subject:"\[time\-nuts\] Comparing PPS from 2 GPS units"


 A fifth solution is to use a pulse delay generator like a DG535. I use this
 to create high-resolution early/late 1PPS sync pulses. They show up on eBay,
 but aren't cheap. For bargains, watch for older model programmable pulse
 delay generators by BNC (Berkeley Nucleonics Corporation).

Thanks.  Those are more $$$ than I'm interested in right now, but might be a 
useful tool sometime in the future.

Another approach is to use a scope: trigger on one PPS and adjust the delay 
(which might be negative) and sweep speed so you can see the other PPS 
signal.  Maybe I'll play with this to see what sort of results I can get.


 Lastly, there are cute little delay boxes (www.ebay.com/itm/150962422699)
 that might work. Not sure how stable they are at the ns level. But it would
 be fun to measure. If someone opens one of these please tell us if it's a
 coil of wire, some kind of LRC filter delay, or if they use those Dallas
 delay chips. Which is another solution for you -- google or eBay search for:
 silicon delay line. 

You can make a reasonable delay line by using the lumped circuit 
approximation for the L and C for the appropriate impedance transmission 
line.  I assume that's what's in the delay boxes.  I should try that 
sometime.  Thanks for the reminder.

The delay chips I've looked at before used gate delays.  I think they were 
Motorola rather than Dallas.  I just poked at a few Maxim data sheets.  I 
didn't find out how they implemented the delays.

I think some of the clock recovery chips tune delays by tweaking the 
threshold voltage.


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Re: [time-nuts] Comparing PPS from 2 GPS units

On Mon, 17 Dec 2012 10:19:43 -0800, Hal Murray
hmur...@megapathdsl.net wrote:


 A fifth solution is to use a pulse delay generator like a DG535. I use this
 to create high-resolution early/late 1PPS sync pulses. They show up on eBay,
 but aren't cheap. For bargains, watch for older model programmable pulse
 delay generators by BNC (Berkeley Nucleonics Corporation).

Thanks.  Those are more $$$ than I'm interested in right now, but might be a 
useful tool sometime in the future.

Another approach is to use a scope: trigger on one PPS and adjust the delay 
(which might be negative) and sweep speed so you can see the other PPS 
signal.  Maybe I'll play with this to see what sort of results I can get.


 Lastly, there are cute little delay boxes (www.ebay.com/itm/150962422699)
 that might work. Not sure how stable they are at the ns level. But it would
 be fun to measure. If someone opens one of these please tell us if it's a
 coil of wire, some kind of LRC filter delay, or if they use those Dallas
 delay chips. Which is another solution for you -- google or eBay search for:
 silicon delay line. 

You can make a reasonable delay line by using the lumped circuit 
approximation for the L and C for the appropriate impedance transmission 
line.  I assume that's what's in the delay boxes.  I should try that 
sometime.  Thanks for the reminder.

The delay chips I've looked at before used gate delays.  I think they were 
Motorola rather than Dallas.  I just poked at a few Maxim data sheets.  I 
didn't find out how they implemented the delays.

I think some of the clock recovery chips tune delays by tweaking the 
threshold voltage.

I have been testing just using adjustable RC delays into a logic gate
to generate pretrigger pulses for sampling oscilloscopes.  Accuracy
depends on a complete reset of the capacitor and tracking between the
RC charge voltage and gate threshold voltage.  Worst cast jitter for
TTL has been in the 100s of picoseconds range because of supply
voltage sensitivity.  Different families of TTL and CMOS logic all
performed about the same.

Here is the jitter measurement that came from the RC logic gate delay
test:

http://www.banishedsouls.org/c2df3757f1/PG506/PDJ%20lolcat.jpg

Much better is to use a differential comparator or differential input
ECL which solves the threshold variation errors and a fast (it really
isn't all that fast) ramp generator with a precision reset.  The
differential input allows the ramp rate and threshold voltage to be
linked allowing ratiometric operation to reject power supply or
reference voltage variation and noise.

My next pretrigger generator is going the differential comparator or
differential ECL route with a fast ramp and precision reset.  I expect
jitter to be significantly better than 10s of picoseconds for delays
up to about 100 nanoseconds.  If I get down to 10 picoseconds of
jitter, I will be happy since I have no real way to measure much below
that.

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Re: [time-nuts] Comparing PPS from 2 GPS units

Hi

With R-C delay generators, temperature coefficient is likely to be an issue. 
NPO will get you to 30 ppm/C. Most resistors will be up in the 50 or so ppm / C 
range. On top of that you have the contributions of what ever strays might be 
running around. 

If you are trying to set up say a 1 us delay, you will get ~ 50 ps per degree C 
in your delay. That's a lot .

Bob

On Dec 17, 2012, at 1:56 PM, David davidwh...@gmail.com wrote:

 On Mon, 17 Dec 2012 10:19:43 -0800, Hal Murray
 hmur...@megapathdsl.net wrote:
 
 
 A fifth solution is to use a pulse delay generator like a DG535. I use this
 to create high-resolution early/late 1PPS sync pulses. They show up on eBay,
 but aren't cheap. For bargains, watch for older model programmable pulse
 delay generators by BNC (Berkeley Nucleonics Corporation).
 
 Thanks.  Those are more $$$ than I'm interested in right now, but might be a 
 useful tool sometime in the future.
 
 Another approach is to use a scope: trigger on one PPS and adjust the delay 
 (which might be negative) and sweep speed so you can see the other PPS 
 signal.  Maybe I'll play with this to see what sort of results I can get.
 
 
 Lastly, there are cute little delay boxes (www.ebay.com/itm/150962422699)
 that might work. Not sure how stable they are at the ns level. But it would
 be fun to measure. If someone opens one of these please tell us if it's a
 coil of wire, some kind of LRC filter delay, or if they use those Dallas
 delay chips. Which is another solution for you -- google or eBay search for:
 silicon delay line. 
 
