Re: [time-nuts] Broken Ovenaire OSC 85-50
Here is my two cents worth
20 mv output, sure sounds like something is broken.
It should be fixed before it is modified.
The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe.
The "Grn" labeled wire, FreqCtrl input should be about 1/2 VCC for testing.
If you do 'need' to modify the gain,
It would seem better to bypass the 470 ohm resistor with a cap in series with the 47 ohms.
ws
----- Original Message -----
From: "Mike Monett" xde-l2g3@myamail.com
To: time-nuts@febo.com
Sent: Friday, July 03, 2009 11:50 AM
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
An update on the Broken Ovenaire OSC 85-50.
I prepared a 'schematic' of the Output Board and the Oscillator
Board (attached) and I have lots of pictures of the external unit
and the insides if anyone is interested.
I resoldered all connections and replaced all transistors on the
Output Board and the Oscillator Board all to no benefit. I
measured all the components with an LCR meter and found the 0.01
uF bypass on the 330 ohm resistor in the emitter circuit of the
output transistor of the Output Board to be low and with a high
ESR. I replaced this with about a 20% increase in output amplitude
but still inadequate. I replaced the rest of the 0.01 uF caps on
the output board with no additional benefit. I transiently
disconnected the Red wires from the Oven Controller board and
there was no increase in output or significant increase in voltage
to the Oscillator Board.
Therefore, it appeared that a 'low output crystal' (if such a
thing exists) was the only logical explanation that I could come
up with. That seeming to be the case, there appeared to be only 4
options. 1. Toss the OCXO (sorry, too much effort so far). 2.
Build an external amplifier (seemingly too much additional
effort). 3. Try to adjust on the bias of the oscillator transistor
to achieve a higher output (seemed too 'iffy'). Or 4. Lower the
value of the resistor in the emitter circuit of the Oscillator
Board to get more gain out of the last stage in the Oscillator
Board.
I replaced the 470 ohm resistor with a 47 ohm resistor and the
amplitude increased to about 0.4 V P-P into a 50 ohm load and was
sufficient to make it a usable OCXO again.
I reassembled, resealed with Epoxy and all seems well so far.
If anyone wants pictures or other info, please let me know.
Thanks for all the suggestions and help.
Joe
Joe,
Congratulations on getting your system to work!
A couple of things. First, trying to measure the currents in the
circuit with a ferrite toroid won't do you much good. You don't know
what the currents should be, and the secondary of the toroid
transformer requires a termination resistor. The value changes with
the turns ratio.
Just from looking at the circuit, the RF currents will be extremely
low. This requires a large number of turns on the secondary, which
will probably resonate at or below the 10MHz operating frequency due
to stray capacitance from the connection to the scope. So it is
unlikely you will get any useful progress in this direction.
However, from the values on your schematic, the output tank circuit
resonates at 9.602MHz with a Q of 9.6. So the tank is already well
below resonance, which attenuates the output voltage.
Any stray capacitance you add to the circuit will bring the resonant
frequency lower, further aggravating the loss in signal.
The output tank is tapped with the 75pF and 91pF in series. This
further attenuates the signal.
I'd change the circuit to a single capacitor across the tank with a
small trim capacitor to tune it to resonance.
To get the signal into 50 ohms for distribution, I'd add a limiter
if you can tolerate a square wave output, or a good emitter follower
if you need a sine wave. Take the output from the collector of the
2N2369 to get the maximum signal amplitude.
Your original post mentions an output amplitude of 20mV. If the
normal amplitude is around 2V, this represents a loss of 40dB. This
is a huge loss in signal. The circuit obviously worked at one time,
so there may well be some other hidden problem.
It is possible the crystal is damaged, but this seems unlikely. A
crystal oscillator probably won't even start if the signal level is
down 40dB.
You can check the oscillator and crystal in SPICE. Normally, the
high Q of the crystal will make the analysis very slow. It could
take many hours for the simulation to begin oscillating and
stabilize at the final amplitude. The transient analysis requires a
very fine time step for accuracy, and you could run out of memory
before the simulation was complete.
I have developed a much faster way of analyzing a crystal oscillator
in SPICE. Instead of requiring tens or hundreds of thousands of
simulated cycles, this method gives accurate results in only a few
dozen cycles. For more information, please see "SPICE Analysis of
Crystal Oscillators"
http://pstca.com/spice/xtal/clapp.htm
You can estimate the value of the crystal ESR by finding the Q of
your crystal and working backwards.
I'm attaching a gif of your schematic for reference. This is rotated
90 degrees and enhanced in LView Pro to improve the contrast.
Please let me know if you have any questions.
Thanks,
Mike
I did not realize that this post would generate this much discussion.
While I have a BEE and MSEE, I am a practicing Cardiac Electrophysiologist
and it has been some time since I thought about such issues. I have learned
a lot though from the discussions and as medicine as we know it winds down,
interests in EE will grow.
I agree with Warren. It should be fixed before modified. However, I could
not find anything that was 'broken' with the possible exception of the XTAL.
As I tried various things, I did notice from time to time some reluctance to
oscillate suggesting that the oscillator stage was an issue. With no
obvious failure and no hope of finding a replacement XTAL, I had to choose
other options.
The real problem is size. There is no room for added components, at least
on the Oscillator Board which is inside a sealed oven. There is only room
for changing components. I would have liked to try adding a resistor and
capacitor to the emitter circuit of the amplifier transistor on the
Oscillator Board but there is no room. I have pictures if anyone is
interested. The Oscillator Board is inside a metal can about 0.5x1.5x2.0 cm
that has a heater coil wrapped around the outside and an Oven Controller
Board attached to the outside. This package is surrounded by foam with the
Output Board on one face of the foam, mounted to one wall of the outside
metal package. The bottom of the metal package has 2 feed thru's, plus a
ground connection. One is 5 VDC and the other is the 10MHz out.
