Re: [time-nuts] Subject: Re: GPS 1PPS, phase lock vs frequency lock, design

2019-06-23 Thread Karl Lautman 
Hi, Leo.  The web pages for your precision frequency references say they use 
PLL.  Is that just for frequency generation, and you use FLL for resyncing?

Karl




On Sun, Jun 23, 2019 at 7:01 AM -0700, "Leo Bodnar" 
mailto:l...@leobodnar.com>> wrote:


I have to draw your attention to practical aspects of why some designs use FLL 
rather than PLL.

Consider a GPS locked OCXO outputting GPS synced 10MHz signal.

Properly designed control loop will not produce much (if any) difference when 
the reference (GPS signal) is present.  In the end, integral of zero is zero.

When reference (GPS lock) is lost the things are very similar too, holdover is 
just flying blind in the rough direction you were facing last.  Accumulating 
frequency and phase offset on the way.

However, when reference is restored the things are much different.
After regaining the reference (which in case of GPS signal has unambiguous 
absolute time embedded into its phase) *proper* PLL loop will try to correct 
for slipped phase at the highest slew rate.  This can be huge.  If phase has 
drifted 1ms apart the loop will have to slew the phase all the way until it 
gets those 10,000 cycles out of the way.  This usually looks ugly in frequency 
domain and is very disrupting if you are using the device as frequency 
reference rather than an absolute time reference.

Proper FLL loop will just gently (and reasonably quickly) get your frequency 
back and forget about all the lost phase.  Which is what a lot of users want.

Initially, I have used PLL mode on GPS clocks that I am making, but switched 
over to FLL during the last few years.

Cheers
Leo
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Re: [time-nuts] Cloudflare

2019-06-22 Thread Karl Lautman 
I bought one of these 
(https://www.ebay.com/itm/GPSDO-10M-Output-GPS-Disciplined-Oscillator-Clock-Sinusoidal-Wave-RS232-US-SHIP/172933685909?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649)
 a couple of months ago. I only have a 9-digit frequency counter to measure it 
with, and the counter only has a 1 ppm TCXO, but, subject to those constraints, 
it's been rock solid. Lot less expensive than a Trimble. Interior photos here 
(https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/msg2457417/#msg2457417).

Karl

-Original Message-
From: time-nuts  On Behalf Of Don Meadows
Sent: Friday, June 21, 2019 7:28 AM
To: time-nuts@lists.febo.com
Subject: [time-nuts] GPSDO 10MHZ Splitter

I don’t have a GPSDO yet, I just can’t decide on one.
I am leaning to the Trimble, but it’s still undecided.

Could anyone comment on buying a “Refurbished by Seller”
GPSDO on E-bay. They are a few dollars cheaper, but I really want one I can 
have trust and confidence in.

Sorry for the long post.
Thanks, Don



Sent from Mail for Windows 10

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On Sat, Jun 22, 2019 at 3:00 PM -0700, "Hal Murray" 
mailto:hmur...@megapathdsl.net>> wrote:



kb...@n1k.org said:
> Given the relatively low cost of a GPS based “Stratum 1” NTP, it’s not 
> real
> clear  why (at the end of the paper) they go off and “exchange emails
> individually with the  organizations that run stratum 1 servers, as well as
> negotiate permission to use them.”  to source the root time for the system. 
> I
> would have thought that some sort of combo  of on site and off site sources
> would be at the “top of the tree”.

I have no inside information... Maybe reading between some lines.

It's a tangled mess.

Some of their 180 sites do not have stratum 1 servers and/or they may want to
use external stratum 1 servers for sanity check and backup.  Many sites with
stratum 1 servers do not want the load they would get from general public
access but are happy to allow access for a good reason.  Negotiating that
access would probably involve email.

They are using (old) shared key authentication.  (probably because the servers
they want to talk to don't support NTS yet)  That requires out of band
communications to setup the shared key.  Email is probably the most convenient
way to do that.


--
These are my opinions.  I hate spam.





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Re: [time-nuts] GPSDO question

2019-06-02 Thread Karl Lautman 
>I just got a BG7TBL.  I am in the process of evaluating it now.  Preliminary 
>result: +/- 10 mHz after calibration 
>(and powered up for one week).  If your RTC is good to 1-1/2 ppm over a 50 
>degree range it should be better 
>over a 5 degree range indoors.
>
>Andy Backus

Hi, Andy.  What's the date on your front panel?  Mine is 2019-03-25 (see pic 
here:  http://tinyurl.com/y4cf69k7).  How did you calibrate yours?  I thought 
the GPS did that.

