Re: [time-nuts] Switching regulator replacement for 7805

[Scott Stobbe]

Well a sigma-delta modulator in loose terms is an error amplifier around a
quantizer, so you get 1/loopgain rejection of quantization noise (in other
words the noise is shaped out in frequency). Resulting in a noise spectrum
that converges in 1/N versus 1/sqrt(N) for flat Gaussian noise, versus
lobes and nulls for a single sinusoid.

I totally agree that the first step is to reduce the switching residual
that is generated, even half a bond wire at say 1 nH is 13 mOhms at 2 MHz,
combine that with a power converter running 30% ripple current of a 1A
output is 300mA ripple current resulting in 4 mV just on half a bondwire.
Equivalently a 10 uF MLCC should be able to hit 10 mOhms at 2 MHz before
hitting its SRF.

On Sun, Dec 4, 2016 at 5:58 PM, Attila Kinali  wrote:

> On Sun, 4 Dec 2016 16:22:02 -0500
> Scott Stobbe  wrote:
>
> > If you wanted to be nutty you wouldn't go PWM at all, just like
> > fractional-N sythns don't just mash 2 divider values. You would
> sigma-delta
> > modulate your power stage. I don't know if you can buy one COTS, but
> there
> > are plenty of papers on rolling your own.
>
> I guess you are refering to spread-spectrum techniques.
> Such DC/DC converters exist, but are usually those with high power
> ratings. IMHO it is also not worth the effort, as its main use is
> to meet EMI emission requirements. The only application that comes
> to my mind where spread-spectrum actually helps are high sensitiv
> radio receivers where every spur is a nuisance. For most other
> use, and time-nuts use in particular, it is much less useful.
> The noise energy is not gone. It is still there, just spread over
> a large bandwidth. In time measurement applications, noise is
> integrated over time _and_ frequency. Thus even if the noise is
> spread over a large bandwidth, the energy will still contribute
> to the uncertainty and degrade the ADEV. It will be just harder
> to identify as the peak is now much smaller and wanders in frequency.
>
> It is much better to the design such, that as little as possible
> of the switching energy leaks out of the DC/DC converter and filter
> out the rest.
>
> Depending on the application, another possible application is to
> sync up the DC/DC converter to the "main" clock source. This makes
> the switching noise then coherent to the system, which either makes
> it average out completely, or possible to filter it out in the digital
> domain using a deep notch-filter in receiver applications.
>
>
> Attila Kinali
> --
> Malek's Law:
> Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] Switching regulator replacement for 7805

[jimlux]

On 12/4/16 2:59 PM, Attila Kinali wrote:

On Sun, 4 Dec 2016 13:28:44 -0800
jimlux  wrote:


I little series L and another C (so you have a pi low pass) can make a
huge difference.  If the load current is reasonably constant, then the
drop across the series R of the L will be constant, so you can bump the
dc/dc output to compensate.  It's pretty easy to get 60dB of rejection
from a C-L-C pi, and for 2MHz, the parts are physically small.


Wouldn't it be better to use a ferrite bead instead, for this application?
The much lower series capacitance and thus higher self-resonance frequency
should help damping the spurs.

sure, if you can get enough L.  The other thing is that SMD inductors 
can be placed by machine, which isn't necessarily the case with ferrite 
beads (depending on how you do them).


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Re: [time-nuts] UCCM GPSDO

[Tim Lister]

On Sun, Dec 4, 2016 at 3:04 PM, Bryan _  wrote:
> I think the designation "UCCM" actually applies to the Symmetricom GPSDO 
> boards. Since most of these tend to come salvaged from China, tongue in cheek 
> I suspect "Unusable, Crushed, Cr_p, Mangled"
>
>
> Do the Trimble units report UCCM from the serial port?

Mine does and it was sold as a 'Trimble Inside'... Lady Heather
identifies it as a Trimble board and it doesn't seem to lose the
survey position on power-off, which I believe is a feature of the
Symmetricom version of the boards. I think the Symmetricom boards also
report 'UCCM-P >' as their prompt (based on the eevblog thread) which
mine doesn't (just 'UCCM >').

>
> -=Bryan=-
>

Cheers,
Tim
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Re: [time-nuts] UCCM GPSDO

[William H. Fite]

Unbelievably Crude Clock Mechanism:)

On Sunday, December 4, 2016, Bryan _  wrote:

> I think the designation "UCCM" actually applies to the Symmetricom GPSDO
> boards. Since most of these tend to come salvaged from China, tongue in
> cheek I suspect "Unusable, Crushed, Cr_p, Mangled"
>
>
> Do the Trimble units report UCCM from the serial port?
>
>
>
> -=Bryan=-
>
>
>
>
> 
> From: time-nuts > on behalf of
> Tim Lister >
> Sent: December 4, 2016 3:00 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] UCCM GPSDO
>
> On Sun, Dec 4, 2016 at 2:50 PM, Larry McDavid  > wrote:
> > Does anyone know the origin of the "UCCM" designation for the Trimble
> GPSDO
> > boards recently popular here?
> >
> > Is "UCCM" a valid model number, is it an acronym or is it something else?
> >
> > I've packaged several of these Trimble boards and I've seen about four
> > others, none of which was marked "UCCM." I've seen one on-line picture
> of a
> > packaged board that shows a separate label with "UCCM" marked.
> >
> > GPSCon already supports these "UCCM" boards and the next release of Lady
> > Heather is expected to support them also, so there is some acceptance of
> > this "UCCM" designation. But, what is the origin of this term and is it
> > valid?
>
> That's what the command prompt says when you connect to it over serial
> and it shows up in various places in response to commands such as
> SYST:STAT? I haven't taken my reboxed GPSDO apart to see if it says
> UCCM anywhere else on the board.
>
> >
> > --
> > Best wishes,
> >
> > Larry McDavid W6FUB
>
> Cheers,
> Tim
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> time and frequency measurement and related topics. To see the collection of
> prior postings to ...
>
>
>
> and follow the instructions there.
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Re: [time-nuts] UCCM GPSDO

[Bryan _]

I think the designation "UCCM" actually applies to the Symmetricom GPSDO 
boards. Since most of these tend to come salvaged from China, tongue in cheek I 
suspect "Unusable, Crushed, Cr_p, Mangled"


Do the Trimble units report UCCM from the serial port?



-=Bryan=-





From: time-nuts  on behalf of Tim Lister 

Sent: December 4, 2016 3:00 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] UCCM GPSDO

On Sun, Dec 4, 2016 at 2:50 PM, Larry McDavid  wrote:
> Does anyone know the origin of the "UCCM" designation for the Trimble GPSDO
> boards recently popular here?
>
> Is "UCCM" a valid model number, is it an acronym or is it something else?
>
> I've packaged several of these Trimble boards and I've seen about four
> others, none of which was marked "UCCM." I've seen one on-line picture of a
> packaged board that shows a separate label with "UCCM" marked.
>
> GPSCon already supports these "UCCM" boards and the next release of Lady
> Heather is expected to support them also, so there is some acceptance of
> this "UCCM" designation. But, what is the origin of this term and is it
> valid?

