Discussion:
Furuno GT-87
(too old to reply)
Mark Sims
2018-03-16 00:14:25 UTC
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Bob Darlington shipped me a GT-8736 to test. It is a small, Motorola M12 format GPS receiver with a claim to fame of +/- 1.7 ns sawtooth error. I was unable to test it until recently because my M12 to Adafruit adapter board was fab'd with holes drilled too small for the 2x5 pin 0.05" M12 pin header. I got in some headers and bodged one onto the top of the adapter board and used a cable (from Adafruit) to interconnect the two boards.

Besides the M12 binary format the GT87 can also talk Furuno ESIP format. Lady Heather now fully supports ESIP data (basically just NMEA with some custom sentences, similar to Furuno's PFEC protocol (which Heather also supports)... why Furuno felt they needed Yet Another Protocol is beyond me). ESIP mode provides better control and monitoring than the Motorola mode. Oh, and don't believe/do anything you might read about putting the G87 into PFEC mode... it effectively bricks the unit and puts it into some unknown binary language.

The G87 supports GPS and GLONASS (with Galileo supposedly on the way) and SBAS. I typically track over 22 satellites. The thing is very sensitive. I disconnected the antenna from the 3" MMCX to BNC antenna pigtail I was using and could still track some satellites indoors.

Anyway, I connected the 1PPS output to a TAPR TICC and did some measurements. It's rather impressive. The span of the 1PPS was around +/- 4 nsec over 24 hours. ADEV is in the mid E-13's at 10,000 seconds. It should make for a rather nice GPSDO.
Mark Sims
2018-03-16 18:30:07 UTC
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I re-confgured the GT-87 to just use GPS satellites (the posted data had GPS, SBAS, and GLONASS enabled). The 1PPS span was mostly +/- 2.5 ns, with a few excursions to the +/- 3.5 ns range.

I'll try GLONASS only next.

I looks like Furuno is not going to add Galileo support to the GT-87 firmware.
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Bob kb8tq
2018-03-16 21:26:52 UTC
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Hi

I wonder if they will ever get around to dropping the “Galileo with firmware update” statements
from *all* there spec sheets for the GT-87 and Opus-7 devices……

There has always been the basic issue of *how* an end user would be able to get such an update.
Furuno does not seem to have a channel for distributing that sort of thing.

Bob
Post by Mark Sims
I re-confgured the GT-87 to just use GPS satellites (the posted data had GPS, SBAS, and GLONASS enabled). The 1PPS span was mostly +/- 2.5 ns, with a few excursions to the +/- 3.5 ns range.
I'll try GLONASS only next.
I looks like Furuno is not going to add Galileo support to the GT-87 firmware.
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Ulrich Rohde via time-nuts
2018-03-16 23:57:36 UTC
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https://synergymwave.com/articles/2013/04/full_article.pdf
 
This may be still of interest... happy weekend, 73  de Ulrich, N1UL

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Gerhard Hoffmann
2018-04-15 17:01:01 UTC
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Post by Ulrich Rohde via time-nuts
https://synergymwave.com/articles/2013/04/full_article.pdf
This may be still of interest... happy weekend, 73  de Ulrich, N1UL
Since the weather did not look so nice this weekend, I canceled a
2-day motorcycle tour and tried the much applauded Colpitts
instead.

I think it is not possible to make it closer to the published circuit.
OK, I dismissed the 0.5fF C0 modifier which is probably only a
placeholder for simulation experiments. I had no 200nH parts, so I took
220nH, 150 nH did not make a difference other than less output voltage.
I did not test the buffer stage because the BFG540 is obsolete
and I could not find anything that fits its weird pinout.

From the Altium Designer to .pdf, to Laser printout on foil as a
photo mask and the contact copy to the unpopulated pcb can be
done in a good hour, so it's a nice weekender.

Circuit:       <
https://www.flickr.com/photos/***@N07/41468657011/in/album-72157662535945536/
   >
Layout:      <
https://www.flickr.com/photos/***@N07/40754928234/in/album-72157662535945536/
  >
Hardware: <
https://www.flickr.com/photos/***@N07/41427204622/in/album-72157662535945536/
  >

It turned out that the circuit, as it is,  leaves the choice of the
overtone to the crystal.
From a collection of 100...120MHz crystals not one worked at the
intended overtone.
There were results from 20 to 70 MHz.
The test point is where the BFG540 emitter would be.

