Re: [time-nuts] Trimble Thunderbolt CPR?

[Bob Camp]

Hi

If you dig into “things Trimble” they pretty much *never* publish info on what 
is 
inside their designs. They actually go to great lengths both with software and 
hardware
to keep things out of the public domain. One example is the odd labeling on the 
TBolt 
OCXO. Other than what can easily be read off of chips, there is not a lot of 
information 
about the TBolt wiring. 

Bob

> On Jul 28, 2015, at 3:11 PM, skipp Isaham via time-nuts  
> wrote:
> 
> Trimble Thunderbolt CPR?  
> 
> An Ebay purchased Trimble Thunderbolt arrived DOA, it has no rs-232 output 
> and I should also check the 10 MHz output soon. I'd like to have an initial 
> look at a diagram to see if there are any "user serviceable parts" on board. 
> 
> Initial web searching suggests the schematic is not easily located. 
> 
> Would anyone have a source (even if I have to pay for it) of a diagram and/or 
> any initial suggestions to trouble shoot an appearing to be dead Thunderbolt. 
> 
> I have a working Thunderbolt available for relative comparisons, sitting 
> right next 
> to the DOA unit. 
> 
> Again, thank you in advance for your replies. 
> 
> regards, 
> 
> skipp 
> 
> skipp025 at yahoo dot com 
> 
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Re: [time-nuts] Source of Rubidium Lamp for Efratom FRK

[Bob Camp]

Hi

The Efratom bulbs have a “magic mix” of gas in them. The only place I have ever 
bought them is direct from Efratom. They were fairly expensive back in the 
early 90’s …

Bob

> On Jul 28, 2015, at 9:56 AM, Mike Niven  wrote:
> 
> Would anyone know of a source of the Rubidium bulb fitted in the Efratom FRK 
> (and probably other FRx) standards?  I have repaired and refurbished my Racal 
> 9475, which is fitted with the older style FRK (not -H or -L) module.  It is 
> working properly at present but the lamp voltage is down to 5.5V, which is 
> below the stated minimum of 6V.  I have tried rejuvenating the bulb using a 
> hot air gun, as described by Corby, but this has had no obvious impact.  
> Hence, I have little feel for how much life the existing lamp has left and a 
> spare would be good for my peace of mind.
> 
> Many thanks.
> 
> Mike
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Re: [time-nuts] Trimble Thunderbolt CPR?

[Azelio Boriani]

As already noted on this list, the TBolt schematic diagram is sort of
a Holy Grail quest...

On Tue, Jul 28, 2015 at 9:11 PM, skipp Isaham via time-nuts
 wrote:
> Trimble Thunderbolt CPR?
>
> An Ebay purchased Trimble Thunderbolt arrived DOA, it has no rs-232 output
> and I should also check the 10 MHz output soon. I'd like to have an initial
> look at a diagram to see if there are any "user serviceable parts" on board.
>
> Initial web searching suggests the schematic is not easily located.
>
> Would anyone have a source (even if I have to pay for it) of a diagram and/or
> any initial suggestions to trouble shoot an appearing to be dead Thunderbolt.
>
> I have a working Thunderbolt available for relative comparisons, sitting 
> right next
> to the DOA unit.
>
> Again, thank you in advance for your replies.
>
> regards,
>
> skipp
>
> skipp025 at yahoo dot com
>
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Re: [time-nuts] Trimble Thunderbolt CPR?

[Pete Lancashire]

Are they the same version ?

-pete

On Tue, Jul 28, 2015 at 12:11 PM, skipp Isaham via time-nuts <
time-nuts@febo.com> wrote:

> Trimble Thunderbolt CPR?
>
> An Ebay purchased Trimble Thunderbolt arrived DOA, it has no rs-232 output
> and I should also check the 10 MHz output soon. I'd like to have an initial
> look at a diagram to see if there are any "user serviceable parts" on
> board.
>
> Initial web searching suggests the schematic is not easily located.
>
> Would anyone have a source (even if I have to pay for it) of a diagram
> and/or
> any initial suggestions to trouble shoot an appearing to be dead
> Thunderbolt.
>
> I have a working Thunderbolt available for relative comparisons, sitting
> right next
> to the DOA unit.
>
> Again, thank you in advance for your replies.
>
> regards,
>
> skipp
>
> skipp025 at yahoo dot com
>
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>
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[time-nuts] Fwd: Re: Wikipedia and Residual Phase Noise

[Gerhard Hoffmann]

 Weitergeleitete Nachricht 
Betreff:Re: [time-nuts] Wikipedia and Residual Phase Noise
Datum:  Tue, 28 Jul 2015 14:54:47 +0200
Von:Gerhard Hoffmann 
Antwort an: g...@hoffmann-hochfrequenz.de
An: time-nuts@febo.com



Am 14.07.2015 um 02:32 schrieb KA2WEU--- via time-nuts:
 

With your kind permission I (totally ) disagree with you . We make 10 GHz
oscillators which are almost getting close to the Poseidon Sapphire , but


 optical?


the post power amplifier
at 10 Ghz has a much higher noise floor then the source . I have not yet
solved the problem

My new FSWP (R&S) Analyzer can measure down to - 190dBc/Hz .



