Re: [time-nuts] A silly question ...

[Bill Byrom]

In addition to nonlinear issues with output amplifiers,  filters have
poor performance when improperly terminated. This can lead to harmonic
distortion and that can be a problem. You want the duty cycle to be
exactly 50%. See:https://tf.boulder.nist.gov/general/pdf/1437.pdf
--
Bill Byrom N5BB



On Fri, Sep 28, 2018, at 10:30 AM, Dana Whitlow wrote:
> Hi,
> 
> There is one other issue that can bite you if you fail to properly
> terminate the output of a source:
> 
> Depending on the source's design, an essentially unloaded output
> can have a substantially higher voltage swing than expected (by
> 2X if the source impedance is actually 50 ohms), possibly leading
> to the output stage's going into clipping, which can in turn distort
> the timing, possibly even in an unstable manner.
> So if you want to play the "unterminated game", at least take a
> look at the waveform to be sure it's still a clean sinewave.  I've
> noticed such distortion on my PRS-10, for example, although I've
> seen no evidence of unstable timing results.  But in this arena,
> it generally pays to be fussy.
> 
> Dana Whitlow
> 
> On Fri, Sep 28, 2018 at 7:06 AM Bill Byrom
>  wrote:> 
>> On Thu, Sep 27, 2018, at 11:55 AM, Dave B via time-nuts wrote:
>>> Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and
>>> having>>> the output of the OCXO on Ch2, the resulting display on Ch2 of
>> course>>> drifts in relation to the static waveform on Ch1.  (Both nice
>>> sinusoids.)
>> The Tek 465 analog cathode ray oscilloscope was/is a very flexible
>> instrument. But this flexibility allows you to set up the
>> instrument in>> ways which will not allow this commonly used oscillator 
>> comparison
>> technique to work correctly. Since you are interested in these
>> instruments, here are some details about setting up the
>> instrument for>> such comparisons.
>> (1) The Tek 465 is not a dual beam oscilloscope. Dual beam
>> oscilloscopes>>   (such as the Tektronix 556 and 7844) use a special CRT 
>> which
>>   incorporates two independent electron guns. Each electron gun
>>   assembly has a set of vertical and horizontal deflection plates.
>>   There are two vertical amplifiers (one for each electron gun) and
>>   two horizontal sweep systems (one for each electron gun). If
>>   you had>>   a dual beam oscilloscope you could compare oscillator#1 to
>>   oscillator#2 while  simultaneously comparing oscillator#3 with
>>   oscillator#4. It's like having two independent oscilloscopes
>>   sharing>>   the same CRT display.
>> (2) The Tek 465 single beam oscilloscope can display two  traces on
>> the>>   display using one of two methods:(a) Chopped trace display:
>>   This mode>> works well at low sweep rates (such
>>   as 1 ms/div) but causes trouble at fast sweep rates (such as 1
>>   us/div). The displayed trace is switched between Channel 1 and
>>   Channel 2 at a fixed rate of about 500 kHz.(b) Alternate trace
>> display: This mode works well at high sweep rates
>>   but is hard to see at low sweep rates. The scope alternates between>>   
>> displaying one sweep of Channel 1 and one sweep of Channel 2.
>> (3) The trigger source setting is crucial to using this technique to>>   
>> compare oscillators. The technique does not require you to display>>   two 
>> channels. What is important is that you display one oscillator>>   while 
>> triggering on the other oscillator. The trigger source can
>>   be set to:(a) CH 1: The Channel 2 display will drift if the two
>> signals have a
>>   varying phase relationship.(b) CH 2: The Channel 1 display will
>>   drift>> if the two signals have a
>>   varying phase relationship.(c) NORM (normal): The trigger
>>   system gets>> input from the channel being
>>   displayed at that moment. So in chopped trace display mode the
>>   trigger is rapidly switched between CH1 and CH2, and in alternate
>>   trace display mode the trigger alternates between CH1 and CH2 on
>>   alternate sweeps. In all cases, you should not use NORM trigger
>>   source with both channels displayed when comparing oscillators!(d)>> EXT: 
>> You apply the trigger signal to the external trigger input
>>   connector. This works well well when comparing oscillators. If you>>   use 
>> alternate trace display mode and an external trigger, you can
>>   compare oscillator#1 (on CH 1) to oscillator#0 (on the external
>>   trigger input) while you are also comparing oscillator#2 (on CH2)
>>   oscillator#0. So you could compare two oscillators (one on CH1 and>>   the 
>> other on CH2) to a GPSDO (on the external trigger input).
>> (4) When comparing oscillators, the fractional frequency difference
>>   (such as ppm Parts Per Million or ppb Parts Per Billion) you can
>>   measure depends on the oscilloscope sweep rate. What you are really>>   
>> measuring is the drift of the time delay between the edge (or zero>>   
>> crossing of a sine wave) of one signal relative to an edge or zero>>   
>> crossing of another signal. The relationship 