 You can make a reasonable delay line by using the lumped circuit 
 approximation for the L and C for the appropriate impedance transmission 
 line.  I assume that's what's in the delay boxes.  I should try that 
 sometime.  Thanks for the reminder.
 
 The delay chips I've looked at before used gate delays.  I think they were 
 Motorola rather than Dallas.  I just poked at a few Maxim data sheets.  I 
 didn't find out how they implemented the delays.
 
 I think some of the clock recovery chips tune delays by tweaking the 
 threshold voltage.
 
 I have been testing just using adjustable RC delays into a logic gate
 to generate pretrigger pulses for sampling oscilloscopes.  Accuracy
 depends on a complete reset of the capacitor and tracking between the
 RC charge voltage and gate threshold voltage.  Worst cast jitter for
 TTL has been in the 100s of picoseconds range because of supply
 voltage sensitivity.  Different families of TTL and CMOS logic all
 performed about the same.
 
 Here is the jitter measurement that came from the RC logic gate delay
 test:
 
 http://www.banishedsouls.org/c2df3757f1/PG506/PDJ%20lolcat.jpg
 
 Much better is to use a differential comparator or differential input
 ECL which solves the threshold variation errors and a fast (it really
 isn't all that fast) ramp generator with a precision reset.  The
 differential input allows the ramp rate and threshold voltage to be
 linked allowing ratiometric operation to reject power supply or
 reference voltage variation and noise.
 
 My next pretrigger generator is going the differential comparator or
 differential ECL route with a fast ramp and precision reset.  I expect
 jitter to be significantly better than 10s of picoseconds for delays
 up to about 100 nanoseconds.  If I get down to 10 picoseconds of
 jitter, I will be happy since I have no real way to measure much below
 that.
 
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Re: [time-nuts] Comparing PPS from 2 GPS units

You would not want to do this for long delays obviously.  A digital
counter with the delay used as a vernier would be more appropriate
there.  That gets complicated fast if the input is asynchronous.

Analog first order compensation of the temperature coefficient is
straightforward using the same techniques that are used for voltage to
frequency converters.  Unfortunately, polystyrene capacitors are no
longer produced.  Digital calibration might be easier to design and
would be a good idea for verification of performance anyway.

I wonder what the temperature coefficient is of the Maxim's
programmable delay lines.  I do not see it in their datasheets.  The
On semiconductor one I checked is greater than 1000ppm/C but its
maximum delay is 12.5 nanoseconds.

On Mon, 17 Dec 2012 14:04:54 -0500, Bob Camp li...@rtty.us wrote:

Hi

With R-C delay generators, temperature coefficient is likely to be an issue. 
NPO will get you to 30 ppm/C. Most resistors will be up in the 50 or so ppm / 
C range. On top of that you have the contributions of what ever strays might 
be running around. 

If you are trying to set up say a 1 us delay, you will get ~ 50 ps per degree 
C in your delay. That's a lot .

Bob

On Dec 17, 2012, at 1:56 PM, David davidwh...@gmail.com wrote:

 On Mon, 17 Dec 2012 10:19:43 -0800, Hal Murray
 hmur...@megapathdsl.net wrote:
 
 
 A fifth solution is to use a pulse delay generator like a DG535. I use this
 to create high-resolution early/late 1PPS sync pulses. They show up on 
 eBay,
 but aren't cheap. For bargains, watch for older model programmable pulse
 delay generators by BNC (Berkeley Nucleonics Corporation).
 
 Thanks.  Those are more $$$ than I'm interested in right now, but might be 
 a 
 useful tool sometime in the future.
 
 Another approach is to use a scope: trigger on one PPS and adjust the delay 
 (which might be negative) and sweep speed so you can see the other PPS 
 signal.  Maybe I'll play with this to see what sort of results I can get.
 
 
 Lastly, there are cute little delay boxes (www.ebay.com/itm/150962422699)
 that might work. Not sure how stable they are at the ns level. But it would
 be fun to measure. If someone opens one of these please tell us if it's a
 coil of wire, some kind of LRC filter delay, or if they use those Dallas
 delay chips. Which is another solution for you -- google or eBay search 
 for:
 silicon delay line. 
 
 You can make a reasonable delay line by using the lumped circuit 
 approximation for the L and C for the appropriate impedance transmission 
 line.  I assume that's what's in the delay boxes.  I should try that 
 sometime.  Thanks for the reminder.
 
 The delay chips I've looked at before used gate delays.  I think they were 
 Motorola rather than Dallas.  I just poked at a few Maxim data sheets.  I 
 didn't find out how they implemented the delays.
 
 I think some of the clock recovery chips tune delays by tweaking the 
 threshold voltage.
 
 I have been testing just using adjustable RC delays into a logic gate
 to generate pretrigger pulses for sampling oscilloscopes.  Accuracy
 depends on a complete reset of the capacitor and tracking between the
 RC charge voltage and gate threshold voltage.  Worst cast jitter for
 TTL has been in the 100s of picoseconds range because of supply
 voltage sensitivity.  Different families of TTL and CMOS logic all
 performed about the same.
 
 Here is the jitter measurement that came from the RC logic gate delay
 test:
 
 http://www.banishedsouls.org/c2df3757f1/PG506/PDJ%20lolcat.jpg
 
 Much better is to use a differential comparator or differential input
 ECL which solves the threshold variation errors and a fast (it really
 isn't all that fast) ramp generator with a precision reset.  The
 differential input allows the ramp rate and threshold voltage to be
 linked allowing ratiometric operation to reject power supply or
 reference voltage variation and noise.
 
 My next pretrigger generator is going the differential comparator or
 differential ECL route with a fast ramp and precision reset.  I expect
 jitter to be significantly better than 10s of picoseconds for delays
 up to about 100 nanoseconds.  If I get down to 10 picoseconds of
 jitter, I will be happy since I have no real way to measure much below
 that.
 
 ___
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 To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
 and follow the instructions there.