How do you do _that_? 20-cornered hat with 20 ADCs and references?
The ADCs and FPGAs would be cheap enough, the references less so.



Wish me luck, Ulrich



Wish granted, Gerhard DK4XP  ;-)









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[time-nuts] Modified Allan Deviation and counter averaging

[Poul-Henning Kamp]

Sorry this is a bit long-ish, but I figure I'm saving time putting
in all the details up front.

The canonical time-nut way to set up a MVAR measurement is to feed
two sources to a HP5370 and measure the time interval between their
zero crossings often enough to resolve any phase ambiguities caused
by frequency differences.

The computer unfolds the phase wrap-arounds, and calculates the
MVAR using the measurement rate, typically 100, 10 or 1 Hz, as the
minimum Tau.

However, the HP5370 has noise-floor in the low picoseconds, which
creates the well known diagonal left bound on what we can measure
this way.

So it is tempting to do this instead:

Every measurement period, we let the HP5370 do a burst of 100
measurements[*] and feed the average to MVAR, and push the diagonal
line an order of magnitude (sqrt(100)) further down.

At its specified rate, the HP5370 will take 1/30th of a second to
do a 100 sample average measurement.

If we are measuring once each second, that's only 3% of the Tau.

No measurement is ever instantaneous, simply because the two zero
crossings are not happening right at the mesurement epoch.

If I measure two 10MHz signals the canonical way, the first zero
crossing could come as late as 100(+epsilon) nanoseconds after the
epoch, and the second as much as 100(+epsilon) nanoseconds later.

An actual point of the measurement doesn't even exist, but picking
with the midpoint we get an average delay of 75ns, worst case 150ns.

That works out to one part in 13 million which is a lot less than 3%,
but certainly not zero as the MVAR formula pressume.

Eyeballing it, 3% is well below the reproducibility I see on MVAR
measurements, and I have therefore waved the method and result
through, without a formal proof.

However, I have very carefully made sure to never show anybody
any of these plots because of the lack of proof.

Thanks to Johns Turbo-5370 we can do burst measurements at much
higher rates than 3000/s, and thus potentially push the diagonal
limit more than a decade to the left, while still doing minimum
violence to the mathematical assumptions under MVAR.

[*] The footnote is this: The HP5370 firwmare does not make triggered
bust averages an easy measurement, but we can change that, in
particular with Johns Turbo-5370.

But before I attempt to do that, I would appreciate if a couple of
the more math-savy time-nuts could ponder the soundness of the
concept.

Apart from the delayed measurement point, I have not been able
to identify any issues.

The frequency spectrum filtered out by the averaging is wy to
the left of our minimum Tau. 

Phase wrap-around inside bursts can be detected and unfolded
in the processing.

Am I overlooking anything ?


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] how to find low noise transistors

[KA2WEU--- via time-nuts]

Good questions , I am looking forward to the answers, this is  my area of 
work ... Ulrich N1UL 
 
 
In a message dated 7/28/2015 1:45:55 P.M. Eastern Daylight Time,  
dk...@arcor.de writes:

Am  20.07.2015 um 01:57 schrieb KA2WEU--- via time-nuts:
> Good evening,  this turns out to be a good discussion...
>   
> Any  more inputs ?  73 de Ulrich
>   
>

1. To get  a gut feeling about the virtues of nonlinear noise simulation: 
how much  phase noise will we typically lose if we stay with linear 
simulation? I  mean, we have been told so often how important it is that 
the amplifier  offers a constant (low) impedance to the crystal and that 
the smallest  nonlinearity would be an invitation to noise up conversion. 
It does not  take a lot of conversion gain when one looks at -150 dBc. 
So, even if we  use a HB simulator, the DUT will have to be pretty linear.


2. What  do you consider the optimum AGC for, say, a Driscoll or Butler 
at 100 MHz?  In my current work, most of the logic is triple module 
redundant and the  oscillator is a single point of failure. Stopping 
oscillation at an EFC  extreme would be a nightmare, but phase noise 
performance still cannot be  ignored.


3. Is there any work on AGC vs. post tuning  drift?


4. In [1] there are is some treatment about removing 1/f  noise of a RF 
transistor by active LF feedback. It is applied to a BFR93A  and the 
effect can be seen clearly. There are other faster transistors  that 
would need that much more urgently, and for > 40 dB of 1/f noise  
probably more loop gain would be required. I can see a place for an  
ADA4898 here… Also, there are 1K resistors in the bases of both the RF  
and the AF transistors while we are discussing here replicating the  
transistors to shrink the effective base spreading resistance. It seems  
that the improvement could be much larger.


BTW I got -145dBc  @100MHz @100Hz with mass production BFR93 transistors 
in Butlers, and the  limit seemed to be ONLY the crystal; most crystals 
were much worse, even  when they had comparable parameters and were from 
the same  batch.


5. One must always find a balance between optimum close-in  or far-out 
noise. The emitter input impedance of a 2 stage Butler  sustaining 
amplifier may serve as an example. Make it small and there will  be only 
a slight operating Q degradation - but less power available to the  input 
of the sustaining amp. with a given crystal current; needing more  gain 
and raising the floor.
Make it larger, and you get less operating  Q and better floor.