That's what the command prompt says when you connect to it over serial
and it shows up in various places in response to commands such as
SYST:STAT? I haven't taken my reboxed GPSDO apart to see if it says
UCCM anywhere else on the board.

>
> --
> Best wishes,
>
> Larry McDavid W6FUB

Cheers,
Tim
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Re: [time-nuts] Switching regulator replacement for 7805

[Attila Kinali]

On Sun, 4 Dec 2016 16:41:13 -0500
John Ackermann N8UR  wrote:

> The little OCXO I used for testing goes from about 850ma cold to 200ma 
> hot (at 5V) and I noticed a very different appearance of the spectrum as 
> the current dropped -- at high current, the switching spurs were quite 
> narrow, but as the current dropped (and particularly below some 
> threshold I don't remember) the spurs widened out quite a bit.

This is exactly the PWM to PFM mode switch I described earlier.

The 850mA are probably high enough that the DC/DC converter works
in PWM mode, thus switching with a constant frequency, even if the
load changes. On the other hand 200mA of a 1A converter is low enough
that it's most likely in the PFM region, where every small change
(or noise) causes the switching frequency to change.

Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] UCCM GPSDO

[Tim Lister]

On Sun, Dec 4, 2016 at 2:50 PM, Larry McDavid  wrote:
> Does anyone know the origin of the "UCCM" designation for the Trimble GPSDO
> boards recently popular here?
>
> Is "UCCM" a valid model number, is it an acronym or is it something else?
>
> I've packaged several of these Trimble boards and I've seen about four
> others, none of which was marked "UCCM." I've seen one on-line picture of a
> packaged board that shows a separate label with "UCCM" marked.
>
> GPSCon already supports these "UCCM" boards and the next release of Lady
> Heather is expected to support them also, so there is some acceptance of
> this "UCCM" designation. But, what is the origin of this term and is it
> valid?

That's what the command prompt says when you connect to it over serial
and it shows up in various places in response to commands such as
SYST:STAT? I haven't taken my reboxed GPSDO apart to see if it says
UCCM anywhere else on the board.

>
> --
> Best wishes,
>
> Larry McDavid W6FUB

Cheers,
Tim
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Re: [time-nuts] Switching regulator replacement for 7805

[Attila Kinali]

On Sun, 4 Dec 2016 13:28:44 -0800
jimlux  wrote:

> I little series L and another C (so you have a pi low pass) can make a 
> huge difference.  If the load current is reasonably constant, then the 
> drop across the series R of the L will be constant, so you can bump the 
> dc/dc output to compensate.  It's pretty easy to get 60dB of rejection 
> from a C-L-C pi, and for 2MHz, the parts are physically small.

Wouldn't it be better to use a ferrite bead instead, for this application?
The much lower series capacitance and thus higher self-resonance frequency
should help damping the spurs.

Or am I missing something?

Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] Switching regulator replacement for 7805

[Attila Kinali]

On Sun, 4 Dec 2016 16:22:02 -0500
Scott Stobbe  wrote:

> If you wanted to be nutty you wouldn't go PWM at all, just like
> fractional-N sythns don't just mash 2 divider values. You would sigma-delta
> modulate your power stage. I don't know if you can buy one COTS, but there
> are plenty of papers on rolling your own.

I guess you are refering to spread-spectrum techniques.
Such DC/DC converters exist, but are usually those with high power
ratings. IMHO it is also not worth the effort, as its main use is
to meet EMI emission requirements. The only application that comes
to my mind where spread-spectrum actually helps are high sensitiv
radio receivers where every spur is a nuisance. For most other
use, and time-nuts use in particular, it is much less useful.
The noise energy is not gone. It is still there, just spread over
a large bandwidth. In time measurement applications, noise is
integrated over time _and_ frequency. Thus even if the noise is
spread over a large bandwidth, the energy will still contribute
to the uncertainty and degrade the ADEV. It will be just harder
to identify as the peak is now much smaller and wanders in frequency.

It is much better to the design such, that as little as possible
of the switching energy leaks out of the DC/DC converter and filter
out the rest.

Depending on the application, another possible application is to
sync up the DC/DC converter to the "main" clock source. This makes
the switching noise then coherent to the system, which either makes
it average out completely, or possible to filter it out in the digital
domain using a deep notch-filter in receiver applications.


Attila Kinali
-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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[time-nuts] UCCM GPSDO

[Larry McDavid]

Does anyone know the origin of the "UCCM" designation for the Trimble 
GPSDO boards recently popular here?


Is "UCCM" a valid model number, is it an acronym or is it something else?

I've packaged several of these Trimble boards and I've seen about four 
others, none of which was marked "UCCM." I've seen one on-line picture 
of a packaged board that shows a separate label with "UCCM" marked.


GPSCon already supports these "UCCM" boards and the next release of Lady 
Heather is expected to support them also, so there is some acceptance of 
this "UCCM" designation. But, what is the origin of this term and is it 
valid?


--
Best wishes,

Larry McDavid W6FUB
Anaheim, California  (SE of Los Angeles, near Disneyland)
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Re: [time-nuts] Switching regulator replacement for 7805

[Bob Camp]

Hi

I doubt that there is a significant demand for 10 ma output switchers. The 
benefit of going from 12V to 2V as a switcher compared to linear is mighty 
small. As a guess, I’d say that anything much under a watt is not worth doing
in this arena. That gets you up to at least 100 ma at the normal conversion 
ranges. I would also suggest that the regulator you are replacing is only a 
1A part. That places an upper limit on what makes sense. 

If you really want the SMT parts, get an oven. A converted toaster oven is 
a dirt cheap way to do it. 

Bob

> On Dec 4, 2016, at 4:09 PM, Attila Kinali  wrote:
> 
> On Sun, 4 Dec 2016 15:45:55 -0500
> Bob Camp  wrote:
> 
>> Given that the parts to build one are fairly easy to get and that we likely 
>> have “nutty” 
>> EMI requirements. Maybe a small board that drops into a 78xx footprint is 
>> the 
>> better solution. 
> 
> I don't fully agree. To go full "nutty" you would want to use the chips
> in the QFN packages, as those have shorter leads and a large ground pad
> to keep EMI down. But soldering an 0.5mm QFN by hand is impossible
> (believe me, I tried) and not everyone has an oven. Also a lot of the
> EMI performance depend on what output current you expect. Using a 1A
> design for 10mA is a good way to get poor EMI performance as the
> chip will go from PWM (aka fixed frequency) to PFM (aka fixed on time)
> mode under low load to increase efficiency. The same goes for input
> voltage. So we would need to do multiple designs for different 
> output current and input voltage ranges... which kind of defeats
> the purpose of "a small board that drops into".
> 
> What could be done, though, is a small board with all components,
> but the inductor on it. So then one could select the right inductor
> for the application and solder it on. Using an inductor that is easy
> to solder (like e.g. WE-PD3) with a wide selection of values should
> do the trick.
> 
>   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] Switching regulator replacement for 7805

[John Ackermann N8UR]

On 12/04/2016 04:34 PM, jimlux wrote:


Even for time-nuts, I suspect we're not looking to eke out the last
percent of efficiency from 96% to 97%, or handle wildly varying loads,
etc.  Nor are we usually looking for absolute minimum parts cost.


