[time-nuts] Chinese GPS Survey Antenna

[Gary E. Miller]

Time-nuts!

A while back there was a discussion of cheap Chinese GPS survey
antennas.

I purchased a TOPGNSS model GN-GGB0710..  Took about a month to
arrive.  They claim GPS L1 L2 GLONASS G1 G2 BDS B1 B2 B3 and Galileo.

I bought it on aliexpress for $75 inc. shipping.

https://www.aliexpress.com/item/NEW-3-3-18V-High-precision-high-gain-measurement-GNSS-GPS-GLONASS-BDS-Cors-rtk-GNSS/32815576155.html

Specs are here:

http://www.topgnss.com/gnssmodule/showproduct.php?lang=en=59

Antenna connection is a simple TNC connector and mounts on a standard
5/8-11 thread.  They say 3.3 to 18V.  I'm running it on 5V.
Construction quality seems fine.  Just as in the picture.

After a few hours of use I can say it is a nice little antenna.  I
seem to be getting good strong L1, L2, L5 and GALILEO signals on all
elevations and azimuths.

A gross comparison to my Trimble 22020 shows the two as roughly
comparable. Except I get stronger GALILEO on the TOPGNSS.  I have no
way to push either antenna to the limit.

Many thanks to the list for some fine product suggestions.  Add this
one to the list.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com  Tel:+1 541 382 8588

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin
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[time-nuts] Dual GPSDO - any advantage?

[John Green]

With regard to two GPSDOs, it is an interesting experiment. I have two
Tbolts, both 2.2 firmware, both fed from the same antenna, both with
factory default settings, and I see differences. They are about 2 feet
apart on my bench and everything is pretty stable, +/- 20 nS or so until
the heat kicks on. Then, the time difference between the two 10 MHz outputs
goes wild. Go figure.
Regarding eBay and deadbeat sellers, they are much better than in the past.
I got ripped off by an unscrupulous seller some years ago and eBay just
told me they had closed their eBay account. Today, If I don't get my item
fairly fast, I file a complaint right away. An unscrupulous seller will try
a delaying tactic to get you to wait until the time for eBay to do anything
has run out.  I had an issue with a Chinese seller once and PayPal told me
they couldn't issue a refund because they didn't have access to the
seller's bank account.
Yeah, sure. The worst abuse I have heard of by eBay/PayPal was a case where
a local guitar store owner sold a rather expensive, $4,000 + guitar to
someone in England. He got paid, then a few days later, he got an email
from eBay saying that the buyer had reported the item as fake and destroyed
it. They took the money back out of his bank account and wouldn't listen to
anything he had to say. Yes, there are unscrupulous buyers too.
Oh, I ordered one of those $9.50 GPSDOs too. I doubt I will ever see it. I
am not too optimistic about getting my money back either. We'll see.
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[time-nuts] HP 3455A 6.5 digit DVM for shipping cost

[Perry Sandeen via time-nuts]

Esteemed List Members (was Yo Dudes)
I have a HP 3455A 6.5 digit DVM that has stopped working.  When turned on it 
fails to complete the self-check routine.  The display lights briefly.
I will send it to anyone who will pay shipping from 92220, Banning, CA. 17 x 20 
x 3.5 inches.  Approx 20 pounds.
If interested please send email directly to me at sandeenpa at yahoo dot com. 
(please do not reply on the list.
Regards,
Perrier
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Re: [time-nuts] TCVCXO Adjustment

[Bob kb8tq]

Hi

In a commercial setting calibration would be done against a local standard. 
It might be checked with a counter. It also might be checked against something
more complex. 

A reasonable level of calibration would be 0.1 ppm. Anything much more accurate
than that would be quickly swamped by the temperature coefficient of a typical 
TCXO. 

Simply put, 0.1 ppm is 1 microsecond over 10 seconds. If your time code is 
capable of
resolving 1 us, monitor the output of the board for 10 seconds. If it is lower 
accuracy, 
the time period would be longer. It does get a bit impractical on something 
like a 1 ms
code ….

The sensitivity of the TCXO should be reasonably well understood. That should 
give 
you a ppm / bit sort of number. As an example, a 10 ppm trim range might not be 
that crazy. Your 12 bit DAC would give you roughly 0.01 ppm per bit. 

Since your typical PC does not have anything in it that is accurate to 0.1 ppm, 
you 
still need something as a reference to compare things to. A GPS module or a 
GPSDO
are probably the easiest things to get ahold of. 

