[time-nuts] Frequency Ensemble

[Mark Sims]

Lady Heather can output RINEX (v2.xx and 3.xx files) for most receivers that 
output pseudorange and/or carrier phase data.   I have tested it with the Ublox 
4T, 5T, 6T, 8T, F9P, and F9T receivers.  Also the Venus RTK receivers, Trimble 
NetRS,  Ashtech Z12,, NVS08, Trimble timing receivers, and a few others.

With my horrible antenna location L1/L2 devices yield positions error ellipses 
around 10 mm. lat/lon and 50mm altitude  L1 only devices are around 100 mm.   
People with better antenna locations have reported error ellipses is the low mm 
range.  

The Trimble receivers are currently a bit wonky since I have some issues 
calculating pseudoranges from the Trimble data.  I didn't have Trimble issues 
before CSRS-PPP "upgraded" their processing software.

The version of Heather that I am currently working on can apply sawtooth 
corrections to the PPS output measured by a counter such as the TAPR-TICC in 
order to make a better "paper clock".

--
>  As Bob says, the ublox chipsets from generation 6 onwards are probably
the best value as they can be configured to output the raw
measurements for precise position/time.
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Re: [time-nuts] Frequency Ensemble

[Michael Wouters]

The f9p is about 3 times better than  the ublox m8t. Will post a plot
later..

Cheers
Michael

On Tue, 19 Mar 2019 at 9:00 am, Bob kb8tq  wrote:

> Hi
>
> ….. and here I was wondering if it had ever gone out :) Glad it made it.
>
> No, I did not run any single frequency units beside it. It is much better
> than any similar plot
> I’ve done in the past on an L1 only part.
>
> Indeed, as long as you just look at the first ~ 100 seconds, the
> “reference standard” is less of an issue.
> A fairly typical OCXO will hang in there at 2 ppt or so out to a couple
> hundred seconds.
> You can get a very good idea of what’s what simply by going out that far.
> Indeed you might spend
> some “quality time” finding a working example of something like a MT-260.
> That’s part of the fun ….
> Some of the better parts will be 5 MHz units. A HP 5335 can come in handy
> to turn 5 MHz into
> 10 MHz ….. there are a lot of ways to get that done.
>
> Yes LH and a TAPPR TICC would also help in the process …. still need those
> 25 orders :)
>
> Bob
>
> > On Mar 18, 2019, at 3:29 PM, Dan Kemppainen 
> wrote:
> >
> > Bob,
> >
> > I recalled the plot you posted a few days ago. Nice plot on the F9P,
> BTW. Thanks for posting that.
> >
> > I don't supposed you happened to be recording a similar plot with a L1
> only Ublox part at the same time by chance, did you? I think it would be
> interesting to compare a 6T or M8 part to the F9P. (I lack a standard good
> enough to compare them to...)
> >
> > Thanks!
> > Dan
> >
> >
> >
> >
> > On 3/18/2019 1:00 PM, time-nuts-requ...@lists.febo.com wrote:
> >> Message: 2
> >> Date: Mon, 18 Mar 2019 12:26:55 -0400
> >> From: Bob kb8tq
> >> To: Discussion of precise time and frequency measurement
> >>  
> >> Subject: Re: [time-nuts] Frequency Ensemble
> >> Message-ID:<88460ea2-6034-48d1-a77a-fed1f824d...@n1k.org>
> >> Content-Type: text/plain;charset=utf-8
> >> Hi
> >> There are a variety of GPS devices that put out a PPS. uBlox makes
> some, there
> >> are a number of other companies that do so. The PPS comes out modulo
> the local
> >> timebase. On a precision part, there is a ?sawtooth correction? message
> that also
> >> comes out to further quantify the best guess time of that pulse.
> >> Noise wise, even with correction you are lucky to get a one second ADEV
> in the
> >> 1 to 2 ppb range with a typical L1 receiver. With a L1 / L2 device like
> the F9P,
> >> you might do a bit better than that.
> >> The ADEV of your other sources at short tau will be much better than
> the GPS PPS
> >> noise. As you average out over long periods, the GPS will win the race.
> >> Bob
> >
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>
>
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Re: [time-nuts] Frequency Ensemble

[Bob kb8tq]

Hi

You can access an “NTRIP stream” from various free sites. There is some 
mumbo jumbo on some of them to get an account. There are streams dedicated
to “clock and orbit correction”. CLK11 and CLK93 are two fairly common ones.