The little OCXO I used for testing goes from about 850ma cold to 200ma 
hot (at 5V) and I noticed a very different appearance of the spectrum as 
the current dropped -- at high current, the switching spurs were quite 
narrow, but as the current dropped (and particularly below some 
threshold I don't remember) the spurs widened out quite a bit.

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Re: [time-nuts] Switching regulator replacement for 7805

[jimlux]

On 12/4/16 1:09 PM, Attila Kinali wrote:

On Sun, 4 Dec 2016 15:45:55 -0500
Bob Camp  wrote:


Given that the parts to build one are fairly easy to get and that we likely 
have “nutty”
EMI requirements. Maybe a small board that drops into a 78xx footprint is the
better solution.


I don't fully agree. To go full "nutty" you would want to use the chips
i




or buy a few of each of the commercial modules and test them.  They are 
an all-in-one solution with all the usual features about overtemp, 
overcurrent, etc.


What you'd need to do is characterize their noise properties over load 
(something not in the datasheet), and then you could design a LC filter 
to knock down the rest.  Or do the LDO regulator thing.. it's not 
entirely clear that a dc/dc followed by a suitable LDO might not come 
out ahead of a dc/dc followed by a filter.


Even for time-nuts, I suspect we're not looking to eke out the last 
percent of efficiency from 96% to 97%, or handle wildly varying loads, 
etc.  Nor are we usually looking for absolute minimum parts cost.


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Re: [time-nuts] Switching regulator replacement for 7805

[jimlux]

On 12/4/16 12:14 PM, John Ackermann N8UR wrote:

That's a very good point... the design I'm testing the regulator in has
a fair bit of C filtering, but no series L.



I little series L and another C (so you have a pi low pass) can make a 
huge difference.  If the load current is reasonably constant, then the 
drop across the series R of the L will be constant, so you can bump the 
dc/dc output to compensate.  It's pretty easy to get 60dB of rejection 
from a C-L-C pi, and for 2MHz, the parts are physically small.



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Re: [time-nuts] Switching regulator replacement for 7805

[Scott Stobbe]

If you wanted to be nutty you wouldn't go PWM at all, just like
fractional-N sythns don't just mash 2 divider values. You would sigma-delta
modulate your power stage. I don't know if you can buy one COTS, but there
are plenty of papers on rolling your own.

On Sun, Dec 4, 2016 at 4:09 PM, Attila Kinali  wrote:

> On Sun, 4 Dec 2016 15:45:55 -0500
> Bob Camp  wrote:
>
> > Given that the parts to build one are fairly easy to get and that we
> likely have “nutty”
> > EMI requirements. Maybe a small board that drops into a 78xx footprint
> is the
> > better solution.
>
> I don't fully agree. To go full "nutty" you would want to use the chips
> in the QFN packages, as those have shorter leads and a large ground pad
> to keep EMI down. But soldering an 0.5mm QFN by hand is impossible
> (believe me, I tried) and not everyone has an oven. Also a lot of the
> EMI performance depend on what output current you expect. Using a 1A
> design for 10mA is a good way to get poor EMI performance as the
> chip will go from PWM (aka fixed frequency) to PFM (aka fixed on time)
> mode under low load to increase efficiency. The same goes for input
> voltage. So we would need to do multiple designs for different
> output current and input voltage ranges... which kind of defeats
> the purpose of "a small board that drops into".
>
> What could be done, though, is a small board with all components,
> but the inductor on it. So then one could select the right inductor
> for the application and solder it on. Using an inductor that is easy
> to solder (like e.g. WE-PD3) with a wide selection of values should
> do the trick.
>
> 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
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
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>
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Re: [time-nuts] Switching regulator replacement for 7805

[Attila Kinali]

On Sun, 4 Dec 2016 15:45:55 -0500
Bob Camp  wrote:

> Given that the parts to build one are fairly easy to get and that we likely 
> have “nutty” 
> EMI requirements. Maybe a small board that drops into a 78xx footprint is the 
> better solution. 

I don't fully agree. To go full "nutty" you would want to use the chips
in the QFN packages, as those have shorter leads and a large ground pad
to keep EMI down. But soldering an 0.5mm QFN by hand is impossible
(believe me, I tried) and not everyone has an oven. Also a lot of the
EMI performance depend on what output current you expect. Using a 1A
design for 10mA is a good way to get poor EMI performance as the
chip will go from PWM (aka fixed frequency) to PFM (aka fixed on time)
mode under low load to increase efficiency. The same goes for input
voltage. So we would need to do multiple designs for different 
output current and input voltage ranges... which kind of defeats
the purpose of "a small board that drops into".

What could be done, though, is a small board with all components,
but the inductor on it. So then one could select the right inductor
for the application and solder it on. Using an inductor that is easy
to solder (like e.g. WE-PD3) with a wide selection of values should
do the trick.

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] Switching regulator 12 > 4 V (3.3)

[Tim Shoppa]

I use the LM2574 for a lot of one-off applications the past decade or more.
For a 4V application you would start with LM2574-ADJ. It is available in
8-pin DIP, although the surface mount part is just as amenable to
dead-bugging, and does 0.5 amp no problem and runs perfectly cool. It does
not take (by modern standards) the smallest switching inductors and I
always do additional LC filtering at both input and output, so in terms of
"board space" this is quite a hog compared to more modern higher frequency
switchers.

Tim N3QE

On Sun, Dec 4, 2016 at 2:46 PM, KA2WEU--- via time-nuts 
wrote:

> Who has a good recommendation for a switching power supply circuit, 12V DC
> in, 4 V/ 500mA out , Exactly 3.3 for IC voltage.
>
> 73 de Ulrich
>
>
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Re: [time-nuts] Switching regulator replacement for 7805

[Bob Camp]

Hi

Given that the parts to build one are fairly easy to get and that we likely 
have “nutty” 
EMI requirements. Maybe a small board that drops into a 78xx footprint is the 
better solution. 

Bob

> On Dec 4, 2016, at 3:39 PM, Adrian Godwin  wrote:
> 
> At Farnell, they're listed under Power Supplies rather than Switching
> Regulators (which is a subdivision of Semiconductors).
> 
> It makes sense since one is a board product and the other a chip, but when
> the board product is a drop-in replacement for a TO220, less sense!
> 
> 
> On Sun, Dec 4, 2016 at 7:44 PM, John Ackermann N8UR  wrote:
> 
>> And Digikey does stock the Murata part, for about $4.30.  Why I couldn't
>> find it when searching their site for switching regulators, I don't know.
>> 
>> John
>> 
>> 
>> 
>> On 12/04/2016 02:39 PM, John Ackermann N8UR wrote:
>> 
>>> Thanks for that pointer!  When I searched Digikey, I wasn't able to find
>>> anything that was in the 3-lead TO-220 case.  I will definitely check
>>> out the Murata units, as I suspect they perform better than this one.
>>> 
>>> John
>>> 
>>> On 12/04/2016 02:01 PM, Adrian Godwin wrote:
>>> 
 Thanks for this. I've seen something similar from Murata :
 
 http://uk.farnell.com/murata-power-solutions/oki-78sr-5-1-5-
 w36-c/converter-dc-dc-1-o-p-7-5w-1-5a/dp/2102101
 
 
 Since they're a mainstream supplier of inductors they may have managed
 better performance - it would be interesting to compare.
 