Only 10% of a crystal batch seem to provide  excellent close-in noise, 
the others being easily 10 dB worse. These  others are more or less free 
(at least already paid for). They still could  be used as a post-filter 
to shrink the noise floor. It would be necessary  to de-Q them with 
resistors so that they can withstand the power and that  they do not 
spoil the close-in noise.

Or use a bridge xtal filter  that has no crystal resonance on the center 
frequency. That would require  some discipline when tuning the oscillator 
to avoid blowing the filter  crystals. Far out the noise still would 
decrease by 6 dB/oct  Fourier-frequency-wise. 20 dB better makes the 
difference between OK and  excellent.

[1] Rohde/Newkirk: RF/Microwave Circuit Design for Wireless  
Applications, Wiley

very short excerpt for a few days on <  
https://picasaweb.google.com/lh/photo/XUfeAuD8TvNqBOMuJiPtltMTjNZETYmyPJy0li
ipFm0?feat=directlink>

73,  Gerhard, DK4XP
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[time-nuts] Trimble Thunderbolt CPR?

[skipp Isaham via time-nuts]

Trimble Thunderbolt CPR?  

An Ebay purchased Trimble Thunderbolt arrived DOA, it has no rs-232 output 
and I should also check the 10 MHz output soon. I'd like to have an initial 
look at a diagram to see if there are any "user serviceable parts" on board. 

Initial web searching suggests the schematic is not easily located. 

Would anyone have a source (even if I have to pay for it) of a diagram and/or 
any initial suggestions to trouble shoot an appearing to be dead Thunderbolt. 

I have a working Thunderbolt available for relative comparisons, sitting right 
next 
to the DOA unit. 

Again, thank you in advance for your replies. 

regards, 

skipp 

skipp025 at yahoo dot com 

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Re: [time-nuts] Lab upgrade

[Robert LaJeunesse]

One of the cheap and dirty ways to find a short is current tracing. Use a 
voltage and current limited source and a matching detector to find where the 
current flows. I've used a current limited DC supply as the source and, for the 
detector, an old DVM with 10uV resolution. For an AC approach a simple audio 
oscillator (or function generator) works nicely as the source, while a the 
detector starts with an audio playback tape head (from an old VCR), then some 
sort of amplifier-speaker, or maybe just an oscilloscope. If you are lucky you 
have an old HP logic pulser and current tracer set that do the same thing...

Bob L.

> ...
> 
> I'll buzz out the pins on  the connnector there and see if I can find the
> probably short and let people know.
> 
> Cheers
> Jason
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Re: [time-nuts] Wikipedia and Residual Phase Noise

[Gerhard Hoffmann]

Am 14.07.2015 um 02:32 schrieb KA2WEU--- via time-nuts:

Dear Magnus,
  
With your kind permission I (totally ) disagree with you . We make 10 GHz

oscillators which are almost getting close to the Poseidon Sapphire , but

optical?

the post power amplifier
at 10 Ghz has a much higher noise floor then the source . I have not yet
solved the problem
  
My new FSWP (R&S) Analyzer can measure down to - 190dBc/Hz .

How do you do _that_? 20-cornered hat with 20 ADCs and references?
The ADCs and FPGAs would be cheap enough, the references less so.

  
Wish me luck, Ulrich
  


Wish granted, Gerhard DK4XP  ;-)







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[time-nuts] Bliley Crystal TC92 pinouts ?

[Mark Spencer]

Hi, I'm wondering if anyone has the pinouts or other info for a Bliley Crystal 
TC92 temperature stabilizer.   This is a unit about the size of a soup can with 
a 7 pin base.

The unit i have apparently contains a 100 kc crystal and it would be fun to 
fire this up and see if i can persuade the crystal to oscillate.  It looks to 
be 1950's to 1970's vintage.

Any info would be appreciated.   Yes I realize I can probably figure things out 
with an ohm meter (: but thought I would ask first.

All the best
Mark Spencer 

Sent from my iPad
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Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)

[jerry shirᴀr]

So you think Skipp Isaham's oscillator has feedback pulses at the peak of
the sinewave?  Interesting.

Jerry

On Mon, Jul 27, 2015 at 8:58 PM, Bill Byrom  wrote:

> Bob, I think you meant to write: "Hook a 100 pf cap from emitter
> to ground."
>
> Also remember that the feedback loop can use multiple active devices.
> You can design a crystal oscillator which has only linear loading on the
> crystal but which has nonlinear characteristics somewhere in the
> feedback loop. Some oscillators use a filter to insure that only a
> linear signal is fed back from a very nonlinear amplifier in the loop.
> The output can be taken from various places in the feedback loop, and
> the harmonic content varies depending on that location.
>
> One idea is to only add energy to the crystal at the peak of the
> sinewave voltage, when the derivative of the voltage is zero. If a short
> pulse is added at the peak the amplitude is increased without
> significantly affecting the phase. But if the pulse is added at the
> middle "zero crossing" of the sinewave (with resepect to the peak-to-
> peak swing) where the derivative is large, the phase can be affected by
> the feedback. Ideally you want to add just enough energy each cycle to
> overcome the energy lost in the crystal due to limited Q.
>
> If the feedback loop is linear, then the noise generated by the active
> and passive devices is continuously fed back to the crystal, generating
> amplitude noise. Due to the angle of the feedback (described above) and
> AM to PM conversion due to device characteristics (junction capacitance
> changes with voltage), some of the amplitude noise gets converted to
> phase noise. The total resulting noise sidebands (made up of both
> ampitude and phase noise) is what everyone wants to minimize.
>
> You could also use a feedback loop which was very nonlinear by using an
> active switch with a low ON resistance (so hopefully a low noise figure
> when closed) to send spikes back to the crystal resonator at the peak of
> the voltage waveform. If you could arrange the circuit so that the duty
> cycle of this switch was low, the residual noise would only be amplified
> and fed back to the crystal resonator over a small portion of each
> cycle, reducing the average noise figure of the oscillator. If the
> feedback circuit is highly nonlinear the amplitude noise might be
> clipped and reduced. Of course, the jitter in the feedback circuit is
> important.
>
> The active devices need to be well bypassed at audio frequencies so that
> low frequency shot noise isn't amplified with high efficiency. Since the
> junction capacitance (and other AM to PM conversion sources) in
> downstream amplifiers can be affected by audio frequency noise, I think
> that it's very important that such noise isn't allowed to phase modulate
> the desired RF signal.
>
> --
> Bill Byrom N5BB
>
>
>
> On Mon, Jul 27, 2015, at 05:39 PM, Bob Camp wrote:
> > Hi
> >
> >
> >> On Jul 27, 2015, at 11:52 AM, jerry shirᴀr 
> wrote:
> >>
> >> Here's the rub Bob. I have been trying to find a way or have you explain
> >> how a high harmonic oscillator stage
> >
> > You are confusing the current through the crystal with the current in the
> > oscillator transistor.
> > So:
> >
> > Connect a 2N918 with the collector to +12V through a 50 ohm resistor. AC
> > couple that resistor to your spectrum analyzer.
> > Connect the base of the transistor with a 10K to +12 and a 10K to ground
> > Connect a 1K ohm resistor from the emitter of the transistor to ground
> > Hook a 100 pf cap from base to emitter
> > Hook a 100 pf cap from emitter to base
> > Hook a 10.0 MHz fundamental crystal with a resistance of < 10 ohms  to
> > the base of the transistor.
> > Hook a 32 pf cap from the other side of the crystal to ground
> >
> > I **hope** that’s specific enough for you.
> >
> > That circuit **will** oscillate.
> >
> > Look at the current on the 50 ohm resistor. It’s got plenty of harmonics.
> >
> > With me so far or is this still to theoretical?
> >
> > Now, this **does** get a bit exciting, but it’s the way this circuit has
> > been analyzed since the 1930’s (when it used a tube):
> >
> > You shift the ground to the emitter for the purposes of seeing what’s
> > going on. You now have an “input side” and an “output side” to
> > the active stage. This lets you break the loop for analysis.
> >
> > In this format, the current in the collector is more clearly flowing
> > through the 1K resistor and one of the 100 pf caps.
> > The current that passes through the crystal flows through the other 100
> > pf cap (and the base) to ground.
> >
> > The current in the oscillator stage is every bit as nonlinear as you saw
> > before.
> >
> > Since this is an oscillator, the current flows in a loop. There is no
> > independent current in any one leg. They all are related.
> > If you want to see this, hook up an oscilloscope to the collector
> > resistor and apply power to the oscillator. The output does not
> > go instant

Re: [time-nuts] Square to sine wave symmetrical conversion

[Charles Steinmetz]

Jerry wrote:


I don't understand why when there is already a clean crystal current in
the circuit, someone wouldn't want to take advantage of that signal and
use that rather than add filters and poor biasing to the mix to claim that
something can be done when we are talking about ideal situations where
the lowest phase noise is desired.


It was I who originally described the "high harmonic" oscillator, so 
I'll respond.  I didn't suggest that you'd *want* to do that.  You 
said you couldn't even imagine how one would build an oscillator with 
high harmonics, and I detailed one way.  And while it's not the most 
promising way to design a low-PN oscillator, it *is* a design that 
has been used in many commercially produced oscillators over the years.


And there are reasons for using at least some features of the design 
-- it is very robust over changes in component values and 
characteristics, so the designer can be confident that thousands can 
be made and they will all oscillate and have a predictable output 
amplitude.  This is not always the case with low-distortion designs 
that have very little excess gain.  Remember, while time-nuts and 
hams can select components and tweak every oscillator they make 
individually, manufacturers who are turning them out in quantity for 
sale at a reasonable price have more limited options.  Finally, it is 
not always convenient to tap the resonator current directly, and 
where it is possible the need to avoid loading the resonator may 
compromise noise performance.


So -- I was not suggesting that the architecture I described is the 
best way (or even a good way) to make a low-PN oscillator, but there 
are reasons why it has, nevertheless, been used by the designers of 
many commercial products.


Best regards,

Charles



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Re: [time-nuts] how to find low noise transistors

[Gerhard Hoffmann]

Am 20.07.2015 um 01:57 schrieb KA2WEU--- via time-nuts:

Good evening, this turns out to be a good discussion...
  
