Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[MLewis]

On 14/02/2017 9:23 PM, Chris Albertson wrote:

On Tue, Feb 14, 2017 at 7:31 AM, MLewis  wrote:



- a dedicated machine/box for unencumbered acceptance of PPS, and
- for systems with a business need, a dedicated NTP server/box disciplined
by the PPS source (with dedicated communication), while maintaining
internet NTP sources as backup for when the PPS source fails?
Is there a better way?
Other considerations?


Don't ever think about "backup servers".  NTP will always select the "best"
reference clocks.   The best ones are defined as the subset of references
that track each other.

Best practice today is to have two independent NTP servers and two GPS
receivers.   It is best if these are independent as you can make them,
different buildings if you can.   I would even use different brands of
hardware to protect against a bug.   Then throughout your company all your
PCs are configured to look at both NTP servers

Each server is configured to use the GPS reference clock, the other "twin"
NTP server as well as about five Internet "pool" servers.

If your location does not have an Internet connection. ( YES this can
happen.  I've worked on computers that process classified information and
these computers never have Internet access.)  You can configure them so
they run in "orphan mode" that is they all use each other as reference
clocks.  Then when GPS is lost thenoormal NTP clock selection algorithm
will select the subset of PCs that all agree on what the time is.   The
outliers tent to get ignored.When GPS comes back up the system makes a
gradual and graceful recovery.


Chris Albertson
Redondo Beach, California
That dual set model is new to me. Interesting to see its fall-back on 
failures. And the offline model.


It's the poor-man's version of that model that I was aiming for (and 
one, not two sets of receiver-with-server):
- A small box as "GPS receiver" with NTP, receiving the PPS from a GPS 
timing module.
- That box as a source to an NTP Server that also looks at six internet 
pool sources (pools are the 'backup' if GPS/receiver-box fails).

- My systems (two boxes) look to the NTP Server for their time reference.

With all everyone has responded with, as a novice to this I have a lot 
of reading to do...

then some choices to make.

Thanks to all

Michael



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[time-nuts] HP 105B FS

[Perry Sandeen via time-nuts]

List,
I'm selling my HP 105B that has been "cooking" for the last 6 months and the 
meter readings are all in the OK region and has a 5 MHz output which hasn't 
been calibrated.
It has the pre-10811 10 MHz oscillator type and the PS is the of the earlier 
version where the regulating transistor is mounted separately to the chassis.
Asking $250 plush shipping from 92220.  I can remove the original Ni-Cad 
battery for disposal at a approved disposal facility if one wishes.  This will 
reduce the shipping weight 3-5 pounds.
If interested, please send me an ORIGINAL email off list so it doesn't get 
lumped with other TN emails.
Regards,
Perrier
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Chris Albertson]

On Tue, Feb 14, 2017 at 7:31 AM, MLewis  wrote:

>
>
> - a dedicated machine/box for unencumbered acceptance of PPS, and
> - for systems with a business need, a dedicated NTP server/box disciplined
> by the PPS source (with dedicated communication), while maintaining
> internet NTP sources as backup for when the PPS source fails?
> Is there a better way?
> Other considerations?


Don't ever think about "backup servers".  NTP will always select the "best"
reference clocks.   The best ones are defined as the subset of references
that track each other.

Best practice today is to have two independent NTP servers and two GPS
receivers.   It is best if these are independent as you can make them,
different buildings if you can.   I would even use different brands of
hardware to protect against a bug.   Then throughout your company all your
PCs are configured to look at both NTP servers

Each server is configured to use the GPS reference clock, the other "twin"
NTP server as well as about five Internet "pool" servers.

If your location does not have an Internet connection. ( YES this can
happen.  I've worked on computers that process classified information and
these computers never have Internet access.)  You can configure them so
they run in "orphan mode" that is they all use each other as reference
clocks.  Then when GPS is lost thenoormal NTP clock selection algorithm
will select the subset of PCs that all agree on what the time is.   The
outliers tent to get ignored.When GPS comes back up the system makes a
gradual and graceful recovery.