 
 On Sun, Dec 4, 2016 at 6:50 PM, John Ackermann N8UR 
 wrote:
 
 I found a cute little switching regulator that's a drop-in
> replacement for
> an LM7805: http://www.ebay.com/itm/261243604047
> 
> I got a couple to play with, mainly to see how bad the noise would be.
> Here are spectrum analyzer and PN shots comparing a cheap surplus
> OCXO when
> driven by a regular 7805 and by the switching replacement.
> 
> The switching frequency is supposed to be 2 MHz but you can see that
> it's
> more like 2.4 MHz.  Whether this performance is sufficient for any
> application is up to you.  It sure runs a lot cooler than a 7805,
> though!
> 
> John
> 
> 
> 
> 
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Re: [time-nuts] Switching regulator replacement for 7805

[Adrian Godwin]

At Farnell, they're listed under Power Supplies rather than Switching
Regulators (which is a subdivision of Semiconductors).

It makes sense since one is a board product and the other a chip, but when
the board product is a drop-in replacement for a TO220, less sense!


On Sun, Dec 4, 2016 at 7:44 PM, John Ackermann N8UR  wrote:

> And Digikey does stock the Murata part, for about $4.30.  Why I couldn't
> find it when searching their site for switching regulators, I don't know.
>
> John
> 
>
>
> On 12/04/2016 02:39 PM, John Ackermann N8UR wrote:
>
>> Thanks for that pointer!  When I searched Digikey, I wasn't able to find
>> anything that was in the 3-lead TO-220 case.  I will definitely check
>> out the Murata units, as I suspect they perform better than this one.
>>
>> John
>> 
>> On 12/04/2016 02:01 PM, Adrian Godwin wrote:
>>
>>> Thanks for this. I've seen something similar from Murata :
>>>
>>> http://uk.farnell.com/murata-power-solutions/oki-78sr-5-1-5-
>>> w36-c/converter-dc-dc-1-o-p-7-5w-1-5a/dp/2102101
>>>
>>>
>>> Since they're a mainstream supplier of inductors they may have managed
>>> better performance - it would be interesting to compare.
>>>
>>>
>>> On Sun, Dec 4, 2016 at 6:50 PM, John Ackermann N8UR 
>>> wrote:
>>>
>>> I found a cute little switching regulator that's a drop-in
 replacement for
 an LM7805: http://www.ebay.com/itm/261243604047

 I got a couple to play with, mainly to see how bad the noise would be.
 Here are spectrum analyzer and PN shots comparing a cheap surplus
 OCXO when
 driven by a regular 7805 and by the switching replacement.

 The switching frequency is supposed to be 2 MHz but you can see that
 it's
 more like 2.4 MHz.  Whether this performance is sufficient for any
 application is up to you.  It sure runs a lot cooler than a 7805,
 though!

 John




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Re: [time-nuts] Switching regulator 12 > 4 V (3.3)

[Attila Kinali]

Moin Ulrich,

On Sun, 4 Dec 2016 14:46:34 -0500
KA2WEU--- via time-nuts  wrote:

> Who has a good recommendation for a switching power supply circuit, 12V DC  
> in, 4 V/ 500mA out , Exactly 3.3 for IC voltage.

You can either use one of the DC/DC converter modules by Muarata/Cui/..
or run your own. The former is of course easier and faster if you
just need something working. The later is IMHO the recommended approach
if you are doing your own board anyways, as you can tailor the DC/DC
converter to your needs and thus ensure minimal ripple/EMI.

Overall, doing your own DC/DC converter is pretty easy, if you know
a bit of RF design and know where the current flows. Using a modern
DC/DC converter chip like the LMR14006 will get you there with an
easy to solder case. Additionally you will need a Schottky diode that
can withstand some beating (aka high reverse recovery). TI lists the
NXP PMEG6010 in their reference design. As inductor I would probably
go with one of the Würth WE-TPC series (low resistance, high saturation
current and nicely shielded). Add some ceramic capacitors (something
like 10-100µF), and you are done.

For PCB layout, keep the current path from input capacitor to DC/DC
converter ground; the path from switching output over the diode to converter
ground; the path from switching output over inductor output capacitor
to converter ground as short as possible. Add as many ground vias as
possible and at least one complete, uncut ground plane directly underneath
all components. If possible use multiple GND planes. Even though this
thing should not generate much heat (with efficiencies >80% it should
be less than 0.4W for your requirements) it is still quite a bit if it
gets stuck somewhere. Thus the ground planes should be large and also
cover the back side to dissipate the heat.

For additional EMI reduction, put the inductor such, that the start
of the winding points in direction of the DC/DC converter and diode.


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] Switching regulator replacement for 7805

[Bob Camp]

Hi

The most common thing to miss on decoupling a switcher is that both the output 
*and* the input will generate crud that sprays all over the place. Series L on 
both 
the input and output are a really good idea. Microhenry (as opposed to 
milihenry) 
chokes are generally good enough. Values are dictated more by board space than 
anything else. 22 uH is not a bad starting point. A SRF above 3 MHz would be a 
good idea :)

Bob

> On Dec 4, 2016, at 3:14 PM, John Ackermann N8UR  wrote:
> 
> That's a very good point... the design I'm testing the regulator in has a 
> fair bit of C filtering, but no series L.
> 
> On 12/04/2016 02:45 PM, Chris Albertson wrote:
>> Surprisingly good as a drop-in replacement.
>> 
>> Question:  Suppose you are doing a new design and had space on the PCB for
>> one more small passive part.  I wonder how the performance of the switcher
>> with an LC filter compares with the 7805.Yes, I think this is fair.  It
>> is a trade off, It costs me one more inductor but I gain hugely reduced
>> power consumption and heat.
>> 
>> Or stated another way:  You have shown the noise difference for drop in to
>> existing circuit.  What about two roughly equivalent new design circuits?
>> How much to we pay in dollars and complexity to get equivalent noise?
>> 
>> Thanks a lot for this work.  Headed over to eBay right now
>> 
>>  (My application uses LiPo battery and needs to have stable voltage as the
>> battery drains but my current solution is noisyand those 78xx chips waste
>> far to much power. )
>> 
>> On Sun, Dec 4, 2016 at 10:50 AM, John Ackermann N8UR  wrote:
>> 
>>> I found a cute little switching regulator that's a drop-in replacement for
>>> an LM7805: http://www.ebay.com/itm/261243604047
>>> 
>>> I got a couple to play with, mainly to see how bad the noise would be.
>>> Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO when
>>> driven by a regular 7805 and by the switching replacement.
>>> 
>>> The switching frequency is supposed to be 2 MHz but you can see that it's
>>> more like 2.4 MHz.  Whether this performance is sufficient for any
>>> application is up to you.  It sure runs a lot cooler than a 7805, though!
>>> 
>>> John
>>> 
>>> 
>>> 
>>> 
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>> 
>> 
>> 
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Re: [time-nuts] Switching regulator 12 > 4 V (3.3)

[KA2WEU--- via time-nuts]

Thanks, I came too late into this discussion, yes the preferred voltage is  
3.3 V, but if decoupled by a emitter follower , maybe 4 V is a good  choice.
 