While with better equipment one might be able to find a problem, it was
certainly not obvious to me.
Do XTAL's fail often? If so, by what mechanism? Slowly fade away? Sudden
death? I am not experienced enough to know this answer but in all my years
with various HAM gear, I do not recall the failure of a single XTAL.
However, none of these were in an oven.
Thanks again for all the useful information.
Joe
None the less, with a simple change of resistor, the gain in the amplifier
stage increased and, at least so far, problem solved.
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of WarrenS
Sent: Friday, July 03, 2009 7:49 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
Here is my two cents worth
20 mv output, sure sounds like something is broken.
It should be fixed before it is modified.
The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe. The "Grn"
labeled wire, FreqCtrl input should be about 1/2 VCC for testing. If you
do 'need' to modify the gain,
It would seem better to bypass the 470 ohm resistor with a cap in series
with the 47 ohms.
ws
----- Original Message -----
From: "Mike Monett" xde-l2g3@myamail.com
To: time-nuts@febo.com
Sent: Friday, July 03, 2009 11:50 AM
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
An update on the Broken Ovenaire OSC 85-50.
I prepared a 'schematic' of the Output Board and the Oscillator
Board (attached) and I have lots of pictures of the external unit
and the insides if anyone is interested.
I resoldered all connections and replaced all transistors on the
Output Board and the Oscillator Board all to no benefit. I
measured all the components with an LCR meter and found the 0.01
uF bypass on the 330 ohm resistor in the emitter circuit of the
output transistor of the Output Board to be low and with a high
ESR. I replaced this with about a 20% increase in output amplitude
but still inadequate. I replaced the rest of the 0.01 uF caps on
the output board with no additional benefit. I transiently
disconnected the Red wires from the Oven Controller board and
there was no increase in output or significant increase in voltage
to the Oscillator Board.
Therefore, it appeared that a 'low output crystal' (if such a
thing exists) was the only logical explanation that I could come
up with. That seeming to be the case, there appeared to be only 4
options. 1. Toss the OCXO (sorry, too much effort so far). 2.
Build an external amplifier (seemingly too much additional
effort). 3. Try to adjust on the bias of the oscillator transistor
to achieve a higher output (seemed too 'iffy'). Or 4. Lower the
value of the resistor in the emitter circuit of the Oscillator
Board to get more gain out of the last stage in the Oscillator
Board.
I replaced the 470 ohm resistor with a 47 ohm resistor and the
amplitude increased to about 0.4 V P-P into a 50 ohm load and was
sufficient to make it a usable OCXO again.
I reassembled, resealed with Epoxy and all seems well so far.
If anyone wants pictures or other info, please let me know.
Thanks for all the suggestions and help.
Joe
Joe,
Congratulations on getting your system to work!
A couple of things. First, trying to measure the currents in the
circuit with a ferrite toroid won't do you much good. You don't know
what the currents should be, and the secondary of the toroid
transformer requires a termination resistor. The value changes with
the turns ratio.
Just from looking at the circuit, the RF currents will be extremely
low. This requires a large number of turns on the secondary, which
will probably resonate at or below the 10MHz operating frequency due
to stray capacitance from the connection to the scope. So it is
unlikely you will get any useful progress in this direction.
However, from the values on your schematic, the output tank circuit
resonates at 9.602MHz with a Q of 9.6. So the tank is already well
below resonance, which attenuates the output voltage.
Any stray capacitance you add to the circuit will bring the resonant
frequency lower, further aggravating the loss in signal.
The output tank is tapped with the 75pF and 91pF in series. This
further attenuates the signal.
I'd change the circuit to a single capacitor across the tank with a
small trim capacitor to tune it to resonance.
To get the signal into 50 ohms for distribution, I'd add a limiter
if you can tolerate a square wave output, or a good emitter follower
if you need a sine wave. Take the output from the collector of the
2N2369 to get the maximum signal amplitude.
Your original post mentions an output amplitude of 20mV. If the
normal amplitude is around 2V, this represents a loss of 40dB. This
is a huge loss in signal. The circuit obviously worked at one time,
so there may well be some other hidden problem.
It is possible the crystal is damaged, but this seems unlikely. A
crystal oscillator probably won't even start if the signal level is
down 40dB.
You can check the oscillator and crystal in SPICE. Normally, the
high Q of the crystal will make the analysis very slow. It could
take many hours for the simulation to begin oscillating and
stabilize at the final amplitude. The transient analysis requires a
very fine time step for accuracy, and you could run out of memory
before the simulation was complete.
I have developed a much faster way of analyzing a crystal oscillator
in SPICE. Instead of requiring tens or hundreds of thousands of
simulated cycles, this method gives accurate results in only a few
dozen cycles. For more information, please see "SPICE Analysis of
Crystal Oscillators"
http://pstca.com/spice/xtal/clapp.htm
You can estimate the value of the crystal ESR by finding the Q of
your crystal and working backwards.
I'm attaching a gif of your schematic for reference. This is rotated
90 degrees and enhanced in LView Pro to improve the contrast.
Please let me know if you have any questions.
Thanks,
Mike
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
I agree with Warren. The VCC seems way too low. Interestingly, noone else seems to think so,
or did not notice it.
Bill....WB6BNQ
WarrenS wrote:
Here is my two cents worth
20 mv output, sure sounds like something is broken.
It should be fixed before it is modified.
The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe.
The "Grn" labeled wire, FreqCtrl input should be about 1/2 VCC for testing.