Chris Albertson
Redondo Beach, California
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Denny Page]

> On Feb 14, 2017, at 15:14, J. Grizzard  wrote:
> 
> I really recommend the PC Engines apu2c hardware. Just a touch over $100,
> schematics available, hardware serial port, GPIO, 1588-capable PHY, CPU
> crystal accessible if you want to try a clockblock-type hack, great
> support, and just decent all around.
> 

Have you fit a GPS receiver to it?

Denny

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[time-nuts] Austron 1250A FS

[Perry Sandeen via time-nuts]

List,
I am selling my Austron 1250A.  The meter readings are all in the OK range and 
has a 5 MHz output which I've not calibrated. It's in good cosmetic condition.
It comes with the factory manual,extender board, relay rack mounting brackets, 
spare fuses and a AN connector for attaching an external battery pack. The one 
problem it may have as I was told when I bought it is that the rear EFC might 
not work. (I never took the time to find out if it is a problem,  I just 
powered it up.  Has been in continuous operation for over 6 months.) 
Asking $250 plus shipping from 92220.  If the buyer wishes, I can remove the 
Ni-Cad battery pack and dispose of it in an approved recycler and save some 
money on the shipping.
If interested, please send me an ORIGINAL email so it won't get mixed in the TN 
nuts posts.
Regards,
Perrier



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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[J. Grizzard]

I really recommend the PC Engines apu2c hardware. Just a touch over $100,
schematics available, hardware serial port, GPIO, 1588-capable PHY, CPU
crystal accessible if you want to try a clockblock-type hack, great
support, and just decent all around.

There's also test pads for the PHY that could be used to do PPS directly
to that for PTP purposes, but I haven't quite yet figured out exactly
how to set that up. But the pads are there!

(hint: Order direct from manufacturer, not via a US distributor. You'll
save money and the shipping is still really quite fast.)

-j

On Tue, Feb 14, 2017 at 05:26:16PM -0500, Scott Stobbe wrote:
> Something like this would make a great NTP server.
> https://www.digikey.com/products/en?keywords=P0286-ND
> 
> Too bad they didn't include a PTP 1588 capable PHY...
> 
> On Tue, Feb 14, 2017 at 12:33 PM, Chris Albertson  > wrote:
> 
> > Here is a something that could work.  It has a real serial port and you
> > could add more ethernet controllers, uses very little power and cost only
> > $60.
> > www.newegg.com/
> >  > N82E16813157497_re=j1900-_-13-157-497-_-Product>
> >
> > There are other boards like this that use the same J1900 CPU.   I'm
> > thinking about using this as th machine tool (milling machine) controller.
> >
> > On Tue, Feb 14, 2017 at 4:26 AM, Bob Camp  wrote:
> >
> > > Hi
> > >
> > > A direct port might be a +/- 100 ns sort of thing most of the time and a
> > > +/-10 us
> > > thing every so often under some OS???s. Most desktop operating systems are
> > > not
> > > designed to prioritize random pin interrupts. A dirt cheap MCU coded with
> > > a few
> > > (hundred) lines of assembly code may be a better option than a typical
> > > desktop.
> > > Complicating this further is the degree to which some OS???s can be
> > directly
> > > or
> > > indirectly optimized. Install *this* package and it all goes nuts.
> > Install
> > > that package
> > >  and not much happens ???.
> > >
> > > Bob
> > >
> > > > On Feb 13, 2017, at 11:07 AM, Ruslan Nabioullin  > >
> > > wrote:
> > > >
> > > > Hi, generally speaking, what are the performance differences between
> > the
> > > following: 1. direct RS-232 (i.e., what I believe is a standard PCI card
> > > offering RS-232---essentially UARTs interfaced more-or-less directly to
> > the
> > > PCI bus); 2. RS-232 via USB; 3. PPS decoding PCI cards (which might also
> > > have an IRIG input or even an onboard GNSS receiver).
> > > >
> > > > Thanks in advance,
> > > > Ruslan
> > > > ___
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> > >
> >
> >
> >
> > --
> >
> > Chris Albertson
> > Redondo Beach, California
> > ___
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Bob Camp]

Hi

If you want a 1588 PHY and are on a budget:

https://www.digikey.com/products/en/development-boards-kits-programmers/evaluation-boards-embedded-mcu-dsp/786?k=freescale+freedom==freescale+freedom=24619=ffe00312%2C7e80098=0=0=0=1=0=0=0=25

Drop NTP into it and let it rip.