Bob

> On Apr 10, 2018, at 7:10 PM, Wayne Holder  wrote:
> 
> I'm designing a small, portable, SMPTE LTC Timecode Generator
>  as an open source/hardware
> project for amateur filmmakers and videographers.  LTC Timecode is
> typically recorded on the audio tracks of cameras and sound recorders so
> the video and sound comments can be automatically sync'd later.  I'm
> planing on using a small, SMD TCVCXO such as the LFTVXO075806Cutt
> ,
> which is spec'd at a frequency tolerance or +/- 1 PPM and a frequency
> stability of 0.28 PPM and a yearly aging of +/- 1 PPM max/year which, to
> me, seems pretty impressive for a part that costs about $8.
> 
> Since the TCVCXO includes a voltage control input, my plan is to also add
> a 12-Bit Digital-to-Analog Converter with EEPROM Memory, such as the
> Microchip MCP4725
> 
> to
> provide a way to initially check and calibrate the frequency after surface
> mount soldering and also later to compensate for aging.  But since this is
> intended as an open source/hardware project rather than a commercially
> manufactured one, I've been pondering how someone building the device would
> be able to easily and reliably calibrate it.
> 
> I'm basing the design around the Arduino, so the device could, in theory,
> use the USB Serial connection as a way to connect to a calibration program
> running on a PC.  I have a few idea on how to attempt to do this, but this
> is new territory for me, so I'm asking for advice and/or thoughts on how
> feasible this might be.  Is this a crazy, impractical idea given that all
> the builder will probably have available to perform the calibration is a
> regular PC and an Internet connection, or is there a way to make it work?
> 
> Wayne
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[time-nuts] TCVCXO Adjustment

[Wayne Holder]

I'm designing a small, portable, SMPTE LTC Timecode Generator
 as an open source/hardware
project for amateur filmmakers and videographers.  LTC Timecode is
typically recorded on the audio tracks of cameras and sound recorders so
the video and sound comments can be automatically sync'd later.  I'm
planing on using a small, SMD TCVCXO such as the LFTVXO075806Cutt
,
which is spec'd at a frequency tolerance or +/- 1 PPM and a frequency
stability of 0.28 PPM and a yearly aging of +/- 1 PPM max/year which, to
me, seems pretty impressive for a part that costs about $8.

Since the TCVCXO includes a voltage control input, my plan is to also add
a 12-Bit Digital-to-Analog Converter with EEPROM Memory, such as the
Microchip MCP4725

to
provide a way to initially check and calibrate the frequency after surface
mount soldering and also later to compensate for aging.  But since this is
intended as an open source/hardware project rather than a commercially
manufactured one, I've been pondering how someone building the device would
be able to easily and reliably calibrate it.

I'm basing the design around the Arduino, so the device could, in theory,
use the USB Serial connection as a way to connect to a calibration program
running on a PC.  I have a few idea on how to attempt to do this, but this
is new territory for me, so I'm asking for advice and/or thoughts on how
feasible this might be.  Is this a crazy, impractical idea given that all
the builder will probably have available to perform the calibration is a
regular PC and an Internet connection, or is there a way to make it work?

Wayne
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Re: [time-nuts] Wavecrest DTS2075

[Charles Steinmetz]

John wrote:


It's more a burst-mode and averaging analyzer like the HP 5371/5372.  But it 
can do sustained time interval measurements if you mess around enough with the 
settings.  And the resolution is down in the very low picoseconds.

But it's big, awkwardly shaped, and has a jet turbine fan.


All of what John says is spot on.  It's beastly heavy, too.

One rather important thing I'd add -- make sure it comes with (or you 
have access to) the Wavecrest software.  The instrument by itself is 
close to brain-dead without it -- only a small subset of the most basic 
functions is available in manual/local mode.


Best regards,

Charles


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Re: [time-nuts] Cheap jitter measurements

[Gary E. Miller]

Yo Hal!

On Tue, 10 Apr 2018 15:41:41 -0700
Hal Murray  wrote:

> > Yeah, but the granularity is much worse.  
> 
> Do you have code that demonstrates that?  (or tell me how and I'll
> try it)

Look in gpsd git head.  In the contrib directory here is a program:
clock_test.c 

It tests the time to do two back to back clock_gettime().  Output
looks like this:

# ./clock_test 
samples 101, delay 1000 ns
min 67 ns, max 302 ns, mean 176 ns, median 197 ns, StdDev 52 ns

You run it a few times and you will see the granularity in the
measurements is 10's of ns, or more, depending on your CPU.

Probably better discussed on the gpsd-users@ or NTPsec devel@ mailing
list.  67 ns not exactly time-nuts precision.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com  Tel:+1 541 382 8588

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin


pgpqBySAD6eqr.pgp
Description: OpenPGP digital signature
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Re: [time-nuts] WWVB Time

[Graham / KE9H]

Did you move it near a desktop PC or other computer, or move a desktop, or
other PC, video screen or switching power supply in the vicinity of the
Symmetricom or WWVB antenna?

I am learning the hard way that PC and LED/LCD video screens are horrible
generators of noise in the LF spectrum.