Any more inputs ?  73 de Ulrich
  



1. To get a gut feeling about the virtues of nonlinear noise simulation: 
how much phase noise will we typically lose if we stay with linear 
simulation? I mean, we have been told so often how important it is that 
the amplifier offers a constant (low) impedance to the crystal and that 
the smallest nonlinearity would be an invitation to noise up conversion. 
It does not take a lot of conversion gain when one looks at -150 dBc. 
So, even if we use a HB simulator, the DUT will have to be pretty linear.



2. What do you consider the optimum AGC for, say, a Driscoll or Butler 
at 100 MHz? In my current work, most of the logic is triple module 
redundant and the oscillator is a single point of failure. Stopping 
oscillation at an EFC extreme would be a nightmare, but phase noise 
performance still cannot be ignored.



3. Is there any work on AGC vs. post tuning drift?


4. In [1] there are is some treatment about removing 1/f noise of a RF 
transistor by active LF feedback. It is applied to a BFR93A and the 
effect can be seen clearly. There are other faster transistors that 
would need that much more urgently, and for > 40 dB of 1/f noise 
probably more loop gain would be required. I can see a place for an 
ADA4898 here… Also, there are 1K resistors in the bases of both the RF 
and the AF transistors while we are discussing here replicating the 
transistors to shrink the effective base spreading resistance. It seems 
that the improvement could be much larger.



BTW I got -145dBc @100MHz @100Hz with mass production BFR93 transistors 
in Butlers, and the limit seemed to be ONLY the crystal; most crystals 
were much worse, even when they had comparable parameters and were from 
the same batch.



5. One must always find a balance between optimum close-in or far-out 
noise. The emitter input impedance of a 2 stage Butler sustaining 
amplifier may serve as an example. Make it small and there will be only 
a slight operating Q degradation - but less power available to the input 
of the sustaining amp. with a given crystal current; needing more gain 
and raising the floor.

Make it larger, and you get less operating Q and better floor.

Only 10% of a crystal batch seem to provide excellent close-in noise, 
the others being easily 10 dB worse. These others are more or less free 
(at least already paid for). They still could be used as a post-filter 
to shrink the noise floor. It would be necessary to de-Q them with 
resistors so that they can withstand the power and that they do not 
spoil the close-in noise.


Or use a bridge xtal filter that has no crystal resonance on the center 
frequency. That would require some discipline when tuning the oscillator 
to avoid blowing the filter crystals. Far out the noise still would 
decrease by 6 dB/oct Fourier-frequency-wise. 20 dB better makes the 
difference between OK and excellent.


[1] Rohde/Newkirk: RF/Microwave Circuit Design for Wireless 
Applications, Wiley


very short excerpt for a few days on < 
https://picasaweb.google.com/lh/photo/XUfeAuD8TvNqBOMuJiPtltMTjNZETYmyPJy0liipFm0?feat=directlink>


73, Gerhard, DK4XP
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[time-nuts] Source of Rubidium Lamp for Efratom FRK

[Mike Niven]

Would anyone know of a source of the Rubidium bulb fitted in the Efratom FRK 
(and probably other FRx) standards?  I have repaired and refurbished my Racal 
9475, which is fitted with the older style FRK (not -H or -L) module.  It is 
working properly at present but the lamp voltage is down to 5.5V, which is 
below the stated minimum of 6V.  I have tried rejuvenating the bulb using a hot 
air gun, as described by Corby, but this has had no obvious impact.  Hence, I 
have little feel for how much life the existing lamp has left and a spare would 
be good for my peace of mind.

Many thanks.

Mike
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Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)

[Bob Camp]

Hi

Yup, the second cap goes to ground not in parallel with the first cap.


> On Jul 27, 2015, at 10:42 PM, jerry shirᴀr  wrote:
> 
> Thanks Bob,
> 
> I had no intention of being offensive.  It is just my manner.  Forgive me.

I get a bit feisty from time to time - sorry about that.

> 
> First of all, I think you had intended to say "100pF from emitter to
> ground" rather than "100pF from emitter to base."  I think that's a typo.
> 
> Next, how much crystal drive level is there?  I guess it depends on the
> crystal resistance, but I think there will be a lot of crystal current.

Which is not unintentional ….that circuit will have pretty good phase noise for 
a
simple to wire circuit. 

> 
> Then I don't know why you would purposely want to clip the signal of the
> oscillator, but it is the designer's prerogative.

Ok, how would you propose to build an oscillator that does not have limiting,
since 99.999% of all precision (and otherwise) crystal oscillators have that 
feature?

Without a limiter in the feedback loop, there is no way to meet Barkenhausen’s 
criteria 
on a fast enough basis.

>  For low noise
> applications, I have always used an AGC so the oscillator will have a lot
> of drive at startup and then backs off greatly for steady state operation.

Which speeds up startup.

> You can also more easily control the drive level to a small enough amount
> so that the drive won't mess up the frequency accuracy.  

Except all the AGC does is to eliminate the massive extra gain at startup. It’s
far to slow to take care of the loop it’s self.

> Also the buffer
> from the oscillator stage buffers the actual crystal current so the base to
> emitter noise does not get amplified to the collector and propagated down
> the line.  I could beat a -145dBc/Hz spec at 100Hz and -168dBc/Hz at
> 10kHz.

Both of which are pretty noisy compared to the stuff I do these days. A lot 
depends on 
the frequency ...