Since NTRIP is a real time product (as in < 30 seconds delay) it can be used 
for 
“right now” sort of correction. RTKLIB is probably the most common way to get
the local receiver and an NTRIP stream combined. 

If you just want to play with it ntrip.itsware.net  
port 2101 is a free / no registration source
of the CLK11 stream. They also have various other “correction product” streams
you can play with. 

In theory (though I can in no way prove it yet) you should be able to reduce 
the 
timing errors associated with the broadcast clock and orbit estimates by about 
an order
of magnitude. It is *abundantly* unclear what that translates into in 
nanoseconds due
to a whole lot of layers everything goes through….. 

The NTRIP products are all aimed at surveying applications so there is a lot of 
translation 
involved to get to the sort of time numbers we like to deal with. It should 
help, the big
question is how much (10 is unlikely …. sqrt(10) maybe …. sqrt(10) / 2 … who 
knows ….). 

Bob

> On Mar 18, 2019, at 1:32 PM, Anders Wallin  
> wrote:
> 
> If you search for "GNSS time transfer" you will find a lot of papers etc.
> For example these might get you started:
> https://www.bipm.org/ws/CCTF/TAI_TRAINING/Allowed/Fundamentals/Training-2012-GNSS-Defraigne.pdf
> https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7909843
> 
> I tried to collect some tools for PPP post-processing on github:
> https://github.com/aewallin/ppp-tools
> I am not sure what (open) software exists for common-view analysis...
> PPP uses satellite clock-corrections and orbit-corrections from an IGS
> data-centre. They have "ultra rapid" and "rapid" products (=downloadable
> files) that are available with some days or hours of delay.
> The "final" products can have up to two weeks (?) of delay.
> With a dual-frequency receiver the ionosphere delay can be removed
> ('ionosphere-free L1/L2 linear combination') and my understanding is the
> troposphere-delay (water content) is one of the larger remaining
> uncertainties.
> 
> AW
> 
> 
> On Mon, Mar 18, 2019 at 5:03 PM Rodger via time-nuts <
> time-nuts@lists.febo.com> wrote:
> 
>> 
>> Regarding your comments on collecting raw time data from GPS and post
>> processing it.  Can you provide any reference info, links, etc. with more
>> detail on that topic?
>> Clearly I'd need a GPS that outputs the proper raw messaging and the
>> software for processing it.  I'm somewhat familiar with the techniques
>> involved to improve GPS position data, but hadn't thought about it as much
>> for timing.
>> 
>> Thanks,
>> 
>> Rodger
>> 
>> 
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Re: [time-nuts] Frequency Ensemble

[Bob kb8tq]

Hi

….. and here I was wondering if it had ever gone out :) Glad it made it. 

No, I did not run any single frequency units beside it. It is much better than 
any similar plot
I’ve done in the past on an L1 only part. 

Indeed, as long as you just look at the first ~ 100 seconds, the “reference 
standard” is less of an issue. 
A fairly typical OCXO will hang in there at 2 ppt or so out to a couple hundred 
seconds. 
You can get a very good idea of what’s what simply by going out that far. 
Indeed you might spend
some “quality time” finding a working example of something like a MT-260. 
That’s part of the fun ….
Some of the better parts will be 5 MHz units. A HP 5335 can come in handy to 
turn 5 MHz into
10 MHz ….. there are a lot of ways to get that done. 

Yes LH and a TAPPR TICC would also help in the process …. still need those 25 
orders :) 

Bob

> On Mar 18, 2019, at 3:29 PM, Dan Kemppainen  wrote:
> 
> Bob,
> 
> I recalled the plot you posted a few days ago. Nice plot on the F9P, BTW. 
> Thanks for posting that.
> 
> I don't supposed you happened to be recording a similar plot with a L1 only 
> Ublox part at the same time by chance, did you? I think it would be 
> interesting to compare a 6T or M8 part to the F9P. (I lack a standard good 
> enough to compare them to...)
> 
> Thanks!
> Dan
> 
> 
> 
> 
> On 3/18/2019 1:00 PM, time-nuts-requ...@lists.febo.com wrote:
>> Message: 2
>> Date: Mon, 18 Mar 2019 12:26:55 -0400
>> From: Bob kb8tq
>> To: Discussion of precise time and frequency measurement
>>  
>> Subject: Re: [time-nuts] Frequency Ensemble
>> Message-ID:<88460ea2-6034-48d1-a77a-fed1f824d...@n1k.org>
>> Content-Type: text/plain;charset=utf-8
>> Hi
>> There are a variety of GPS devices that put out a PPS. uBlox makes some, 
>> there
>> are a number of other companies that do so. The PPS comes out modulo the 
>> local
>> timebase. On a precision part, there is a ?sawtooth correction? message that 
>> also
>> comes out to further quantify the best guess time of that pulse.
>> Noise wise, even with correction you are lucky to get a one second ADEV in 
>> the
>> 1 to 2 ppb range with a typical L1 receiver. With a L1 / L2 device like the 
>> F9P,
>> you might do a bit better than that.
>> The ADEV of your other sources at short tau will be much better than the GPS 
>> PPS
>> noise. As you average out over long periods, the GPS will win the race.
>> Bob
> 
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Re: [time-nuts] Frequency Ensemble