<
https://www.flickr.com/photos/***@N07/40754932194/in/album-72157662535945536/
  >
<
https://www.flickr.com/photos/***@N07/41468662151/in/album-72157662535945536/
  >
<
https://www.flickr.com/photos/***@N07/40754931924/in/album-72157662535945536/
  >

I forwent measuring the phase noise.

Call me amateurish again, but I'll stay with the Driscoll. It has the
tank circuit to enforce
the correct overtone and I can adjust the delay so that 0 degrees around
the loop
coincides with maximum dp/df. Maximum Q helps nothing when it does not
happen on the
oscillation frequency.

When I'm asked in a design review how I have made sure that the
frequency of a single point
of failure VCXO is not off by 30 to 80 percent, then I like to have an
answer.



And WRT vastly changing transistor parameters: They don't need to. If
one looks into the emitter
of a BJT at 10 or 20 mA bias, one sees 1 or 2 Ohms.  That depends only
on Ic, K, T, q and some
minor parasitics such as RE.
The emitter is fed by the crystal in Driscoll's case with 50 to 70 Ohms
on resonance, which takes
nice care of the transistor's shot noise. Off frequency it gets even
better, esp. with C0 compensation.

The base is fed with a huge step down ratio, so the base voltage is
stiff. The cascode isolates from the
effects of the tank circuit and it can easily be bootstrapped. If one
dislikes Schottky limiting, one can
duplicate the cascode transistor and divert some of the RF current to
nirvana and not to the transformer,
whenever the AGC voltage wants that.
So the environment of the crystal and the sustaining amplifier can be
very, very time-invariant.
The whole thing is just a current conveyor belt with the crystal
enforcing the current trough the
whole cascode to the tank/load. The output IS the resonator current.

That is the very same structure as the proposals to extract to output
"directly from the resonator,
where it has the best SNR".
Given the little bit of power that we can steal from the resonator: must
we really split it between
extraction amplifier and sustaining amplifier right at the location
where the signal is weakest?

When we can build an extraction amplifier that adds less noise than the
sustaining amplifier, why don't
we take the feedback also from there and cut out the sust.amp. and the
signal power it requires?
The Driscoll does that.



regards,
Gerhard, DK4XP

(the loyal heretic :-)









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Bob kb8tq
2018-04-15 18:28:43 UTC
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Hi
Post by Gerhard Hoffmann
Post by Ulrich Rohde via time-nuts
https://synergymwave.com/articles/2013/04/full_article.pdf
This may be still of interest... happy weekend, 73 de Ulrich, N1UL
Since the weather did not look so nice this weekend, I canceled a
2-day motorcycle tour and tried the much applauded Colpitts
instead.
I think it is not possible to make it closer to the published circuit.
OK, I dismissed the 0.5fF C0 modifier which is probably only a
placeholder for simulation experiments. I had no 200nH parts, so I took
220nH, 150 nH did not make a difference other than less output voltage.
I did not test the buffer stage because the BFG540 is obsolete
and I could not find anything that fits its weird pinout.
From the Altium Designer to .pdf, to Laser printout on foil as a
photo mask and the contact copy to the unpopulated pcb can be
done in a good hour, so it's a nice weekender.
For a conventional overtone Colpitts, you should have a bypass cap on R9. Without the bypass, the “tank”
L4 + C11 will have very low Q. It is also likely that some portion of the “R” will get into the resonant loop.