Can you please copy /past me the info?  Thanks Ulrich 
 
 
 
 
In a message dated 12/4/2016 3:12:18 P.M. Eastern Standard Time,  
jim...@earthlink.net writes:

On  12/4/16 11:46 AM, KA2WEU--- via time-nuts wrote:
> Who has a good  recommendation for a switching power supply circuit, 12V 
DC
> in, 4 V/  500mA out , Exactly 3.3 for IC voltage.
>
do you need 4V or  3.3V?

I'd start with one of the modular parts we've been  discussing.  They 
typically have 9-18V input range and whatever you  want out.

Since I have the Mouser search page up, P78A03-0500 is $3.71  in qty 1, 
3.3V out @ 0.5A, 6-28V in.  ABout 85%  efficient
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Re: [time-nuts] Switching regulator replacement for 7805

[John Ackermann N8UR]

That's a very good point... the design I'm testing the regulator in has 
a fair bit of C filtering, but no series L.


On 12/04/2016 02:45 PM, Chris Albertson wrote:

Surprisingly good as a drop-in replacement.

Question:  Suppose you are doing a new design and had space on the PCB for
one more small passive part.  I wonder how the performance of the switcher
with an LC filter compares with the 7805.Yes, I think this is fair.  It
is a trade off, It costs me one more inductor but I gain hugely reduced
power consumption and heat.

Or stated another way:  You have shown the noise difference for drop in to
existing circuit.  What about two roughly equivalent new design circuits?
How much to we pay in dollars and complexity to get equivalent noise?

Thanks a lot for this work.  Headed over to eBay right now

  (My application uses LiPo battery and needs to have stable voltage as the
battery drains but my current solution is noisyand those 78xx chips waste
far to much power. )

On Sun, Dec 4, 2016 at 10:50 AM, John Ackermann N8UR  wrote:


I found a cute little switching regulator that's a drop-in replacement for
an LM7805: http://www.ebay.com/itm/261243604047

I got a couple to play with, mainly to see how bad the noise would be.
Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO when
driven by a regular 7805 and by the switching replacement.

The switching frequency is supposed to be 2 MHz but you can see that it's
more like 2.4 MHz.  Whether this performance is sufficient for any
application is up to you.  It sure runs a lot cooler than a 7805, though!

John




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Re: [time-nuts] Switching regulator 12 > 4 V (3.3)

[jimlux]

On 12/4/16 11:46 AM, KA2WEU--- via time-nuts wrote:

Who has a good recommendation for a switching power supply circuit, 12V DC
in, 4 V/ 500mA out , Exactly 3.3 for IC voltage.


do you need 4V or 3.3V?

I'd start with one of the modular parts we've been discussing.  They 
typically have 9-18V input range and whatever you want out.


Since I have the Mouser search page up, P78A03-0500 is $3.71 in qty 1, 
3.3V out @ 0.5A, 6-28V in.  ABout 85% efficient

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Re: [time-nuts] Switching regulator replacement for 7805

[jimlux]

On 12/4/16 11:45 AM, Chris Albertson wrote:

Surprisingly good as a drop-in replacement.

Question:  Suppose you are doing a new design and had space on the PCB for
one more small passive part.  I wonder how the performance of the switcher
with an LC filter compares with the 7805.Yes, I think this is fair.  It
is a trade off, It costs me one more inductor but I gain hugely reduced
power consumption and heat.

Or stated another way:  You have shown the noise difference for drop in to
existing circuit.  What about two roughly equivalent new design circuits?
How much to we pay in dollars and complexity to get equivalent noise?


What we just did was use a discrete Linear Tech DC/DC, with carefully 
chosen output voltage, followed by a LDO with very, very good PSRR at 
high frequencies.


You could probably do the same with the modular parts- saves you 
designing the DC/DC - the Cui parts (and I'm sure the others) can adjust 
the output voltage with a single resistor and they have very wide input 
voltage range, although I don't know if they can do buck/boost, or just 
buck.


For our application we had an existing DC/DC design, so in theory, we 
saved time by reusing it - whether or not that's really true, I'm not 
sure, different voltages, different load currents, etc.  It might have 
been easier/cheaper/faster to use a modular DC/DC - assuming it doesn't 
have some sort of latchup or other single event effects.







Thanks a lot for this work.  Headed over to eBay right now

 (My application uses LiPo battery and needs to have stable voltage as the
battery drains but my current solution is noisyand those 78xx chips waste
far to much power. )

On Sun, Dec 4, 2016 at 10:50 AM, John Ackermann N8UR  wrote:


I found a cute little switching regulator that's a drop-in replacement for
an LM7805: http://www.ebay.com/itm/261243604047

I got a couple to play with, mainly to see how bad the noise would be.
Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO when
driven by a regular 7805 and by the switching replacement.

The switching frequency is supposed to be 2 MHz but you can see that it's
more like 2.4 MHz.  Whether this performance is sufficient for any
application is up to you.  It sure runs a lot cooler than a 7805, though!

John




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Re: [time-nuts] Switching regulator replacement for 7805

[jimlux]

On 12/4/16 11:39 AM, John Ackermann N8UR wrote:

Thanks for that pointer!  When I searched Digikey, I wasn't able to find
anything that was in the 3-lead TO-220 case.  I will definitely check
out the Murata units, as I suspect they perform better than this one.



The Cui parts are also available in a TO-220 pinout

Mouser has them  V7805-1000 for example, in a variety of configurations 
and ratings, but a bit more expensive.. $5-10


Maybe you need to search for DC/DC converter or something?

I found them a few years ago because I was looking for surface mount 
power converters



Seems there's tons of them from a variety of mfrs, judging from the 
Mouser search engine



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Re: [time-nuts] Switching regulator 12 > 4 V (3.3)

[KA2WEU--- via time-nuts]

Who has a good recommendation for a switching power supply circuit, 12V DC  
in, 4 V/ 500mA out , Exactly 3.3 for IC voltage.
 
73 de Ulrich 
 
 
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Re: [time-nuts] Switching regulator replacement for 7805

[Chris Albertson]

Surprisingly good as a drop-in replacement.