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Re: [time-nuts] Comparing PPS from 2 GPS units

2012-12-17 Thread M. Simon

Nice pulse delay generator:

http://www.edn.com/file/14660-Figure_1.pdf

The article that goes with it:

http://www.edn.com/design/analog/4323671/Dual-flip-flop-forms-simple-delayed-pulse-generator


The delay is analog - charging a capacitor until it crosses a threshold. So I 
don't know if it is good enough. But I did find it interesting. The order of 
the delay is 1 to 250 uSec. Faster parts would get you into shorter delays. 

If you had two of these operating on a common trigger...

Simon


Engineering is the art of making what you want from what you can get at a 
profit.




 From: David davidwh...@gmail.com
To: Discussion of precise time and frequency measurement time-nuts@febo.com 
Sent: Monday, December 17, 2012 6:56 PM
Subject: Re: [time-nuts] Comparing PPS from 2 GPS units
 
On Mon, 17 Dec 2012 10:19:43 -0800, Hal Murray
hmur...@megapathdsl.net wrote:


 A fifth solution is to use a pulse delay generator like a DG535. I use this
 to create high-resolution early/late 1PPS sync pulses. They show up on eBay,
 but aren't cheap. For bargains, watch for older model programmable pulse
 delay generators by BNC (Berkeley Nucleonics Corporation).

Thanks.  Those are more $$$ than I'm interested in right now, but might be a 
useful tool sometime in the future.

Another approach is to use a scope: trigger on one PPS and adjust the delay 
(which might be negative) and sweep speed so you can see the other PPS 
signal.  Maybe I'll play with this to see what sort of results I can get.


 Lastly, there are cute little delay boxes (www.ebay.com/itm/150962422699)
 that might work. Not sure how stable they are at the ns level. But it would
 be fun to measure. If someone opens one of these please tell us if it's a
 coil of wire, some kind of LRC filter delay, or if they use those Dallas
 delay chips. Which is another solution for you -- google or eBay search for:
 silicon delay line. 

You can make a reasonable delay line by using the lumped circuit 
approximation for the L and C for the appropriate impedance transmission 
line.  I assume that's what's in the delay boxes.  I should try that 
sometime.  Thanks for the reminder.

The delay chips I've looked at before used gate delays.  I think they were 
Motorola rather than Dallas.  I just poked at a few Maxim data sheets.  I 
didn't find out how they implemented the delays.

I think some of the clock recovery chips tune delays by tweaking the 
threshold voltage.

I have been testing just using adjustable RC delays into a logic gate
to generate pretrigger pulses for sampling oscilloscopes.  Accuracy
depends on a complete reset of the capacitor and tracking between the
RC charge voltage and gate threshold voltage.  Worst cast jitter for
TTL has been in the 100s of picoseconds range because of supply
voltage sensitivity.  Different families of TTL and CMOS logic all
performed about the same.

Here is the jitter measurement that came from the RC logic gate delay
test:

http://www.banishedsouls.org/c2df3757f1/PG506/PDJ%20lolcat.jpg

Much better is to use a differential comparator or differential input
ECL which solves the threshold variation errors and a fast (it really
isn't all that fast) ramp generator with a precision reset.  The
differential input allows the ramp rate and threshold voltage to be
linked allowing ratiometric operation to reject power supply or
reference voltage variation and noise.

My next pretrigger generator is going the differential comparator or
differential ECL route with a fast ramp and precision reset.  I expect
jitter to be significantly better than 10s of picoseconds for delays
up to about 100 nanoseconds.  If I get down to 10 picoseconds of
jitter, I will be happy since I have no real way to measure much below
that.

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Re: [time-nuts] Comparing PPS from 2 GPS units

Hi

I believe you will find that NPO's are your best bet by far for short delays.

The R's and C's on a simple semi are going to have some pretty major tempco's. 
If they go with a fancy process they can change that. Normally to keep things 
cheap they use the simple process.

Bob

On Dec 17, 2012, at 2:55 PM, David davidwh...@gmail.com wrote:

 You would not want to do this for long delays obviously.  A digital
 counter with the delay used as a vernier would be more appropriate
 there.  That gets complicated fast if the input is asynchronous.
 
 Analog first order compensation of the temperature coefficient is
 straightforward using the same techniques that are used for voltage to
 frequency converters.  Unfortunately, polystyrene capacitors are no
 longer produced.  Digital calibration might be easier to design and
 would be a good idea for verification of performance anyway.
 
 I wonder what the temperature coefficient is of the Maxim's
 programmable delay lines.  I do not see it in their datasheets.  The
 On semiconductor one I checked is greater than 1000ppm/C but its
 maximum delay is 12.5 nanoseconds.
 
 On Mon, 17 Dec 2012 14:04:54 -0500, Bob Camp li...@rtty.us wrote:
 
 Hi
 
 With R-C delay generators, temperature coefficient is likely to be an issue. 
 NPO will get you to 30 ppm/C. Most resistors will be up in the 50 or so ppm 
 / C range. On top of that you have the contributions of what ever strays 
 might be running around. 
 
 If you are trying to set up say a 1 us delay, you will get ~ 50 ps per 
 degree C in your delay. That's a lot .
 
 Bob
 
 On Dec 17, 2012, at 1:56 PM, David davidwh...@gmail.com wrote:
 
 On Mon, 17 Dec 2012 10:19:43 -0800, Hal Murray
 hmur...@megapathdsl.net wrote:
 
 
 A fifth solution is to use a pulse delay generator like a DG535. I use 
 this
 to create high-resolution early/late 1PPS sync pulses. They show up on 
 eBay,
 but aren't cheap. For bargains, watch for older model programmable pulse
 delay generators by BNC (Berkeley Nucleonics Corporation).
 
 Thanks.  Those are more $$$ than I'm interested in right now, but might be 
 a 
 useful tool sometime in the future.
 
 Another approach is to use a scope: trigger on one PPS and adjust the 
 delay 
 (which might be negative) and sweep speed so you can see the other PPS 
 signal.  Maybe I'll play with this to see what sort of results I can get.
 