Bob
Post by Gerhard Hoffmann
It turned out that the circuit, as it is, leaves the choice of the overtone to the crystal.
From a collection of 100...120MHz crystals not one worked at the intended overtone.
There were results from 20 to 70 MHz.
The test point is where the BFG540 emitter would be.
I forwent measuring the phase noise.
Call me amateurish again, but I'll stay with the Driscoll. It has the tank circuit to enforce
the correct overtone and I can adjust the delay so that 0 degrees around the loop
coincides with maximum dp/df. Maximum Q helps nothing when it does not happen on the
oscillation frequency.
When I'm asked in a design review how I have made sure that the frequency of a single point
of failure VCXO is not off by 30 to 80 percent, then I like to have an answer.
And WRT vastly changing transistor parameters: They don't need to. If one looks into the emitter
of a BJT at 10 or 20 mA bias, one sees 1 or 2 Ohms. That depends only on Ic, K, T, q and some
minor parasitics such as RE.
The emitter is fed by the crystal in Driscoll's case with 50 to 70 Ohms on resonance, which takes
nice care of the transistor's shot noise. Off frequency it gets even better, esp. with C0 compensation.
The base is fed with a huge step down ratio, so the base voltage is stiff. The cascode isolates from the
effects of the tank circuit and it can easily be bootstrapped. If one dislikes Schottky limiting, one can
duplicate the cascode transistor and divert some of the RF current to nirvana and not to the transformer,
whenever the AGC voltage wants that.
So the environment of the crystal and the sustaining amplifier can be very, very time-invariant.
The whole thing is just a current conveyor belt with the crystal enforcing the current trough the
whole cascode to the tank/load. The output IS the resonator current.
That is the very same structure as the proposals to extract to output "directly from the resonator,
where it has the best SNR".
Given the little bit of power that we can steal from the resonator: must we really split it between
extraction amplifier and sustaining amplifier right at the location where the signal is weakest?
When we can build an extraction amplifier that adds less noise than the sustaining amplifier, why don't
we take the feedback also from there and cut out the sust.amp. and the signal power it requires?
The Driscoll does that.
regards,
Gerhard, DK4XP
(the loyal heretic :-)
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Lars Walenius
2018-03-17 20:34:43 UTC
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Thanks Marks,



Just a question about what reference you used for the TICC?



Another question is about the orange and gray scale with respective 8 and 22ns span. The orange says TIEb and the gray PHchB. What are they? You talk about +-4ns over 24hours but what are the 22ns span when?



Best regards

Lars



________________________________
Från: time-nuts <time-nuts-***@febo.com> för Mark Sims <***@hotmail.com>
Skickat: Friday, March 16, 2018 1:14:25 AM
Till: time-***@febo.com
Ämne: [time-nuts] Furuno GT-87

Bob Darlington shipped me a GT-8736 to test. It is a small, Motorola M12 format GPS receiver with a claim to fame of +/- 1.7 ns sawtooth error. I was unable to test it until recently because my M12 to Adafruit adapter board was fab'd with holes drilled too small for the 2x5 pin 0.05" M12 pin header. I got in some headers and bodged one onto the top of the adapter board and used a cable (from Adafruit) to interconnect the two boards.

Besides the M12 binary format the GT87 can also talk Furuno ESIP format. Lady Heather now fully supports ESIP data (basically just NMEA with some custom sentences, similar to Furuno's PFEC protocol (which Heather also supports)... why Furuno felt they needed Yet Another Protocol is beyond me). ESIP mode provides better control and monitoring than the Motorola mode. Oh, and don't believe/do anything you might read about putting the G87 into PFEC mode... it effectively bricks the unit and puts it into some unknown binary language.

The G87 supports GPS and GLONASS (with Galileo supposedly on the way) and SBAS. I typically track over 22 satellites. The thing is very sensitive. I disconnected the antenna from the 3" MMCX to BNC antenna pigtail I was using and could still track some satellites indoors.

Anyway, I connected the 1PPS output to a TAPR TICC and did some measurements. It's rather impressive. The span of the 1PPS was around +/- 4 nsec over 24 hours. ADEV is in the mid E-13's at 10,000 seconds. It should make for a rather nice GPSDO.

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Mark Sims
2018-03-18 00:43:03 UTC
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The TICC reference is a HP-5071A cesium beam oscillator with high performance tube. The GT-87 is connected to the TICC channel B input. The TICC is running in timestamp mode.

The orange plot is the Time Interval Error of the 1PPS signal... the difference between 1 second and the measured 1PPS.

The grey plot is the accumulated phase error for channel B.

I just finished the measurement of the GT87 running on GLONASS sats only. The PPS span was still in the +/-4 ns range with a couple of points +/- 6 ns. However the ADEV measurements on the 1PPS were 3 (at tau-100 secs) to 5 times higher. (at tau=10000 seconds). I am typically tracking 5-8 GLONASS sats.

