[time-nuts] Serial-Ethernet

[Joseph Gray]

I just thought I'd report about a serial to Ethernet interface I just
bought. I got one of these:

http://www.amazon.com/gp/product/B00ATV2DX2

At the moment it is hooked up to my Z3801A and I am using Z38XX.exe
from across the network. Using the included software and driver, I
have the RS232 port mapped to COM 7 on my local PC.

I bought this particular model not only because of price, but because
it also does RS422. I will test this capability with my Lucent GPSDO
with the RS422 ports. If it works, I'll order another one just for the
Lucent.

Joe Gray
W5JG
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[time-nuts] Z3801A holdover

[Joseph Gray]

I just took a look at my Z3801A that has been in holdover for some
time. I have been too busy to do anything about it until now.

Before looking at the receiver stats just now, my first guess was that
the Oncore GPS board went bad. However, I see that it is currently
tracking 4 sats. I also see that the 1pps is invalid. Does this still
point to a failed Oncore board?

Attached is a screenshot showing the receiver stats.

I will open this thing up over the weekend to check voltages and such.
Until then, any tips on where to look are appreciated.

Joe Gray
W5JG
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[time-nuts] Racal Option 04E OCXO

[Larry McDavid]

I have many pictures and complete schematics of the Racal 04E optional 
OCXO used in many Racal counters. Ask if interested.


--
Best wishes,

Larry McDavid W6FUB
Anaheim, California  (SE of Los Angeles, near Disneyland)
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Jim Harman]

On Wed, Feb 24, 2016 at 2:53 PM, Nick Sayer via time-nuts <
time-nuts@febo.com> wrote:

> I can measure 1 ppb, but it takes 1000 seconds to do it ... My
> understanding is that better GPSDOs are able to provide for more granular
> phase detection.


It doesn't take a lot of hardware to get about 1000x better than that. The
Arduino-based design Lars Walenius posted a while ago can take a reading
every second with a resolution of about 1 nsec. It uses an HC390 divider to
reduce a 10 MHz OCXO to 1 MHz. The 1 MHz and pps pulse from the GPS feed an
HC4046 phase comparator, producing a 1 pps pulse 0-1 usec wide, with the
width proportional to the phase difference. This feeds one diode and an RC
network to make a ramp with its peak height (0 - 2.5V) proportional to the
phase difference. This feeds the processor's 10-bit A/D converter, which is
set for 2.5V full scale.The 1 pps signal triggers the A/D, capturing the
height of the pulse. One more resistor discharges the capacitor between
pulses. Because the discharge time constant is much longer than the
interrupt latency and A/D conversion time, the A/D captures the peak value.

I have been experimenting with this design for some time, with a lot of
learning along the way. Of course there are always potential improvements,
but the current design works surprisingly well. If someone can provide
access to a good set of test gear (I am in CT), I could better quantify the
performance.

My latest schematic is attached.


-- 

--Jim Harman


Arduino GPSDO Schematic v4.pdf
Description: Adobe PDF document
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Bob Camp]

Hi

WWVB DSO’s were a pretty common thing back in the 70’s and 80’s. You could hold 
fractions of a ppm with them. With manual intervention / scheduling you could 
get into 
the “couple ppb” range on a good week. 

Comparative numbers would be 1x10^-11 on a GPSDO. All the same qualifiers about 
“is that really this or that” apply equally (or more so) to it’s WWVB cousin. 

Bob

> On Feb 24, 2016, at 5:22 PM, Hal Murray  wrote:
> 
> 
>> From what others on the list have said before, WWVB offers performance
>> that's at least a couple orders of magnitude worse than GPS, even if you
>> correct for all of the expected diurnal variations in LF propagation. Given
>> that a fairly pedestrian GPS module offers a nominal PPS accuracy of ~10ns
>> for $25... 
> 
> Yes.  But it would be fun to measure the diurnal variations.
> 
> I thought WWVB was actually good at that.  It's ground wave rather than 
> bouncing off the ionosphere.  But I'd like to measure both WWVB and WWV.
> 
> Has anybody built a WWV(B)DSO?  You would need a stable oscillator so you 
> could average over days or weeks rather than hours.  I'm thinking of a 
> surplus rubidium.  Maybe a manual screwdriver adjustment would be good enough 
> and a PIC/AVR to make a PPS and fake GPRMC.
> 
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[time-nuts] A few more FEI FE-405B oscillators available