--- Graham

==

On Tue, Apr 10, 2018 at 4:15 PM, Tom Van Baak  wrote:

> > Hi, all of a sudden my Symmetricom comparator/clock has been locking up
> on time.
> > It has been about a week so far. Did they change the code? Anyone else
> seeing that?
> > Doug K6JEY
>
> Hi Doug,
>
> That would be too good to be true. I asked NIST just now and they report:
> "We have not changed the code or power level. All things remain the same."
>
> So let's debug this on your end.
> - What make/model WWVB receiver are you using?
> - Can you check the accuracy of the time or frequency output against GPS /
> GPSDO. Is it NIST accurate or a bad copy of 60 kHz?
> - Did you power-up any new instrument in the past week, one that might
> cause 60 kHz harmonics?
> - Can you check with 'scope or spectrum analyzer what your environment
> looks like near 60 kHz?
> - Do you have a curious neighbor who is experimenting with a WWVB
> simulator...
>
> /tvb
>
> - Original Message -
> From: "Doug Millar via time-nuts" 
> To: 
> Sent: Tuesday, April 10, 2018 1:23 PM
> Subject: [time-nuts] WWVB Time
>
>
> Hi, all of a sudden my Symmetricom comparator/clock has been locking up on
> time. It has been about a week so far. Did they change the code? Anyone
> else seeing that? Doug K6JEY
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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

Gary said:
>> The API  for the kernel clock can be read to a ns.  I don't see ntpd
>> having much use for finer grain than that.  I should look at the
>> source to see what the internal details look like.

> Yeah, but the granularity is much worse.

Do you have code that demonstrates that?  (or tell me how and I'll try it)

I think most modern kernels derive time from a cycle-count register.  So the 
basic clock should be accurate to a cycle.  Yes, that's worse than a ns on 
slow CPUs.

-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Wavecrest DTS2075

[John Ackermann N8UR]

It's more a burst-mode and averaging analyzer like the HP 5371/5372.  But it 
can do sustained time interval measurements if you mess around enough with the 
settings.  And the resolution is down in the very low picoseconds.

But it's big, awkwardly shaped, and has a jet turbine fan.

John

On Apr 10, 2018, 6:00 PM, at 6:00 PM, Bruce Griffiths 
 wrote:
>Its more accurate and has less measurement noise than the SR620.
>
>The input bandwidth is also greater.
>
>The accuracy is no better than that of a modern TDC chip, however its
>measurement noise is lower.
>
>Bruce
>
>> 
>> On 11 April 2018 at 07:17 Gerhard Hoffmann 
>wrote:
>> 
>> I have been offered a DTS2075. Is this generally regarded as a
>step
>> 
>> forward if you already have a SR620 or is it more or less the
>same
>> 
>> league? Are there any hidden pearls or caveats?
>> 
>> TIA and best regards,
>> 
>> Gerhard
>> 
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Re: [time-nuts] Dual GPSDO - any advantage?

[Richard Solomon]

In the past I have had excellent experiences with e-Bay when it comes to

bad sellers. If the parts never arrive, there is no question, I got a refund.

If the parts were not as described, still no problems.


e-Bay seems to have been more on the side of the Buyer lately. A far cry

from their early days when the Seller's word was Gospel.


73, Dick, W1KSZ


Sent from Outlook

From: time-nuts  on behalf of Dr. David Kirkby 

Sent: Tuesday, April 10, 2018 12:24:41 PM
To: Discussion of precise time and frequency measurement
Cc: gandal...@aol.com
Subject: Re: [time-nuts] Dual GPSDO - any advantage?

On 10 April 2018 at 17:11, Clint Jay  wrote:

> Sad to say I think I was right, the listings have been pulled already and
> the seller now has zero items for sale.
>

The listing has not been pulled. Yes the seller has 0 to sell, but because
he has sold out of the 100. I still have the purchase in my purchase
history, and no messages from eBay about fraud.

>
> Get those paypal refund cases logged.
>

One would need to wait until they don't arrive. Luckily they were not much.

Then it is better to complain to eBay first. If you don't get any
satisfaction from eBay, then you can go to PayPal. But by going directly to
PayPal, you will have lost the chance to get a refund via eBay. So the
sensible order to try to get refunds is

1) eBay
2) PayPal
3) Chargeback on credit card.

Never advance to stage PayPal unless you have exhaused attempts at eBay.
Never make a chargeback unless you have exhaused atttempts at both eBay and
PayPal.

Sometimes it can be a bit of an uphill struggle to get refunds from eBay
for dodgy sellers, but in this case it should be fairly easy if the goods
don't arrive. On the off-chance they do, we have scored well.


Clint. M0UAW IO83
>


Dave G8WRB.
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Re: [time-nuts] Cheap jitter measurements

[Bob kb8tq]

Hi

> On Apr 10, 2018, at 5:05 PM, Dan Kemppainen  wrote:
> 
> Hi Bob,
> 
> The performance counter does not use the system time calls, NTP, etc. It's an 
> independent counter clocked from raw CPU clock. So you have a ~300pS 
> Timestamping counter in the processor. Why not use that hardware to do the 
> measurement? Does the signal have to exit the PC to measure it?
> 
> Yes, getting ~300pS out of the code calls is probably unrealistic for various 
> reasons, however 300nS should be easily achievable.

One point might that there is a *long* way between 300 ps and 300 ns. Another 
point would be that the CPU clock architecture is very 
different from one brand CPU to the next. If I’m on a 32 bit ARM, I have very 
different “this and that” than I do on a modern Intel CPU. 
I will not dispute the 300 ns number, it’s probably a good guess. The *hope* is 
that with some sort of software magic, the same sort of
thing can be done here as with GPS modules. You accept that positioning the 
pulse to 300 ns is “as good as it gets”. You then do this 
and that to estimate and report how far off it was. 