Question:  Suppose you are doing a new design and had space on the PCB for
one more small passive part.  I wonder how the performance of the switcher
with an LC filter compares with the 7805.Yes, I think this is fair.  It
is a trade off, It costs me one more inductor but I gain hugely reduced
power consumption and heat.

Or stated another way:  You have shown the noise difference for drop in to
existing circuit.  What about two roughly equivalent new design circuits?
How much to we pay in dollars and complexity to get equivalent noise?

Thanks a lot for this work.  Headed over to eBay right now

 (My application uses LiPo battery and needs to have stable voltage as the
battery drains but my current solution is noisyand those 78xx chips waste
far to much power. )

On Sun, Dec 4, 2016 at 10:50 AM, John Ackermann N8UR  wrote:

> I found a cute little switching regulator that's a drop-in replacement for
> an LM7805: http://www.ebay.com/itm/261243604047
>
> I got a couple to play with, mainly to see how bad the noise would be.
> Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO when
> driven by a regular 7805 and by the switching replacement.
>
> The switching frequency is supposed to be 2 MHz but you can see that it's
> more like 2.4 MHz.  Whether this performance is sufficient for any
> application is up to you.  It sure runs a lot cooler than a 7805, though!
>
> John
>
>
>
>
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>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Switching regulator replacement for 7805

[John Ackermann N8UR]

And Digikey does stock the Murata part, for about $4.30.  Why I couldn't 
find it when searching their site for switching regulators, I don't know.


John


On 12/04/2016 02:39 PM, John Ackermann N8UR wrote:

Thanks for that pointer!  When I searched Digikey, I wasn't able to find
anything that was in the 3-lead TO-220 case.  I will definitely check
out the Murata units, as I suspect they perform better than this one.

John

On 12/04/2016 02:01 PM, Adrian Godwin wrote:

Thanks for this. I've seen something similar from Murata :

http://uk.farnell.com/murata-power-solutions/oki-78sr-5-1-5-w36-c/converter-dc-dc-1-o-p-7-5w-1-5a/dp/2102101


Since they're a mainstream supplier of inductors they may have managed
better performance - it would be interesting to compare.


On Sun, Dec 4, 2016 at 6:50 PM, John Ackermann N8UR  wrote:


I found a cute little switching regulator that's a drop-in
replacement for
an LM7805: http://www.ebay.com/itm/261243604047

I got a couple to play with, mainly to see how bad the noise would be.
Here are spectrum analyzer and PN shots comparing a cheap surplus
OCXO when
driven by a regular 7805 and by the switching replacement.

The switching frequency is supposed to be 2 MHz but you can see that
it's
more like 2.4 MHz.  Whether this performance is sufficient for any
application is up to you.  It sure runs a lot cooler than a 7805,
though!

John




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Re: [time-nuts] Switching regulator replacement for 7805

[Poul-Henning Kamp]

In message <5844656d.5010...@febo.com>, John Ackermann N8UR writes:

>I found a cute little switching regulator that's a drop-in replacement 
>for an LM7805: http://www.ebay.com/itm/261243604047

Traco has had the TSN and TSR series for some years now, and they
perform nicely in all applications where I have plugged them in.

Havn't tried an OCXO though.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Switching regulator replacement for 7805

[John Ackermann N8UR]

Thanks for that pointer!  When I searched Digikey, I wasn't able to find 
anything that was in the 3-lead TO-220 case.  I will definitely check 
out the Murata units, as I suspect they perform better than this one.


John

On 12/04/2016 02:01 PM, Adrian Godwin wrote:

Thanks for this. I've seen something similar from Murata :

http://uk.farnell.com/murata-power-solutions/oki-78sr-5-1-5-w36-c/converter-dc-dc-1-o-p-7-5w-1-5a/dp/2102101

Since they're a mainstream supplier of inductors they may have managed
better performance - it would be interesting to compare.


On Sun, Dec 4, 2016 at 6:50 PM, John Ackermann N8UR  wrote:


I found a cute little switching regulator that's a drop-in replacement for
an LM7805: http://www.ebay.com/itm/261243604047

I got a couple to play with, mainly to see how bad the noise would be.
Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO when
driven by a regular 7805 and by the switching replacement.

The switching frequency is supposed to be 2 MHz but you can see that it's
more like 2.4 MHz.  Whether this performance is sufficient for any
application is up to you.  It sure runs a lot cooler than a 7805, though!

John




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Re: [time-nuts] Switching regulator replacement for 7805

[jimlux]

On 12/4/16 10:50 AM, John Ackermann N8UR wrote:

I found a cute little switching regulator that's a drop-in replacement
for an LM7805: http://www.ebay.com/itm/261243604047

I got a couple to play with, mainly to see how bad the noise would be.
Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO
when driven by a regular 7805 and by the switching replacement.

The switching frequency is supposed to be 2 MHz but you can see that
it's more like 2.4 MHz.  Whether this performance is sufficient for any
application is up to you.  It sure runs a lot cooler than a 7805, though!




I've used a bunch of the Cui 7800 replacement switchers - they're 
typically in a 4 (or 9) surface mount DIP that's kind of tall for the 1 
Amp version, and a sort of fat 3 pin through hole for the 0.5 amp 
version.  I used the 1A parts because they have a "shutdown" pin and you 
can adjust the voltage.


http://www.cui.com/product/power/dc-dc-converters/non-isolated/0.5-a-output-current/p7805-s-series

As I recall, they're in that 2 MHz-ish frequency as well.

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Re: [time-nuts] Switching regulator replacement for 7805

[Adrian Godwin]

Thanks for this. I've seen something similar from Murata :

http://uk.farnell.com/murata-power-solutions/oki-78sr-5-1-5-w36-c/converter-dc-dc-1-o-p-7-5w-1-5a/dp/2102101

Since they're a mainstream supplier of inductors they may have managed
better performance - it would be interesting to compare.


On Sun, Dec 4, 2016 at 6:50 PM, John Ackermann N8UR  wrote:

> I found a cute little switching regulator that's a drop-in replacement for
> an LM7805: http://www.ebay.com/itm/261243604047
>
> I got a couple to play with, mainly to see how bad the noise would be.
> Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO when
> driven by a regular 7805 and by the switching replacement.
>
> The switching frequency is supposed to be 2 MHz but you can see that it's
> more like 2.4 MHz.  Whether this performance is sufficient for any
> application is up to you.  It sure runs a lot cooler than a 7805, though!
>
> John
>
>
>
>
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Re: [time-nuts] Switching regulator replacement for 7805

[Attila Kinali]

On Sun, 4 Dec 2016 13:50:21 -0500
John Ackermann N8UR  wrote:

> I found a cute little switching regulator that's a drop-in replacement 
> for an LM7805: http://www.ebay.com/itm/261243604047
> 
> I got a couple to play with, mainly to see how bad the noise would be. 
> Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO 
> when driven by a regular 7805 and by the switching replacement.
> 
> The switching frequency is supposed to be 2 MHz but you can see that 
> it's more like 2.4 MHz.  Whether this performance is sufficient for any 
> application is up to you.  It sure runs a lot cooler than a 7805, though!