[Skip Withrow]

Hello time-nuts,

I have a few more of the characterized Frequency Electronics, Inc. FE-405B
oscillators available.  These units have ADEV plots by Corby Dawson from 1
to over 1000 seconds.  All the units have had the temperature compensation
disabled (but it is easy to reverse if desired, though the unit does have
to be opened).  Power required is 5V and 15V DC, output is 15MHz sine, and
they have the same serial interface as the FE-5680 rubidiums with a step
size of 1.05x10E-14.  After being on for a while aging generally seems to
be in the very low parts in 10E-11 per day.

ADEV for these units is generally some parts in 10E-13 from 1s to
100-1000s.  Price is $200 each plus shipping.  If you are interested in a
unit I will send you the ADEV plot of the unit that you will receive.
First come, first served with the best units going first.

I also have one unit that is almost flat at 1.1-1.6 X10E-12 from 1 to 256
seconds.  Will let this one go for $150 plus shipping.

Payment can be with PayPal or credit card.  Please contact via email at
s...@rdrelectronics.com.

Regards,
Skip Withrow
RDR Electronics, Inc.
303-790-1830




This email has been sent from a virus-free computer protected by Avast.
www.avast.com 
<#DDB4FAA8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Bob Camp]

Hi

The tick is a burst of audio at a fairly low frequency. You are going to need 
pretty
good conditions to get 0.1 ms. The fade process over much of the day will 
spread 
that out a *lot*.

Bob

> On Feb 24, 2016, at 5:11 PM, Tim Shoppa  wrote:
> 
> Hal -
>  In my experience over more than a decade, the ntpd WWV audio refclock has
> jitter circa 0.1ms.
> 
>  This is not nanosecond-time-nut PPS territory. But it is more than good
> enough for WAN ntpd.
> 
>  I use a Ten-Tec RX-320 as a cheap frequency-agile receiver for WWV. In
> between 5MHz/10MHz/15MHz usually one or two bands are open from me to
> Colorado.
> 
>  On the subject of WWVB - if you are near Colorado then you can have 24x7
> reachability, day or night. For me on the east coast, WWVB 60kHz is
> reliable in darkness but not in daylight.
> 
> Tim.
> 
> On Wed, Feb 24, 2016 at 1:56 PM, Hal Murray  wrote:
> 
>> 
>> tsho...@gmail.com said:
>>> My opinion if you want to serve reliable time through a longer GPS
>> outage:
>>> add a WWV or WWVB based radio clock. e.g. a shortwave radio and https://
>>> www.eecis.udel.edu/~mills/ntp/html/drivers/driver36.html
>> 
>> Do you have any graphs comparing WWV or WWVB to GPS when your GPS is
>> working
>> correctly?
>> 
>> When I run out of other things on my list, I'd like to collect that data.
>> What receivers do people recommend?
>> 
>> I have one of the low cost WWVB receiver modules but I never got any useful
>> data out of it.  Maybe it's time to try again.  It might work better on the
>> end of a long cable to get it away from all the EMI in my office.
>> 
>> 
>> --
>> These are my opinions.  I hate spam.
>> 
>> 
>> 
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>> 
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Bob Camp]

Hi

If you are looking at pool service, the first question would be how you connect 
to the backbone. 

If you are running something asymmetric (DSL / cable modem) you already have 
enough of an 
offset that it alone it far bigger than any other error in your system. Even 
with fancier connections,
asymmetry can be an issue. 

Next thing to look at is how heavily loaded your connection becomes. A lot of 
links have limited 
bandwidth in both directions, but traffic loads that are much heavier in one 
direction. It does not
take much single direction buffering to take that up to a significant level.

Bob

> On Feb 24, 2016, at 9:22 AM, Neil Green  wrote:
> 
> I currently operate a stratum 1 NTP server in the NTP pool using a U-Blox 
> Max-7Q GPS module with PPS attached to, variously, a Raspberry Pi via GPIO or 
> a Celeron mini PC via serial DB-9. The machine does nothing but serve time to 
> the pool. Operating systems of choice are Debian or FreeBSD.
> 
> 
> What would be my next step up be, hardware-wise, in terms of improving 
> precision, stability, etc? A GPSDO? Budget is limited as far as these things 
> go - about £150 UK/$210 US.
> 
> 
> I appreciate this is basic stuff compared to the usual discussions but this 
> doesn't seem the right question to ask on the NTP lists. Any help 
> appreciated. Thanks.
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Tim Shoppa]

Hal -
  In my experience over more than a decade, the ntpd WWV audio refclock has
jitter circa 0.1ms.