Re: [time-nuts] XKCD on time :)

[Dana Whitlow]

David Van Horn,

You're on the right track, but what would you do about those pesky leap
seconds?

Dana


On Fri, Sep 28, 2018 at 2:48 PM Artek Manuals 
wrote:

> H  Farce-Book hadn't considered that approach .. some sort
> of (ready for this )
>
> "subliminal millennial  mind control" !!
>
>   The gnomes and I will go to work on it immediately !
>
> -DC
>
> On 9/28/2018 3:11 PM, David Van Horn wrote:
> > By expanding facebook significantly, I plan to keep the millennials
> occupied in such a way that they are peaceful, happy, and complacent.
> > Ad revenues could support the whole program.
> >
> > Solid state electronics seems to be something we will need to tolerate,
> but we can require tubes to be allowed to participate.
> >
> > 
> >
> > -Original Message-
> > From: time-nuts  On Behalf Of Artek
> Manuals
> > Sent: Friday, September 28, 2018 12:55 PM
> > To: time-nuts@lists.febo.com >> skipp via time-nuts <
> time-nuts@lists.febo.com>
> > Subject: Re: [time-nuts] XKCD on time
> >
> > David
> >
> > 1) Before I make a donation what is your plan to control the
> millennial's ?
> >
> > 2) Could we outlaw solid state electronics (or at least custom IC's) and
> go back to vacuum tubes while we are at
> >
> > Dave
> >
> > On 9/28/2018 1:53 PM, Martin VE3OAT wrote:
> >> I love GMT.  All of this UTC stuff is ... revisionist!
> >> My cheque is in the mail.
> >> ... MartinVE3OAT
> >>
> >> David Van Horn wrote :
> >>> When I am global dictator, we will all run on GMT and all time
> >>> zones, summer time, DST and similar nonsense will be abolished.
> >>>
> >>> I am accepting campaign donations!  ?
> >>>
> >> ___
> >> time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go
> >> to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> >> and follow the instructions there.
> >>
> > --
> > Dave
> > manu...@artekmanuals.com
> > www.ArtekManuals.com
> >
> >
> > ---
> > This email has been checked for viruses by Avast antivirus software.
> > https://www.avast.com/antivirus
> >
> >
> > ___
> > time-nuts mailing list -- time-nuts@lists.febo.com
> > To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
> > ___
> > time-nuts mailing list -- time-nuts@lists.febo.com
> > To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
>
> --
> Dave
> manu...@artekmanuals.com
> www.ArtekManuals.com
>
>
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>
___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

Re: [time-nuts] XKCD on time :)

[Artek Manuals]

H  Farce-Book hadn't considered that approach .. some sort 
of (ready for this )


"subliminal millennial  mind control" !!

 The gnomes and I will go to work on it immediately !

-DC

On 9/28/2018 3:11 PM, David Van Horn wrote:

By expanding facebook significantly, I plan to keep the millennials occupied in 
such a way that they are peaceful, happy, and complacent.
Ad revenues could support the whole program.

Solid state electronics seems to be something we will need to tolerate, but we 
can require tubes to be allowed to participate.



