Re: [time-nuts] PPS phase between two GPS units.

[Dan Kemppainen]

Hi all,

Thanks for all the responses.

The GPS units were swapped on the splitter ports, and the phase 
difference did in fact change. It changed from 21nS to around 5nS. Not 
exactly what was expected, although it would tend to indicate the RF 
path is not the same through the splitter.


Last night a 'symmetrical splitter' was made up using a mini circuits 
ZFRSC-42. Both of the outputs to the GPS units were AC coupled. A bias T 
was inserted directly on the antenna feed with external power feeding 
the new splitter antenna port.


The PPS's are now very close, about 1 nS average difference. If this 
holds solid, in a few days I'll swap splitter ports again.


Thanks,
Dan










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Re: [time-nuts] PPS phase between two GPS units.

[paul swed]

Dan
Great and at least for me it makes sense from the active splitters I have
seen that use diodes to allow one receiver to power the pre-amp.
In my 8 way you have the diodes and L+Cs. The powered path is essentially
the diode turned on.
The non powered is a reverse biased diode and the C around the diode and
then the Ls of the DC path. Something like that.
I did the same thing as you in the 8 way splitter.
Separate DC bias feeding upstream to a intermediate amp ahead of the
splitter to make up for the 8 way splitter loss about 16 db as I recall.
With humor I am finding 8 ports isn't quite enough! Silly.
Regards
Paul
WB8TSL


On Wed, Dec 23, 2015 at 11:11 AM, Dan Kemppainen 
wrote:

> Hi all,
>
> Thanks for all the responses.
>
> The GPS units were swapped on the splitter ports, and the phase difference
> did in fact change. It changed from 21nS to around 5nS. Not exactly what
> was expected, although it would tend to indicate the RF path is not the
> same through the splitter.
>
> Last night a 'symmetrical splitter' was made up using a mini circuits
> ZFRSC-42. Both of the outputs to the GPS units were AC coupled. A bias T
> was inserted directly on the antenna feed with external power feeding the
> new splitter antenna port.
>
> The PPS's are now very close, about 1 nS average difference. If this holds
> solid, in a few days I'll swap splitter ports again.
>
> Thanks,
> Dan
>
>
>
>
>
>
>
>
>
>
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Re: [time-nuts] PPS phase between two GPS units.

[Tommy Phone]

Seems to me you could adjust the feed line length value in one of the receivers 
to zero out the difference as it appears that the path length is slightly 
different.

>From Tom Holmes, N8ZM

> On Dec 23, 2015, at 11:11 AM, Dan Kemppainen  wrote:
> 
> Hi all,
> 
> Thanks for all the responses.
> 
> The GPS units were swapped on the splitter ports, and the phase difference 
> did in fact change. It changed from 21nS to around 5nS. Not exactly what was 
> expected, although it would tend to indicate the RF path is not the same 
> through the splitter.
> 
> Last night a 'symmetrical splitter' was made up using a mini circuits 
> ZFRSC-42. Both of the outputs to the GPS units were AC coupled. A bias T was 
> inserted directly on the antenna feed with external power feeding the new 
> splitter antenna port.
> 
> The PPS's are now very close, about 1 nS average difference. If this holds 
> solid, in a few days I'll swap splitter ports again.
> 
> Thanks,
> Dan
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
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Re: [time-nuts] PPS phase between two GPS units.

[Graham / KE9H]

Are they running off the same power supply?
If so, I would run them from different power supplies as an experiment.
--- Graham

==

On Tue, Dec 22, 2015 at 6:19 AM, Attila Kinali  wrote:

> On Tue, 22 Dec 2015 11:57:55 +0100
> Mike Cook  wrote:
>
> > > A sampling difference of 1 cycle with 48Mhz clocks would give you ~21ns
> > offset if not using sawtooth correction. Can you do the sawtooth
> correction
> > and see if the offset is reduced?
>
> This is the most likely explanation. The LEA-6 modules use a 24MHz
> oscillator
> which is doubled for the processor, leading to the 48MHz clock.
>
> >   Good thinking Brian. But I would expect the difference to wander from
> 21s
> > UNLESS the the two receivers clocks are lock stepping. Injection locking
> > might do this if the two module are physically close enough.
>
> Injection locking wont work by simply playing the modules close to
> eachother.
> The oscillators are shielded well enough that quite some injection energy
> would
> be needed. Unless the TIMEPULSE2 output of one module is used to generate a
> 8MHz signal which is directly injected into the power suplly of the other,
> i
> don't see how injection locking would work. And even then, I wouldn't be
> sure
> if injection locking could be acheived.
>
> What could be done, though, is to lift the shield over the cpu side of the
> LEA-6, unsolder the oscillator and use an external 24MHz oscillator to
> supply both LEA-6 modules.
>
> If you do this, you could even go as far as to use the sawtooth correction
> message to stear the reference oscillator. That way you wouldn't need to
> measure the PPS output and could to a "fully" digital control system
> instead.
>
> Attila Kinali
>
> --
> It is upon moral qualities that a society is ultimately founded. All
> the prosperity and technological sophistication in the world is of no
> use without that foundation.
>  -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] PPS phase between two GPS units.

[Brian Inglis]

On 2015-12-21 18:24, d...@irtelemetrics.com wrote:

So I've been playing with some timing hardware here, and have noticed something 
rather curious. I have two otherwise identical Lea-6T GPS modules, configured 
exactly the same. These units are tied to the same antenna, with a splitter 
with the same length cables running to each unit. They were given the same 
survey coordinates. Initially there was not any appreciable difference between 
the PPS outputs. The outputs were on average within about one nS of each other. 
However after a day or two they started to display a difference of about 21nS 
between the PPS outputs. This is also evident in the GPSDO output, as the phase 
of the 10Mhz is also skewed by 21nS or so.

A few days ago I started a 48 hour survey. The came up virtually identical 
coordinates at the end of that survey. After the survey the phase is still 21nS 
different.

At this point, my only thought is the GPS splitter. It's DC coupled to one 
unit, and AC coupled to the other. It is possible there are some delays on one 
output vs. the other due to the blocking caps and bypass inductor in the 
splitter. I've tried swapping the GPSDO units on the splitter, so we'll see 
what happens there.
Can anyone offer any insight as to why the two units may have a different PPS 
output timing? It's not really a problem, more of a curiosity and mildly 
academic exercise.


A sampling difference of 1 cycle with 48Mhz clocks would give you ~21ns offset 
if not using sawtooth correction. Can you do the sawtooth correction and see if 
the offset is reduced?

--
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
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Re: [time-nuts] PPS phase between two GPS units.

[Hal Murray]

paulsw...@gmail.com said:
> I think you are doing the right test to see if the splitter delay is the
> issue 21 ns is mighty small and a real possibility. 

21 ns is huge.  That's 10 inches of PCB trace.  74AC00 at 5V is 6.6 ns, so 
that's 3 gates.

But in any case, it would be obvious after the OP swapped the cables.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] PPS phase between two GPS units.

[Andrea Baldoni]

On Mon, Dec 21, 2015 at 08:24:37PM -0500, d...@irtelemetrics.com wrote:

> difference of about 21nS between the PPS outputs. This is also evident in
> the GPSDO output, as the phase of the 10Mhz is also skewed by 21nS or so. 

21nS are about 1/48MHz, if internally LEA-6T has this clock and the PPS
output is not sawtooth corrected, you just have one of the two one clock tick
ahead of the other.

Best regards,
Andrea Baldoni
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Re: [time-nuts] PPS phase between two GPS units.

[timeok]

To verify if the where the delay is generated, antenna and splitter or GPS,  
simply invert the antenna cable on the GPSs antenna connector and verify if the 
delay change as sign.