 
 Lastly, there are cute little delay boxes (www.ebay.com/itm/150962422699)
 that might work. Not sure how stable they are at the ns level. But it 
 would
 be fun to measure. If someone opens one of these please tell us if it's a
 coil of wire, some kind of LRC filter delay, or if they use those Dallas
 delay chips. Which is another solution for you -- google or eBay search 
 for:
 silicon delay line. 
 
 You can make a reasonable delay line by using the lumped circuit 
 approximation for the L and C for the appropriate impedance transmission 
 line.  I assume that's what's in the delay boxes.  I should try that 
 sometime.  Thanks for the reminder.
 
 The delay chips I've looked at before used gate delays.  I think they were 
 Motorola rather than Dallas.  I just poked at a few Maxim data sheets.  I 
 didn't find out how they implemented the delays.
 
 I think some of the clock recovery chips tune delays by tweaking the 
 threshold voltage.
 
 I have been testing just using adjustable RC delays into a logic gate
 to generate pretrigger pulses for sampling oscilloscopes.  Accuracy
 depends on a complete reset of the capacitor and tracking between the
 RC charge voltage and gate threshold voltage.  Worst cast jitter for
 TTL has been in the 100s of picoseconds range because of supply
 voltage sensitivity.  Different families of TTL and CMOS logic all
 performed about the same.
 
 Here is the jitter measurement that came from the RC logic gate delay
 test:
 
 http://www.banishedsouls.org/c2df3757f1/PG506/PDJ%20lolcat.jpg
 
 Much better is to use a differential comparator or differential input
 ECL which solves the threshold variation errors and a fast (it really
 isn't all that fast) ramp generator with a precision reset.  The
 differential input allows the ramp rate and threshold voltage to be
 linked allowing ratiometric operation to reject power supply or
 reference voltage variation and noise.
 
 My next pretrigger generator is going the differential comparator or
 differential ECL route with a fast ramp and precision reset.  I expect
 jitter to be significantly better than 10s of picoseconds for delays
 up to about 100 nanoseconds.  If I get down to 10 picoseconds of
 jitter, I will be happy since I have no real way to measure much below
 that.
 
 ___
 time-nuts mailing list -- time-nuts@febo.com
 To unsubscribe, go to 
 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
 and follow the instructions there.
 
 
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 To

Re: [time-nuts] Comparing PPS from 2 GPS units


li...@rtty.us said:
 If you are trying to set up say a 1 us delay, you will get ~ 50 ps per
 degree C in your delay. That's a lot . 

A while ago, t...@leapsecond.com said:
 A long delay cable is fine too. If these are timing receivers you probably
 don't need more than 100 ns of delay, once you figure out which receiver is
 ahead of the other. The cable tempco is low enough not to worry about. 

100 ns is 50-100 feet.  That's a reasonable length to work with.  But I was 
curious about the temperature coefficient.  Google found this:
  http://www.hepl.hiroshima-u.ac.jp/phx/notes/cable/cable.html
which says:
# Belden 8240 (solid) shows a temperature coefficient of around 
-0.252ps/m/deg in a temperature range between -20 and 30 deg. The coefficient 
becomes steeper beyond 30 deg.
# Belden 8219 (foam) shows a larger temperature coefficient of around -0.352 
ps/m/deg than that of 8240 in the similar temperature range. The coefficient 
becomes steeper beyond 30 deg, but less steeper than that of 8240.
# Fujikura RG58-A/U shows the smallest temperature coefficient of around 
-0.152 ps/m/deg, but in a narrow temperature range between -10 and 20 deg. 
The coefficient beyond 20 deg is much steeper than the others.

To pick round numbers, 30 meters and 3 C and 0.25 ps/m/C gives 25 ps.


-- 
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Re: [time-nuts] Comparing PPS from 2 GPS units

2012-12-17 Thread Bruce Griffiths

Its actually a relatively low performance implementation of a classic 
technique.
The ramp capacitor reset switch (a saturated transistor) has a 
relatively slow turnoff and poorly defined reset voltage.


For shorter time delays lower capacitance current source and reset 
devices are required.


Decoupling of the current sensing device in the control loop from the 
current source device emitter is desirable.


ECL delay chips using this technique complete with a DAC to set the 
comparator threshold used to be available.


A classic reset switch uses a current driven pair of matched shottky 
diodes to ensure fast switching coupled with a relatively low offset 
voltage.


Techniques to produce stable longer delays:

1) Use a stable (phase locked) gated oscillator to produce a well 
defined long delay using pulse counting together with a triggered ramp + 
DAC + comparator for fine adjustment.

The HP5359A delay generator is an example of this technique.

2) Use a synchroniser plus counter for the coarse delay followed by a 
triggered ramp + DAC and comparator.
The synchroniser delay is measured and the result used to adjust the 
fine delay to compensate for the variable synchroniser delay.
Analog techniques where the fine delay ramp is stopped and held by the 
synchroniser outpt and then resumed by the digital delay output 
transition have also been used.



Bruce

M. Simon wrote:

Nice pulse delay generator:

http://www.edn.com/file/14660-Figure_1.pdf

The article that goes with it:

http://www.edn.com/design/analog/4323671/Dual-flip-flop-forms-simple-delayed-pulse-generator


The delay is analog - charging a capacitor until it crosses a threshold. So I 
don't know if it is good enough. But I did find it interesting. The order of 
the delay is 1 to 250 uSec. Faster parts would get you into shorter delays.

If you had two of these operating on a common trigger...

Simon


Engineering is the art of making what you want from what you can get at a 
profit.



   


From: Daviddavidwh...@gmail.com
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Sent: Monday, December 17, 2012 6:56 PM
Subject: Re: [time-nuts] Comparing PPS from 2 GPS units

On Mon, 17 Dec 2012 10:19:43 -0800, Hal Murray
hmur...@megapathdsl.net  wrote:

 
   

A fifth solution is to use a pulse delay generator like a DG535. I use this
to create high-resolution early/late 1PPS sync pulses. They show up on eBay,
but aren't cheap. For bargains, watch for older model programmable pulse
delay generators by BNC (Berkeley Nucleonics Corporation).
 