Bob


> On Feb 14, 2017, at 5:26 PM, Scott Stobbe  wrote:
> 
> Something like this would make a great NTP server.
> https://www.digikey.com/products/en?keywords=P0286-ND
> 
> Too bad they didn't include a PTP 1588 capable PHY...
> 
> On Tue, Feb 14, 2017 at 12:33 PM, Chris Albertson > wrote:
> 
>> Here is a something that could work.  It has a real serial port and you
>> could add more ethernet controllers, uses very little power and cost only
>> $60.
>> www.newegg.com/
>> > N82E16813157497_re=j1900-_-13-157-497-_-Product>
>> 
>> There are other boards like this that use the same J1900 CPU.   I'm
>> thinking about using this as th machine tool (milling machine) controller.
>> 
>> On Tue, Feb 14, 2017 at 4:26 AM, Bob Camp  wrote:
>> 
>>> Hi
>>> 
>>> A direct port might be a +/- 100 ns sort of thing most of the time and a
>>> +/-10 us
>>> thing every so often under some OS’s. Most desktop operating systems are
>>> not
>>> designed to prioritize random pin interrupts. A dirt cheap MCU coded with
>>> a few
>>> (hundred) lines of assembly code may be a better option than a typical
>>> desktop.
>>> Complicating this further is the degree to which some OS’s can be
>> directly
>>> or
>>> indirectly optimized. Install *this* package and it all goes nuts.
>> Install
>>> that package
>>> and not much happens ….
>>> 
>>> Bob
>>> 
 On Feb 13, 2017, at 11:07 AM, Ruslan Nabioullin >> 
>>> wrote:
 
 Hi, generally speaking, what are the performance differences between
>> the
>>> following: 1. direct RS-232 (i.e., what I believe is a standard PCI card
>>> offering RS-232---essentially UARTs interfaced more-or-less directly to
>> the
>>> PCI bus); 2. RS-232 via USB; 3. PPS decoding PCI cards (which might also
>>> have an IRIG input or even an onboard GNSS receiver).
 
 Thanks in advance,
 Ruslan
 ___
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 To unsubscribe, go to https://www.febo.com/cgi-bin/
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>>> 
>> 
>> 
>> 
>> --
>> 
>> Chris Albertson
>> Redondo Beach, California
>> ___
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Scott Stobbe]

Something like this would make a great NTP server.
https://www.digikey.com/products/en?keywords=P0286-ND

Too bad they didn't include a PTP 1588 capable PHY...

On Tue, Feb 14, 2017 at 12:33 PM, Chris Albertson  wrote:

> Here is a something that could work.  It has a real serial port and you
> could add more ethernet controllers, uses very little power and cost only
> $60.
> www.newegg.com/
>  N82E16813157497_re=j1900-_-13-157-497-_-Product>
>
> There are other boards like this that use the same J1900 CPU.   I'm
> thinking about using this as th machine tool (milling machine) controller.
>
> On Tue, Feb 14, 2017 at 4:26 AM, Bob Camp  wrote:
>
> > Hi
> >
> > A direct port might be a +/- 100 ns sort of thing most of the time and a
> > +/-10 us
> > thing every so often under some OS’s. Most desktop operating systems are
> > not
> > designed to prioritize random pin interrupts. A dirt cheap MCU coded with
> > a few
> > (hundred) lines of assembly code may be a better option than a typical
> > desktop.
> > Complicating this further is the degree to which some OS’s can be
> directly
> > or
> > indirectly optimized. Install *this* package and it all goes nuts.
> Install
> > that package
> >  and not much happens ….
> >
> > Bob
> >
> > > On Feb 13, 2017, at 11:07 AM, Ruslan Nabioullin  >
> > wrote:
> > >
> > > Hi, generally speaking, what are the performance differences between
> the
> > following: 1. direct RS-232 (i.e., what I believe is a standard PCI card
> > offering RS-232---essentially UARTs interfaced more-or-less directly to
> the
> > PCI bus); 2. RS-232 via USB; 3. PPS decoding PCI cards (which might also
> > have an IRIG input or even an onboard GNSS receiver).
> > >
> > > Thanks in advance,
> > > Ruslan
> > > ___
> > > 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.
> >
>
>
>
> --
>
> Chris Albertson
> Redondo Beach, California
> ___
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Tom Van Baak]

> Hence, wouldn't Best Practice be boxes loaded with only the bare OS and 
> software for the time-related tasks?