If you do 'need' to modify the gain,
It would seem better to bypass the 470 ohm resistor with a cap in series with the 47 ohms.
ws
WarrenS wrote:
Here is my two cents worth
20 mv output, sure sounds like something is broken.
It should be fixed before it is modified.
The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe.
Not so, if the resistor values are correct this is the voltage that one
should get.
The question that remains: Is the voltage what the designer intended?
With the Colpitts oscillator used limiting in the oscillator transistor
(usually by current cutoff) is used to limit the amplitude.
Just increasing the voltage without checking the resultant crystal
current will be within permissable limits can be counter productive.
The "Grn" labeled wire, FreqCtrl input should be about 1/2 VCC for testing.
If you do 'need' to modify the gain,
It would seem better to bypass the 470 ohm resistor with a cap in series with the 47 ohms.
ws
Bruce
----- Original Message -----
From: "Mike Monett" xde-l2g3@myamail.com
To: time-nuts@febo.com
Sent: Friday, July 03, 2009 11:50 AM
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
An update on the Broken Ovenaire OSC 85-50.
I prepared a 'schematic' of the Output Board and the Oscillator
Board (attached) and I have lots of pictures of the external unit
and the insides if anyone is interested.
I resoldered all connections and replaced all transistors on the
Output Board and the Oscillator Board all to no benefit. I
measured all the components with an LCR meter and found the 0.01
uF bypass on the 330 ohm resistor in the emitter circuit of the
output transistor of the Output Board to be low and with a high
ESR. I replaced this with about a 20% increase in output amplitude
but still inadequate. I replaced the rest of the 0.01 uF caps on
the output board with no additional benefit. I transiently
disconnected the Red wires from the Oven Controller board and
there was no increase in output or significant increase in voltage
to the Oscillator Board.
Therefore, it appeared that a 'low output crystal' (if such a
thing exists) was the only logical explanation that I could come
up with. That seeming to be the case, there appeared to be only 4
options. 1. Toss the OCXO (sorry, too much effort so far). 2.
Build an external amplifier (seemingly too much additional
effort). 3. Try to adjust on the bias of the oscillator transistor
to achieve a higher output (seemed too 'iffy'). Or 4. Lower the
value of the resistor in the emitter circuit of the Oscillator
Board to get more gain out of the last stage in the Oscillator
Board.
I replaced the 470 ohm resistor with a 47 ohm resistor and the
amplitude increased to about 0.4 V P-P into a 50 ohm load and was
sufficient to make it a usable OCXO again.
I reassembled, resealed with Epoxy and all seems well so far.
If anyone wants pictures or other info, please let me know.
Thanks for all the suggestions and help.
Joe
Joe,
Congratulations on getting your system to work!
A couple of things. First, trying to measure the currents in the
circuit with a ferrite toroid won't do you much good. You don't know
what the currents should be, and the secondary of the toroid
transformer requires a termination resistor. The value changes with
the turns ratio.
Just from looking at the circuit, the RF currents will be extremely
low. This requires a large number of turns on the secondary, which
will probably resonate at or below the 10MHz operating frequency due
to stray capacitance from the connection to the scope. So it is
unlikely you will get any useful progress in this direction.
However, from the values on your schematic, the output tank circuit
resonates at 9.602MHz with a Q of 9.6. So the tank is already well
below resonance, which attenuates the output voltage.
Any stray capacitance you add to the circuit will bring the resonant
frequency lower, further aggravating the loss in signal.
The output tank is tapped with the 75pF and 91pF in series. This
further attenuates the signal.
I'd change the circuit to a single capacitor across the tank with a
small trim capacitor to tune it to resonance.
To get the signal into 50 ohms for distribution, I'd add a limiter
if you can tolerate a square wave output, or a good emitter follower
if you need a sine wave. Take the output from the collector of the
2N2369 to get the maximum signal amplitude.
Your original post mentions an output amplitude of 20mV. If the
normal amplitude is around 2V, this represents a loss of 40dB. This
is a huge loss in signal. The circuit obviously worked at one time,
so there may well be some other hidden problem.
It is possible the crystal is damaged, but this seems unlikely. A
crystal oscillator probably won't even start if the signal level is
down 40dB.
You can check the oscillator and crystal in SPICE. Normally, the
high Q of the crystal will make the analysis very slow. It could
take many hours for the simulation to begin oscillating and
stabilize at the final amplitude. The transient analysis requires a
very fine time step for accuracy, and you could run out of memory
before the simulation was complete.
I have developed a much faster way of analyzing a crystal oscillator
in SPICE. Instead of requiring tens or hundreds of thousands of
simulated cycles, this method gives accurate results in only a few
dozen cycles. For more information, please see "SPICE Analysis of
Crystal Oscillators"
http://pstca.com/spice/xtal/clapp.htm
You can estimate the value of the crystal ESR by finding the Q of
your crystal and working backwards.
I'm attaching a gif of your schematic for reference. This is rotated
90 degrees and enhanced in LView Pro to improve the contrast.
Please let me know if you have any questions.
Thanks,
Mike
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
WB6BNQ wrote:
I agree with Warren. The VCC seems way too low. Interestingly, noone else seems to think so,
or did not notice it.
Bill....WB6BNQ
It was noticed, but it is consistent with the resistor values used in
the circuit.
The crystal current is determined by the dc emitter current of the
oscillator transistor.
Thus one cannot arbitrarily increase Vcc without considering the
consequences for the crystal current etc.
Bruce
WarrenS wrote:
Here is my two cents worth
20 mv output, sure sounds like something is broken.
It should be fixed before it is modified.
The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe.
The "Grn" labeled wire, FreqCtrl input should be about 1/2 VCC for testing.