Thanks.  Those are more $$$ than I'm interested in right now, but might be a
useful tool sometime in the future.

Another approach is to use a scope: trigger on one PPS and adjust the delay
(which might be negative) and sweep speed so you can see the other PPS
signal.  Maybe I'll play with this to see what sort of results I can get.


   

Lastly, there are cute little delay boxes (www.ebay.com/itm/150962422699)
that might work. Not sure how stable they are at the ns level. But it would
be fun to measure. If someone opens one of these please tell us if it's a
coil of wire, some kind of LRC filter delay, or if they use those Dallas
delay chips. Which is another solution for you -- google or eBay search for:
silicon delay line.
 

You can make a reasonable delay line by using the lumped circuit
approximation for the L and C for the appropriate impedance transmission
line.  I assume that's what's in the delay boxes.  I should try that
sometime.  Thanks for the reminder.

The delay chips I've looked at before used gate delays.  I think they were
Motorola rather than Dallas.  I just poked at a few Maxim data sheets.  I
didn't find out how they implemented the delays.

I think some of the clock recovery chips tune delays by tweaking the
threshold voltage.
   

I have been testing just using adjustable RC delays into a logic gate
to generate pretrigger pulses for sampling oscilloscopes.  Accuracy
depends on a complete reset of the capacitor and tracking between the
RC charge voltage and gate threshold voltage.  Worst cast jitter for
TTL has been in the 100s of picoseconds range because of supply
voltage sensitivity.  Different families of TTL and CMOS logic all
performed about the same.

Here is the jitter measurement that came from the RC logic gate delay
test:

http://www.banishedsouls.org/c2df3757f1/PG506/PDJ%20lolcat.jpg

Much better is to use a differential comparator or differential input
ECL which solves the threshold variation errors and a fast (it really
isn't all that fast) ramp generator with a precision reset.  The
differential input allows the ramp rate and threshold voltage to be
linked allowing ratiometric operation to reject power supply or
reference voltage variation and noise.

My next pretrigger generator is going the differential comparator or
differential ECL route with a fast ramp and precision reset.  I

Re: [time-nuts] Comparing PPS from 2 GPS units

2012-12-17 Thread Gerhard Hoffmann


Am 17.12.2012 19:56, schrieb David:



My next pretrigger generator is going the differential comparator or
differential ECL route with a fast ramp and precision reset.  I expect
jitter to be significantly better than 10s of picoseconds for delays
up to about 100 nanoseconds.  If I get down to 10 picoseconds of
jitter, I will be happy since I have no real way to measure much below
that.



That should be easy to do. I did a trigger pulse  delay for a
54750A scope. You need abt. 25 nsec delay to see the trigger event.
I did it with ooold 10K ECL I still had around and a few meters of
semi rigid cable. The semi rigid is surprisingly compact when wound
on a piece of plastic tube.

There was not much difference when watching the output of an
ADCMP580 comparator, via trigger delay or via internal trigger
and waiting a few clocks with the built-in delay.

The ADCMP580 is a fine chip, btw. You get a lot of speed for
not too much money. (digikey)

I will rebuild the trigger delay over xmas, this time with
CML to remove most of a systematic error in my scope setup.

CML is much more friendly than ECL/PECL from a probing
point of view. No need to carry Vtt to the scope and have
a problematic bias tee there, or shifting the supplies
until all happens to fit...

regards, Gerhard


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Re: [time-nuts] Comparing PPS from 2 GPS units

Hi

The nice thing about a spool of coax is that it's got a bit of thermal mass. It 
will average out a lot of minor temperature ups and downs. 

Bob

On Dec 17, 2012, at 4:34 PM, Hal Murray hmur...@megapathdsl.net wrote:

 
 li...@rtty.us said:
 If you are trying to set up say a 1 us delay, you will get ~ 50 ps per
 degree C in your delay. That's a lot . 
 
 A while ago, t...@leapsecond.com said:
 A long delay cable is fine too. If these are timing receivers you probably
 don't need more than 100 ns of delay, once you figure out which receiver is
 ahead of the other. The cable tempco is low enough not to worry about. 
 
 100 ns is 50-100 feet.  That's a reasonable length to work with.  But I was 
 curious about the temperature coefficient.  Google found this:
  http://www.hepl.hiroshima-u.ac.jp/phx/notes/cable/cable.html
 which says:
 # Belden 8240 (solid) shows a temperature coefficient of around 
 -0.252ps/m/deg in a temperature range between -20 and 30 deg. The coefficient 
 becomes steeper beyond 30 deg.
 # Belden 8219 (foam) shows a larger temperature coefficient of around -0.352 
 ps/m/deg than that of 8240 in the similar temperature range. The coefficient 
 becomes steeper beyond 30 deg, but less steeper than that of 8240.
 # Fujikura RG58-A/U shows the smallest temperature coefficient of around 
 -0.152 ps/m/deg, but in a narrow temperature range between -10 and 20 deg. 
 The coefficient beyond 20 deg is much steeper than the others.
 
 To pick round numbers, 30 meters and 3 C and 0.25 ps/m/C gives 25 ps.
 
 
 -- 
 These are my opinions.  I hate spam.
 
 
 
 
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Re: [time-nuts] Comparing PPS from 2 GPS units

I wish there was an source for helically wound shielded differential
transmission line like the type used in later analog oscilloscopes.
The only place I know where to find it is oscilloscope part mules.

Essentially it was transmission line with a ridiculously low velocity
factor.  It is great for building instant digital delay lines up to
the low 10s of nanoseconds range in a small space.

On Mon, 17 Dec 2012 20:04:15 -0500, Bob Camp li...@rtty.us wrote:

Hi

The nice thing about a spool of coax is that it's got a bit of thermal mass. 
It will average out a lot of minor temperature ups and downs. 