If you find yourself in a situation like this -- where your timing seems to 
improve the less load you have -- that's a sure sign that you're doing the 
timing wrong in the first place.

Best practices are to do 1PPS timing in hardware using capture registers (which 
almost every microcontroller has). That way there's a separation between the 
critical act of *making* a timing measurement from the non-critical act of 
*delivering* the measurement result the operating system. You still use 
interrupts -- but now the purpose of the interrupt is simply to indicate that a 
fresh measurement result is ready, rather than the interrupt itself being the 
measurement. The result is that the time stamp / capture register method is 
immune to interrupt latency and system load issues.

Best practices number two are to replace the crystal on the motherboard with a 
TCXO or OCXO. Then, with the help of NTP, your computer is finally acting like 
a GPSDO.

/tvb

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Re: [time-nuts] Vintage Frequency Measurement

[Peter Vince]

On 14 February 2017 at 04:23, Raj  wrote:

> I have a Marconi T.F. 643 C, in Megacycles !
>

Ah, a sensible, descriptive name for the unit.  Some of these modern units
really do Hert(z) :-)

 Peter
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Re: [time-nuts] Vintage Frequency Measurement

[Bob Camp]

HI

What frequency is the crystal and what sized package is it in? 

Bob

> On Feb 14, 2017, at 11:20 AM, Scott Stobbe  wrote:
> 
> Taking a second look in the manual, they specifically call out that its not
> an AT or BT, so I'm not sure what it would be.
> 
> Interestingly they describe the thermometer as space-saving and trouble
> free alternative to a heater and thermostat apparatus (I guess they weren't
> called ovens yet?)
> 
> On Mon, Feb 13, 2017 at 10:11 PM, Bob Camp  wrote:
> 
>> Hi
>> 
>> 
>>> On Feb 13, 2017, at 8:15 PM, Scott Stobbe 
>> wrote:
>>> 
>>> On Mon, Feb 13, 2017 at 6:41 PM, Bob Camp  wrote:
>>> 
 
 
 I think what you would find is that it *is* a fairly normal AT cut and
>> the
 data book
 that came with the instrument plotted out the data for the specific
 crystal in
 the device. The usable temperature range was fairly small, so the plot
>> will
 be pretty linear.
 
>>> 
>>> Attached is a plot of crystal calibrators temperature stability. Span is
>>> roughly 65 degC.
>> 
>> Which eyeballs out to be pretty close to an AT. Without knowing the PPM
>> scale there isn’t much way to be sure.
>> 
>>> 
>>> One of the other aspects I think is intriguing is the DC PSRR of a vacuum
>>> tube crystal oscillator. In the case of a bjt based oscillator you have
>> the
>>> C-V relation for depletion capacitance and the base-emitter dynamic
>>> capacitance as a function of collector current. I would suspect that for
>> a
>>> one active device oscillator, tube vs bjt, a tube crystal oscillator
>> would
>>> be less sensitive to small power supply variations (+- 10% ).
>> 
>> Except you *do* have miller effect which pretty much messes things up
>> for a triode. A pentode is a bit less sensitive, but you still have issues.
>> 
>>> Which is a
>>> convenient attribute for a poorly/unregulated battery supply in the
>> vacuum
>>> tube case. Unless filament current has an appreciable impact on
>> frequency,
>>> I wouldn't think so…
>> 
>> Umm… e …. check it out :)
>> Oddly enough, I remember a high school physics lab where they had us plot
>> the effect of filament voltage on plate current and gain. Seemed like a
>> weird
>> thing to do to me at the time. Turns out the teacher grew up with
>> microwave tubes
>> that were tuned by varying the filament. Who knew ???  Pretty strange
>> stuff if
>> you ask me.
>> 
>> The bigger issue is the tubes get hot. The heat varies with supply voltage.
>> Temperature change is the result. That temperature change messes up
>> oscillator stability. You pretty much have to wait for things to hit
>> equilibrium
>> before you do useful stuff ( = let it warm up for an hour or four).
>> 
>> Bob
>> 
>> 
>> 
>>> __
>> _
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Bob Camp]