The GT87 sends an "accuracy" value. In GLONASS only mode the GT87 reports an accuracy of 12 ns. With GPS enabled it tends to say 5-6 ns, but I have seen it as low as 2 ns.
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Lars Walenius
2018-03-18 17:25:01 UTC
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So the orange is the second to second timestamp difference minus 1s, or the period time measured every second minus 1s. As the period is very close to 1s the frequency difference just will be the negative value so what the graph shows is the same as eg Stable 32’s frequency data for 1s but negative. As in e.g. http://www.leapsecond.com/pages/tbolt-8d/ . Also the orange line for me more seems to be the difference between adjacent ”saw tooth correction data” + some hardware noise as the edges of the PPS is very dependent on the TCXO frequency for two successive edges.

The gray line seems to be more interesting as it is what I in Stable 32 believe is called phase data.

Would be interesting to know how Furano calculates “accuracy”.

See forward for more data from the GPS and GLONASS comparison. Don´t remember to have seen anything of that from someone else!
Thanks Lars



________________________________
Från: time-nuts <time-nuts-***@febo.com> för Mark Sims <***@hotmail.com>
Skickat: Sunday, March 18, 2018 1:43:03 AM
Till: time-***@febo.com
Ämne: [time-nuts] Furuno GT-87

The TICC reference is a HP-5071A cesium beam oscillator with high performance tube. The GT-87 is connected to the TICC channel B input. The TICC is running in timestamp mode.

The orange plot is the Time Interval Error of the 1PPS signal... the difference between 1 second and the measured 1PPS.

The grey plot is the accumulated phase error for channel B.

I just finished the measurement of the GT87 running on GLONASS sats only. The PPS span was still in the +/-4 ns range with a couple of points +/- 6 ns. However the ADEV measurements on the 1PPS were 3 (at tau-100 secs) to 5 times higher. (at tau=10000 seconds). I am typically tracking 5-8 GLONASS sats.

The GT87 sends an "accuracy" value. In GLONASS only mode the GT87 reports an accuracy of 12 ns. With GPS enabled it tends to say 5-6 ns, but I have seen it as low as 2 ns.
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Ulrich Rohde via time-nuts
2018-04-15 18:20:22 UTC
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Good work,
 
yes, we did not include the fundamental frequency suppressor in the circuit diagram,  we needed the oscillator for the evaluation of the test equipment at the time..
 
happy Sunday evening ... Dj2LR
 
In a message dated 4/15/2018 2:02:01 PM Eastern Standard Time, ***@arcor.de writes:

 
Post by Ulrich Rohde via time-nuts
https://synergymwave.com/articles/2013/04/full_article.pdf
This may be still of interest... happy weekend, 73  de Ulrich, N1UL
Since the weather did not look so nice this weekend, I canceled a
2-day motorcycle tour and tried the much applauded Colpitts
instead.

I think it is not possible to make it closer to the published circuit.
OK, I dismissed the 0.5fF C0 modifier which is probably only a
placeholder for simulation experiments. I had no 200nH parts, so I took
220nH, 150 nH did not make a difference other than less output voltage.
I did not test the buffer stage because the BFG540 is obsolete
and I could not find anything that fits its weird pinout.

From the Altium Designer to .pdf, to Laser printout on foil as a
photo mask and the contact copy to the unpopulated pcb can be
done in a good hour, so it's a nice weekender.

Circuit:       <
https://www.flickr.com/photos/***@N07/41468657011/in/album-72157662535945536/
   >
Layout:      <
https://www.flickr.com/photos/***@N07/40754928234/in/album-72157662535945536/
  >
Hardware: <
https://www.flickr.com/photos/***@N07/41427204622/in/album-72157662535945536/
  >

It turned out that the circuit, as it is,  leaves the choice of the
overtone to the crystal.
From a collection of 100...120MHz crystals not one worked at the
intended overtone.
There were results from 20 to 70 MHz.
The test point is where the BFG540 emitter would be.

<
https://www.flickr.com/photos/***@N07/40754932194/in/album-72157662535945536/
  >
<
https://www.flickr.com/photos/***@N07/41468662151/in/album-72157662535945536/
  >
<
https://www.flickr.com/photos/***@N07/40754931924/in/album-72157662535945536/
  >

I forwent measuring the phase noise.