Bob

On Dec 17, 2012, at 4:34 PM, Hal Murray hmur...@megapathdsl.net wrote:

 
 li...@rtty.us said:
 If you are trying to set up say a 1 us delay, you will get ~ 50 ps per
 degree C in your delay. That's a lot . 
 
 A while ago, t...@leapsecond.com said:
 A long delay cable is fine too. If these are timing receivers you probably
 don't need more than 100 ns of delay, once you figure out which receiver is
 ahead of the other. The cable tempco is low enough not to worry about. 
 
 100 ns is 50-100 feet.  That's a reasonable length to work with.  But I was 
 curious about the temperature coefficient.  Google found this:
  http://www.hepl.hiroshima-u.ac.jp/phx/notes/cable/cable.html
 which says:
 # Belden 8240 (solid) shows a temperature coefficient of around 
 -0.252ps/m/deg in a temperature range between -20 and 30 deg. The 
 coefficient 
 becomes steeper beyond 30 deg.
 # Belden 8219 (foam) shows a larger temperature coefficient of around -0.352 
 ps/m/deg than that of 8240 in the similar temperature range. The coefficient 
 becomes steeper beyond 30 deg, but less steeper than that of 8240.
 # Fujikura RG58-A/U shows the smallest temperature coefficient of around 
 -0.152 ps/m/deg, but in a narrow temperature range between -10 and 20 deg. 
 The coefficient beyond 20 deg is much steeper than the others.
 
 To pick round numbers, 30 meters and 3 C and 0.25 ps/m/C gives 25 ps.

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Re: [time-nuts] Comparing PPS from 2 GPS units

2012-12-17 Thread Daniel Mendes

Like this?

http://www.ebay.com/itm/Tektronix-Delay-Line-for-475-Oscilloscope-New-/290824098279?pt=LH_DefaultDomain_0hash=item43b67791e7

Em 17/12/2012 23:39, David escreveu:

I wish there was an source for helically wound shielded differential
transmission line like the type used in later analog oscilloscopes.
The only place I know where to find it is oscilloscope part mules.

Essentially it was transmission line with a ridiculously low velocity
factor. It is great for building instant digital delay lines up to
the low 10s of nanoseconds range in a small space.

On Mon, 17 Dec 2012 20:04:15 -0500, Bob Camp li...@rtty.us wrote:

The nice thing about a spool of coax is that it's got a bit of thermal mass. It
will average out a lot of minor temperature ups and downs.

Bob

On Dec 17, 2012, at 4:34 PM, Hal Murray hmur...@megapathdsl.net wrote:

li...@rtty.us said:

If you are trying to set up say a 1 us delay, you will get ~ 50 ps per
degree C in your delay. That's a lot .

A while ago, t...@leapsecond.com said:

A long delay cable is fine too. If these are timing receivers you probably
don't need more than 100 ns of delay, once you figure out which receiver is
ahead of the other. The cable tempco is low enough not to worry about.

100 ns is 50-100 feet. That's a reasonable length to work with. But I was
curious about the temperature coefficient. Google found this:
http://www.hepl.hiroshima-u.ac.jp/phx/notes/cable/cable.html
which says:
# Belden 8240 (solid) shows a temperature coefficient of around
-0.252ps/m/deg in a temperature range between -20 and 30 deg. The coefficient
becomes steeper beyond 30 deg.
# Belden 8219 (foam) shows a larger temperature coefficient of around -0.352
ps/m/deg than that of 8240 in the similar temperature range. The coefficient
becomes steeper beyond 30 deg, but less steeper than that of 8240.
# Fujikura RG58-A/U shows the smallest temperature coefficient of around
-0.152 ps/m/deg, but in a narrow temperature range between -10 and 20 deg.
The coefficient beyond 20 deg is much steeper than the others.

To pick round numbers, 30 meters and 3 C and 0.25 ps/m/C gives 25 ps.

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Re: [time-nuts] Comparing PPS from 2 GPS units

Hi

At some point the whole get it onto the board / get it off the board thing 
becomes the main issue. Then it's easier to just make the delay line part of 
the PC layout.

Bob

On Dec 17, 2012, at 8:39 PM, David davidwh...@gmail.com wrote:

 I wish there was an source for helically wound shielded differential
 transmission line like the type used in later analog oscilloscopes.
 The only place I know where to find it is oscilloscope part mules.
 
 Essentially it was transmission line with a ridiculously low velocity
 factor.  It is great for building instant digital delay lines up to
 the low 10s of nanoseconds range in a small space.
 
 On Mon, 17 Dec 2012 20:04:15 -0500, Bob Camp li...@rtty.us wrote:
 
 Hi
 
 The nice thing about a spool of coax is that it's got a bit of thermal mass. 
 It will average out a lot of minor temperature ups and downs. 
 
 Bob
 
 On Dec 17, 2012, at 4:34 PM, Hal Murray hmur...@megapathdsl.net wrote:
 
 
 li...@rtty.us said:
 If you are trying to set up say a 1 us delay, you will get ~ 50 ps per
 degree C in your delay. That's a lot . 
 
 A while ago, t...@leapsecond.com said:
 A long delay cable is fine too. If these are timing receivers you probably
 don't need more than 100 ns of delay, once you figure out which receiver is
 ahead of the other. The cable tempco is low enough not to worry about. 
 
 100 ns is 50-100 feet.  That's a reasonable length to work with.  But I was 
 curious about the temperature coefficient.  Google found this:
 http://www.hepl.hiroshima-u.ac.jp/phx/notes/cable/cable.html
 which says:
 # Belden 8240 (solid) shows a temperature coefficient of around 
 -0.252ps/m/deg in a temperature range between -20 and 30 deg. The 
 coefficient 
 becomes steeper beyond 30 deg.
 # Belden 8219 (foam) shows a larger temperature coefficient of around 
 -0.352 
 ps/m/deg than that of 8240 in the similar temperature range. The 
 coefficient 
 becomes steeper beyond 30 deg, but less steeper than that of 8240.
 # Fujikura RG58-A/U shows the smallest temperature coefficient of around 
 -0.152 ps/m/deg, but in a narrow temperature range between -10 and 20 deg. 
 The coefficient beyond 20 deg is much steeper than the others.
 