-Original Message-
From: time-nuts  On Behalf Of Artek Manuals
Sent: Friday, September 28, 2018 12:55 PM
To: time-nuts@lists.febo.com >> skipp via time-nuts 
Subject: Re: [time-nuts] XKCD on time

David

1) Before I make a donation what is your plan to control the millennial's ?

2) Could we outlaw solid state electronics (or at least custom IC's) and go 
back to vacuum tubes while we are at

Dave

On 9/28/2018 1:53 PM, Martin VE3OAT wrote:

I love GMT.  All of this UTC stuff is ... revisionist!
My cheque is in the mail.
... Martin    VE3OAT

David Van Horn wrote :

When I am global dictator, we will all run on GMT and all time
zones, summer time, DST and similar nonsense will be abolished.

I am accepting campaign donations!  ?


___
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go
to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.


--
Dave
manu...@artekmanuals.com
www.ArtekManuals.com


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.


--
Dave
manu...@artekmanuals.com
www.ArtekManuals.com


___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

Re: [time-nuts] XKCD on time

[David Van Horn]

By expanding facebook significantly, I plan to keep the millennials occupied in 
such a way that they are peaceful, happy, and complacent.
Ad revenues could support the whole program.

Solid state electronics seems to be something we will need to tolerate, but we 
can require tubes to be allowed to participate.



-Original Message-
From: time-nuts  On Behalf Of Artek Manuals
Sent: Friday, September 28, 2018 12:55 PM
To: time-nuts@lists.febo.com >> skipp via time-nuts 
Subject: Re: [time-nuts] XKCD on time

David

1) Before I make a donation what is your plan to control the millennial's ?

2) Could we outlaw solid state electronics (or at least custom IC's) and go 
back to vacuum tubes while we are at

Dave

On 9/28/2018 1:53 PM, Martin VE3OAT wrote:
> I love GMT.  All of this UTC stuff is ... revisionist!
> My cheque is in the mail.
> ... Martin    VE3OAT
>
> David Van Horn wrote :
> >
> > When I am global dictator, we will all run on GMT and all time 
> > zones, summer time, DST and similar nonsense will be abolished.
> >
> > I am accepting campaign donations!  ?
> >
>
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go 
> to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>

--
Dave
manu...@artekmanuals.com
www.ArtekManuals.com


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

Re: [time-nuts] XKCD on time

[Artek Manuals]

David

1) Before I make a donation what is your plan to control the millennial's ?

2) Could we outlaw solid state electronics (or at least custom IC's) and 
go back to vacuum tubes while we are at


Dave

On 9/28/2018 1:53 PM, Martin VE3OAT wrote:

I love GMT.  All of this UTC stuff is ... revisionist!
My cheque is in the mail.
... Martin    VE3OAT

David Van Horn wrote :
>
> When I am global dictator, we will all run on GMT and all time
> zones, summer time, DST and similar nonsense will be abolished.
>
> I am accepting campaign donations!  ?
>

___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com

and follow the instructions there.



--
Dave
manu...@artekmanuals.com
www.ArtekManuals.com


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

[time-nuts] Shera Data Output format?

[Dan Rae]

I'm trying to interpret the Data output from my recently resurrected 
Shera GPSDO. now with the last version of the PIC firmware.


The first block is the Phase difference, and the second the DAC value, 
that I understand.  The third block has five digits; what I don't get 
nor can find anything about are the meaning of these. The last digit is 
apparently the Value of N, the third seems to show 1 when the "High" LED 
is on, but what is the significance of the fourth digit, 5 in the 
snippet below.  I see it doesn't change when I implemented the AutoN 
facility below.


Any insight will be gratefully received!

Dan

00773 00175 00052
00774 00165 00052
00774 00167 00053
00776 00152 00053
00778 00137 00053
00775 00161 00053
00775 00163 00053
00775 00164 00053
00779 00133 00053
00776 00157 00053
00773 00183 00053
00776 00160 00053
00771 00202 00053
00777 00155 00053
00775 00172 00053
00778 00149 00053
00778 00150 00053
N05#0
5
00779 00142 00053
00777 00158 00053
00779 00143 00053
00777 00159 00053
00778 00152 00053
00778 00153 00053
00776 00169 00053


___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

Re: [time-nuts] A silly question ...