Cool! Thanks a lot! I wondered quite some time how much worse these
things would be. Did you also do some EMI measurements? 
For what is worth, the spectrum below 1MHz looks pretty decent,
especially considering how badly done the layout on those boards
are. They must have completely ignored the layout guidelines in
the datasheet.. :-/

If you have the time and leasure, it would be nice if you could
compare them to the OKI-78SR series from Murata. I would suspect
they perform quite a bit better on noise and EMI...beside being
cheaper and easier to source :-)


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] Best Chance GPS module

[Bob Camp]

Hi

If you watch the “jump” process. The thing that inevitably is being added or 
subtracted is a long path 
sat. For timing those are the worst of the bunch. Unless you have a way to 
fully correct the ionosphere 
(really good data or a multi band receiver) they will always be contributing an 
error. This is where the common
advice “crank up the minimum elevation angle” comes from. Since it degrades 
survey performance, you 
can’t do it blindly. If you …ummm … e …. have a computer program to work 
out the angle that always 
gives you 5 sats in view, you probably could come up with a pretty good number.

Bob


> On Dec 4, 2016, at 12:53 PM, Mark Sims  wrote:
> 
> The Trimble timing receivers have a "single satellite" operating mode that 
> says to only use the highest elevation satellite that it sees (or you can set 
> a specific single satellite to track).   It would be interesting to see how 
> the performance compares to its standard "overdetermined clock" mode.  It 
> might help in situations where you have a poor sky view.  
> 
> The Trimble devices tend to jump around quite a bit whenever the tracked 
> satellites it is using changes.  Having an accurate position helps minimize 
> the jumps.
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Re: [time-nuts] Best Chance GPS module

[Bob Camp]

Hi

A 12 hour survey done with WAAS turned on is likely to be better than one with 
WAAS turned off. 
How good a 96 hour survey with WAAS on and off is something of a toss up.

Bob

> On Dec 4, 2016, at 1:35 PM, Chris Albertson  wrote:
> 
> On Sun, Dec 4, 2016 at 9:16 AM, Mark Sims  wrote:
> 
>> For some unmentioned reason Ublox recommends disabling WAAS for precision
>> time applications.  Doesn't make much sense to me
>> 
>> 
> It turns out that your self-survey position is much better then a WAAS
> correct position. WAAS is about 1.5 meters I bet a 12 hour self survey is
> about 0.5 meters
> 
> Are we still talking about NTP?  If so this kind of stuff is lost in the
> noise and will never show up on your system clock.
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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Re: [time-nuts] Best Chance GPS module

[Chris Albertson]

On Sun, Dec 4, 2016 at 9:16 AM, Mark Sims  wrote:

> For some unmentioned reason Ublox recommends disabling WAAS for precision
> time applications.  Doesn't make much sense to me
>
>
It turns out that your self-survey position is much better then a WAAS
correct position. WAAS is about 1.5 meters I bet a 12 hour self survey is
about 0.5 meters

Are we still talking about NTP?  If so this kind of stuff is lost in the
noise and will never show up on your system clock.

-- 

Chris Albertson
Redondo Beach, California
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[time-nuts] Best Chance GPS module

[Mark Sims]

The Trimble timing receivers have a "single satellite" operating mode that says 
to only use the highest elevation satellite that it sees (or you can set a 
specific single satellite to track).   It would be interesting to see how the 
performance compares to its standard "overdetermined clock" mode.  It might 
help in situations where you have a poor sky view.  

The Trimble devices tend to jump around quite a bit whenever the tracked 
satellites it is using changes.  Having an accurate position helps minimize the 
jumps.
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Re: [time-nuts] Best Chance GPS module

[Bob Camp]

Hi

That is the standard recommendation from all of the module manufacturers when 
running in timing (as opposed to survey) mode. 
It is based on empirical data that indicates WAAS degrades timing performance 
once the survey is compete. There are a lot of SBAS
systems out there, so who knows which systems were tested and when they checked 
them.

Bob


> On Dec 4, 2016, at 12:16 PM, Mark Sims  wrote:
> 
> For some unmentioned reason Ublox recommends disabling WAAS for precision 
> time applications.  Doesn't make much sense to me
> 
> ---
> 
>> Frühauf proposed using satellite dishes on WAAS satellites for
> improved timing accuracy/stability[1].
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[time-nuts] Best Chance GPS module

[Mark Sims]

For some unmentioned reason Ublox recommends disabling WAAS for precision time 
applications.  Doesn't make much sense to me
   
---

> Frühauf proposed using satellite dishes on WAAS satellites for
improved timing accuracy/stability[1].
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[time-nuts] HP53131A RS232 question ANSWERED!!!

[cdelect]

Thanks to a reply from Angus the 53131A is sending data every sample
now!!!

"Something to check - in the 'Utility' menu, if the HP-IB is set to
'Talk' rather than a numeric address, it does just what you describe
and only sends data every few seconds.
Angus.

Thanks

Corby

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Re: [time-nuts] Best Chance GPS module

[Bob Camp]

Hi

Simple example:

Single sat straight overhead, well compensated by broadcast ionosphere. All 
survey error in the X direction.

Multiple sats all clustered at the horizon. Cluster located on the +X axis. 
Ionosphere not well modeled over the 
much longer path. 

Yes this *is* a bit contrived. It’s also what can happen in an “overhanging 
balcony” sort of antenna location.  I can 
also make it happen pretty easily from a USB stick indoors and locating “just 
right” relative to the windows. 

Bob


> On Dec 4, 2016, at 10:45 AM, Attila Kinali  wrote:
> 
> On Sun, 4 Dec 2016 09:46:45 -0500
> Bob Camp  wrote:
> 
>> It’s possible (but unlikely) to have a single sat in a “perfect” location 
>> give
>> you a better solution than a group of sats in a really crummy location ….. 
>> This is yet another reason for wanting a full sky view. Seeing several 
>> sats at a crummy angle may still be a less than ideal thing. 
> 
> Frühauf proposed using satellite dishes on WAAS satellites for
> improved timing accuracy/stability[1]. Unfortunately, I have not
> seen any good analysis of the achieved performance.
> 
>   Attila Kinali
> 
> 
> [1] "WAAS for Telecom applications", Hugo Frühauf, 2003, updated 2011
> http://hugofruehauf.com/pdf/24-WAAS_for_Telecom_2003-upd_2011.pdf
> 
> -- 
> 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] Best Chance GPS module

[Attila Kinali]

On Sun, 4 Dec 2016 09:46:45 -0500
Bob Camp  wrote:

> It’s possible (but unlikely) to have a single sat in a “perfect” location give
> you a better solution than a group of sats in a really crummy location ….. 
> This is yet another reason for wanting a full sky view. Seeing several 
> sats at a crummy angle may still be a less than ideal thing. 

Frühauf proposed using satellite dishes on WAAS satellites for
improved timing accuracy/stability[1]. Unfortunately, I have not
seen any good analysis of the achieved performance.