If you do 'need' to modify the gain,
It would seem better to bypass the 470 ohm resistor with a cap in series with the 47 ohms.
ws
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Joe
You can always try to see how it performs with a cheap crystal, padding
out the ESR with a resistor to determine the ESR limit at which the
circuit fails to oscillate.
The crystal current doesn't depend strongly on the crystal operating
Q(as long as the circuit oscillates), so using a cheap crystal in a test
should give some idea of the oscillator circuit behaviour.
Some means of estimating the actual crystal ESR should give some clues
to the crystal health.
Crystals can develop cracks or break, electrode contacts can become
disconnected etc.
Early WWII crystals in non hermetic packages often used to fail in a
relatively short time.
Once the circuit is working correctly, you want substantial output you
can always add an external amplifier.
Bruce
J. L. Trantham wrote:
I did not realize that this post would generate this much discussion.
While I have a BEE and MSEE, I am a practicing Cardiac Electrophysiologist
and it has been some time since I thought about such issues. I have learned
a lot though from the discussions and as medicine as we know it winds down,
interests in EE will grow.
I agree with Warren. It should be fixed before modified. However, I could
not find anything that was 'broken' with the possible exception of the XTAL.
As I tried various things, I did notice from time to time some reluctance to
oscillate suggesting that the oscillator stage was an issue. With no
obvious failure and no hope of finding a replacement XTAL, I had to choose
other options.
The real problem is size. There is no room for added components, at least
on the Oscillator Board which is inside a sealed oven. There is only room
for changing components. I would have liked to try adding a resistor and
capacitor to the emitter circuit of the amplifier transistor on the
Oscillator Board but there is no room. I have pictures if anyone is
interested. The Oscillator Board is inside a metal can about 0.5x1.5x2.0 cm
that has a heater coil wrapped around the outside and an Oven Controller
Board attached to the outside. This package is surrounded by foam with the
Output Board on one face of the foam, mounted to one wall of the outside
metal package. The bottom of the metal package has 2 feed thru's, plus a
ground connection. One is 5 VDC and the other is the 10MHz out.
While with better equipment one might be able to find a problem, it was
certainly not obvious to me.
Do XTAL's fail often? If so, by what mechanism? Slowly fade away? Sudden
death? I am not experienced enough to know this answer but in all my years
with various HAM gear, I do not recall the failure of a single XTAL.
However, none of these were in an oven.
Thanks again for all the useful information.
Joe
None the less, with a simple change of resistor, the gain in the amplifier
stage increased and, at least so far, problem solved.
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of WarrenS
Sent: Friday, July 03, 2009 7:49 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
Here is my two cents worth
20 mv output, sure sounds like something is broken.
It should be fixed before it is modified.
The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe. The "Grn"
labeled wire, FreqCtrl input should be about 1/2 VCC for testing. If you
do 'need' to modify the gain,
It would seem better to bypass the 470 ohm resistor with a cap in series
with the 47 ohms.
ws
----- Original Message -----
From: "Mike Monett" xde-l2g3@myamail.com
To: time-nuts@febo.com
Sent: Friday, July 03, 2009 11:50 AM
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
An update on the Broken Ovenaire OSC 85-50.
I prepared a 'schematic' of the Output Board and the Oscillator
Board (attached) and I have lots of pictures of the external unit
and the insides if anyone is interested.
I resoldered all connections and replaced all transistors on the
Output Board and the Oscillator Board all to no benefit. I
measured all the components with an LCR meter and found the 0.01
uF bypass on the 330 ohm resistor in the emitter circuit of the
output transistor of the Output Board to be low and with a high
ESR. I replaced this with about a 20% increase in output amplitude
but still inadequate. I replaced the rest of the 0.01 uF caps on
the output board with no additional benefit. I transiently
disconnected the Red wires from the Oven Controller board and
there was no increase in output or significant increase in voltage
to the Oscillator Board.
Therefore, it appeared that a 'low output crystal' (if such a
thing exists) was the only logical explanation that I could come
up with. That seeming to be the case, there appeared to be only 4
options. 1. Toss the OCXO (sorry, too much effort so far). 2.
Build an external amplifier (seemingly too much additional
effort). 3. Try to adjust on the bias of the oscillator transistor
to achieve a higher output (seemed too 'iffy'). Or 4. Lower the
value of the resistor in the emitter circuit of the Oscillator
Board to get more gain out of the last stage in the Oscillator
Board.
I replaced the 470 ohm resistor with a 47 ohm resistor and the
amplitude increased to about 0.4 V P-P into a 50 ohm load and was
sufficient to make it a usable OCXO again.
I reassembled, resealed with Epoxy and all seems well so far.
If anyone wants pictures or other info, please let me know.
Thanks for all the suggestions and help.
Joe
Joe,
Congratulations on getting your system to work!
A couple of things. First, trying to measure the currents in the
circuit with a ferrite toroid won't do you much good. You don't know
what the currents should be, and the secondary of the toroid
transformer requires a termination resistor. The value changes with
the turns ratio.
Just from looking at the circuit, the RF currents will be extremely
low. This requires a large number of turns on the secondary, which
will probably resonate at or below the 10MHz operating frequency due
to stray capacitance from the connection to the scope. So it is
unlikely you will get any useful progress in this direction.
However, from the values on your schematic, the output tank circuit
resonates at 9.602MHz with a Q of 9.6. So the tank is already well
below resonance, which attenuates the output voltage.
Any stray capacitance you add to the circuit will bring the resonant
frequency lower, further aggravating the loss in signal.
The output tank is tapped with the 75pF and 91pF in series. This
further attenuates the signal.
I'd change the circuit to a single capacitor across the tank with a
small trim capacitor to tune it to resonance.