[Tom Curlee]

This is assuming that your oscilloscope is set at 100 nS/DIV.  My Tek 2465A 
will sweep at 5 nS/DIV normally, and 500 pS/DIV when the sweep is set to X10.  
If I'm figuring correctly, this will allow 1e-12 in 432 seconds.  I use a stop 
watch to time the zero crossings of the sine wave - something like:

Assuming the wave moved 5 divisions in 185 seconds:   (500 pS * 5 DIV)/185 
seconds = 13.5e-12 ppm.    (I think this is correct.  tvb?)

Since a 10 MHz sine wave tends to look like a flat line at 500 pS/DIV, I often 
set the vertical V/DIV to 2 mV/DIV.

Tom




  From: Tom Van Baak 
 To: Discussion of precise time and frequency measurement 
 
 Sent: Thursday, September 27, 2018 11:19 AM
 Subject: Re: [time-nuts] A silly question ...
   
> "I think", that if for example, it takes 1 second to drift one cycle,
> that works out at 0.1 ppm. If it takes 2 seconds, it's 0.05 ppm, if it
> takes 5 seconds, it's 0.02 ppm etc. Is that correct?

Yes. At 10 MHz one full cycle is 100 ns. So if the cycles are drifting by 100 
ns per second that's 100e-9 s / 1 s = 1e-7 = 0.1 ppm.

At these levels of frequency accuracy, using a 'scope is plenty good enough. In 
fact, it's more educational and somehow more enjoyable to watch analog 
sinewaves drift past each other than it is to see the digital display of boring 
frequency counter.

Where the 'scope method starts to break down is when the frequency error gets 
down to the ppb level. At 1e-9 it will take 100 s for the waveforms to drift by 
one cycle. And at 1e-12 you would have to wait an entire day (100 ns / 86400 s 
= 1.157e-12).

On the other hand, with frequency offsets this low you don't have to sit there 
the whole time. One trick would be to take a photo of the 'scope once an hour, 
or, say, once every 1000 s. If you played that back at 1 fps you'd have a 1000x 
"time magnifier".

/tvb

___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.


   
___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

Re: [time-nuts] XKCD on time

[Martin VE3OAT]

I love GMT.  All of this UTC stuff is ... revisionist!
My cheque is in the mail.
... MartinVE3OAT

David Van Horn wrote :
>
> When I am global dictator, we will all run on GMT and all time
> zones, summer time, DST and similar nonsense will be abolished.
>
> I am accepting campaign donations!  ?
>

___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

Re: [time-nuts] XKCD on time :)

[David Van Horn]

When I am global dictator, we will all run on GMT and all time zones, summer 
time, DST and similar nonsense will be abolished.
I am accepting campaign donations!  

-Original Message-
From: time-nuts  On Behalf Of Hal Murray
Sent: Friday, September 28, 2018 2:59 AM
To: time-nuts@lists.febo.com
Cc: Hal Murray 
Subject: [time-nuts] XKCD on time :)

  https://xkcd.com/2050/

A new meaning for rubber seconds.


-- 
These are my opinions.  I hate spam.




___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

Re: [time-nuts] A silly question ...

[Dana Whitlow]

Hi,

There is one other issue that can bite you if you fail to properly
terminate the output of a source:

Depending on the source's design, an essentially unloaded output
can have a substantially higher voltage swing than expected (by
2X if the source impedance is actually 50 ohms), possibly leading
to the output stage's going into clipping, which can in turn distort
the timing, possibly even in an unstable manner.
So if you want to play the "unterminated game", at least take a
look at the waveform to be sure it's still a clean sinewave.  I've
noticed such distortion on my PRS-10, for example, although I've
seen no evidence of unstable timing results.  But in this arena,
it generally pays to be fussy.