Luciano




On Tue 22/12/15 02:24 , d...@irtelemetrics.com wrote:

> Hi All,
>  
> So I've been playing with some timing hardware here, and have noticed 
> something rather curious. I have two otherwise identical Lea-6T GPS 
> modules, configured exactly the same. These units are tied to the same 
> antenna, with a splitter with the same length cables running to each 
> unit. They were given the same survey coordinates. Initially there was 
> not any appreciable difference between the PPS outputs. The outputs 
> were on average within about one nS of each other. However after a day 
> or two they started to display a difference of about 21nS between the 
> PPS outputs. This is also evident in the GPSDO output, as the phase of 
> the 10Mhz is also skewed by 21nS or so. 
>  
> A few days ago I started a 48 hour survey. The came up virtually 
> identical coordinates at the end of that survey. After the survey the 
> phase is still 21nS different. 
>  
> At this point, my only thought is the GPS splitter. It's DC coupled to 
> one unit, and AC coupled to the other. It is possible there are some 
> delays on one output vs. the other due to the blocking caps and bypass 
> inductor in the splitter. I've tried swapping the GPSDO units on the 
> splitter, so we'll see what happens there. 
>  
> Can anyone offer any insight as to why the two units may have a 
> different PPS output timing? It's not really a problem, more of a 
> curiosity and mildly academic exercise. 
>  
> Thanks,
> Dan
>  
>  
>  
>  
>  
>  
> 
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> 
> 
> Links:
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Re: [time-nuts] PPS phase between two GPS units.

[Alexander Pummer]

swap the two receivers and see which one is leading, if leading is 
changing the delay difference is with the antenna signal distribution

73
KJ6UHN
Alex
On 12/21/2015 8:03 PM, paul swed wrote:

I think you are doing the right test to see if the splitter delay is the
issue 21 ns is mighty small and a real possibility.
Regards
Paul
WB8TSL

On Mon, Dec 21, 2015 at 8:24 PM,  wrote:


Hi All,

So I've been playing with some timing hardware here, and have noticed
something rather curious. I have two otherwise identical Lea-6T GPS
modules, configured exactly the same. These units are tied to the same
antenna, with a splitter with the same length cables running to each unit.
They were given the same survey coordinates. Initially there was not any
appreciable difference between the PPS outputs. The outputs were on average
within about one nS of each other. However after a day or two they started
to display a difference of about 21nS between the PPS outputs. This is also
evident in the GPSDO output, as the phase of the 10Mhz is also skewed by
21nS or so.

A few days ago I started a 48 hour survey. The came up virtually identical
coordinates at the end of that survey. After the survey the phase is still
21nS different.

At this point, my only thought is the GPS splitter. It's DC coupled to one
unit, and AC coupled to the other. It is possible there are some delays on
one output vs. the other due to the blocking caps and bypass inductor in
the splitter. I've tried swapping the GPSDO units on the splitter, so we'll
see what happens there.
Can anyone offer any insight as to why the two units may have a different
PPS output timing? It's not really a problem, more of a curiosity and
mildly academic exercise.
Thanks,
Dan







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-
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Version: 2016.0.7294 / Virus Database: 4489/11227 - Release Date: 12/21/15


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Re: [time-nuts] PPS phase between two GPS units.

[Mike Cook]

> Le 22 déc. 2015 à 06:16, Brian Inglis  a 
> écrit :
> 
> On 2015-12-21 18:24, d...@irtelemetrics.com wrote:
>> So I've been playing with some timing hardware here, and have noticed 
>> something rather curious. I have two otherwise identical Lea-6T GPS modules, 
>> configured exactly the same. These units are tied to the same antenna, with 
>> a splitter with the same length cables running to each unit. They were given 
>> the same survey coordinates. Initially there was not any appreciable 
>> difference between the PPS outputs. The outputs were on average within about 
>> one nS of each other. However after a day or two they started to display a 
>> difference of about 21nS between the PPS outputs. This is also evident in 
>> the GPSDO output, as the phase of the 10Mhz is also skewed by 21nS or so.
>> 
>> A few days ago I started a 48 hour survey. The came up virtually identical 
>> coordinates at the end of that survey. After the survey the phase is still 
>> 21nS different.
>> 
>> At this point, my only thought is the GPS splitter. It's DC coupled to one 
>> unit, and AC coupled to the other. It is possible there are some delays on 
>> one output vs. the other due to the blocking caps and bypass inductor in the 
>> splitter. I've tried swapping the GPSDO units on the splitter, so we'll see 
>> what happens there.
>> Can anyone offer any insight as to why the two units may have a different 
>> PPS output timing? It's not really a problem, more of a curiosity and mildly 
>> academic exercise.
> 
> A sampling difference of 1 cycle with 48Mhz clocks would give you ~21ns 
> offset if not using sawtooth correction. Can you do the sawtooth correction 
> and see if the offset is reduced?
> 