> 
> I don't have anything here to breadboard these things up.  I don't
> understand why when there is already a clean crystal current in the
> circuit,

Possibly for one of three reasons:

1) They don’t want to degrade the Q (or more correctly phase slope) of the 
crystal by putting the resistance of the buffer in series with it.
2) They want better isolation in a single oscillator stage than they get with a 
series arrangement.
3) They want to double (or triple) the output frequency 

*and* do any / all of these things without degrading (and actually in case 1 
improving) the phase noise. 

> someone wouldn't want to take advantage of that signal and use
> that rather than add filters and poor biasing to the mix to claim that
> something can be done when we are talking about ideal situations where the
> lowest phase noise is desired.

Your claim is that harmonics in the oscillator will keep you from having low 
phase noise. That simply is not correct. 

> 
> Someday you might end up needing to design a low noise oscillator and you
> will need to consider these design obstacles.

Well oddly enough, I have designed a few (thousand) low noise oscillators over 
the
last 4 or 5 decades. I’ve also torn down more oscillators than I can count and 
looked
at how they are done. The “no limiting” crystal oscillator has never popped up 
in any 
of that. It’s also never shown up in any of the papers, going back into the 
1920’s. 

Put simply:

You (even with an AGC) will have a few db of excess gain. That gain causes part 
of the 
loop current to be converted to harmonic energy. That energy does not circulate 
with the
same efficiency as the main mode. (crystals have “harmonics”, or more commonly 
acoustic
overtones). To say that there is one part of the oscillator that is the crystal
and another part that is the sustaining stage is fine. To say that the 
oscillator is only one
or the other half of that complete circuit is not correct. 

> 
> Take care, Bob.

Have fun

Bob

> 
> Jerry
> 
> On Mon, Jul 27, 2015 at 5:39 PM, Bob Camp  wrote:
> 
>> Hi
>> 
>> 
>>> On Jul 27, 2015, at 11:52 AM, jerry shirᴀr  wrote:
>>> 
>>> Here's the rub Bob. I have been trying to find a way or have you explain
>>> how a high harmonic oscillator stage
>> 
>> You are confusing the current through the crystal with the current in the
>> oscillator transistor.
>> So:
>> 
>> Connect a 2N918 with the collector to +12V through a 50 ohm resistor. AC
>> couple that resistor to your spectrum analyzer.
>> Connect the base of the transistor with a 10K to +12 and a 10K to ground
>> Connect a 1K ohm resistor from the emitter of the transistor to ground
>> Hook a 100 pf cap from base to emitter
>> Hook a 100 pf cap from emitter to base
>> Hook a 10.0 MHz fundamental crystal with a resistance of < 10 ohms  to the
>> base of the transistor.
>> Hook a 32 pf cap from the other side of the crystal to ground
>> 
>> I *hope* that’s specific enough for you.
>> 
>> That circuit *will* oscillate.
>> 
>> Look at the current on the 50 ohm resistor. It’s got plenty of ha

Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)

[Gerhard Hoffmann]

Am 28.07.2015 um 03:58 schrieb Bill Byrom N5BB:

[ nice and understandable summary of the Lee / Hajimiri ideas ]


OTOH with this Dirac-style resonator feeding one collects the
noise sidebands from order 1 to MAXINT and one needs to align
all these harmonics nicely.

It also does not help against low frequency effects that require
stability over many cycles, such as the 1/f region.

And it is only half the work. We not only need to feed the resonator,
we also want RF from it. Thus, to stay in this principle, the sustaining
amplifier would have to fetch its input also in Dirac style.

Now we are pretty close to an  ultra wideband  nonlinear loop gain.
Any low pass filtering would have to be done in front of the feeding
pulse former, or the harmonics will not align. And apart from
BW limiting we need something to set the net loop phase to 0.

The pulse output of the sustaining amplifier is also not nice to use
unless we want to feed a sampler or 1:2-FlipFlop.

Output filtering via the resonator, say, in the elegant Burgeon(?) style
would also be forbidden.

As I see it, L/H creates a lot of problems, and worse, it does not
provide a design algorithm, even if we accept the complications.


regards, Gerhard,  DK4XP


(Arghh, I'm writing this on a 4*2 thread machine at 3.8 GHz, and
Thunderbird produces typing delays...  Turbo-C on Z80 with a
Wyse-50 terminal felt better.)


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Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)

[jerry shirᴀr]

Thanks Bob,

I had no intention of being offensive.  It is just my manner.  Forgive me.

First of all, I think you had intended to say "100pF from emitter to
ground" rather than "100pF from emitter to base."  I think that's a typo.

Next, how much crystal drive level is there?  I guess it depends on the
crystal resistance, but I think there will be a lot of crystal current.

Then I don't know why you would purposely want to clip the signal of the
oscillator, but it is the designer's prerogative.  For low noise
applications, I have always used an AGC so the oscillator will have a lot
of drive at startup and then backs off greatly for steady state operation.
You can also more easily control the drive level to a small enough amount
so that the drive won't mess up the frequency accuracy.  Also the buffer
from the oscillator stage buffers the actual crystal current so the base to
emitter noise does not get amplified to the collector and propagated down
the line.  I could beat a -145dBc/Hz spec at 100Hz and -168dBc/Hz at
10kHz.