[Dan Kemppainen]

Bob,

I recalled the plot you posted a few days ago. Nice plot on the F9P, 
BTW. Thanks for posting that.


I don't supposed you happened to be recording a similar plot with a L1 
only Ublox part at the same time by chance, did you? I think it would be 
interesting to compare a 6T or M8 part to the F9P. (I lack a standard 
good enough to compare them to...)


Thanks!
Dan




On 3/18/2019 1:00 PM, time-nuts-requ...@lists.febo.com wrote:

Message: 2
Date: Mon, 18 Mar 2019 12:26:55 -0400
From: Bob kb8tq
To: Discussion of precise time and frequency measurement

Subject: Re: [time-nuts] Frequency Ensemble
Message-ID:<88460ea2-6034-48d1-a77a-fed1f824d...@n1k.org>
Content-Type: text/plain;   charset=utf-8

Hi

There are a variety of GPS devices that put out a PPS. uBlox makes some, there
are a number of other companies that do so. The PPS comes out modulo the local
timebase. On a precision part, there is a ?sawtooth correction? message that 
also
comes out to further quantify the best guess time of that pulse.

Noise wise, even with correction you are lucky to get a one second ADEV in the
1 to 2 ppb range with a typical L1 receiver. With a L1 / L2 device like the F9P,
you might do a bit better than that.

The ADEV of your other sources at short tau will be much better than the GPS PPS
noise. As you average out over long periods, the GPS will win the race.

Bob


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Re: [time-nuts] Frequency Ensemble

[Tim Lister]

On Mon, Mar 18, 2019 at 8:03 AM Rodger via time-nuts
 wrote:
>
> Tom,
>
> Thanks for the explanation of clock ensembles.  That answered a few
> questions I've had for a while.
> Regarding your comments on collecting raw time data from GPS and post
> processing it.  Can you provide any reference info, links, etc. with more
> detail on that topic?
> Clearly I'd need a GPS that outputs the proper raw messaging and the
> software for processing it.  I'm somewhat familiar with the techniques
> involved to improve GPS position data, but hadn't thought about it as much
> for timing.

As Bob says, the ublox chipsets from generation 6 onwards are probably
the best value as they can be configured to output the raw
measurements for precise position/time. There is info on configuring
these at OpenStreetMap and rtklibexplorer's wiki and blog respectively
and I also added a howto on my blog on doing this
(https://adventuresinprecision.space/howtos/precise-gps-positions/)

The OpenTTP project has code for capturing the raw data (ublox M8's
are supported right now, I am working on adding support for -6T and
the main developers are looking at adding support for the new ublox F9
chips) and software for doing the GPS Common View processing. I am
just starting to dig into this but need to get the last bit of the
ublox6 support working in order to give it some valid data to play
with. The other easily available GPS receiver that OpenTTP supports is
the Trimble Resolution T which I think has been "end-of-lifed" by
Trimble which has pros of being available cheap on ebay and cons of
not being able to buy a brand new "official" board unlike with the
ublox 8 and 9 receivers.

>
> Thanks,
>
> Rodger
>

Cheers,
Tim

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Re: [time-nuts] Frequency Ensemble

[Michael Wouters]

This project www.openttp.org provides software for post-processing of raw
data for time-transfer from some currently available single frequency
receivers. It provides CGGTTS and RINEX, the latter for use with the
various PPP services. There are some tools in there too for doing eg common
view and all-in-view comparisons. If you want to try it out, the develop
branch in the GitHub repo is the place to start. I'll be talking about it
at IFCS-EFTF.