Call me amateurish again, but I'll stay with the Driscoll. It has the
tank circuit to enforce
the correct overtone and I can adjust the delay so that 0 degrees around
the loop
coincides with maximum dp/df. Maximum Q helps nothing when it does not
happen on the
oscillation frequency.

When I'm asked in a design review how I have made sure that the
frequency of a single point
of failure VCXO is not off by 30 to 80 percent, then I like to have an
answer.



And WRT vastly changing transistor parameters: They don't need to. If
one looks into the emitter
of a BJT at 10 or 20 mA bias, one sees 1 or 2 Ohms.  That depends only
on Ic, K, T, q and some
minor parasitics such as RE.
The emitter is fed by the crystal in Driscoll's case with 50 to 70 Ohms
on resonance, which takes
nice care of the transistor's shot noise. Off frequency it gets even
better, esp. with C0 compensation.

The base is fed with a huge step down ratio, so the base voltage is
stiff. The cascode isolates from the
effects of the tank circuit and it can easily be bootstrapped. If one
dislikes Schottky limiting, one can
duplicate the cascode transistor and divert some of the RF current to
nirvana and not to the transformer,
whenever the AGC voltage wants that.
So the environment of the crystal and the sustaining amplifier can be
very, very time-invariant.
The whole thing is just a current conveyor belt with the crystal
enforcing the current trough the
whole cascode to the tank/load. The output IS the resonator current.

That is the very same structure as the proposals to extract to output
"directly from the resonator,
where it has the best SNR".
Given the little bit of power that we can steal from the resonator: must
we really split it between
extraction amplifier and sustaining amplifier right at the location
where the signal is weakest?

When we can build an extraction amplifier that adds less noise than the
sustaining amplifier, why don't
we take the feedback also from there and cut out the sust.amp. and the
signal power it requires?
The Driscoll does that.



regards,
Gerhard, DK4XP

(the loyal heretic :-)









_______________________________________________
time-nuts mailing list -- time-***@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Ulrich Rohde via time-nuts
2018-04-15 18:27:43 UTC
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Before I forget it, Bernd Neubig seems to build the worlds best Colpitts circuit 100 MHz oscillator and uses my published thought to use the crystal filter as the noise filter to the next stage. I was never able to get the Driscoll oscillator spurious free. Bernd  Neubig can offer more details .
 
Ulrich
 
In a message dated 4/15/2018 2:20:22 PM Eastern Standard Time, ***@aol.com writes:

 
Good work,
 
yes, we did not include the fundamental frequency suppressor in the circuit diagram,  we needed the oscillator for the evaluation of the test equipment at the time..
 
happy Sunday evening ... Dj2LR
 
In a message dated 4/15/2018 2:02:01 PM Eastern Standard Time,
***@arcor.de writes:
 
Post by Ulrich Rohde via time-nuts
https://synergymwave.com/articles/2013/04/full_article.pdf
This may be still of interest... happy weekend, 73  de Ulrich, N1UL
Since the weather did not look so nice this weekend, I canceled a
2-day motorcycle tour and tried the much applauded Colpitts
instead.

I think it is not possible to make it closer to the published circuit.
OK, I dismissed the 0.5fF C0 modifier which is probably only a
placeholder for simulation experiments. I had no 200nH parts, so I took
220nH, 150 nH did not make a difference other than less output voltage.
I did not test the buffer stage because the BFG540 is obsolete
and I could not find anything that fits its weird pinout.

From the Altium Designer to .pdf, to Laser printout on foil as a
photo mask and the contact copy to the unpopulated pcb can be
done in a good hour, so it's a nice weekender.

Circuit:       <
https://www.flickr.com/photos/***@N07/41468657011/in/album-72157662535945536/
   >
Layout:      <
https://www.flickr.com/photos/***@N07/40754928234/in/album-72157662535945536/
  >
Hardware: <
https://www.flickr.com/photos/***@N07/41427204622/in/album-72157662535945536/
  >

It turned out that the circuit, as it is,  leaves the choice of the
overtone to the crystal.
From a collection of 100...120MHz crystals not one worked at the
intended overtone.
There were results from 20 to 70 MHz.
The test point is where the BFG540 emitter would be.