I don't have anything here to breadboard these things up.  I don't
understand why when there is already a clean crystal current in the
circuit, someone wouldn't want to take advantage of that signal and use
that rather than add filters and poor biasing to the mix to claim that
something can be done when we are talking about ideal situations where the
lowest phase noise is desired.

Someday you might end up needing to design a low noise oscillator and you
will need to consider these design obstacles.

Take care, Bob.

Jerry

On Mon, Jul 27, 2015 at 5:39 PM, Bob Camp  wrote:

> Hi
>
>
> > On Jul 27, 2015, at 11:52 AM, jerry shirᴀr  wrote:
> >
> > Here's the rub Bob. I have been trying to find a way or have you explain
> > how a high harmonic oscillator stage
>
> You are confusing the current through the crystal with the current in the
> oscillator transistor.
> So:
>
> Connect a 2N918 with the collector to +12V through a 50 ohm resistor. AC
> couple that resistor to your spectrum analyzer.
> Connect the base of the transistor with a 10K to +12 and a 10K to ground
> Connect a 1K ohm resistor from the emitter of the transistor to ground
> Hook a 100 pf cap from base to emitter
> Hook a 100 pf cap from emitter to base
> Hook a 10.0 MHz fundamental crystal with a resistance of < 10 ohms  to the
> base of the transistor.
> Hook a 32 pf cap from the other side of the crystal to ground
>
> I *hope* that’s specific enough for you.
>
> That circuit *will* oscillate.
>
> Look at the current on the 50 ohm resistor. It’s got plenty of harmonics.
>
> With me so far or is this still to theoretical?
>
> Now, this *does* get a bit exciting, but it’s the way this circuit has
> been analyzed since the 1930’s (when it used a tube):
>
> You shift the ground to the emitter for the purposes of seeing what’s
> going on. You now have an “input side” and an “output side” to
> the active stage. This lets you break the loop for analysis.
>
> In this format, the current in the collector is more clearly flowing
> through the 1K resistor and one of the 100 pf caps.
> The current that passes through the crystal flows through the other 100 pf
> cap (and the base) to ground.
>
> The current in the oscillator stage is every bit as nonlinear as you saw
> before.
>
> Since this is an oscillator, the current flows in a loop. There is no
> independent current in any one leg. They all are related.
> If you want to see this, hook up an oscilloscope to the collector resistor
> and apply power to the oscillator. The output does not
> go instantly to a full output. It slowly builds up to the full value. The
> current circulates around the loop *many* times as the
> stage oscillates.
>
> Now:
>
> Break the circuit (AC) at any of the connection points. It stops
> oscillating. (A DC break also does the same thing, but that’s cheating).
> Without everything hooked in a loop, you do not have oscillation.
>
> Next:
>
> Charles posted a long list of interesting transistors a few messages back.
> Try them one at a time and look at phase noise at 20 KHz offset.
> You will find that some are better than others. Take a look at the
> harmonics in the collector. They don’t correlate with the phase noise…
>
> So, unless you are looking at the crystal as being the oscillator (which
> it is not), there’s not much way to say that there are no harmonics
> running around in this circuit.
>
> Is that simple enough?
>
> > is even possible and zip. You don't
> > know and I certainly don't know. So there's that.
>
> *IF* your desire is for an explanation, offensive comments probably are
> not a good idea….
>
> Bob
>
> >
> > Jerry
> > On Jul 27, 2015 9:33 AM, "Bob Camp"  wrote:
> >
> >> Hi
> >>
> >> Here’s the basic point:
> >>
> >> What is *required* for low phase noise?
> >>
> >> If you can build *one* oscillator that violates a “law” then that “law”
> is
> >> not
> >> valid. In tis case the question is “do you *need* low harmonics in the
> >> oscillato

Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)

[Bill Byrom]

Bob, I think you meant to write: "Hook a 100 pf cap from emitter
to ground."

Also remember that the feedback loop can use multiple active devices.
You can design a crystal oscillator which has only linear loading on the
crystal but which has nonlinear characteristics somewhere in the
feedback loop. Some oscillators use a filter to insure that only a
linear signal is fed back from a very nonlinear amplifier in the loop.
The output can be taken from various places in the feedback loop, and
the harmonic content varies depending on that location.

One idea is to only add energy to the crystal at the peak of the
sinewave voltage, when the derivative of the voltage is zero. If a short
pulse is added at the peak the amplitude is increased without
significantly affecting the phase. But if the pulse is added at the
middle "zero crossing" of the sinewave (with resepect to the peak-to-
peak swing) where the derivative is large, the phase can be affected by
the feedback. Ideally you want to add just enough energy each cycle to
overcome the energy lost in the crystal due to limited Q.

If the feedback loop is linear, then the noise generated by the active
and passive devices is continuously fed back to the crystal, generating
amplitude noise. Due to the angle of the feedback (described above) and
AM to PM conversion due to device characteristics (junction capacitance
changes with voltage), some of the amplitude noise gets converted to
phase noise. The total resulting noise sidebands (made up of both
ampitude and phase noise) is what everyone wants to minimize.