-Original Message-
From: time-nuts  On Behalf Of Andy Backus
Sent: Sunday, June 2, 2019 2:11 PM
To: Discussion of precise time and frequency measurement 

Subject: Re: [time-nuts] GPSDO question

I just got a BG7TBL.  I am in the process of evaluating it now.  Preliminary 
result: +/- 10 mHz after calibration (and powered up for one week).  If your 
RTC is good to 1-1/2 ppm over a 50 degree range it should be better over a 5 
degree range indoors.

Andy Backus


From: time-nuts  on behalf of Karl Lautman 

Sent: Sunday, June 2, 2019 10:18 AM
To: time-nuts@lists.febo.com
Subject: [time-nuts] GPSDO question

Time newb here.  I'm designing a digital clock based on a microprocessor and 
external time source.  I only need about 1 minute/year accuracy, so I settled 
on the Micro Crystal 
RV-8803-C7<https://www.mouser.com/ProductDetail/Micro-Crystal/RV-8803-C7-32768kHz-3PPM-TA-QC?qs=7bTaA%2FLYtSY57sitRg9%2Fow%3D%3D>
  RTC which contains a TCXO and is spec'd at 1.5 ppm at 0 - 50 C.  I need to be 
able to verify the timebase accuracy, so I bought a BK Precision 1823A 
frequency counter.  It's only 9 digits, but I only need 7 for this test.  I 
have a 200 MHz scope, which is fine for comparing signals, but it's not nearly 
accurate nor precise enough for this sort of measurement.

The BK's frequency reference is a 1 ppm TCXO, but the counter only provides 8 
digits of precision when running on the internal reference; to get the 9th 
digit you need to use an external reference.  Even though I don't strictly 
"need" this 9th digit, I became curious about how to access it (I sense this 
sort of thing is how people become time nuts).  Long story short, I ended up 
with this<https://www.ebay.com/itm/172933685909> BG7TBL 10 MHz GPSDO.  
Measuring its output with the BK, on the BK's internal reference, it reads as 
10 MHz, so it's not totally bogus, like, 8 MHz.  It has a couple of LEDs which 
allegedly indicate it's GPS locked and its accuracy is better than .05 Hz.

1.  I assume that .05 Hz quality spec is embedded in the GPS signal.  Is that 
correct?  If not, how is it calculated?

2.  Any relatively inexpensive ways to validate the GPSDO's accuracy?  I've 
ordered a cheap, basic ublox GPS 
receiver<https://www.banggood.com/Satellite-Positioning-GPS-Module-For-Arduino-51MCU-STM32-p-1203610.html?utm_design=41_source=emarsys_medium=Shipoutinform171129_campaign=trigger-emarsys_content=Winna_src=email_2671705_eh=cc23797f8242d0691_llid=13041562_lid=104858042_uid=vu2Rtn59cL_warehouse=CN>
 from China with the intension of comparing its output to the GPSDO's on the 
scope.  I realize the ublox signal might be a little jittery, especially if I 
use 10 MHz, but it should still be useable for my purposes.  Am I mistaken?

3.  Anything else I should be aware of with this GPSDO?

Thanks.
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[time-nuts] GPSDO question

2019-06-02 Thread Karl Lautman 
Time newb here.  I'm designing a digital clock based on a microprocessor and 
external time source.  I only need about 1 minute/year accuracy, so I settled 
on the Micro Crystal 
RV-8803-C7
  RTC which contains a TCXO and is spec'd at 1.5 ppm at 0 - 50 C.  I need to be 
able to verify the timebase accuracy, so I bought a BK Precision 1823A 
frequency counter.  It's only 9 digits, but I only need 7 for this test.  I 
have a 200 MHz scope, which is fine for comparing signals, but it's not nearly 
accurate nor precise enough for this sort of measurement.

The BK's frequency reference is a 1 ppm TCXO, but the counter only provides 8 
digits of precision when running on the internal reference; to get the 9th 
digit you need to use an external reference.  Even though I don't strictly 
"need" this 9th digit, I became curious about how to access it (I sense this 
sort of thing is how people become time nuts).  Long story short, I ended up 
with this BG7TBL 10 MHz GPSDO.  
Measuring its output with the BK, on the BK's internal reference, it reads as 
10 MHz, so it's not totally bogus, like, 8 MHz.  It has a couple of LEDs which 
allegedly indicate it's GPS locked and its accuracy is better than .05 Hz.

1.  I assume that .05 Hz quality spec is embedded in the GPS signal.  Is that 
correct?  If not, how is it calculated?

2.  Any relatively inexpensive ways to validate the GPSDO's accuracy?  I've 
ordered a cheap, basic ublox GPS 
receiver
 from China with the intension of comparing its output to the GPSDO's on the 
scope.  I realize the ublox signal might be a little jittery, especially if I 
use 10 MHz, but it should still be useable for my purposes.  Am I mistaken?

3.  Anything else I should be aware of with this GPSDO?

Thanks.
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