<
https://www.flickr.com/photos/***@N07/40754932194/in/album-72157662535945536/
  >
<
https://www.flickr.com/photos/***@N07/41468662151/in/album-72157662535945536/
  >
<
https://www.flickr.com/photos/***@N07/40754931924/in/album-72157662535945536/
  >

I forwent measuring the phase noise.

Call me amateurish again, but I'll stay with the Driscoll. It has the
tank circuit to enforce
the correct overtone and I can adjust the delay so that 0 degrees around
the loop
coincides with maximum dp/df. Maximum Q helps nothing when it does not
happen on the
oscillation frequency.

When I'm asked in a design review how I have made sure that the
frequency of a single point
of failure VCXO is not off by 30 to 80 percent, then I like to have an
answer.



And WRT vastly changing transistor parameters: They don't need to. If
one looks into the emitter
of a BJT at 10 or 20 mA bias, one sees 1 or 2 Ohms.  That depends only
on Ic, K, T, q and some
minor parasitics such as RE.
The emitter is fed by the crystal in Driscoll's case with 50 to 70 Ohms
on resonance, which takes
nice care of the transistor's shot noise. Off frequency it gets even
better, esp. with C0 compensation.

The base is fed with a huge step down ratio, so the base voltage is
stiff. The cascode isolates from the
effects of the tank circuit and it can easily be bootstrapped. If one
dislikes Schottky limiting, one can
duplicate the cascode transistor and divert some of the RF current to
nirvana and not to the transformer,
whenever the AGC voltage wants that.
So the environment of the crystal and the sustaining amplifier can be
very, very time-invariant.
The whole thing is just a current conveyor belt with the crystal
enforcing the current trough the
whole cascode to the tank/load. The output IS the resonator current.

That is the very same structure as the proposals to extract to output
"directly from the resonator,
where it has the best SNR".
Given the little bit of power that we can steal from the resonator: must
we really split it between
extraction amplifier and sustaining amplifier right at the location
where the signal is weakest?

When we can build an extraction amplifier that adds less noise than the
sustaining amplifier, why don't
we take the feedback also from there and cut out the sust.amp. and the
signal power it requires?
The Driscoll does that.



regards,
Gerhard, DK4XP

(the loyal heretic :-)









_______________________________________________
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Gerhard Hoffmann
2018-04-15 20:26:35 UTC
Permalink
Raw Message
Post by Ulrich Rohde via time-nuts
Before I forget it, Bernd Neubig seems to build the worlds best Colpitts circuit 100 MHz oscillator and uses my published thought to use the crystal filter as the noise filter to the next stage. I was never able to get the Driscoll oscillator spurious free. Bernd  Neubig can offer more details .
We had a space-proof USO of his, nice. I don't know what's inside.

When it goes below ~ 140dBc / 100MHz / 100 Hz we found that only 10% of
the crystals were really
good, no matter of Q and extra-extra lapping. I got the idea to build a
notch array from the
other 90 %. That could be done even at elevated carrier levels that a
passband crystal filter would
never survive. One just would have to be sure not to tune the oscillator
over the notches by accident.
I mean, the crystals are there, paid for already and gathering dust.

Their phase noise properties are completely secondary, what matters is
only series resistance and that
they stay on their frequency.

And 6 dB better is a lot there,  even over a limited range around the
carrier.
For example, 6 dB less averaging time in an analyzer for the same result.

73, Gerhard


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Ulrich Rohde via time-nuts
2018-04-16 16:23:35 UTC
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Raw Message
Try again... may be of interest ... Ulrich
 

wenzel crystal oscillator schematic - Google Search
 
In a message dated 4/15/2018 3:00:46 PM Eastern Standard Time, time-***@febo.com writes:

 
Good work,
 
yes, we did not include the fundamental frequency suppressor in the circuit diagram,  we needed the oscillator for the evaluation of the test equipment at the time..
 
happy Sunday evening ... Dj2LR
 
In a message dated 4/15/2018 2:02:01 PM Eastern Standard Time, ***@arcor.de writes:

 
Post by Ulrich Rohde via time-nuts
https://synergymwave.com/articles/2013/04/full_article.pdf
This may be still of interest... happy weekend, 73  de Ulrich, N1UL
Since the weather did not look so nice this weekend, I canceled a
2-day motorcycle tour and tried the much applauded Colpitts
instead.