To get the signal into 50 ohms for distribution, I'd add a limiter
if you can tolerate a square wave output, or a good emitter follower
if you need a sine wave. Take the output from the collector of the
2N2369 to get the maximum signal amplitude.
Your original post mentions an output amplitude of 20mV. If the
normal amplitude is around 2V, this represents a loss of 40dB. This
is a huge loss in signal. The circuit obviously worked at one time,
so there may well be some other hidden problem.
It is possible the crystal is damaged, but this seems unlikely. A
crystal oscillator probably won't even start if the signal level is
down 40dB.
You can check the oscillator and crystal in SPICE. Normally, the
high Q of the crystal will make the analysis very slow. It could
take many hours for the simulation to begin oscillating and
stabilize at the final amplitude. The transient analysis requires a
very fine time step for accuracy, and you could run out of memory
before the simulation was complete.
I have developed a much faster way of analyzing a crystal oscillator
in SPICE. Instead of requiring tens or hundreds of thousands of
simulated cycles, this method gives accurate results in only a few
dozen cycles. For more information, please see "SPICE Analysis of
Crystal Oscillators"
http://pstca.com/spice/xtal/clapp.htm
You can estimate the value of the crystal ESR by finding the Q of
your crystal and working backwards.
I'm attaching a gif of your schematic for reference. This is rotated
90 degrees and enhanced in LView Pro to improve the contrast.
Please let me know if you have any questions.
Thanks,
Mike
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
You can estimate the crystal current by measuring the RF voltage across
the 15pF cap in the oscillator circuit and estimate/measure the varactor
and trimmer capacitors.
Alternatively, temporarily replace all these caps with a 33pF cap
connected from the inductor in series with crystal and ground.
33pf has a reactance of ~500 ohm at 10MHz.
Use a relatively low capacitance probe for this and account for the
probe capacitance in the calaculations.
This should at least allow you to determine if the crystal current is
around 10uA, 100uA or 1mA or more.
Bruce
J. L. Trantham wrote:
I did not realize that this post would generate this much discussion.
While I have a BEE and MSEE, I am a practicing Cardiac Electrophysiologist
and it has been some time since I thought about such issues. I have learned
a lot though from the discussions and as medicine as we know it winds down,
interests in EE will grow.
I agree with Warren. It should be fixed before modified. However, I could
not find anything that was 'broken' with the possible exception of the XTAL.
As I tried various things, I did notice from time to time some reluctance to
oscillate suggesting that the oscillator stage was an issue. With no
obvious failure and no hope of finding a replacement XTAL, I had to choose
other options.
The real problem is size. There is no room for added components, at least
on the Oscillator Board which is inside a sealed oven. There is only room
for changing components. I would have liked to try adding a resistor and
capacitor to the emitter circuit of the amplifier transistor on the
Oscillator Board but there is no room. I have pictures if anyone is
interested. The Oscillator Board is inside a metal can about 0.5x1.5x2.0 cm
that has a heater coil wrapped around the outside and an Oven Controller
Board attached to the outside. This package is surrounded by foam with the
Output Board on one face of the foam, mounted to one wall of the outside
metal package. The bottom of the metal package has 2 feed thru's, plus a
ground connection. One is 5 VDC and the other is the 10MHz out.
While with better equipment one might be able to find a problem, it was
certainly not obvious to me.
Do XTAL's fail often? If so, by what mechanism? Slowly fade away? Sudden
death? I am not experienced enough to know this answer but in all my years
with various HAM gear, I do not recall the failure of a single XTAL.
However, none of these were in an oven.
Thanks again for all the useful information.
Joe
None the less, with a simple change of resistor, the gain in the amplifier
stage increased and, at least so far, problem solved.
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of WarrenS
Sent: Friday, July 03, 2009 7:49 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
Here is my two cents worth
20 mv output, sure sounds like something is broken.
It should be fixed before it is modified.
The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe. The "Grn"
labeled wire, FreqCtrl input should be about 1/2 VCC for testing. If you
do 'need' to modify the gain,
It would seem better to bypass the 470 ohm resistor with a cap in series
with the 47 ohms.
ws
----- Original Message -----
From: "Mike Monett" xde-l2g3@myamail.com
To: time-nuts@febo.com
Sent: Friday, July 03, 2009 11:50 AM
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
An update on the Broken Ovenaire OSC 85-50.
I prepared a 'schematic' of the Output Board and the Oscillator
Board (attached) and I have lots of pictures of the external unit
and the insides if anyone is interested.
I resoldered all connections and replaced all transistors on the
Output Board and the Oscillator Board all to no benefit. I
measured all the components with an LCR meter and found the 0.01
uF bypass on the 330 ohm resistor in the emitter circuit of the
output transistor of the Output Board to be low and with a high
ESR. I replaced this with about a 20% increase in output amplitude
but still inadequate. I replaced the rest of the 0.01 uF caps on
the output board with no additional benefit. I transiently
disconnected the Red wires from the Oven Controller board and
there was no increase in output or significant increase in voltage
to the Oscillator Board.
Therefore, it appeared that a 'low output crystal' (if such a
thing exists) was the only logical explanation that I could come
up with. That seeming to be the case, there appeared to be only 4
options. 1. Toss the OCXO (sorry, too much effort so far). 2.
Build an external amplifier (seemingly too much additional
effort). 3. Try to adjust on the bias of the oscillator transistor
to achieve a higher output (seemed too 'iffy'). Or 4. Lower the
value of the resistor in the emitter circuit of the Oscillator
Board to get more gain out of the last stage in the Oscillator
Board.