Hi

> On Feb 14, 2017, at 10:31 AM, MLewis  wrote:
> 
> 
> 
> On 14/02/2017 7:26 AM, Bob Camp wrote:
>> Hi
>> 
>> A direct port might be a +/- 100 ns sort of thing most of the time and a 
>> +/-10 us
>> thing every so often under some OS’s. Most desktop operating systems are not
>> designed to prioritize random pin interrupts. A dirt cheap MCU coded with a 
>> few
>> (hundred) lines of assembly code may be a better option than a typical 
>> desktop.
>> Complicating this further is the degree to which some OS’s can be directly or
>> indirectly optimized. Install *this* package and it all goes nuts. Install 
>> that package
>>  and not much happens ….
>> 
>> Bob
>> 
> Hence, wouldn't Best Practice be boxes loaded with only the bare OS and 
> software for the time-related tasks?

That would be one approach.

> As in:
> - a dedicated machine/box for unencumbered acceptance of PPS, and
> - for systems with a business need, a dedicated NTP server/box disciplined by 
> the PPS source (with dedicated communication), while maintaining internet NTP 
> sources as backup for when the PPS source fails?
> Is there a better way?

It depends on what you are trying to do. If the objective is to replace a piece 
of test gear
logging 100% of your events at the 100ns level, the computer likely will not 
measure up. If the objective is to run
NTP at the 100 us level, there are a lot more things you can get away with. NTP 
is designed from the 
ground up to be quite tolerant of various issues. 

Bob

> Other considerations?
> 
> Michael
> 
> 
> 
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Chris Albertson]

Here is a something that could work.  It has a real serial port and you
could add more ethernet controllers, uses very little power and cost only
$60.
www.newegg.com/


There are other boards like this that use the same J1900 CPU.   I'm
thinking about using this as th machine tool (milling machine) controller.

On Tue, Feb 14, 2017 at 4:26 AM, Bob Camp  wrote:

> Hi
>
> A direct port might be a +/- 100 ns sort of thing most of the time and a
> +/-10 us
> thing every so often under some OS’s. Most desktop operating systems are
> not
> designed to prioritize random pin interrupts. A dirt cheap MCU coded with
> a few
> (hundred) lines of assembly code may be a better option than a typical
> desktop.
> Complicating this further is the degree to which some OS’s can be directly
> or
> indirectly optimized. Install *this* package and it all goes nuts. Install
> that package
>  and not much happens ….
>
> Bob
>
> > On Feb 13, 2017, at 11:07 AM, Ruslan Nabioullin 
> wrote:
> >
> > Hi, generally speaking, what are the performance differences between the
> following: 1. direct RS-232 (i.e., what I believe is a standard PCI card
> offering RS-232---essentially UARTs interfaced more-or-less directly to the
> PCI bus); 2. RS-232 via USB; 3. PPS decoding PCI cards (which might also
> have an IRIG input or even an onboard GNSS receiver).
> >
> > Thanks in advance,
> > Ruslan
> > ___
> > 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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>



-- 

Chris Albertson
Redondo Beach, California
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[time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Mark Sims]

Beware of Atom based devices...  Many of the Atom chips have a problem where a 
couple of the critical clock output signals have a design problem and they 
start failing after around 18 months.  This problem just became public in the 
last month or so when Cisco warned of impending failures in a lot their routers.

---

> There is a whole class of low power mother boards targeted at the embedded 
market.  A few of them have multiple Ethernets - goof for building firewalls. 
 I haven't found any low cost ones.
  http://www.mini-box.com/Atom
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[MLewis]

On 14/02/2017 7:26 AM, Bob Camp wrote:

Hi

A direct port might be a +/- 100 ns sort of thing most of the time and a +/-10 
us
thing every so often under some OS’s. Most desktop operating systems are not
designed to prioritize random pin interrupts. A dirt cheap MCU coded with a few
(hundred) lines of assembly code may be a better option than a typical desktop.
Complicating this further is the degree to which some OS’s can be directly or
indirectly optimized. Install *this* package and it all goes nuts. Install that 
package
  and not much happens ….