Dana Whitlow

On Fri, Sep 28, 2018 at 7:06 AM Bill Byrom  wrote:

> On Thu, Sep 27, 2018, at 11:55 AM, Dave B via time-nuts wrote:
> > Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and having>
> the output of the OCXO on Ch2, the resulting display on Ch2 of course>
> drifts in relation to the static waveform on Ch1.  (Both nice
> > sinusoids.)
> The Tek 465 analog cathode ray oscilloscope was/is a very flexible
> instrument. But this flexibility allows you to set up the instrument in
> ways which will not allow this commonly used oscillator comparison
> technique to work correctly. Since you are interested in these
> instruments, here are some details about setting up the instrument for
> such comparisons.
> (1) The Tek 465 is not a dual beam oscilloscope. Dual beam oscilloscopes
> (such as the Tektronix 556 and 7844) use a special CRT which
> incorporates two independent electron guns. Each electron gun
> assembly has a set of vertical and horizontal deflection plates.
> There are two vertical amplifiers (one for each electron gun) and
> two horizontal sweep systems (one for each electron gun). If you had
> a dual beam oscilloscope you could compare oscillator#1 to
> oscillator#2 while  simultaneously comparing oscillator#3 with
> oscillator#4. It's like having two independent oscilloscopes sharing
> the same CRT display.
> (2) The Tek 465 single beam oscilloscope can display two  traces on the
> display using one of two methods:(a) Chopped trace display: This mode
> works well at low sweep rates (such
> as 1 ms/div) but causes trouble at fast sweep rates (such as 1
> us/div). The displayed trace is switched between Channel 1 and
> Channel 2 at a fixed rate of about 500 kHz.(b) Alternate trace
> display: This mode works well at high sweep rates
> but is hard to see at low sweep rates. The scope alternates between
> displaying one sweep of Channel 1 and one sweep of Channel 2.
> (3) The trigger source setting is crucial to using this technique to
> compare oscillators. The technique does not require you to display
> two channels. What is important is that you display one oscillator
> while triggering on the other oscillator. The trigger source can
> be set to:(a) CH 1: The Channel 2 display will drift if the two
> signals have a
> varying phase relationship.(b) CH 2: The Channel 1 display will drift
> if the two signals have a
> varying phase relationship.(c) NORM (normal): The trigger system gets
> input from the channel being
> displayed at that moment. So in chopped trace display mode the
> trigger is rapidly switched between CH1 and CH2, and in alternate
> trace display mode the trigger alternates between CH1 and CH2 on
> alternate sweeps. In all cases, you should not use NORM trigger
> source with both channels displayed when comparing oscillators!(d)
> EXT: You apply the trigger signal to the external trigger input
> connector. This works well well when comparing oscillators. If you
> use alternate trace display mode and an external trigger, you can
> compare oscillator#1 (on CH 1) to oscillator#0 (on the external
> trigger input) while you are also comparing oscillator#2 (on CH2)
> oscillator#0. So you could compare two oscillators (one on CH1 and
> the other on CH2) to a GPSDO (on the external trigger input).
> (4) When comparing oscillators, the fractional frequency difference
> (such as ppm Parts Per Million or ppb Parts Per Billion) you can
> measure depends on the oscilloscope sweep rate. What you are really
> measuring is the drift of the time delay between the edge (or zero
> crossing of a sine wave) of one signal relative to an edge or zero
> crossing of another signal. The relationship is:
> Fractional difference = (observed timing change) / (measurement
> interval)Here are some examples:
> Fractional difference in ppm = (time delay drift in us) per second of
> observation timeFractional difference in ppb = (time delay drift in ns)
> per second of
> observation time
> (5) As you can see in my previous section, you need a very fast sweep
> rate (small time/div) to measure small fractional frequency
> differences. This means 

Re: [time-nuts] XKCD on time :)

[jimlux]

On 9/28/18 6:16 AM, Eric Scace wrote:

Which, if I recall correctly, was the system used in Japan immediately before 
the adoption of Western time methods. Each day’s interval between 
sunrise-sunset was divided into a six units… so, in comparison with an absolute 
scale, the absolute duration of each unit of time varied from day to day and 
location to location.

More details here .



and in the Middle East, as well - There were even fancy watches made 
that automatically compensated given the date, so sunrise is at 6, 
midday at noon and sunset at 6.