I replaced the 470 ohm resistor with a 47 ohm resistor and the
amplitude increased to about 0.4 V P-P into a 50 ohm load and was
sufficient to make it a usable OCXO again.
I reassembled, resealed with Epoxy and all seems well so far.
If anyone wants pictures or other info, please let me know.
Thanks for all the suggestions and help.
Joe
Joe,
Congratulations on getting your system to work!
A couple of things. First, trying to measure the currents in the
circuit with a ferrite toroid won't do you much good. You don't know
what the currents should be, and the secondary of the toroid
transformer requires a termination resistor. The value changes with
the turns ratio.
Just from looking at the circuit, the RF currents will be extremely
low. This requires a large number of turns on the secondary, which
will probably resonate at or below the 10MHz operating frequency due
to stray capacitance from the connection to the scope. So it is
unlikely you will get any useful progress in this direction.
However, from the values on your schematic, the output tank circuit
resonates at 9.602MHz with a Q of 9.6. So the tank is already well
below resonance, which attenuates the output voltage.
Any stray capacitance you add to the circuit will bring the resonant
frequency lower, further aggravating the loss in signal.
The output tank is tapped with the 75pF and 91pF in series. This
further attenuates the signal.
I'd change the circuit to a single capacitor across the tank with a
small trim capacitor to tune it to resonance.
To get the signal into 50 ohms for distribution, I'd add a limiter
if you can tolerate a square wave output, or a good emitter follower
if you need a sine wave. Take the output from the collector of the
2N2369 to get the maximum signal amplitude.
Your original post mentions an output amplitude of 20mV. If the
normal amplitude is around 2V, this represents a loss of 40dB. This
is a huge loss in signal. The circuit obviously worked at one time,
so there may well be some other hidden problem.
It is possible the crystal is damaged, but this seems unlikely. A
crystal oscillator probably won't even start if the signal level is
down 40dB.
You can check the oscillator and crystal in SPICE. Normally, the
high Q of the crystal will make the analysis very slow. It could
take many hours for the simulation to begin oscillating and
stabilize at the final amplitude. The transient analysis requires a
very fine time step for accuracy, and you could run out of memory
before the simulation was complete.
I have developed a much faster way of analyzing a crystal oscillator
in SPICE. Instead of requiring tens or hundreds of thousands of
simulated cycles, this method gives accurate results in only a few
dozen cycles. For more information, please see "SPICE Analysis of
Crystal Oscillators"
http://pstca.com/spice/xtal/clapp.htm
You can estimate the value of the crystal ESR by finding the Q of
your crystal and working backwards.
I'm attaching a gif of your schematic for reference. This is rotated
90 degrees and enhanced in LView Pro to improve the contrast.
Please let me know if you have any questions.
Thanks,
Mike
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
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and follow the instructions there.
A couple more thoughts;
Is the VCC (Red wire) current draw correct?.
Should be 1.3 ma (per the schematic values) with the 470 Ohm and
more like 7 plus ma with the 47 ohm.
AND I don't remember seeing, IS the Freq real close AND can it be tuned by the cap and Green wire voltage?
If both answers are YES, at least most things are working correctly.
As Bruce said:
"if the resistor values are correct this is the voltage(s) that one should get"
With the resistors values shown, I agree that all the other voltages are correct given the 2.49 volts,
BUT the 2.49 volt is NOT controlled by any of the values on that schematic, it's just an input.
AND the output amplitude is not yet being controlled by current cut off.
Something that needs to be asked is are all these the correct values.
It sounds like you got them by measuring and not from a "should be" schematic.
One last, way out thought.
It was my belief that very good osc have some sort of AGC to control the amplitude,
ANY chance that the VCC is used as the input to control the amplitude of the Osc output?
If so, could it be that the external AGC that is what broken and supplying too low a VCC voltage to the circuit?
ws
----- Original Message -----
From: "Bruce Griffiths" bruce.griffiths@xtra.co.nz
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Friday, July 03, 2009 8:21 PM
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
WarrenS wrote:
Here is my two cents worth
20 mv output, sure sounds like something is broken.
It should be fixed before it is modified.
The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe.
Not so, if the resistor values are correct this is the voltage that one
should get.
The question that remains: Is the voltage what the designer intended?
With the Colpitts oscillator used limiting in the oscillator transistor
(usually by current cutoff) is used to limit the amplitude.
Just increasing the voltage without checking the resultant crystal
current will be within permissable limits can be counter productive.
The "Grn" labeled wire, FreqCtrl input should be about 1/2 VCC for testing.
If you do 'need' to modify the gain,
It would seem better to bypass the 470 ohm resistor with a cap in series with the 47 ohms.
ws
Bruce
----- Original Message -----
From: "Mike Monett" xde-l2g3@myamail.com
To: time-nuts@febo.com
Sent: Friday, July 03, 2009 11:50 AM
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
An update on the Broken Ovenaire OSC 85-50.
I prepared a 'schematic' of the Output Board and the Oscillator
Board (attached) and I have lots of pictures of the external unit
and the insides if anyone is interested.
I resoldered all connections and replaced all transistors on the
Output Board and the Oscillator Board all to no benefit. I
measured all the components with an LCR meter and found the 0.01
uF bypass on the 330 ohm resistor in the emitter circuit of the
output transistor of the Output Board to be low and with a high
ESR. I replaced this with about a 20% increase in output amplitude
but still inadequate. I replaced the rest of the 0.01 uF caps on
the output board with no additional benefit. I transiently
disconnected the Red wires from the Oven Controller board and
there was no increase in output or significant increase in voltage
to the Oscillator Board.
Therefore, it appeared that a 'low output crystal' (if such a
thing exists) was the only logical explanation that I could come
up with. That seeming to be the case, there appeared to be only 4
options. 1. Toss the OCXO (sorry, too much effort so far). 2.