> 
> If you use the actual NTP PPS capture code with a few extra lines of code 
> added, you should be able to timestamp PPS and NTP values against the 
> performance counter.

The desire would be to get as far away from NTP evaluating it’s self as 
possible. Yes, this is a bit of a philosophical 
sort of thing. If NTP tells us when the pulse was, it’s still very much 
involved. With a pulse out, one can at least begin to evaluate 
what is going on independent of the clock architecture on the CPU and the 
various things the kernel is (or isn’t) doing. 

Why bother? Well, we might learn something about timing …. We might also get a 
way to produce much more accurate
time pulses out of a system. 

If I want to do this same sort of thing with 1588, there are cards out there 
that will do the job. I plug this one in here 
and that one in another system. I grab the PPS outputs from the cards and start 
testing things. Net result is that I 
*can* directly evaluate how well 1588 is doing. Right now with NTP …. not so 
much. 

Bob



> 
> 
> 
> David,
> 
> Correct me if I'm wrong, but the issue with the GetSystemTime calls is they 
> don't use the performance counters. They are system time related calls and 
> affected by UTC/NTP or other system time adjustments.
> 
> The bigger questions is how does NTP query the serial port? Is it in an 
> actual interrupt routine, or is the data captured via software driven event? 
> (I'm betting on a OS driven event).
> 
> Maybe the Dave Hart patches improve the PPS capture???
> 
> The bottom line is it all depends on now the PPS Capture event is handled, 
> and if that's even predictable enough or stable enough to prove useful. The 
> performance counter is, but getting the PPS code to read the counter is still 
> a software problem.
> 
> If you guys want to take this offline and chat about it further, I'd be happy 
> to discuss this without using up bandwidth here.
> 
> Thanks,
> Dan
> 
> 
> 
> 
> On 4/10/2018 4:01 PM, time-nuts-requ...@febo.com wrote:
>> Dan,
>> Take a look at Dave Hart's patches to the Microsoft serial port driver, that
>> does something similar.  The source may be in the NTP distribution, or
>> Meinberg may have a copy.  At one time using the QueryPerfomanceCounter call
>> was an option (look for "QPC").  With Windows-8 and later there is a much
>> more precise GetSystemTime call which NTP uses.
>> I played a little with those calls (in a non-serious way) and wrote some
>> code:
>>   http://www.satsignal.eu/ntp/TSCtime.html
>> based on:
>>   http://www.lochan.org/2005/keith-cl/useful/win32time.html
>> and just messing around!  Perhaps it's of interest or use?
>> Cheers,
>> David
>> -- SatSignal Software - Quality software written to your requirements Web: 
>> http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv
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Re: [time-nuts] Wavecrest DTS2075

[Bruce Griffiths]

Its more accurate and has less measurement noise than the SR620.

The input bandwidth is also greater.

The accuracy is no better than that of a modern TDC chip, however its 
measurement noise is lower.

Bruce

> 
> On 11 April 2018 at 07:17 Gerhard Hoffmann  wrote:
> 
> I have been offered a DTS2075. Is this generally regarded as a step
> 
> forward if you already have a SR620 or is it more or less the same
> 
> league? Are there any hidden pearls or caveats?
> 
> TIA and best regards,
> 
> Gerhard
> 
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> 
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Re: [time-nuts] Cheap jitter measurements

[Dan Kemppainen]

Hi Bob,

The performance counter does not use the system time calls, NTP, etc. 
It's an independent counter clocked from raw CPU clock. So you have a 
~300pS Timestamping counter in the processor. Why not use that hardware 
to do the measurement? Does the signal have to exit the PC to measure it?


Yes, getting ~300pS out of the code calls is probably unrealistic for 
various reasons, however 300nS should be easily achievable.


If you use the actual NTP PPS capture code with a few extra lines of 
code added, you should be able to timestamp PPS and NTP values against 
the performance counter.




David,

Correct me if I'm wrong, but the issue with the GetSystemTime calls is 
they don't use the performance counters. They are system time related 
calls and affected by UTC/NTP or other system time adjustments.


The bigger questions is how does NTP query the serial port? Is it in an 
actual interrupt routine, or is the data captured via software driven 
event? (I'm betting on a OS driven event).


Maybe the Dave Hart patches improve the PPS capture???

The bottom line is it all depends on now the PPS Capture event is 
handled, and if that's even predictable enough or stable enough to prove 
useful. The performance counter is, but getting the PPS code to read the 
counter is still a software problem.


If you guys want to take this offline and chat about it further, I'd be 
happy to discuss this without using up bandwidth here.


Thanks,
Dan




On 4/10/2018 4:01 PM, time-nuts-requ...@febo.com wrote:

Dan,

Take a look at Dave Hart's patches to the Microsoft serial port driver, that
does something similar.  The source may be in the NTP distribution, or
Meinberg may have a copy.  At one time using the QueryPerfomanceCounter call
was an option (look for "QPC").  With Windows-8 and later there is a much
more precise GetSystemTime call which NTP uses.