  Good thinking Brian. But I would expect the difference to wander from 21s 
UNLESS the the two receivers clocks are lock stepping. Injection locking might 
do this if the two module are physically close enough. 

> -- 
> Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
> ___
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"The main function of a modern police force is filling in forms."
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Re: [time-nuts] PPS phase between two GPS units.

[Attila Kinali]

On Tue, 22 Dec 2015 11:57:55 +0100
Mike Cook  wrote:

> > A sampling difference of 1 cycle with 48Mhz clocks would give you ~21ns
> offset if not using sawtooth correction. Can you do the sawtooth correction
> and see if the offset is reduced?

This is the most likely explanation. The LEA-6 modules use a 24MHz oscillator
which is doubled for the processor, leading to the 48MHz clock.

>   Good thinking Brian. But I would expect the difference to wander from 21s
> UNLESS the the two receivers clocks are lock stepping. Injection locking
> might do this if the two module are physically close enough. 

Injection locking wont work by simply playing the modules close to eachother.
The oscillators are shielded well enough that quite some injection energy would
be needed. Unless the TIMEPULSE2 output of one module is used to generate a
8MHz signal which is directly injected into the power suplly of the other, i
don't see how injection locking would work. And even then, I wouldn't be sure
if injection locking could be acheived. 

What could be done, though, is to lift the shield over the cpu side of the
LEA-6, unsolder the oscillator and use an external 24MHz oscillator to
supply both LEA-6 modules.

If you do this, you could even go as far as to use the sawtooth correction
message to stear the reference oscillator. That way you wouldn't need to
measure the PPS output and could to a "fully" digital control system instead.

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] PPS phase between two GPS units.

[paul swed]

I think you are doing the right test to see if the splitter delay is the
issue 21 ns is mighty small and a real possibility.
Regards
Paul
WB8TSL

On Mon, Dec 21, 2015 at 8:24 PM,  wrote:

> Hi All,
>
> So I've been playing with some timing hardware here, and have noticed
> something rather curious. I have two otherwise identical Lea-6T GPS
> modules, configured exactly the same. These units are tied to the same
> antenna, with a splitter with the same length cables running to each unit.
> They were given the same survey coordinates. Initially there was not any
> appreciable difference between the PPS outputs. The outputs were on average
> within about one nS of each other. However after a day or two they started
> to display a difference of about 21nS between the PPS outputs. This is also
> evident in the GPSDO output, as the phase of the 10Mhz is also skewed by
> 21nS or so.
>
> A few days ago I started a 48 hour survey. The came up virtually identical
> coordinates at the end of that survey. After the survey the phase is still
> 21nS different.
>
> At this point, my only thought is the GPS splitter. It's DC coupled to one
> unit, and AC coupled to the other. It is possible there are some delays on
> one output vs. the other due to the blocking caps and bypass inductor in
> the splitter. I've tried swapping the GPSDO units on the splitter, so we'll
> see what happens there.
> Can anyone offer any insight as to why the two units may have a different
> PPS output timing? It's not really a problem, more of a curiosity and
> mildly academic exercise.
> Thanks,
> Dan
>
>
>
>
>
>
>
> ___
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>
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