Cheers
Michael


On Tue, 19 Mar 2019 at 5:08 am, Anders Wallin 
wrote:

> If you search for "GNSS time transfer" you will find a lot of papers etc.
> For example these might get you started:
>
> https://www.bipm.org/ws/CCTF/TAI_TRAINING/Allowed/Fundamentals/Training-2012-GNSS-Defraigne.pdf
> https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7909843
>
> I tried to collect some tools for PPP post-processing on github:
> https://github.com/aewallin/ppp-tools
> I am not sure what (open) software exists for common-view analysis...
> PPP uses satellite clock-corrections and orbit-corrections from an IGS
> data-centre. They have "ultra rapid" and "rapid" products (=downloadable
> files) that are available with some days or hours of delay.
> The "final" products can have up to two weeks (?) of delay.
> With a dual-frequency receiver the ionosphere delay can be removed
> ('ionosphere-free L1/L2 linear combination') and my understanding is the
> troposphere-delay (water content) is one of the larger remaining
> uncertainties.
>
> AW
>
>
> On Mon, Mar 18, 2019 at 5:03 PM Rodger via time-nuts <
> time-nuts@lists.febo.com> wrote:
>
> >
> > Regarding your comments on collecting raw time data from GPS and post
> > processing it.  Can you provide any reference info, links, etc. with more
> > detail on that topic?
> > Clearly I'd need a GPS that outputs the proper raw messaging and the
> > software for processing it.  I'm somewhat familiar with the techniques
> > involved to improve GPS position data, but hadn't thought about it as
> much
> > for timing.
> >
> > Thanks,
> >
> > Rodger
> >
> >
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Re: [time-nuts] Frequency Ensemble

[Anders Wallin]

If you search for "GNSS time transfer" you will find a lot of papers etc.
For example these might get you started:
https://www.bipm.org/ws/CCTF/TAI_TRAINING/Allowed/Fundamentals/Training-2012-GNSS-Defraigne.pdf
https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7909843

I tried to collect some tools for PPP post-processing on github:
https://github.com/aewallin/ppp-tools
I am not sure what (open) software exists for common-view analysis...
PPP uses satellite clock-corrections and orbit-corrections from an IGS
data-centre. They have "ultra rapid" and "rapid" products (=downloadable
files) that are available with some days or hours of delay.
The "final" products can have up to two weeks (?) of delay.
With a dual-frequency receiver the ionosphere delay can be removed
('ionosphere-free L1/L2 linear combination') and my understanding is the
troposphere-delay (water content) is one of the larger remaining
uncertainties.

AW


On Mon, Mar 18, 2019 at 5:03 PM Rodger via time-nuts <
time-nuts@lists.febo.com> wrote:

>
> Regarding your comments on collecting raw time data from GPS and post
> processing it.  Can you provide any reference info, links, etc. with more
> detail on that topic?
> Clearly I'd need a GPS that outputs the proper raw messaging and the
> software for processing it.  I'm somewhat familiar with the techniques
> involved to improve GPS position data, but hadn't thought about it as much
> for timing.
>
> Thanks,
>
> Rodger
>
>
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Re: [time-nuts] Frequency Ensemble

[Bob kb8tq]

Hi

There are a variety of GPS devices that put out a PPS. uBlox makes some, there 
are a number of other companies that do so. The PPS comes out modulo the local
timebase. On a precision part, there is a “sawtooth correction” message that 
also
comes out to further quantify the best guess time of that pulse. 

Noise wise, even with correction you are lucky to get a one second ADEV in the 
1 to 2 ppb range with a typical L1 receiver. With a L1 / L2 device like the F9P,
you might do a bit better than that. 

The ADEV of your other sources at short tau will be much better than the GPS PPS
noise. As you average out over long periods, the GPS will win the race.