I played a little with those calls (in a non-serious way) and wrote some
code:

   http://www.satsignal.eu/ntp/TSCtime.html

based on:

   http://www.lochan.org/2005/keith-cl/useful/win32time.html

and just messing around!  Perhaps it's of interest or use?

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

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Re: [time-nuts] WWVB Time

[Tom Van Baak]

> Hi, all of a sudden my Symmetricom comparator/clock has been locking up on 
> time.
> It has been about a week so far. Did they change the code? Anyone else seeing 
> that?
> Doug K6JEY

Hi Doug,

That would be too good to be true. I asked NIST just now and they report: "We 
have not changed the code or power level. All things remain the same."

So let's debug this on your end.
- What make/model WWVB receiver are you using?
- Can you check the accuracy of the time or frequency output against GPS / 
GPSDO. Is it NIST accurate or a bad copy of 60 kHz?
- Did you power-up any new instrument in the past week, one that might cause 60 
kHz harmonics?
- Can you check with 'scope or spectrum analyzer what your environment looks 
like near 60 kHz?
- Do you have a curious neighbor who is experimenting with a WWVB simulator...

/tvb

- Original Message - 
From: "Doug Millar via time-nuts" 
To: 
Sent: Tuesday, April 10, 2018 1:23 PM
Subject: [time-nuts] WWVB Time


Hi, all of a sudden my Symmetricom comparator/clock has been locking up on 
time. It has been about a week so far. Did they change the code? Anyone else 
seeing that? Doug K6JEY
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[time-nuts] WWVB Time

[Doug Millar via time-nuts]

Hi, all of a sudden my Symmetricom comparator/clock has been locking up on 
time. It has been about a week so far. Did they change the code? Anyone else 
seeing that?     Doug K6JEY
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Re: [time-nuts] Dual GPSDO - any advantage?

[gandalfg8--- via time-nuts]

Unless I copied the number incorrectly earlier it does seem likely that Ebay 
has pulled that auction.

It may still be showing up to those who "bought" them but a straight search on 
that number returns nothing,
either in completed or running listings, nor does it show up now in searches 
for "Trimble GPSDO" which is how I found it earlier.

If anyone's interested, and in case there's still any doubts, one version of 
the Bob Mokia listing under his Ebay ID of amoj1010, that was copied photos and 
all to provide this auction, is still current and is # 252162780444.

Nigel, GM8PZR


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[time-nuts] Wavecrest DTS2075

[Gerhard Hoffmann]

I have been offered a DTS2075. Is this generally regarded as a step

forward if you already have a SR620 or is it more or less the same

league? Are there any hidden pearls or caveats?


TIA and best regards,

Gerhard



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Re: [time-nuts] Dual GPSDO - any advantage?

[ewkehren via time-nuts]

Jürg will have to explain he is in Switzerland  will be tomorrowBert


Sent from my Galaxy Tab® A
 Original message From: CORNACCHIA via time-nuts 
 Date: 4/10/18  2:35 PM  (GMT-05:00) To: ewkehren via 
time-nuts  Subject: Re: [time-nuts] Dual GPSDO - any 
advantage? 
 Bert may I ask how you created the charts (what software are you using).Thank 
You
    On Tuesday, April 10, 2018, 9:04:58 a.m. EDT, ewkehren via time-nuts 
 wrote:  
 
 Looking at the pictures it is the same unit I bought. It is not dual oven bit 
trimble works with LH right now shows tracking 10 satelites.Attached  is data 
that made  me buy a second one for Jürg for $ 129  and one more for me for 
$9.50.What you see is highly filtered data to see long time changes to better 
understand if analog filtering os possible. Planning on using Wenzel 600 sec. 
Filter maybe up to 2000 seconds. Board is ready for order.Top plot is my data 
against my Cs 5061B bottom is original Tbolt against his FTS  Cs. We use 53132 
counters.I think  the new one lends it self better for filtering looking at 
both  with my Tracor, Trimble uses a  much shorter time constant and no short 
1E-10 changes you see on our standard units.Will keep you posted         Bert 
Kehren

Sent from my Galaxy Tab® A
 Original message From: Tim Shoppa  Date: 
4/10/18  6:46 AM  (GMT-05:00) To: Discussion of precise time and frequency 
measurement  Subject: Re: [time-nuts] Dual GPSDO - any 
advantage? 
Most of the Chinese cheapo units have been frequency, not phase locked.

It would be great if you could put the GPSDO outputs into a 2 Channel scope and 
eyeball them for a while to see if they appear in phase (say plus-minus 20ns) 
over a few hours.

Tim N3QE

> On Apr 10, 2018, at 1:43 AM, donald collie  wrote:
> 
> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> error!] They are stated as being new, and use a Trimball dual oven OCXO. I
> plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
> been said that a man with two watches is never happy - unless, of course,
> they agree with each other ;-). Being identical the outputs should be
> coherent, unless one becomes faulty [one advantage of having two - any
> discrepancy and you know something must be wrong]], but is there some
> crafty way I can squeeze a little more "accuracy" out of two than if I only
> used one?
> TIA for your commentsDonald
> Brett Collie ZL4GX
> 
> PS : I have no connection to the eBay seller. The US$9-50 seems to include
> a basic puck antenna, long downlead, and 4 interseries adaptors
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Re: [time-nuts] Dual GPSDO - any advantage?