  This is not nanosecond-time-nut PPS territory. But it is more than good
enough for WAN ntpd.

  I use a Ten-Tec RX-320 as a cheap frequency-agile receiver for WWV. In
between 5MHz/10MHz/15MHz usually one or two bands are open from me to
Colorado.

  On the subject of WWVB - if you are near Colorado then you can have 24x7
reachability, day or night. For me on the east coast, WWVB 60kHz is
reliable in darkness but not in daylight.

Tim.

On Wed, Feb 24, 2016 at 1:56 PM, Hal Murray  wrote:

>
> tsho...@gmail.com said:
> > My opinion if you want to serve reliable time through a longer GPS
> outage:
> > add a WWV or WWVB based radio clock. e.g. a shortwave radio and https://
> > www.eecis.udel.edu/~mills/ntp/html/drivers/driver36.html
>
> Do you have any graphs comparing WWV or WWVB to GPS when your GPS is
> working
> correctly?
>
> When I run out of other things on my list, I'd like to collect that data.
> What receivers do people recommend?
>
> I have one of the low cost WWVB receiver modules but I never got any useful
> data out of it.  Maybe it's time to try again.  It might work better on the
> end of a long cable to get it away from all the EMI in my office.
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Hal Murray]

> From what others on the list have said before, WWVB offers performance
> that's at least a couple orders of magnitude worse than GPS, even if you
> correct for all of the expected diurnal variations in LF propagation. Given
> that a fairly pedestrian GPS module offers a nominal PPS accuracy of ~10ns
> for $25... 

Yes.  But it would be fun to measure the diurnal variations.

I thought WWVB was actually good at that.  It's ground wave rather than 
bouncing off the ionosphere.  But I'd like to measure both WWVB and WWV.

Has anybody built a WWV(B)DSO?  You would need a stable oscillator so you 
could average over days or weeks rather than hours.  I'm thinking of a 
surplus rubidium.  Maybe a manual screwdriver adjustment would be good enough 
and a PIC/AVR to make a PPS and fake GPRMC.



-- 
These are my opinions.  I hate spam.



___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Nick Sayer via time-nuts]

> On Feb 24, 2016, at 8:30 AM, Chris Albertson  
> wrote:
> 
> On Wed, Feb 24, 2016 at 6:22 AM, Neil Green  wrote:
> 
>> 
>> What would be my next step up be, hardware-wise, in terms of improving 
>> precision, stability, etc? A GPSDO? Budget is limited as far as these things 
>> go - about £150 UK/$210 US.
> 
> Given that you already have the GPS and PPS, you can build your own
> GPSDO for very little cost.  The most expensive part is the crystal
> and as long as you are not going for top of the line performance a
> cheaper crystal will do. (You asked about the NEXT step not the LAST
> step)
> 
> A simple GPSDO is, well, simple.  All you do is compare the phase of
> the PPS to the phase of the 10MHz crystal and then adjust the
> frequency of the crystal to keep the phase difference constant.   Can
> be done all in software by a $2 micro controller chip.  By Time Nut
> standards the performance will not be top notch but compared to your
> NTP server it could literally be 10,000 times better   A while back I
> tried to build the cheapest and simplest GPSDO possible and except for
> the price of the crystal and GPS receiver I spent about $5.

The BOM for my GPSDO is similar. It’s not quite $5 until you also exclude the 
DAC ($7), but the GPS module and oscillator are well over 90% of the price.

> Performan ce was such that when I put the cheap GPSDO  10MHz output
> and my Thunderbolt both on a dual trace scope I could see some
> movement in phase over hours long time but over days in stays locked
> 
> First divide the 10MHz crystal to say about 1Mhz using a TTL divider.
> Some (most) micro processor chips have a way that an external signal
> can trap the current value of a counter.  Let both the PPS and the
> 1Mhz do this and look at the difference in counts.