Attila Kinali


[1] "WAAS for Telecom applications", Hugo Frühauf, 2003, updated 2011
http://hugofruehauf.com/pdf/24-WAAS_for_Telecom_2003-upd_2011.pdf

-- 
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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] Best Chance GPS module

[Bob Camp]

Hi

> On Dec 4, 2016, at 6:57 AM, MLewis  wrote:
> 
> 
> On 03/12/2016 12:33 PM, Bob Camp wrote:
>> For an “antenna challenged” location, the T is the better choice. It is 
>> simply an update (as the M8Q) of the earlier uBlox parts. The function is 
>> very similar to the earlier parts. You nail down the antenna location (like 
>> with duct tape) and put the module in survey mode. Eventually it completes 
>> the survey and you save that location. That location is then used as part of 
>> the fixed location setup. This eliminates any need to ever do a survey 
>> again. The reason you want the fixed location operating mode is that it will 
>> work with a single satellite. You don’t need the accuracy, but you do want 
>> to eliminate dropouts.
> Thank you!
> 
> That is exactly what I "thought" I was getting from reading various sources, 
> but I wasn't confident I was getting it right.
> 
> I think:
> - There's GPS Time and with the offset (currently 17 seconds?) in the GPS 
> location message we get UTC Time.
> - The GPS module receives the satellite's GPST, offset, and hence UTC Time, 
> and its location fix allows for correcting for the message delay.
> - A better fix, and that correction is more accurate.
> - With a number of satellites reporting, that correction is more accurate.

Not quite correct. Until the module has a proper fix it does not have useful 
time. The delay from the sats is long enough that for most purposes there is no 
value
in putting out raw time. You *could* re-write the firmware from scratch to do 
it a different way, but that’s the way it works now on all these modules. 

> 
> If the module has a good fix and a good solution from several satellites and 
> is providing me with a local UTC Time that is close to true UTC, but then 
> conditions degrade to a single satellite:
> - will the module be able to maintain a quality correction to true UTC Time?

If it has a properly surveyed location (and thus can calculate the delay in 
getting the signal from the sat) yes. 

> - or perhaps I should be asking: what is the precision from a GPS module's 
> best time solution vs. that from a single satellite.

With a proper survey, it’s in the 10’s of ns. It degrades roughly 1.5 ns / 
meter for typical survey errors. The survey induced error tends to 
show up as a long term (hours) drift in the output. It is slow enough that NTP 
will try to track it. The 10’s of ns basic error is related to things
like ionosphere corrections and that also can be a long term drift. Both errors 
may go up a bit with a single sat. How much depends a lot on 
the geometry involved both with the single sat and the group you replace it 
with. It’s possible (but unlikely) to have a single sat in a “perfect” location 
give
you a better solution than a group of sats in a really crummy location ….. This 
is yet another reason for wanting a full sky view. Seeing several 
sats at a crummy angle may still be a less than ideal thing. 

> - or is that irrelevant given my rather trivial goal of 1 ms precision?

On a LAN, you should be aiming for < 10 us in terms of the time input to the 
main server. Your “delivered time” budget needs to allow for a lot of
different errors that all add up. The idea is to make the time input error 
insignificant compared to the rest. If your time input error is 1 ms, and you
are after 1 ms, the rest of the errors would have to be zero. Depending on your 
setup, they may well be a significant chunk of 1 ms.

> 
> 
>> The module should be set to only put out a PPS when it has a valid timing 
>> solution. You very much do*not*  want it to simply put one out that is based 
>> on the internal oscillator on the module.
>> 
>> Bob
> 
> And here I was thinking that internal oscillator was going to save me by 
> continuing to provide PPS from a recently disciplined TCXO.

The TCXO in the module is not disciplined. A GPSDO is a device that disciplines 
an oscillator. These modules are not GPSDO’s. 
If you have a GPSDO, then “holdover” is what takes care of the PPS output when 
you loose GPS. 

> 
> If I have a good sat solution and am getting PPS for some hours, then it 
> loses all satellites,
>- is the internal TCXO sufficient to trust for a number of minutes?

It may slew at a couple microseconds per second. That’s much worse than just 
ignoring it. 

>- if so, how would I determine how much error for how many minutes?

Measure it under your conditions. It likely will be a bit different each time. 

>- or do I just have to set an alarm, let NTP fall back to the internet 
> hosts, and monitor my data clusters for drift?

That is why the PPS drops out. NTP then knows to ignore it and go do it’s own 
thing. That is a much better solution than 
tracking a slewing source. 

> 
> I'd guess this is related to the Best Practices I saw that said that for time 
> critical applications, as a minimum: use a local GPS time source, but have 
> NTP polling four or more NTP hosts (non GPS based) through t

Re: [time-nuts] Best Chance GPS module

[MLewis]

On 03/12/2016 12:33 PM, Bob Camp wrote:

For an “antenna challenged” location, the T is the better choice. It is simply 
an update (as the M8Q) of the earlier uBlox parts. The function is very similar 
to the earlier parts. You nail down the antenna location (like with duct tape) 
and put the module in survey mode. Eventually it completes the survey and you 
save that location. That location is then used as part of the fixed location 
setup. This eliminates any need to ever do a survey again. The reason you want 
the fixed location operating mode is that it will work with a single satellite. 
You don’t need the accuracy, but you do want to eliminate dropouts.

Thank you!

That is exactly what I "thought" I was getting from reading various 
sources, but I wasn't confident I was getting it right.


I think:
- There's GPS Time and with the offset (currently 17 seconds?) in the 
GPS location message we get UTC Time.
- The GPS module receives the satellite's GPST, offset, and hence UTC 
Time, and its location fix allows for correcting for the message delay.

- A better fix, and that correction is more accurate.
- With a number of satellites reporting, that correction is more accurate.

If the module has a good fix and a good solution from several satellites 
and is providing me with a local UTC Time that is close to true UTC, but 
then conditions degrade to a single satellite:
- will the module be able to maintain a quality correction to true UTC 
Time?
- or perhaps I should be asking: what is the precision from a GPS 
module's best time solution vs. that from a single satellite.

- or is that irrelevant given my rather trivial goal of 1 ms precision?



The module should be set to only put out a PPS when it has a valid timing 
solution. You very much do*not*  want it to simply put one out that is based on 
the internal oscillator on the module.

Bob


And here I was thinking that internal oscillator was going to save me by 
continuing to provide PPS from a recently disciplined TCXO.


If I have a good sat solution and am getting PPS for some hours, then it 
loses all satellites,

- is the internal TCXO sufficient to trust for a number of minutes?
- if so, how would I determine how much error for how many minutes?
- or do I just have to set an alarm, let NTP fall back to the 
internet hosts, and monitor my data clusters for drift?


I'd guess this is related to the Best Practices I saw that said that for 
time critical applications, as a minimum: use a local GPS time source, 
but have NTP polling four or more NTP hosts (non GPS based) through the 
internet as backup if the GPS system goes out.

Or in my case, simply if I can't track a sat.

Thanks,

Michael


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