[Dr. David Kirkby]

On 10 April 2018 at 16:56, donald collie  wrote:

> I have the Chinapost tracking numbers, so I don`t think it`s a scam - just
> real good value.


I hope you are right, but I doubt you are.

It is not uncommon to be sent fake tracking numbers.

I was 99% sure a Keithley 2002 8.5 digit meter for £900 was a scam, but
decided to play along with it, just in case it was not. The seller claimed
to have sent it, send me a FedEx tracking number, but said if he did not
receive payment by bank transfer within 24 hours he would cancel the
shipment. The tracking number was NOT to the real FedEx site, but something
made to look like FedEx.

Even if you have the real Chinese post office tracking number, it could be
the same number sent to 100 people. I doubt it has your detailed location
on it.

I hope you are right, and they are a good buy, as I bought 10 of them. But
I doubt they are real. I'm 99% sure they are a scam, but are not bothered,
as a scam like that would easily result in one willing an eBay dispute.

Dave
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Re: [time-nuts] Cheap jitter measurements

[Bob kb8tq]

Hi

> On Apr 10, 2018, at 2:59 PM, Hal Murray  wrote:
> 
> 
> kb...@n1k.org said:
>> Yes, but looping back to the start of this thread, the intent is to actually
>> measure the jitter directly.  That’s where the whole need for a stamped
>> pulse comes from. To paraphrase the earlier comments, the intent is to get
>> away from a “self reported” result and actually do a direct measurement.  
> 
> I think that should be a reasonable project.
> 
> 1) Write some code to grab the time, send a pulse, grab the time.  Log that.
> 2) Use a time-stamp counter to log the time of the pulse.
> 3) Write the software to merge the two log files.

Provided you can get NTP (and not just the kernel) to time the pulse accurately 
it 
would work. It’s a bit more cumbersome than a message out of a serial port. 

Bob


> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] Dual GPSDO - any advantage?

[Dr. David Kirkby]

On 10 April 2018 at 17:11, Clint Jay  wrote:

> Sad to say I think I was right, the listings have been pulled already and
> the seller now has zero items for sale.
>

The listing has not been pulled. Yes the seller has 0 to sell, but because
he has sold out of the 100. I still have the purchase in my purchase
history, and no messages from eBay about fraud.

>
> Get those paypal refund cases logged.
>

One would need to wait until they don't arrive. Luckily they were not much.

Then it is better to complain to eBay first. If you don't get any
satisfaction from eBay, then you can go to PayPal. But by going directly to
PayPal, you will have lost the chance to get a refund via eBay. So the
sensible order to try to get refunds is

1) eBay
2) PayPal
3) Chargeback on credit card.

Never advance to stage PayPal unless you have exhaused attempts at eBay.
Never make a chargeback unless you have exhaused atttempts at both eBay and
PayPal.

Sometimes it can be a bit of an uphill struggle to get refunds from eBay
for dodgy sellers, but in this case it should be fairly easy if the goods
don't arrive. On the off-chance they do, we have scored well.


Clint. M0UAW IO83
>


Dave G8WRB.
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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

kb...@n1k.org said:
> Yes, but looping back to the start of this thread, the intent is to actually
> measure the jitter directly.  That’s where the whole need for a stamped
> pulse comes from. To paraphrase the earlier comments, the intent is to get
> away from a “self reported” result and actually do a direct measurement.  

I think that should be a reasonable project.

1) Write some code to grab the time, send a pulse, grab the time.  Log that.
2) Use a time-stamp counter to log the time of the pulse.
3) Write the software to merge the two log files.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Dual GPSDO - any advantage?

[CORNACCHIA via time-nuts]

 Bert may I ask how you created the charts (what software are you using).Thank 
You
On Tuesday, April 10, 2018, 9:04:58 a.m. EDT, ewkehren via time-nuts 
 wrote:  
 
 Looking at the pictures it is the same unit I bought. It is not dual oven bit 
trimble works with LH right now shows tracking 10 satelites.Attached  is data 
that made  me buy a second one for Jürg for $ 129  and one more for me for 
$9.50.What you see is highly filtered data to see long time changes to better 
understand if analog filtering os possible. Planning on using Wenzel 600 sec. 
Filter maybe up to 2000 seconds. Board is ready for order.Top plot is my data 
against my Cs 5061B bottom is original Tbolt against his FTS  Cs. We use 53132 
counters.I think  the new one lends it self better for filtering looking at 
both  with my Tracor, Trimble uses a  much shorter time constant and no short 
1E-10 changes you see on our standard units.Will keep you posted         Bert 
Kehren

Sent from my Galaxy Tab® A
 Original message From: Tim Shoppa  Date: 
4/10/18  6:46 AM  (GMT-05:00) To: Discussion of precise time and frequency 
measurement  Subject: Re: [time-nuts] Dual GPSDO - any 
advantage? 
Most of the Chinese cheapo units have been frequency, not phase locked.