 To pick round numbers, 30 meters and 3 C and 0.25 ps/m/C gives 25 ps.
 
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Re: [time-nuts] Comparing PPS from 2 GPS units

That is the stuff but Tektronix had some with an even smaller
diameter. It would be nice to have a new source as I would hate to
cannibalize oscilloscopes for it.

On Mon, 17 Dec 2012 23:43:21 -0200, Daniel Mendes dmend...@gmail.com
wrote:

Like this?

http://www.ebay.com/itm/Tektronix-Delay-Line-for-475-Oscilloscope-New-/290824098279?pt=LH_DefaultDomain_0hash=item43b67791e7

Em 17/12/2012 23:39, David escreveu:
I wish there was an source for helically wound shielded differential
transmission line like the type used in later analog oscilloscopes.
The only place I know where to find it is oscilloscope part mules.

Essentially it was transmission line with a ridiculously low velocity
factor. It is great for building instant digital delay lines up to
the low 10s of nanoseconds range in a small space.

On Mon, 17 Dec 2012 20:04:15 -0500, Bob Camp li...@rtty.us wrote:

The nice thing about a spool of coax is that it's got a bit of thermal
mass. It will average out a lot of minor temperature ups and downs.

Bob

On Dec 17, 2012, at 4:34 PM, Hal Murray hmur...@megapathdsl.net wrote:

li...@rtty.us said:
If you are trying to set up say a 1 us delay, you will get ~ 50 ps per
degree C in your delay. That's a lot .
A while ago, t...@leapsecond.com said:
A long delay cable is fine too. If these are timing receivers you probably
don't need more than 100 ns of delay, once you figure out which receiver
is
ahead of the other. The cable tempco is low enough not to worry about.
100 ns is 50-100 feet. That's a reasonable length to work with. But I was
curious about the temperature coefficient. Google found this:
http://www.hepl.hiroshima-u.ac.jp/phx/notes/cable/cable.html
which says:
# Belden 8240 (solid) shows a temperature coefficient of around
-0.252ps/m/deg in a temperature range between -20 and 30 deg. The
coefficient
becomes steeper beyond 30 deg.
# Belden 8219 (foam) shows a larger temperature coefficient of around
-0.352
ps/m/deg than that of 8240 in the similar temperature range. The
coefficient
becomes steeper beyond 30 deg, but less steeper than that of 8240.
# Fujikura RG58-A/U shows the smallest temperature coefficient of around
-0.152 ps/m/deg, but in a narrow temperature range between -10 and 20 deg.
The coefficient beyond 20 deg is much steeper than the others.

To pick round numbers, 30 meters and 3 C and 0.25 ps/m/C gives 25 ps.
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Re: [time-nuts] Comparing PPS from 2 GPS units

I have seen the small diameter, about like RG-174, delay cable used
for patching PC boards after the fact.  That is how I know it exists.
:)

I just have not found a source for it.

On Mon, 17 Dec 2012 20:47:34 -0500, Bob Camp li...@rtty.us wrote:

Hi

At some point the whole get it onto the board / get it off the board thing 
becomes the main issue. Then it's easier to just make the delay line part of 
the PC layout.

Bob

On Dec 17, 2012, at 8:39 PM, David davidwh...@gmail.com wrote:

 I wish there was an source for helically wound shielded differential
 transmission line like the type used in later analog oscilloscopes.
 The only place I know where to find it is oscilloscope part mules.
 
 Essentially it was transmission line with a ridiculously low velocity
 factor.  It is great for building instant digital delay lines up to
 the low 10s of nanoseconds range in a small space.
 
 On Mon, 17 Dec 2012 20:04:15 -0500, Bob Camp li...@rtty.us wrote:
 
 Hi
 
 The nice thing about a spool of coax is that it's got a bit of thermal 
 mass. It will average out a lot of minor temperature ups and downs. 
 
 Bob
 
 On Dec 17, 2012, at 4:34 PM, Hal Murray hmur...@megapathdsl.net wrote:
 
 
 li...@rtty.us said:
 If you are trying to set up say a 1 us delay, you will get ~ 50 ps per
 degree C in your delay. That's a lot . 
 
 A while ago, t...@leapsecond.com said:
 A long delay cable is fine too. If these are timing receivers you probably
 don't need more than 100 ns of delay, once you figure out which receiver 
 is
 ahead of the other. The cable tempco is low enough not to worry about. 
 
 100 ns is 50-100 feet.  That's a reasonable length to work with.  But I 
 was 
 curious about the temperature coefficient.  Google found this:
 http://www.hepl.hiroshima-u.ac.jp/phx/notes/cable/cable.html
 which says:
 # Belden 8240 (solid) shows a temperature coefficient of around 
 -0.252ps/m/deg in a temperature range between -20 and 30 deg. The 
 coefficient 
 becomes steeper beyond 30 deg.
 # Belden 8219 (foam) shows a larger temperature coefficient of around 
 -0.352 
 ps/m/deg than that of 8240 in the similar temperature range. The 
 coefficient 
 becomes steeper beyond 30 deg, but less steeper than that of 8240.
 # Fujikura RG58-A/U shows the smallest temperature coefficient of around 
 -0.152 ps/m/deg, but in a narrow temperature range between -10 and 20 deg. 
 The coefficient beyond 20 deg is much steeper than the others.
 
 To pick round numbers, 30 meters and 3 C and 0.25 ps/m/C gives 25 ps.

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Re: [time-nuts] Comparing PPS from 2 GPS units

2012-12-17 Thread Jim Lux


On 12/17/12 5:39 PM, David wrote:

I wish there was an source for helically wound shielded differential
transmission line like the type used in later analog oscilloscopes.
The only place I know where to find it is oscilloscope part mules.