I wrote some software to drive a 3325 via GPIB which in turn drove a 
battery wall clock to do this (that project started out as a "mars time" 
clock..)  Kind of a waste of time (is such a thing possible on 
time-nuts?) but it was an interesting problem to take a "tick per 
second" analog indicator and turn it into what is essentially an 
"arbitrary rate clock".  You could also use it to make a "where is the 
mooon or mars" indicator.




___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

Re: [time-nuts] XKCD on time :)

[Peter Vince]

Also the ancient Egyptians through to the Romans;  See:

https://en.wikipedia.org/wiki/12-hour_clock#History_and_use



On Fri, 28 Sep 2018 at 14:17, Eric Scace  wrote:
>
> Which, if I recall correctly, was the system used in Japan immediately
before the adoption of Western time methods. Each day’s interval between
sunrise-sunset was divided into a six units… so, in comparison with an
absolute scale, the absolute duration of each unit of time varied from day
to day and location to location.
>
> More details here .


> > On 2018 Sep 28, at 04:58 , Hal Murray  wrote:
> >
> >  https://xkcd.com/2050/
> >
> > A new meaning for rubber seconds.
___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

Re: [time-nuts] XKCD on time :)

[Eric Scace]

Which, if I recall correctly, was the system used in Japan immediately before 
the adoption of Western time methods. Each day’s interval between 
sunrise-sunset was divided into a six units… so, in comparison with an absolute 
scale, the absolute duration of each unit of time varied from day to day and 
location to location.

More details here .

> On 2018 Sep 28, at 04:58 , Hal Murray  wrote:
> 
>  https://xkcd.com/2050/
> 
> A new meaning for rubber seconds.
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to 
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.

___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

Re: [time-nuts] A silly question ...

[Bill Byrom]

On Thu, Sep 27, 2018, at 11:55 AM, Dave B via time-nuts wrote:
> Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and having> the 
> output of the OCXO on Ch2, the resulting display on Ch2 of course> drifts in 
> relation to the static waveform on Ch1.  (Both nice
> sinusoids.)
The Tek 465 analog cathode ray oscilloscope was/is a very flexible
instrument. But this flexibility allows you to set up the instrument in
ways which will not allow this commonly used oscillator comparison
technique to work correctly. Since you are interested in these
instruments, here are some details about setting up the instrument for
such comparisons.
(1) The Tek 465 is not a dual beam oscilloscope. Dual beam oscilloscopes
(such as the Tektronix 556 and 7844) use a special CRT which
incorporates two independent electron guns. Each electron gun
assembly has a set of vertical and horizontal deflection plates.
There are two vertical amplifiers (one for each electron gun) and
two horizontal sweep systems (one for each electron gun). If you had
a dual beam oscilloscope you could compare oscillator#1 to
oscillator#2 while  simultaneously comparing oscillator#3 with
oscillator#4. It's like having two independent oscilloscopes sharing
the same CRT display.
(2) The Tek 465 single beam oscilloscope can display two  traces on the
display using one of two methods:(a) Chopped trace display: This mode works 
well at low sweep rates (such
as 1 ms/div) but causes trouble at fast sweep rates (such as 1
us/div). The displayed trace is switched between Channel 1 and
Channel 2 at a fixed rate of about 500 kHz.(b) Alternate trace display: 
This mode works well at high sweep rates
but is hard to see at low sweep rates. The scope alternates between
displaying one sweep of Channel 1 and one sweep of Channel 2.
(3) The trigger source setting is crucial to using this technique to
compare oscillators. The technique does not require you to display
two channels. What is important is that you display one oscillator
while triggering on the other oscillator. The trigger source can
be set to:(a) CH 1: The Channel 2 display will drift if the two signals 
have a
varying phase relationship.(b) CH 2: The Channel 1 display will drift if 
the two signals have a
varying phase relationship.(c) NORM (normal): The trigger system gets input 
from the channel being
displayed at that moment. So in chopped trace display mode the
trigger is rapidly switched between CH1 and CH2, and in alternate
trace display mode the trigger alternates between CH1 and CH2 on
alternate sweeps. In all cases, you should not use NORM trigger
source with both channels displayed when comparing oscillators!(d) EXT: You 
apply the trigger signal to the external trigger input
connector. This works well well when comparing oscillators. If you
use alternate trace display mode and an external trigger, you can
compare oscillator#1 (on CH 1) to oscillator#0 (on the external
trigger input) while you are also comparing oscillator#2 (on CH2)
oscillator#0. So you could compare two oscillators (one on CH1 and
the other on CH2) to a GPSDO (on the external trigger input).
(4) When comparing oscillators, the fractional frequency difference
(such as ppm Parts Per Million or ppb Parts Per Billion) you can
measure depends on the oscilloscope sweep rate. What you are really
measuring is the drift of the time delay between the edge (or zero
crossing of a sine wave) of one signal relative to an edge or zero
crossing of another signal. The relationship is:
Fractional difference = (observed timing change) / (measurement
interval)Here are some examples:
Fractional difference in ppm = (time delay drift in us) per second of
observation timeFractional difference in ppb = (time delay drift in ns) per 
second of
observation time
(5) As you can see in my previous section, you need a very fast sweep
rate (small time/div) to measure small fractional frequency
differences. This means that for a small fractional frequency
difference with a moderately low measured oscillator frequency (such
as 1 MHz), you may not see any edges for a long time when you use a
small time/div. The Tek 465 has a delayed timebase, and you can use
this feature to move the signal edge (or zero crossing) onto the
screen. You can then watch the signal for a few seconds to determine
the timing drift rate. If the edge is drifting at 10 ns per 10
seconds, the fractional difference is 1 ppb (1 part in 10^9). If the
displayed oscillator edge is drifting to the left (earlier in time),
the displayed oscillator frequency is higher than the reference
oscillator you are using for the trigger. If the displayed
oscillator edge is drifting to the right (later in time), the
displayed oscillator frequency is lower than the reference
oscillator you are using 