It would be great if you could put the GPSDO outputs into a 2 Channel scope and 
eyeball them for a while to see if they appear in phase (say plus-minus 20ns) 
over a few hours.

Tim N3QE

> On Apr 10, 2018, at 1:43 AM, donald collie  wrote:
> 
> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> error!] They are stated as being new, and use a Trimball dual oven OCXO. I
> plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
> been said that a man with two watches is never happy - unless, of course,
> they agree with each other ;-). Being identical the outputs should be
> coherent, unless one becomes faulty [one advantage of having two - any
> discrepancy and you know something must be wrong]], but is there some
> crafty way I can squeeze a little more "accuracy" out of two than if I only
> used one?
> TIA for your commentsDonald
> Brett Collie ZL4GX
> 
> PS : I have no connection to the eBay seller. The US$9-50 seems to include
> a basic puck antenna, long downlead, and 4 interseries adaptors
> ___
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Re: [time-nuts] Dual GPSDO - any advantage?

[CORNACCHIA via time-nuts]

 How did You Pay for them, I cannot make a payment
On Tuesday, April 10, 2018, 2:01:41 p.m. EDT, W7SLS - Scott Scheirman 
 wrote:  
 
 I ordered 2.  We shall see
Scott
No connection with seller(s)

Sent from my iPhone

> On Apr 10, 2018, at 7:13 AM, gandalfg8--- via time-nuts  
> wrote:
> 
> 
> 
> 
> Is this auction # 273145006434, actually showing at $9.77 here in the UK, and 
> from a recently registered zero rated seller?
> 
> If so, and given that the auction text, and perhaps the photos too, seem to 
> be taken from one or more of Bob Mokia's
> auctions dating back a couple of years or so, and that this price is 
> approximately $100 below the norm, perhaps
> a degree of caution might be worthwhile.
> 
> It's either a very sad mistake, from the seller's point of view anyway, or 
> perhaps something a little more devious!
> 
> Nigel, GM8PZR
> 
> 
> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> error!] They are stated as being new, and use a Trimball dual oven OCXO. I
> plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
> been said that a man with two watches is never happy - unless, of course,
> they agree with each other ;-). Being identical the outputs should be
> coherent, unless one becomes faulty [one advantage of having two - any
> discrepancy and you know something must be wrong]], but is there some
> crafty way I can squeeze a little more "accuracy" out of two than if I only
> used one?
> TIA for your commentsDonald
> Brett Collie ZL4GX
> 
> PS : I have no connection to the eBay seller. The US$9-50 seems to include
> a basic puck antenna, long downlead, and 4 interseries adaptors
> 
> 
> 
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Re: [time-nuts] Dual GPSDO - any advantage?

[Bob kb8tq]

Hi

Looks like 100 is all he had (or all he put up on this auction). It will be 
interesting to see what
(if anything) we all get …..

Bob

> On Apr 10, 2018, at 12:44 PM, W7SLS - Scott Scheirman  
> wrote:
> 
> I ordered 2.  We shall see
> Scott
> No connection with seller(s)
> 
> Sent from my iPhone
> 
>> On Apr 10, 2018, at 7:13 AM, gandalfg8--- via time-nuts  
>> wrote:
>> 
>> 
>> 
>> 
>> Is this auction # 273145006434, actually showing at $9.77 here in the UK, 
>> and from a recently registered zero rated seller?
>> 
>> If so, and given that the auction text, and perhaps the photos too, seem to 
>> be taken from one or more of Bob Mokia's
>> auctions dating back a couple of years or so, and that this price is 
>> approximately $100 below the norm, perhaps
>> a degree of caution might be worthwhile.
>> 
>> It's either a very sad mistake, from the seller's point of view anyway, or 
>> perhaps something a little more devious!
>> 
>> Nigel, GM8PZR
>> 
>> 
>> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
>> error!] They are stated as being new, and use a Trimball dual oven OCXO. I
>> plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
>> been said that a man with two watches is never happy - unless, of course,
>> they agree with each other ;-). Being identical the outputs should be
>> coherent, unless one becomes faulty [one advantage of having two - any
>> discrepancy and you know something must be wrong]], but is there some
>> crafty way I can squeeze a little more "accuracy" out of two than if I only
>> used one?
>> TIA for your commentsDonald
>> Brett Collie ZL4GX
>> 
>> PS : I have no connection to the eBay seller. The US$9-50 seems to include
>> a basic puck antenna, long downlead, and 4 interseries adaptors
>> 
>> 
>> 
>> ___
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Re: [time-nuts] Cheap jitter measurements

[Bob kb8tq]

Hi


> On Apr 10, 2018, at 12:23 PM, David J Taylor via time-nuts 
>  wrote:
> 
> Hi,
> 
> Yes, but isn't generating pulses OUT of a PC with low latency/jitter one
> of the difficult issues?
> 
> If we (somebody smarter than me...) flip this around and modify a copy
> NTP to grab the QueryPerformanceCounter value when it gets a PPS pulse
> and log that count, don't we now have a way to compare the high
> resolution uncorrected counter to NTP and the external PPS?