You mean RG65
http://www.awcwire.com/ProductSpec.aspx?id=M17/34-RG65-Coaxial-Cable
or RG186
http://www.awcwire.com/ProductSpec.aspx?id=RG186-Coaxial-Cable


there's a place in Nevada (Reno, I think) that makes that stuff.. it's a 
helically loaded coaxial delay line.  I was looking for it a few years 
ago for a radar target simulator for Phoenix.


http://www.allenavionics.com/Info_Srv/SpecifyingDelayLinesPage2.htm


There's also a magnetostrictive delay line...


These days, for RF/Radar purposes, people either digitize or use SAW or 
BAW devices.




Essentially it was transmission line with a ridiculously low velocity
factor.  It is great for building instant digital delay lines up to
the low 10s of nanoseconds range in a small space.

On Mon, 17 Dec 2012 20:04:15 -0500, Bob Camp li...@rtty.us wrote:


Hi

The nice thing about a spool of coax is that it's got a bit of thermal mass. It 
will average out a lot of minor temperature ups and downs.

Bob

On Dec 17, 2012, at 4:34 PM, Hal Murray hmur...@megapathdsl.net wrote:



li...@rtty.us said:

If you are trying to set up say a 1 us delay, you will get ~ 50 ps per
degree C in your delay. That's a lot .


A while ago, t...@leapsecond.com said:

A long delay cable is fine too. If these are timing receivers you probably
don't need more than 100 ns of delay, once you figure out which receiver is
ahead of the other. The cable tempco is low enough not to worry about.


100 ns is 50-100 feet.  That's a reasonable length to work with.  But I was
curious about the temperature coefficient.  Google found this:
  http://www.hepl.hiroshima-u.ac.jp/phx/notes/cable/cable.html
which says:
# Belden 8240 (solid) shows a temperature coefficient of around
-0.252ps/m/deg in a temperature range between -20 and 30 deg. The coefficient
becomes steeper beyond 30 deg.
# Belden 8219 (foam) shows a larger temperature coefficient of around -0.352
ps/m/deg than that of 8240 in the similar temperature range. The coefficient
becomes steeper beyond 30 deg, but less steeper than that of 8240.
# Fujikura RG58-A/U shows the smallest temperature coefficient of around
-0.152 ps/m/deg, but in a narrow temperature range between -10 and 20 deg.
The coefficient beyond 20 deg is much steeper than the others.

To pick round numbers, 30 meters and 3 C and 0.25 ps/m/C gives 25 ps.


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Re: [time-nuts] Comparing PPS from 2 GPS units


jim...@earthlink.net said:
 You mean RG65 http://www.awcwire.com/ProductSpec.aspx?id=M17/
 34-RG65-Coaxial-Cable or RG186 http://www.awcwire.com/ProductSpec.aspx?id=RG1
 86-Coaxial-Cable 

Interesting stuff.  Thanks.

RG-65 says no longer available.  It also says:
  Coaxial Delay Line 0.15 uSec/ft
(Am I having troubles counting zeros, or is that seriously slow?)
  Nom. Imp. 950
  Vel. of Prop. 2 (no units)
  Cond. MaterialMagnet Wire Helix
(What is magnet wire, and what does helix mean and how does it effect 
coax?)


RG186 says:
  Shield Material   Magnet Wire   [What does that mean?]
  Nom. Imp. 1000

The cable on scope probes (at least fancy ones) has a tiny conductor.  I 
think that translates into high impedance.


-- 
These are my opinions.  I hate spam.




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Re: [time-nuts] Comparing PPS from 2 GPS units

2012-12-17 Thread Jim Lux


On 12/17/12 9:40 PM, Hal Murray wrote:


jim...@earthlink.net said:

You mean RG65 http://www.awcwire.com/ProductSpec.aspx?id=M17/
34-RG65-Coaxial-Cable or RG186 http://www.awcwire.com/ProductSpec.aspx?id=RG1
86-Coaxial-Cable


Interesting stuff.  Thanks.

RG-65 says no longer available.  It also says:
   Coaxial Delay Line 0.15 uSec/ft
(Am I having troubles counting zeros, or is that seriously slow?)

Yes, seriously slow.. 150 ns/ft, vs 1ns/ft in free space..



   Nom. Imp.950
   Vel. of Prop.2 (no units)
   Cond. Material   Magnet Wire Helix
(What is magnet wire, and what does helix mean and how does it effect
coax?)


RG186 says:
   Shield Material  Magnet Wire   [What does that mean?]
   Nom. Imp.1000

The cable on scope probes (at least fancy ones) has a tiny conductor.  I
think that translates into high impedance.





No.. this stuff has a helically wound center conductor (so the L per 
unit length is very high).. impedance is sqrt (L/C) so the Z is high 
(1000 ohms).. prop velocity is 1/sqrt(LC), so big L means slow prop..


This stuff is incredibly lossy..

Some of it has the center conductor wound around a soft iron core wire 
to increase the inductance.









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Re: [time-nuts] Comparing PPS from 2 GPS units

2012-12-17 Thread Bruce Griffiths


Hal Murray wrote:

jim...@earthlink.net said:
   

You mean RG65 http://www.awcwire.com/ProductSpec.aspx?id=M17/
34-RG65-Coaxial-Cable or RG186 http://www.awcwire.com/ProductSpec.aspx?id=RG1
86-Coaxial-Cable
 

Interesting stuff.  Thanks.

RG-65 says no longer available.  It also says:
   Coaxial Delay Line 0.15 uSec/ft
(Am I having troubles counting zeros, or is that seriously slow?)
   Nom. Imp.950
   Vel. of Prop.2 (no units)
   Cond. Material   Magnet Wire Helix
(What is magnet wire, and what does helix mean and how does it effect
coax?)

   

Magnet wire is enamelled wire (usually copper).

RG186 says:
   Shield Material  Magnet Wire   [What does that mean?]
   Nom. Imp.1000

The cable on scope probes (at least fancy ones) has a tiny conductor.  I
think that translates into high impedance.


   

Bruce

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Re: [time-nuts] Comparing PPS from 2 GPS units