Bob

> On Mar 18, 2019, at 9:56 AM, Rodger via time-nuts  
> wrote:
> 
> Tom,
> 
> Thanks for the explanation of clock ensembles.  That answered a few
> questions I've had for a while.
> Regarding your comments on collecting raw time data from GPS and post
> processing it.  Can you provide any reference info, links, etc. with more
> detail on that topic?
> Clearly I'd need a GPS that outputs the proper raw messaging and the
> software for processing it.  I'm somewhat familiar with the techniques
> involved to improve GPS position data, but hadn't thought about it as much
> for timing.
> 
> Thanks,
> 
> Rodger
> 
> -Original Message-
> From: time-nuts  On Behalf Of Tom Van Baak
> Sent: Sunday, March 17, 2019 3:00 PM
> To: Discussion of precise time and frequency measurement
> 
> Subject: Re: [time-nuts] Frequency Ensemble
> 
>> Hi Everyone,I like to know if it possible to run let say 10 GPSDO, 16 
>> Rb clock together and take the average to control 1 "master clock" and
> have better stability ?
>> like what BIPM or NIST doing.
>> I have search about ensemble system but I have no idea how much 
>> advantage I get from some clock that I already have.Thank You Anton
> 
> Anton,
> 
> The rule-of-thumb is that, *under the right conditions*, N clocks will
> perform sqrt(N) better than 1 clock.
> 
> So yes, NIST, USNO, PTB, BIPM -- all the big boys -- use ensemble
> techniques. But the key is that they mostly use cesium clocks, not OCXO or
> Rb clocks from eBay. Laboratory cesium standards don't suffer from frequency
> drift. The other key is that the clocks are independent. Under these
> conditions one can obtain sqrt(N) advantage.
> 
> The problem with using cheap OCXO or Rb clocks is that they drift, and this
> drift may depend on make / model / environment; all of which are possibly
> common mode for you. This means the full sqrt(N) assumption is likely not
> valid.
> 
> The problem with using GPSDO is that they are not independent clocks. In
> fact, they aren't clocks at all: they are just noisy radio receivers,
> implementing "time transfer" from the USNO GPS master clock, which is
> related to but not equal to UTC(USNO) which is related to but not equal to
> UTC itself. There's a lot of common mode error amongst a set of GPSDO. This
> means the full sqrt(N) assumption is likely not valid.
> 
> Those who use GPS for highest accuracy tend not to use GPSDO. Instead they
> just collect raw timing information and post-process it some hours to weeks
> later. That is, they want to know
>what time-it-was-precisely
> rather than
>what time-it-is-approximately.
> A GPSDO only does the latter.
> 
> /tvb
> 
> 
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> 
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Re: [time-nuts] FTS-4040/A - Looking for voltage on switching power supply

[Taka Kamiya via time-nuts]

30V seems to be the answer.  I am going to attempt to repair the factory 
switcher.  I found one electrolytic gone and few other things suspect.  So I 
will know for sure.  Model number (custom) suggests 30V as well.  As to 
manuals, I can go as old as 4040B, but not A.  I do have an option of using it 
with 24V external.  

--- 
(Mr.) Taka Kamiya
I'm stuck in a wormhole  Hello, worms! 

On Monday, March 18, 2019, 11:03:42 AM EDT, gandalfg8--- via time-nuts 
 wrote:  
 
 I believe the FTS-4040 was originallly a Time and Frequency Solutions product 
and the manual for their FTS-4060 can be found here.
www.to-way.com/tf/4060man.pdf
That shows the pre-regulator DC power requirements as a nominal 26 V, with a 
range of 22 to 30 V.

I'm not sure how relevant this would be to the FTS-4040 but wouldn't be too 
surprised if there are similarities.
Nigel, GM8PZR


Now it is certain the failure is power supply.  I fed 26V into DC port and 
everything is working as before.  I'd rather replace this faulty supply.  
Question is, 24V?  28V?  30V?  or 28.45V?  This power supply appears to be a 
custom unit.  Still looking for spec on power supply.
At least it's not the cesium tube 
phew!--- 
(Mr.) Taka Kamiya
I'm stuck in a wormhole  Hello, worms! 

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Re: [time-nuts] Frequency Ensemble

[Rodger via time-nuts]

Tom,

Thanks for the explanation of clock ensembles.  That answered a few
questions I've had for a while.
Regarding your comments on collecting raw time data from GPS and post
processing it.  Can you provide any reference info, links, etc. with more
detail on that topic?
Clearly I'd need a GPS that outputs the proper raw messaging and the
software for processing it.  I'm somewhat familiar with the techniques
involved to improve GPS position data, but hadn't thought about it as much
for timing.

Thanks,

Rodger

-Original Message-
From: time-nuts  On Behalf Of Tom Van Baak
Sent: Sunday, March 17, 2019 3:00 PM
To: Discussion of precise time and frequency measurement

Subject: Re: [time-nuts] Frequency Ensemble

> Hi Everyone,I like to know if it possible to run let say 10 GPSDO, 16 
> Rb clock together and take the average to control 1 "master clock" and
have better stability ?
> like what BIPM or NIST doing.
> I have search about ensemble system but I have no idea how much 
> advantage I get from some clock that I already have.Thank You Anton

Anton,

The rule-of-thumb is that, *under the right conditions*, N clocks will
perform sqrt(N) better than 1 clock.