Bob

Hence, wouldn't Best Practice be boxes loaded with only the bare OS and 
software for the time-related tasks?

As in:
- a dedicated machine/box for unencumbered acceptance of PPS, and
- for systems with a business need, a dedicated NTP server/box 
disciplined by the PPS source (with dedicated communication), while 
maintaining internet NTP sources as backup for when the PPS source fails?

Is there a better way?
Other considerations?

Michael



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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Denny Page]

> On Feb 13, 2017, at 23:47, Hal Murray  wrote:
> 
> There is a whole class of low power mother boards targeted at the embedded 
> market.  A few of them have multiple Ethernets - goof for building firewalls. 
> I haven't found any low cost ones.

This one might be of interest:

https://www.kickstarter.com/projects/874883570/marvell-espressobin-board?token=6a67e544
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[time-nuts] Hp5065A temperature sensitivity

[timeok]

   Another info about the HP5065A.
   Some test Cooling the HP5065A from 39.5 to 29.5°C (chassis temperature) show 
a 2E-13 / °C, positive slope.
   The first graph show the frequency drift, the second the temperature drop 
and the voltage at the A15 pin 2 (magnetic field set point regulator).
   I am working on a project to compensate pressure and temperature starting 
from the Corby Dawson study.
   I am planning to made an smd version of the board.
   This circuit with some minor change can be applied to any Rubidium standard.
   Luciano
   Timeok


[GPIB0--9--INSTR].pdf
Description: Adobe PDF document
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Re: [time-nuts] Vintage Frequency Measurement

[Bob Camp]

Hi

That was one of the reasons I was a bit amazed high school students
were doing it as a lab exercise. The presence of high voltage here and 
there is something that you simply would not see in a similar school
today …

Bob

> On Feb 13, 2017, at 11:19 PM, Alex Pummer  wrote:
> 
> just be careful, because if you under-heat the cathode you could kill it
> 
> 73
> 
> Alex
> 
> 
> On 2/13/2017 7:11 PM, Bob Camp wrote:
>> Hi
>> 
>> 
>>> On Feb 13, 2017, at 8:15 PM, Scott Stobbe  wrote:
>>> 
>>> On Mon, Feb 13, 2017 at 6:41 PM, Bob Camp  wrote:
>>> 
 
 I think what you would find is that it *is* a fairly normal AT cut and the
 data book
 that came with the instrument plotted out the data for the specific
 crystal in
 the device. The usable temperature range was fairly small, so the plot will
 be pretty linear.
 
>>> Attached is a plot of crystal calibrators temperature stability. Span is
>>> roughly 65 degC.
>> Which eyeballs out to be pretty close to an AT. Without knowing the PPM
>> scale there isn’t much way to be sure.
>> 
>>> One of the other aspects I think is intriguing is the DC PSRR of a vacuum
>>> tube crystal oscillator. In the case of a bjt based oscillator you have the
>>> C-V relation for depletion capacitance and the base-emitter dynamic
>>> capacitance as a function of collector current. I would suspect that for a
>>> one active device oscillator, tube vs bjt, a tube crystal oscillator would
>>> be less sensitive to small power supply variations (+- 10% ).
>> Except you *do* have miller effect which pretty much messes things up
>> for a triode. A pentode is a bit less sensitive, but you still have issues.
>> 
>>> Which is a
>>> convenient attribute for a poorly/unregulated battery supply in the vacuum
>>> tube case. Unless filament current has an appreciable impact on frequency,
>>> I wouldn't think so…
>> Umm… e …. check it out :)
>> Oddly enough, I remember a high school physics lab where they had us plot
>> the effect of filament voltage on plate current and gain. Seemed like a weird
>> thing to do to me at the time. Turns out the teacher grew up with microwave 
>> tubes
>> that were tuned by varying the filament. Who knew ???  Pretty strange stuff 
>> if
>> you ask me.
>> 
>> The bigger issue is the tubes get hot. The heat varies with supply voltage.
>> Temperature change is the result. That temperature change messes up
>> oscillator stability. You pretty much have to wait for things to hit 
>> equilibrium
>> before you do useful stuff ( = let it warm up for an hour or four).
>> 
>> Bob
>> 
>> 
>> 
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> 
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Bob Camp]

Hi

A direct port might be a +/- 100 ns sort of thing most of the time and a +/-10 
us 
thing every so often under some OS’s. Most desktop operating systems are not
designed to prioritize random pin interrupts. A dirt cheap MCU coded with a few
(hundred) lines of assembly code may be a better option than a typical desktop. 
Complicating this further is the degree to which some OS’s can be directly or
indirectly optimized. Install *this* package and it all goes nuts. Install that 
package
 and not much happens ….