Build an external amplifier (seemingly too much additional
effort). 3. Try to adjust on the bias of the oscillator transistor
to achieve a higher output (seemed too 'iffy'). Or 4. Lower the
value of the resistor in the emitter circuit of the Oscillator
Board to get more gain out of the last stage in the Oscillator
Board.
I replaced the 470 ohm resistor with a 47 ohm resistor and the
amplitude increased to about 0.4 V P-P into a 50 ohm load and was
sufficient to make it a usable OCXO again.
I reassembled, resealed with Epoxy and all seems well so far.
If anyone wants pictures or other info, please let me know.
Thanks for all the suggestions and help.
Joe
Joe,
Congratulations on getting your system to work!
A couple of things. First, trying to measure the currents in the
circuit with a ferrite toroid won't do you much good. You don't know
what the currents should be, and the secondary of the toroid
transformer requires a termination resistor. The value changes with
the turns ratio.
Just from looking at the circuit, the RF currents will be extremely
low. This requires a large number of turns on the secondary, which
will probably resonate at or below the 10MHz operating frequency due
to stray capacitance from the connection to the scope. So it is
unlikely you will get any useful progress in this direction.
However, from the values on your schematic, the output tank circuit
resonates at 9.602MHz with a Q of 9.6. So the tank is already well
below resonance, which attenuates the output voltage.
Any stray capacitance you add to the circuit will bring the resonant
frequency lower, further aggravating the loss in signal.
The output tank is tapped with the 75pF and 91pF in series. This
further attenuates the signal.
I'd change the circuit to a single capacitor across the tank with a
small trim capacitor to tune it to resonance.
To get the signal into 50 ohms for distribution, I'd add a limiter
if you can tolerate a square wave output, or a good emitter follower
if you need a sine wave. Take the output from the collector of the
2N2369 to get the maximum signal amplitude.
Your original post mentions an output amplitude of 20mV. If the
normal amplitude is around 2V, this represents a loss of 40dB. This
is a huge loss in signal. The circuit obviously worked at one time,
so there may well be some other hidden problem.
It is possible the crystal is damaged, but this seems unlikely. A
crystal oscillator probably won't even start if the signal level is
down 40dB.
You can check the oscillator and crystal in SPICE. Normally, the
high Q of the crystal will make the analysis very slow. It could
take many hours for the simulation to begin oscillating and
stabilize at the final amplitude. The transient analysis requires a
very fine time step for accuracy, and you could run out of memory
before the simulation was complete.
I have developed a much faster way of analyzing a crystal oscillator
in SPICE. Instead of requiring tens or hundreds of thousands of
simulated cycles, this method gives accurate results in only a few
dozen cycles. For more information, please see "SPICE Analysis of
Crystal Oscillators"
http://pstca.com/spice/xtal/clapp.htm
You can estimate the value of the crystal ESR by finding the Q of
your crystal and working backwards.
I'm attaching a gif of your schematic for reference. This is rotated
90 degrees and enhanced in LView Pro to improve the contrast.
Please let me know if you have any questions.
Thanks,
Mike
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
WarrenS wrote:
A couple more thoughts;
Is the VCC (Red wire) current draw correct?.
Should be 1.3 ma (per the schematic values) with the 470 Ohm and
more like 7 plus ma with the 47 ohm.
AND I don't remember seeing, IS the Freq real close AND can it be tuned by the cap and Green wire voltage?
If both answers are YES, at least most things are working correctly.
As Bruce said:
"if the resistor values are correct this is the voltage(s) that one should get"
With the resistors values shown, I agree that all the other voltages are correct given the 2.49 volts,
BUT the 2.49 volt is NOT controlled by any of the values on that schematic, it's just an input.
AND the output amplitude is not yet being controlled by current cut off.
Something that needs to be asked is are all these the correct values.
It sounds like you got them by measuring and not from a "should be" schematic.
One last, way out thought.
It was my belief that very good osc have some sort of AGC to control the amplitude,
ANY chance that the VCC is used as the input to control the amplitude of the Osc output?
If so, could it be that the external AGC that is what broken and supplying too low a VCC voltage to the circuit?
ws
The Colpitts crystal oscillator limits the crystal current by being
periodically cutoff for part of the cycle.
There is an optimum duty cycle (usually something like 25%) that
corresponds to minimum phase noise.
The oscillator dc collector current determines the crystal current and
hence the output amplitude.
It is possible to perform AGC by varying the oscillator Vcc but the
output amplifier schematic appears to have no circuitry for this.
Some circuits actually do this, but the oscillator transistor is still
cutoff for part of the oscillator cycle.
The oscillator VCC is fed from a tap in a resistive divider network
(located on the external (to the oven) buffer board) connected between
the 5V supply and ground.
Usually one just varies the emitter (or collector) dc current by
selecting a resistor value.
Bruce
----- Original Message -----
From: "Bruce Griffiths" bruce.griffiths@xtra.co.nz
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Friday, July 03, 2009 8:21 PM
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
WarrenS wrote:
Here is my two cents worth
20 mv output, sure sounds like something is broken.
It should be fixed before it is modified.
The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe.
Not so, if the resistor values are correct this is the voltage that one
should get.
The question that remains: Is the voltage what the designer intended?
With the Colpitts oscillator used limiting in the oscillator transistor
(usually by current cutoff) is used to limit the amplitude.
Just increasing the voltage without checking the resultant crystal
current will be within permissable limits can be counter productive.
The "Grn" labeled wire, FreqCtrl input should be about 1/2 VCC for testing.