So yes, NIST, USNO, PTB, BIPM -- all the big boys -- use ensemble
techniques. But the key is that they mostly use cesium clocks, not OCXO or
Rb clocks from eBay. Laboratory cesium standards don't suffer from frequency
drift. The other key is that the clocks are independent. Under these
conditions one can obtain sqrt(N) advantage.

The problem with using cheap OCXO or Rb clocks is that they drift, and this
drift may depend on make / model / environment; all of which are possibly
common mode for you. This means the full sqrt(N) assumption is likely not
valid.

The problem with using GPSDO is that they are not independent clocks. In
fact, they aren't clocks at all: they are just noisy radio receivers,
implementing "time transfer" from the USNO GPS master clock, which is
related to but not equal to UTC(USNO) which is related to but not equal to
UTC itself. There's a lot of common mode error amongst a set of GPSDO. This
means the full sqrt(N) assumption is likely not valid.

Those who use GPS for highest accuracy tend not to use GPSDO. Instead they
just collect raw timing information and post-process it some hours to weeks
later. That is, they want to know
what time-it-was-precisely
rather than
what time-it-is-approximately.
A GPSDO only does the latter.

/tvb


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[time-nuts] FTS-4040/A - Looking for voltage on switching power supply

[gandalfg8--- via time-nuts]

I believe the FTS-4040 was originallly a Time and Frequency Solutions product 
and the manual for their FTS-4060 can be found here.
www.to-way.com/tf/4060man.pdf
That shows the pre-regulator DC power requirements as a nominal 26 V, with a 
range of 22 to 30 V.

I'm not sure how relevant this would be to the FTS-4040 but wouldn't be too 
surprised if there are similarities.
Nigel, GM8PZR


Now it is certain the failure is power supply.  I fed 26V into DC port and 
everything is working as before.  I'd rather replace this faulty supply.  
Question is, 24V?  28V?  30V?  or 28.45V?  This power supply appears to be a 
custom unit.  Still looking for spec on power supply.
At least it's not the cesium tube 
phew!--- 
(Mr.) Taka Kamiya
I'm stuck in a wormhole  Hello, worms! 

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Re: [time-nuts] Distribution amplifier for 10MHz and 1 pps

[Bob kb8tq]

Hi

CMOS is what you want rather than TTL in this day and age. Propagation delay 
and jitter are
both much better than any of the TTL families. 

NC7SZ125: 

Prop delay 2.6 ns
Output high 50 ma max 32 ma rated 
Output low 50 ma max 32 ma rated
(rated = ~0.5V off rail at 4.5V supply)

74S140

Prop delay 6 ns
Output high 10 ma
Output low 24 ma

74AC04

Prop delay 1 to 10 ns (call it 5 ns)
Output +/- 50 ma max, +/- 24 ma rated

(all above are ok on 5V)

and we could go on and on and on…..

Anytime you do this, you run into odd things on spec sheets so comparisons are 
never perfect. 
I would run things at as high a voltage as possible without creating smoke. The 
chips are normally
faster and quieter at the higher voltage. ( = you can see a phase noise 
improvement going from
5.0 to 5.5V …). 

I would go with a “simple” gate rather than a Schmitt trigger. Phase noise on 
the simple gates
has measured lower each time I’ve checked them. Having the switch points at 
different levels
also tends to mess up duty cycle just a bit. (Good luck measuring that with 
fast edges …..). 