You could also use a feedback loop which was very nonlinear by using an
active switch with a low ON resistance (so hopefully a low noise figure
when closed) to send spikes back to the crystal resonator at the peak of
the voltage waveform. If you could arrange the circuit so that the duty
cycle of this switch was low, the residual noise would only be amplified
and fed back to the crystal resonator over a small portion of each
cycle, reducing the average noise figure of the oscillator. If the
feedback circuit is highly nonlinear the amplitude noise might be
clipped and reduced. Of course, the jitter in the feedback circuit is
important.

The active devices need to be well bypassed at audio frequencies so that
low frequency shot noise isn't amplified with high efficiency. Since the
junction capacitance (and other AM to PM conversion sources) in
downstream amplifiers can be affected by audio frequency noise, I think
that it's very important that such noise isn't allowed to phase modulate
the desired RF signal.

--
Bill Byrom N5BB
 
 
 
On Mon, Jul 27, 2015, at 05:39 PM, Bob Camp wrote:
> Hi
>  
>  
>> On Jul 27, 2015, at 11:52 AM, jerry shirᴀr  wrote:
>>  
>> Here's the rub Bob. I have been trying to find a way or have you explain
>> how a high harmonic oscillator stage
>  
> You are confusing the current through the crystal with the current in the
> oscillator transistor.
> So:
>  
> Connect a 2N918 with the collector to +12V through a 50 ohm resistor. AC
> couple that resistor to your spectrum analyzer.
> Connect the base of the transistor with a 10K to +12 and a 10K to ground
> Connect a 1K ohm resistor from the emitter of the transistor to ground
> Hook a 100 pf cap from base to emitter
> Hook a 100 pf cap from emitter to base
> Hook a 10.0 MHz fundamental crystal with a resistance of < 10 ohms  to
> the base of the transistor.
> Hook a 32 pf cap from the other side of the crystal to ground
>  
> I **hope** that’s specific enough for you.
>  
> That circuit **will** oscillate.
>  
> Look at the current on the 50 ohm resistor. It’s got plenty of harmonics.
>  
> With me so far or is this still to theoretical?
>  
> Now, this **does** get a bit exciting, but it’s the way this circuit has
> been analyzed since the 1930’s (when it used a tube):
>  
> You shift the ground to the emitter for the purposes of seeing what’s
> going on. You now have an “input side” and an “output side” to
> the active stage. This lets you break the loop for analysis.
>  
> In this format, the current in the collector is more clearly flowing
> through the 1K resistor and one of the 100 pf caps.
> The current that passes through the crystal flows through the other 100
> pf cap (and the base) to ground.
>  
> The current in the oscillator stage is every bit as nonlinear as you saw
> before.
>  
> Since this is an oscillator, the current flows in a loop. There is no
> independent current in any one leg. They all are related.
> If you want to see this, hook up an oscilloscope to the collector
> resistor and apply power to the oscillator. The output does not
> go instantly to a full output. It slowly builds up to the full value. The
> current circulates around the loop **many** times as the
> stage oscillates.
>  
> Now:
>  
> Break the circuit (AC) at any of the connection points. It stops
> oscillating. (A DC break also does the same thing, but that’s cheating).
> Without everything hooked i

Re: [time-nuts] Square to sine wave symmetrical conversion

[Bob Camp]

Hi

Just so this does not get to ghastly confusing for those trying to follow along:

 Vig, John R.; Ferre-Pikal, Eva. S.; Camparo, J. C.; Cutler, L. S.; Maleki, L.; 
Riley, W. J.; Stein, S. R.; Thomas, C.; Walls, F. L.; White, J. D. (26 March 
1999), IEEE Standard Definitions of Physical Quantities for Fundamental 
Frequency and Time Metrology – Random Instabilities, IEEE, ISBN 
 
0-7381-1754-4 
, IEEE Std 
1139-1999

On page 2 defines phase noise as:

 ℒ(f)=Sφ(f)/2 where the "phase instability" Sφ(f) is the one-sided spectral 
density of a signal's phase deviation. 

(Yes, that’s a bit of cut and paste from Wikipedia. I believe that their 
citation is correct.) 

Put another way, it’s what a phase noise test set measures (HP 3048 or 
whatever). It’s also the part of the spectral noise (as opposed to AM noise) 
that goes up 
as 20*log(N) when you multiply the signal’s frequency by N. 

Phase jitter and cycle jitter are not the same quantity. 

Bob


> On Jul 27, 2015, at 1:28 PM, Charles Steinmetz  wrote:
> 
> Bob wrote:
> 
>> In tis case the question is "do you *need* low harmonics in the oscillator
>> stage to get low phase noise?"
> 
> Note that there are actually two questions.  One is WRT the phase noise of 
> the oscillator itself, and the other WRT the phase noise of a system that 
> integrates the oscillator.  In particular, even harmonics in the oscillator 
> proper generate additional phase noise in the system when the signal is 
> AC-coupled and/or DC-restored, and when it is fed to a zero-cross detector or 
> other circuit that is sensitive to the symmetry of the waveform.
> 
> NIST published a paper on this.[1]  There is other research describing and 
> quantifying the phenomenon, as well.
> 
> Best regards,
> 
> Charles
> 
> 
> [1]  "The Effect of Harmonic Distortion on Phase errors in Frequency 
> Distribution and Synthesis," Walls and Ascarrunz  
> 
> 
> 
> 
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