If you do 'need' to modify the gain,
It would seem better to bypass the 470 ohm resistor with a cap in series with the 47 ohms.
ws
Bruce
----- Original Message -----
From: "Mike Monett" xde-l2g3@myamail.com
To: time-nuts@febo.com
Sent: Friday, July 03, 2009 11:50 AM
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
An update on the Broken Ovenaire OSC 85-50.
I prepared a 'schematic' of the Output Board and the Oscillator
Board (attached) and I have lots of pictures of the external unit
and the insides if anyone is interested.
I resoldered all connections and replaced all transistors on the
Output Board and the Oscillator Board all to no benefit. I
measured all the components with an LCR meter and found the 0.01
uF bypass on the 330 ohm resistor in the emitter circuit of the
output transistor of the Output Board to be low and with a high
ESR. I replaced this with about a 20% increase in output amplitude
but still inadequate. I replaced the rest of the 0.01 uF caps on
the output board with no additional benefit. I transiently
disconnected the Red wires from the Oven Controller board and
there was no increase in output or significant increase in voltage
to the Oscillator Board.
Therefore, it appeared that a 'low output crystal' (if such a
thing exists) was the only logical explanation that I could come
up with. That seeming to be the case, there appeared to be only 4
options. 1. Toss the OCXO (sorry, too much effort so far). 2.
Build an external amplifier (seemingly too much additional
effort). 3. Try to adjust on the bias of the oscillator transistor
to achieve a higher output (seemed too 'iffy'). Or 4. Lower the
value of the resistor in the emitter circuit of the Oscillator
Board to get more gain out of the last stage in the Oscillator
Board.
I replaced the 470 ohm resistor with a 47 ohm resistor and the
amplitude increased to about 0.4 V P-P into a 50 ohm load and was
sufficient to make it a usable OCXO again.
I reassembled, resealed with Epoxy and all seems well so far.
If anyone wants pictures or other info, please let me know.
Thanks for all the suggestions and help.
Joe
Joe,
Congratulations on getting your system to work!
A couple of things. First, trying to measure the currents in the
circuit with a ferrite toroid won't do you much good. You don't know
what the currents should be, and the secondary of the toroid
transformer requires a termination resistor. The value changes with
the turns ratio.
Just from looking at the circuit, the RF currents will be extremely
low. This requires a large number of turns on the secondary, which
will probably resonate at or below the 10MHz operating frequency due
to stray capacitance from the connection to the scope. So it is
unlikely you will get any useful progress in this direction.
However, from the values on your schematic, the output tank circuit
resonates at 9.602MHz with a Q of 9.6. So the tank is already well
below resonance, which attenuates the output voltage.
Any stray capacitance you add to the circuit will bring the resonant
frequency lower, further aggravating the loss in signal.
The output tank is tapped with the 75pF and 91pF in series. This
further attenuates the signal.
I'd change the circuit to a single capacitor across the tank with a
small trim capacitor to tune it to resonance.
To get the signal into 50 ohms for distribution, I'd add a limiter
if you can tolerate a square wave output, or a good emitter follower
if you need a sine wave. Take the output from the collector of the
2N2369 to get the maximum signal amplitude.
Your original post mentions an output amplitude of 20mV. If the
normal amplitude is around 2V, this represents a loss of 40dB. This
is a huge loss in signal. The circuit obviously worked at one time,
so there may well be some other hidden problem.
It is possible the crystal is damaged, but this seems unlikely. A
crystal oscillator probably won't even start if the signal level is
down 40dB.
You can check the oscillator and crystal in SPICE. Normally, the
high Q of the crystal will make the analysis very slow. It could
take many hours for the simulation to begin oscillating and
stabilize at the final amplitude. The transient analysis requires a
very fine time step for accuracy, and you could run out of memory
before the simulation was complete.
I have developed a much faster way of analyzing a crystal oscillator
in SPICE. Instead of requiring tens or hundreds of thousands of
simulated cycles, this method gives accurate results in only a few
dozen cycles. For more information, please see "SPICE Analysis of
Crystal Oscillators"
http://pstca.com/spice/xtal/clapp.htm
You can estimate the value of the crystal ESR by finding the Q of
your crystal and working backwards.
I'm attaching a gif of your schematic for reference. This is rotated
90 degrees and enhanced in LView Pro to improve the contrast.
Please let me know if you have any questions.
Thanks,
Mike
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Thus one cannot arbitrarily increase Vcc without considering the consequences ...
True, but with the AC voltages as low as they are, I do think it is safe to think that the crystal current should be higher.
I was not suggesting to arbitrarily rise the Vcc, I was asking any chance it is at the wrong voltage???
Even though 2.49 volts is plenty of Vcc to design an osc circuit to run on, It seems like a low, funny voltage to design for, on what I assume is an old product.
ws
----- Original Message -----
From: "Bruce Griffiths" bruce.griffiths@xtra.co.nz
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Friday, July 03, 2009 8:36 PM
Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50
WB6BNQ wrote:
I agree with Warren. The VCC seems way too low. Interestingly, noone else seems to think so,
or did not notice it.
Bill....WB6BNQ
It was noticed, but it is consistent with the resistor values used in
the circuit.
The crystal current is determined by the dc emitter current of the
oscillator transistor.
Thus one cannot arbitrarily increase Vcc without considering the
consequences for the crystal current etc.
Bruce
WarrenS wrote:
Here is my two cents worth
20 mv output, sure sounds like something is broken.
It should be fixed before it is modified.
The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe.
The "Grn" labeled wire, FreqCtrl input should be about 1/2 VCC for testing.
If you do 'need' to modify the gain,
It would seem better to bypass the 470 ohm resistor with a cap in series with the 47 ohms.
ws
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.