Bob






> On Mar 18, 2019, at 2:43 AM, Julien Goodwin  
> wrote:
> 
> The 74S140 (dual 4-input NAND) is the classic TI TTL 50-ohm driver.
> They're still available in DIP & SOIC.
> 
> I'm currently waiting on some boards to arrive so I can try SN74LVC1G17
> as a more modern replacement that's much cheaper and smaller.
> 
> Once I've proven it I'll do a separate thread to the list about the
> whole project, since it's on-topic.
> 
> On 18/3/19 1:27 pm, Bob kb8tq wrote:
>> Hi
>> 
>> CMOS is good. The faster the better. Go to your favorite vendor and find 
>> whatever is “king” this month
>> and that’s what you go with. HC has been around a *long* time and is about 
>> as slow as it gets in terms 
>> of 5V CMOS ( yes, 4000 series is slower still …).  Faster means less delay 
>> in the gate (so lower variation
>> in delay). It also turns out that faster means lower phase noise so lower 
>> jitter. 
>> 
>> Buffers are better than inverters, simply because they have higher output 
>> drive capability. One “favorite”
>> are the x125 and x126 tri-state buffers. NC7SZ125 and NC7SZ126 are two 
>> examples. 
>> 
>> If you want to drive 50 ohms, you likely will need to parallel gates in 
>> order to handle the current. There is 
>> an ongoing debate about source termination vs load termination vs “both 
>> termination” vs “don’t bother”. 
>> I would suggest that terminating one end or the other is a … errr …. really 
>> good idea. 
>> 
>> Lots more information in the archives.
>> 
>> Bob
>> 
>>> On Mar 17, 2019, at 6:39 PM, Taka Kamiya via time-nuts 
>>>  wrote:
>>> 
>>> I'm very curious, too.  Especially when I *just* built one using 74HC04N.  
>>> 
>>> --- 
>>> (Mr.) Taka Kamiya
>>> I'm stuck in a wormhole  Hello, worms! 
>>> 
>>>   On Sunday, March 17, 2019, 4:01:26 PM EDT, Hal Murray 
>>>  wrote:  
>>> 
>>> 
 For 1PPs the main goal is jitter and the selection of the ICs is very 
 tricky 
>>> 
>>> Could you please say more?  Do you mean logic family selection, or chip 
>>> selection within a family?
>>> 
>>> Most modern digital chips are CMOS with an input threshold of VCC/2.  I'd 
>>> expect power supply noise to be important and families with faster 
>>> switching 
>>> times probably make more noise.
>>> 
>>> 
>>> -- 
>>> These are my opinions.  I hate spam.
>>> 
>>> 
>>> 
>>> 
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Re: [time-nuts] Distribution amplifier for 10MHz and 1 pps

[Julien Goodwin]

The 74S140 (dual 4-input NAND) is the classic TI TTL 50-ohm driver.
They're still available in DIP & SOIC.

I'm currently waiting on some boards to arrive so I can try SN74LVC1G17
as a more modern replacement that's much cheaper and smaller.

Once I've proven it I'll do a separate thread to the list about the
whole project, since it's on-topic.

On 18/3/19 1:27 pm, Bob kb8tq wrote:
> Hi
> 
> CMOS is good. The faster the better. Go to your favorite vendor and find 
> whatever is “king” this month
> and that’s what you go with. HC has been around a *long* time and is about as 
> slow as it gets in terms 
> of 5V CMOS ( yes, 4000 series is slower still …).  Faster means less delay in 
> the gate (so lower variation
> in delay). It also turns out that faster means lower phase noise so lower 
> jitter. 
> 
> Buffers are better than inverters, simply because they have higher output 
> drive capability. One “favorite”
> are the x125 and x126 tri-state buffers. NC7SZ125 and NC7SZ126 are two 
> examples. 
> 
> If you want to drive 50 ohms, you likely will need to parallel gates in order 
> to handle the current. There is 
> an ongoing debate about source termination vs load termination vs “both 
> termination” vs “don’t bother”. 
> I would suggest that terminating one end or the other is a … errr …. really 
> good idea. 
> 
> Lots more information in the archives.
> 
> Bob
> 
>> On Mar 17, 2019, at 6:39 PM, Taka Kamiya via time-nuts 
>>  wrote:
>>
>> I'm very curious, too.  Especially when I *just* built one using 74HC04N.  
>>
>> --- 
>> (Mr.) Taka Kamiya
>> I'm stuck in a wormhole  Hello, worms! 
>>
>>On Sunday, March 17, 2019, 4:01:26 PM EDT, Hal Murray 
>>  wrote:  
>>
>>
>>> For 1PPs the main goal is jitter and the selection of the ICs is very 
>>> tricky 
>>
>> Could you please say more?  Do you mean logic family selection, or chip 
>> selection within a family?
>>
>> Most modern digital chips are CMOS with an input threshold of VCC/2.  I'd 
>> expect power supply noise to be important and families with faster switching 
>> times probably make more noise.
>>
>>
>> -- 
>> These are my opinions.  I hate spam.
>>
>>
>>
>>
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> 
> 
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