For mine, the PPS “captures” a 16 bit timer that is clocked directly from the 
oscillator with no prescale. An overflow interrupt extends that timer to 32 
bits, which is enough for 10 MHz to run for a few minutes before overflowing - 
plenty of time to capture phase deltas of a 1 PPS signal.

>From what I have learned about the whole thing so far, the real limiting 
>factor is the phase granularity you can get with just a 1 PPS source. If the 
>GPS module output, say, a 1 kHz signal, a GPSDO would be a lot easier to keep 
>stable at low tau. Mine has a “hump” at sort of 10^2-10^3 tau that I can’t 
>really do a lot about given that the only thing I have to discipline against 
>is a PPS rising edge. I’m sampling 10 second periods, which gives me a base 
>detection threshold of 10 ppb. I track a window of 10 of those for the visual 
>feedback. There, I can measure 1 ppb, but it takes 1000 seconds to do it. My 
>newer version clocks at 20 MHz in an attempt to double the granularity, but 
>from what I’ve been able to measure, it doesn’t do a whole lot about the 
>“stumbling around” at low-ish (10^1-10^3) tau. The performance lower than that 
>is dominated by the oscillator - in my case that’s either around 10^-10 or 
>10^-11 depending on whether you spend the extra $100 or not. :)

My understanding is that better GPSDOs are able to provide for more granular 
phase detection. My system is granular to +/- 1 whole cycle per second of 
sampling. Something clocking a lot faster could come up with a system for 
fractional granularity. I could do that by clocking the logic faster and then 
dividing the output - exactly what I do for the 20 MHz variant - except that 
the 8 bit AVRs I’m using at the moment top out at 20 MHz (at least, they’re not 
supported higher).

It also doesn’t help me personally that my 53220A sort of peters out around 
10^-11 anyway. I can’t really distinguish a Thunderbolt from a Connor Winfield 
OH300 based GPSDO, which clearly isn’t reality.

Getting back to the R.Pi stratum 0 NTP daemon, I’ve got a PI Zero in the NTP 
pool as well. As others have pointed out, there isn’t a whole lot of value to 
be found in attempting to do better over the internet. Attached is the current 
pool monitoring graph for mine. The picture actually is a lot worse than the 
norm - which is represented by the right half of the graph, for the most part. 
Still, you can see that even in the most regular periods, it’s -3 or -4 ms +/- 
1 ms, and that’s with a monitoring station only 300 miles or so away.
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Introduction

[Magnus Danielson]

Dear Enrico,

On 02/24/2016 06:55 AM, Enrico Bellotti wrote:

Hello to all,

first of all, thank you for the great and useful work that the time-nuts
have done over the years.


Welcome!


I have finally been able to gather all my counters (HP5335A, HP51131A,
HP5370A, HP5370B #1, HP5370B #2) and try to do some "simple" measurements.

I have started testing and comparing the instruments I have available using
the approach that was discussed a while ago on the list and also outlined
by John Ackermann (http://www.febo.com/pages/hp5370b/). Specifically, the
Adev for a time interval measurement on a (90ft of) RG58A/U cable.


It's a bit of a cable, so it can eat in on the rise-time somewhat. Did 
you check the risetime?



I have attached a PDF file with the results and some additional details of
the test setup.


Nice setup.


 From what I have understood the Adev at one second is related to the
counter resolution. The results I have obtained seem to be reasonable
except for HP5370B #2. This instrument seems to be marginal at best. Does
anybody know if the measured value for HP5370B #2 is a symptom of a
multifunction or simple need for calibration?


Yes, it is somewhat related. The 1/tau slope you see is expected.
You can usually expect the slope to be in the neighborhood of 
single-shot-resolution/tau, which is rule of thumb. It's more complex as 
it depends on the experienced trigger jitter, which depends on the noise 
and the slew-rate at the trigger point. You can thus optimize the jitter 
by adjusting the start and stop trigger voltage.


The cable delay will act to decorrelate the triggers, but for most 
designs, you don't need to go to 135 ns but can keep them tighter, of 
the benefit of maintaining nice slope. However, when the stop trigger 
comes just handfull of ns after the start trigger, then the remains of 
the start-event can shift the stop trigger. The cable decorrelates this 
effects so it behaves more as separate signals, so that is good.


