory for
oscillators.

I'm NOT saying everyone ought to get that publication. There's lots
of good information around and a lot of that free (for quartz oscillators)
at the various quartz crystal makers' sites. Basic information on
oscillators, types, etc., is in lots of places and publications. The
final word on oscillator performance is its frequency stability over a
hobbyist-designated total environment.

Accuracy of a frequency measuring device to measure that oscillator
frequency is quite another thing. :-)

Len Anderson
retired (from regular hours) electronic engineer person

In article , Avery Fineman
writes
In article , Paul Burridge
writes:

If one can vary the supply over a fairly wide range and the oscillator
only responds by very small changes in output frequency and doesn't
jerk into another frequency/output mode altogether, is this a
sufficient test on its own of that oscillator's likely stability in
the field?
Len Anderson
retired (from regular hours) electronic engineer person

Earned a good living designing (fairly) reliable crystal oscillators for
many years.
The enemy is excess gain or not enough gain.
For non series res designs like Coulpitts/Pierce I always establish a
negative resistance across the crystal that is 3X the max specified
crystal ESR.
See Telequarz app note now Corning)
Or read my orig? Wireless World paper (1968)

For overtones use the resistor substitute method (one or two transistor
Butler) and ensure again that the osc will go with 3X the ESR.
Note the phase shift osc can be converted to series by adding sufficient
L in series with the crystal to establish zero phase.

Higher overtone may need the crystal C0 tuning out.






--
ddwyer

In article , Avery Fineman
writes
In article , Paul Burridge
writes:

If one can vary the supply over a fairly wide range and the oscillator
only responds by very small changes in output frequency and doesn't
jerk into another frequency/output mode altogether, is this a
sufficient test on its own of that oscillator's likely stability in
the field?
Len Anderson
retired (from regular hours) electronic engineer person

Earned a good living designing (fairly) reliable crystal oscillators for
many years.
The enemy is excess gain or not enough gain.
For non series res designs like Coulpitts/Pierce I always establish a
negative resistance across the crystal that is 3X the max specified
crystal ESR.
See Telequarz app note now Corning)
Or read my orig? Wireless World paper (1968)

For overtones use the resistor substitute method (one or two transistor
Butler) and ensure again that the osc will go with 3X the ESR.
Note the phase shift osc can be converted to series by adding sufficient
L in series with the crystal to establish zero phase.

Higher overtone may need the crystal C0 tuning out.






--
ddwyer