I think it is not possible to make it closer to the published circuit.
OK, I dismissed the 0.5fF C0 modifier which is probably only a
placeholder for simulation experiments. I had no 200nH parts, so I took
220nH, 150 nH did not make a difference other than less output voltage.
I did not test the buffer stage because the BFG540 is obsolete
and I could not find anything that fits its weird pinout.

From the Altium Designer to .pdf, to Laser printout on foil as a
photo mask and the contact copy to the unpopulated pcb can be
done in a good hour, so it's a nice weekender.

Circuit:       <
https://www.flickr.com/photos/***@N07/41468657011/in/album-72157662535945536/
   >
Layout:      <
https://www.flickr.com/photos/***@N07/40754928234/in/album-72157662535945536/
  >
Hardware: <
https://www.flickr.com/photos/***@N07/41427204622/in/album-72157662535945536/
  >

It turned out that the circuit, as it is,  leaves the choice of the
overtone to the crystal.
From a collection of 100...120MHz crystals not one worked at the
intended overtone.
There were results from 20 to 70 MHz.
The test point is where the BFG540 emitter would be.

<
https://www.flickr.com/photos/***@N07/40754932194/in/album-72157662535945536/
  >
<
https://www.flickr.com/photos/***@N07/41468662151/in/album-72157662535945536/
  >
<
https://www.flickr.com/photos/***@N07/40754931924/in/album-72157662535945536/
  >

I forwent measuring the phase noise.

Call me amateurish again, but I'll stay with the Driscoll. It has the
tank circuit to enforce
the correct overtone and I can adjust the delay so that 0 degrees around
the loop
coincides with maximum dp/df. Maximum Q helps nothing when it does not
happen on the
oscillation frequency.

When I'm asked in a design review how I have made sure that the
frequency of a single point
of failure VCXO is not off by 30 to 80 percent, then I like to have an
answer.



And WRT vastly changing transistor parameters: They don't need to. If
one looks into the emitter
of a BJT at 10 or 20 mA bias, one sees 1 or 2 Ohms.  That depends only
on Ic, K, T, q and some
minor parasitics such as RE.
The emitter is fed by the crystal in Driscoll's case with 50 to 70 Ohms
on resonance, which takes
nice care of the transistor's shot noise. Off frequency it gets even
better, esp. with C0 compensation.

The base is fed with a huge step down ratio, so the base voltage is
stiff. The cascode isolates from the
effects of the tank circuit and it can easily be bootstrapped. If one
dislikes Schottky limiting, one can
duplicate the cascode transistor and divert some of the RF current to
nirvana and not to the transformer,
whenever the AGC voltage wants that.
So the environment of the crystal and the sustaining amplifier can be
very, very time-invariant.
The whole thing is just a current conveyor belt with the crystal
enforcing the current trough the
whole cascode to the tank/load. The output IS the resonator current.

That is the very same structure as the proposals to extract to output
"directly from the resonator,
where it has the best SNR".
Given the little bit of power that we can steal from the resonator: must
we really split it between
extraction amplifier and sustaining amplifier right at the location
where the signal is weakest?

When we can build an extraction amplifier that adds less noise than the
sustaining amplifier, why don't
we take the feedback also from there and cut out the sust.amp. and the
signal power it requires?
The Driscoll does that.



regards,
Gerhard, DK4XP

(the loyal heretic :-)









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Ulrich Rohde via time-nuts
2018-04-30 21:50:10 UTC
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https://ieee-uffc.org/membership/fellows/ieee-fellows-of-the-uffc-society/
 
Updated list....            73 de Ulrich 
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Magnus Danielson
2018-04-30 23:51:35 UTC
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Thanks Ulrich for bringing this to my attention.

So, the new entry from the T&F side is David Howe, NIST. It's not a bad
achievement, behind this. Just go to the NIST T&F library and read his
articles, and then consider heading the phase-noise group at NIST. Dave
is now semi-retired from NIST, only doing a few things.

Congratulations Dave!

Cheers,
Magnus
Post by Ulrich Rohde via time-nuts
https://ieee-uffc.org/membership/fellows/ieee-fellows-of-the-uffc-society/
 
Updated list....            73 de Ulrich 
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