The ripples you see for shorter taus for PPS signals would be 
interesting to see the reason for, the phase plot should help to 
illustrate the reason. However, it is curious how you provide measures 
from 0.1 s for a 1 Hz (1 s) PPS signal.


However, it is nice to see the relative close correlation between the 
PPS and 1 kHz signals. It would be nice to see if a slew-rate 
measurement of the two sources could be related to the ADEV differences.



Thank you for any comments/suggestions/corrections you may have.


Hope you got some input from my ramblings.

Cheers,
Magnus
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Esa Heikkinen]

What would be my next step up be, hardware-wise, in terms of improving 
precision, stability, etc? A GPSDO? Budget is limited as far as these things go 
- about £150 UK/$210 US.


I have Symmetricom TS2100 with OCXO and GPS upgrades as primary server, 
accessible only at local network. It has about +-50 ns nominal PPS 
accuracy. Then there's another server based on Raspberry Pi2, which is 
accessible from Internet. The PPS from symmetricom is fed to Rpi2 and 
the actual time and date information is passed from TS2100 to Rpi2 with NTP.


Rpi2 can serve about 1 NTP queries per second, according my stress 
tests with ntpload.c test program by Kasper Pedersen. For stress test, 
several PC's are needed, each running few threads of ntpload.c, all 
bombarding the server under test simultaneously. Rpi2 has quad core 
processor, but unfortunately it looks that ntpd can utilize only one 
core. With about 1 ntp queries per second there's only one core with 
100% load and others are basicly idling. Good thing is that you can run 
another tasks simlataneously, without noticeable slowdown.


I also joined the NTP pool (only Finnish one) but then I noticed that 
it's was really bad idea to run any NTP server behind router/firewall. 
When there's rush peaks in NTP pool, there will be several hundreds (I 
had more than 600) NTP queries per second and each from different 
address of course. This will create a lot of sessions in router NAT 
table, in my case there was more than 13000 active sessions according to 
conntrack -C. This may overwhelm the router and in any case it will eat 
lot of RAM on the router. The lesson learnt was that NTP server should 
have it's own direct WAN access without any router. That might also 
decrease the delays. This will be my next setup. The Rpi2 NTP server 
itself seems to be very stable and there was no issues when I did the 
stress test with continuous ~1 queries/sec for about one day.


Regards,

--
73s!
Esa
OH4KJU

___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Hal Murray]

tsho...@gmail.com said:
> My opinion if you want to serve reliable time through a longer GPS outage:
> add a WWV or WWVB based radio clock. e.g. a shortwave radio and https://
> www.eecis.udel.edu/~mills/ntp/html/drivers/driver36.html 

Do you have any graphs comparing WWV or WWVB to GPS when your GPS is working 
correctly?

When I run out of other things on my list, I'd like to collect that data.  
What receivers do people recommend?

I have one of the low cost WWVB receiver modules but I never got any useful 
data out of it.  Maybe it's time to try again.  It might work better on the 
end of a long cable to get it away from all the EMI in my office.


-- 
These are my opinions.  I hate spam.



___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Hal Murray]

nc...@hotmail.co.uk said:
> What would be my next step up be, hardware-wise, in terms of improving
> precision, stability, etc? A GPSDO? Budget is limited as far as these things
> go - about £150 UK/$210 US. 

How good is your antenna?  How often does your current GPS setup run out of 
satellites?


-- 
These are my opinions.  I hate spam.



___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Chris Albertson]

On Wed, Feb 24, 2016 at 6:22 AM, Neil Green  wrote:

>
> What would be my next step up be, hardware-wise, in terms of improving 
> precision, stability, etc? A GPSDO? Budget is limited as far as these things 
> go - about £150 UK/$210 US.

Given that you already have the GPS and PPS, you can build your own
GPSDO for very little cost.  The most expensive part is the crystal
and as long as you are not going for top of the line performance a
cheaper crystal will do. (You asked about the NEXT step not the LAST
step)

A simple GPSDO is, well, simple.  All you do is compare the phase of
the PPS to the phase of the 10MHz crystal and then adjust the
frequency of the crystal to keep the phase difference constant.   Can
be done all in software by a $2 micro controller chip.  By Time Nut
standards the performance will not be top notch but compared to your
NTP server it could literally be 10,000 times better   A while back I
tried to build the cheapest and simplest GPSDO possible and except for
the price of the crystal and GPS receiver I spent about $5.
Performan ce was such that when I put the cheap GPSDO  10MHz output
and my Thunderbolt both on a dual trace scope I could see some
movement in phase over hours long time but over days in stays locked

First divide the 10MHz crystal to say about 1Mhz using a TTL divider.
Some (most) micro processor chips have a way that an external signal
can trap the current value of a counter.  Let both the PPS and the
1Mhz do this and look at the difference in counts.  Adjust the crystal
so the difference remains constant.   Don't worry about details, that
is for latter make it as simple as possible.  Improvement is for
version #2.