Bob

> On Feb 13, 2017, at 11:07 AM, Ruslan Nabioullin  wrote:
> 
> Hi, generally speaking, what are the performance differences between the 
> following: 1. direct RS-232 (i.e., what I believe is a standard PCI card 
> offering RS-232---essentially UARTs interfaced more-or-less directly to the 
> PCI bus); 2. RS-232 via USB; 3. PPS decoding PCI cards (which might also have 
> an IRIG input or even an onboard GNSS receiver).
> 
> Thanks in advance,
> Ruslan
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Hal Murray]

mlewis...@rogers.com said:
> Know of any with an Ethernet port, preferably two, that aren't run from  a
> USB controller?

You didn't put a qualifier on your "any".  (or I missed it)

If you want a Raspberry Pi class board, the BeagleBone Black has a real 
Ethernet, but only one.

If you need 2 real Ethernets, the cheapest approach is probably to get an old 
PC with PCI slots and add a PCI Ethernet card.

There is a whole class of low power mother boards targeted at the embedded 
market.  A few of them have multiple Ethernets - goof for building firewalls. 
 I haven't found any low cost ones.
  http://www.mini-box.com/Atom

Soekris has various boards with multiple Ethernets and no display.
  http://soekris.com/products.html


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

[Hal Murray]

rnabioul...@gmail.com said:
> Hi, generally speaking, what are the performance differences between the
> following: 1. direct RS-232 (i.e., what I believe is a standard PCI card
> offering RS-232---essentially UARTs interfaced more-or-less directly to  the
> PCI bus); 2. RS-232 via USB; 3. PPS decoding PCI cards (which might  also
> have an IRIG input or even an onboard GNSS receiver). 

You didn't say what you are trying to do.

Most OSes can grab a time-stamp when a modem control signal changes.  (I know 
nothing about Windows.)

Latency will depend on the IO hardware, CPU architecture,, the interrupt 
software, and what the CPU is doing: other interrupts, cache faults, and 
stuff like that.

With RS-232 on PCI, the latency in the hardware should be low, as in sub 
microsecond.

USB is polled.  That adds the noise/jitter of the polling interval and the 
opportunities for hanging bridges.
  http://www.leapsecond.com/pages/m12/sawtooth.htm
(That page shows the interaction between the PPS and the GPS receiver clock.  
You get similar graphs with the interaction between PPS and USB clock.)

Most low cost RS-232/USB units are old/slow USB 1.  That polls at 1 ms.  
There is at least 1 chip (FTDI FT232RL) that uses USB 2 which is 8 times 
faster.
  I got a breakout board (TTL levels, not RS-232) from Sparkfun.
https://www.sparkfun.com/products/12731
  Adafruit has USB-RS232 version.  I haven't tried one.
https://www.adafruit.com/product/18

I don't know of any advantages of putting the GPS receiver on the PCI card.  
(other than the obvious of one less lump that needs space on a shelf)

If you have custom logic on a PCI chip, it should be reasonable to get better 
timing.  The simple approach would be to just put a DDS style counter out there 
so reading the clock is as simple as an IO read.  But IO reads are slow.  There 
should be a way to calibrate how slow that is and then use that to calibrate 
normal time keeping.


albertson.ch...@gmail.com said:
> I said "two orders of magnitude"  it might even be three orders. 

3 seems reasonable.  That's milli-second to micro-second.



I think the Linux PPS code has an option to flap a pin on the printer port when 
it sees a PPS.  The idea is that you can measure the latency with a scope: 
trigger on PPS and see how long until the printer pin changes.  I haven't tried 
it.

-- 
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