Re: [time-nuts] A silly question ...

[bill.riches]

This works for me:

1. 10 Mhz to be measured input to vertical channel
2. Standard input to ext trig.
3. Set scope for 10 ns per div. (1 cycle of 10 Mhz will fill up whole
screen)
4 Time the time it takes for trace to move 1 div.  (not the whole cycle -
just one of its sides.)
5. Divide these seconds into 1x10-8 using your calculator.  ( I set 1x10-8
into one of the memories)
6. The answer will give you your  offset.
7. Example:  If it takes 20 seconds for one of the sides of the cycle to
move, your offset is 5x10-10.   
It does not take all day to get a reading,

73

Bill, WA2DVU
Cape May

-Original Message-
From: time-nuts  On Behalf Of Tom Van Baak
Sent: Thursday, September 27, 2018 2:18 PM
To: Discussion of precise time and frequency measurement

Subject: Re: [time-nuts] A silly question ...

> "I think", that if for example, it takes 1 second to drift one cycle, 
> that works out at 0.1 ppm. If it takes 2 seconds, it's 0.05 ppm, if it 
> takes 5 seconds, it's 0.02 ppm etc. Is that correct?

Yes. At 10 MHz one full cycle is 100 ns. So if the cycles are drifting by
100 ns per second that's 100e-9 s / 1 s = 1e-7 = 0.1 ppm.

At these levels of frequency accuracy, using a 'scope is plenty good enough.
In fact, it's more educational and somehow more enjoyable to watch analog
sinewaves drift past each other than it is to see the digital display of
boring frequency counter.

Where the 'scope method starts to break down is when the frequency error
gets down to the ppb level. At 1e-9 it will take 100 s for the waveforms to
drift by one cycle. And at 1e-12 you would have to wait an entire day (100
ns / 86400 s = 1.157e-12).

On the other hand, with frequency offsets this low you don't have to sit
there the whole time. One trick would be to take a photo of the 'scope once
an hour, or, say, once every 1000 s. If you played that back at 1 fps you'd
have a 1000x "time magnifier".

/tvb

___
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.


___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

[time-nuts] XKCD on time :)

[Hal Murray]

  https://xkcd.com/2050/

A new meaning for rubber seconds.


-- 
These are my opinions.  I hate spam.




___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.