The next step up would be something like the Thunderbolt or a much
better DIY GPSDO.






-- 

Chris Albertson
Redondo Beach, California
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Tim Shoppa]

GPSDO's are very nice if you want a bench source for calibration purposes.

On the subject of NTP servers... GPSDO's would be relevant when doing
holdover through a GPS outage measured in days.

My opinion if you want to serve reliable time through a longer GPS outage:
add a WWV or WWVB based radio clock. e.g. a shortwave radio and
https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver36.html

Tim N3QE

On Wed, Feb 24, 2016 at 9:22 AM, Neil Green  wrote:

> I currently operate a stratum 1 NTP server in the NTP pool using a U-Blox
> Max-7Q GPS module with PPS attached to, variously, a Raspberry Pi via GPIO
> or a Celeron mini PC via serial DB-9. The machine does nothing but serve
> time to the pool. Operating systems of choice are Debian or FreeBSD.
>
>
> What would be my next step up be, hardware-wise, in terms of improving
> precision, stability, etc? A GPSDO? Budget is limited as far as these
> things go - about £150 UK/$210 US.
>
>
> I appreciate this is basic stuff compared to the usual discussions but
> this doesn't seem the right question to ask on the NTP lists. Any help
> appreciated. Thanks.
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Introduction

[Mark Spencer]

I've found with my HP5370B's they perform best over a fairly narrow range of 
input signal levels.(1 to 2 volts If I recall correctly ?)  Some 
experiments might be in order for yours.   Virtually all my testing was done 
with 5 or 10 MHz sine waves so this may or may not be helpful in your case.   I 
found in line attenuators and an oscilloscope to be helpful in making 
measurements using my HP5370B's.

I've never done a full alignment of mine so this behaviour may not be typical.

All the best
Mark S


Sent from my iPhone

>> On Feb 24, 2016, at 1:36 AM, Bruce Griffiths  
>> wrote:
>> 
>> On Wednesday, February 24, 2016 12:55:42 AM Enrico Bellotti wrote:
>> Hello to all,
>> 
>> first of all, thank you for the great and useful work that the time-nuts
>> have done over the years.
>> 
>> I have finally been able to gather all my counters (HP5335A, HP51131A,
>> HP5370A, HP5370B #1, HP5370B #2) and try to do some "simple" measurements.
>> 
>> I have started testing and comparing the instruments I have available using
>> the approach that was discussed a while ago on the list and also outlined
>> by John Ackermann (http://www.febo.com/pages/hp5370b/). Specifically, the
>> Adev for a time interval measurement on a (90ft of) RG58A/U cable.
>> 
>> I have attached a PDF file with the results and some additional details of
>> the test setup.
>> 
>> From what I have understood the Adev at one second is related to the
>> counter resolution. The results I have obtained seem to be reasonable
>> except for HP5370B #2. This instrument seems to be marginal at best. Does
>> anybody know if the measured value for HP5370B #2 is a symptom of a
>> multifunction or simple need for calibration?
>> 
>> Thank you for any comments/suggestions/corrections you may have.
>> 
>> Best.
>> Enrico
> Try repeating the test with a low noise external reference/If that doesn't 
> improve the results try realigning the filters etc in the 10-200MHz 
> multiplier.
> 
> Bruce
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> 
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[Pete Stephenson]

On Wed, Feb 24, 2016 at 3:22 PM, Neil Green  wrote:
> I currently operate a stratum 1 NTP server in the NTP pool using a U-Blox 
> Max-7Q GPS module with PPS attached to, variously, a Raspberry Pi via GPIO or 
> a Celeron mini PC via serial DB-9. The machine does nothing but serve time to 
> the pool. Operating systems of choice are Debian or FreeBSD.
>
>
> What would be my next step up be, hardware-wise, in terms of improving 
> precision, stability, etc? A GPSDO? Budget is limited as far as these things 
> go - about £150 UK/$210 US.

For what purpose?

In my experience, NTP is able to sync other systems to within 10-100
microseconds of an NTP server on a LAN. The vagaries of the internet
mean that it's unlikely for NTP clients to sync any closer than a few
tens of milliseconds.

The Pi is a decent system, but its ethernet port is connected via USB,
so accuracy isn't as good as it would be on a different, non-USB
system. It's quite satisfactory for serving time to the internet using
NTP.

A GPSDO is handy if you need better precision (but the Pi and the
internet can't deliver that better precision, so this is not a major
advantage for NTP) or holdover in case of issues with GPS. Many also
emit a stable reference frequency: this is useful for providing a
common reference for test equipment like frequency counters, or for
radio/microwave systems that need very high stability. If you don't
have such needs, a GPSDO will be of limited use.

> I appreciate this is basic stuff compared to the usual discussions but this 
> doesn't seem the right question to ask on the NTP lists. Any help 
> appreciated. Thanks.

Welcome, and thanks for providing a server in the NTP pool.

Cheers!
-Pete

-- 
Pete Stephenson
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Next step up from basic GPS/PPS timekeeping

[David J Taylor]

I currently operate a stratum 1 NTP server in the NTP pool using a U-Blox 
Max-7Q GPS module with PPS attached to, variously, a Raspberry Pi via GPIO 
or a Celeron mini PC via serial DB-9. The machine does nothing but serve 
time to the pool. Operating systems of choice are Debian or FreeBSD.


What would be my next step up be, hardware-wise, in terms of improving 
precision, stability, etc? A GPSDO? Budget is limited as far as these things 
go - about £150 UK/$210 US.


I appreciate this is basic stuff compared to the usual discussions but this 
doesn't seem the right question to ask on the NTP lists. Any help 
appreciated. Thanks.

___

Neil,

A BeagleBone Black might give half the jitter compared to the RPi, but not 
the order of magnitude you may be seeking.


 http://www.satsignal.eu/ntp/BBB-vs-RPi.html

Perhaps purely for serving the pool, the RPi is more than adequate.

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 


___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[time-nuts] Next step up from basic GPS/PPS timekeeping

[Neil Green]

I currently operate a stratum 1 NTP server in the NTP pool using a U-Blox 
Max-7Q GPS module with PPS attached to, variously, a Raspberry Pi via GPIO or a 
Celeron mini PC via serial DB-9. The machine does nothing but serve time to the 
pool. Operating systems of choice are Debian or FreeBSD.


What would be my next step up be, hardware-wise, in terms of improving 
precision, stability, etc? A GPSDO? Budget is limited as far as these things go 
- about £150 UK/$210 US.


I appreciate this is basic stuff compared to the usual discussions but this 
doesn't seem the right question to ask on the NTP lists. Any help appreciated. 
Thanks.
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Introduction

[Bruce Griffiths]

On Wednesday, February 24, 2016 12:55:42 AM Enrico Bellotti wrote:
> Hello to all,
> 
> first of all, thank you for the great and useful work that the time-nuts
> have done over the years.
> 
> I have finally been able to gather all my counters (HP5335A, HP51131A,
> HP5370A, HP5370B #1, HP5370B #2) and try to do some "simple" measurements.
> 
> I have started testing and comparing the instruments I have available using
> the approach that was discussed a while ago on the list and also outlined
> by John Ackermann (http://www.febo.com/pages/hp5370b/). Specifically, the
> Adev for a time interval measurement on a (90ft of) RG58A/U cable.
> 
> I have attached a PDF file with the results and some additional details of
> the test setup.
> 
> From what I have understood the Adev at one second is related to the
> counter resolution. The results I have obtained seem to be reasonable
> except for HP5370B #2. This instrument seems to be marginal at best. Does
> anybody know if the measured value for HP5370B #2 is a symptom of a
> multifunction or simple need for calibration?
> 
> Thank you for any comments/suggestions/corrections you may have.
> 
> Best.
> Enrico
 Try repeating the test with a low noise external reference/If that doesn't 
improve the results try realigning the filters etc in the 10-200MHz multiplier.

Bruce
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.