We would still be relying on NTP to report on it’s self. I can feed the PC a 
PPS from my GPSDO
and let it report on that. Tell it to simply monitor the input, but not use it 
for disciplining. I get information,
but it’s what NTP “thinks of it’s self”. Ideally one would like to get an 
output that can be independently 
measured.

Bob


> 
> Agreed, not trivial. But maybe fun anyway!
> 
> Dan
> 
> 
> Dan,
> 
> Take a look at Dave Hart's patches to the Microsoft serial port driver, that 
> does something similar.  The source may be in the NTP distribution, or 
> Meinberg may have a copy.  At one time using the QueryPerfomanceCounter call 
> was an option (look for "QPC").  With Windows-8 and later there is a much 
> more precise GetSystemTime call which NTP uses.
> 
> I played a little with those calls (in a non-serious way) and wrote some code:
> 
> http://www.satsignal.eu/ntp/TSCtime.html
> 
> based on:
> 
> http://www.lochan.org/2005/keith-cl/useful/win32time.html
> 
> and just messing around!  Perhaps it's of interest or use?
> 
> Cheers,
> David
> -- 
> SatSignal Software - Quality software written to your requirements
> Web: http://www.satsignal.eu
> Email: david-tay...@blueyonder.co.uk
> Twitter: @gm8arv 
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Re: [time-nuts] Cheap jitter measurements

[Bob kb8tq]

Hi



> On Apr 10, 2018, at 11:56 AM, Dan Kemppainen  wrote:
> 
> Hi,
> 
> Yes, but isn't generating pulses OUT of a PC with low latency/jitter one of 
> the difficult issues?
> 
> If we (somebody smarter than me...) flip this around and modify a copy NTP to 
> grab the QueryPerformanceCounter value when it gets a PPS pulse and log that 
> count, don't we now have a way to compare the high resolution uncorrected 
> counter to NTP and the external PPS?

Yes, but looping back to the start of this thread, the intent is to actually 
measure the jitter directly. 
That’s where the whole need for a stamped pulse comes from. To paraphrase the 
earlier comments,
the intent is to get away from a “self reported” result and actually do a 
direct measurement. 

Bob


> 
> Agreed, not trivial. But maybe fun anyway!
> 
> Dan
> 
> 
> On 4/10/2018 11:03 AM, time-nuts-requ...@febo.com wrote:
>> NTP already looks at incoming pulses and reports what it thinks is going on 
>> with them. The desire here
>> is to get a pulse*out*  of the device. Then you can toss it into a 
>> conventional set of gear. From the data
>> you can independently evaluate what’s going on.
>> So more or less:
>> 1) Generate pulse
>> 2) Work out when the pulse went out
>> 3) Compare that to what NTP thinks is going on
>> 4) Generate a message to describe the delta in time
>> No, not trivial ….
>> Bob
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Re: [time-nuts] Dual GPSDO - any advantage?

[W7SLS - Scott Scheirman]

I ordered 2.  We shall see
Scott
No connection with seller(s)

Sent from my iPhone

> On Apr 10, 2018, at 7:13 AM, gandalfg8--- via time-nuts  
> wrote:
> 
> 
> 
> 
> Is this auction # 273145006434, actually showing at $9.77 here in the UK, and 
> from a recently registered zero rated seller?
> 
> If so, and given that the auction text, and perhaps the photos too, seem to 
> be taken from one or more of Bob Mokia's
> auctions dating back a couple of years or so, and that this price is 
> approximately $100 below the norm, perhaps
> a degree of caution might be worthwhile.
> 
> It's either a very sad mistake, from the seller's point of view anyway, or 
> perhaps something a little more devious!
> 
> Nigel, GM8PZR
> 
> 
> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> error!] They are stated as being new, and use a Trimball dual oven OCXO. I
> plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
> been said that a man with two watches is never happy - unless, of course,
> they agree with each other ;-). Being identical the outputs should be
> coherent, unless one becomes faulty [one advantage of having two - any
> discrepancy and you know something must be wrong]], but is there some
> crafty way I can squeeze a little more "accuracy" out of two than if I only
> used one?
> TIA for your commentsDonald
> Brett Collie ZL4GX
> 
> PS : I have no connection to the eBay seller. The US$9-50 seems to include
> a basic puck antenna, long downlead, and 4 interseries adaptors
> 
> 
> 
> ___
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Re: [time-nuts] Cheap jitter measurements

[David J Taylor via time-nuts]

Hi,

Yes, but isn't generating pulses OUT of a PC with low latency/jitter one
of the difficult issues?

If we (somebody smarter than me...) flip this around and modify a copy
NTP to grab the QueryPerformanceCounter value when it gets a PPS pulse
and log that count, don't we now have a way to compare the high
resolution uncorrected counter to NTP and the external PPS?

Agreed, not trivial. But maybe fun anyway!

Dan


Dan,

Take a look at Dave Hart's patches to the Microsoft serial port driver, that 
does something similar.  The source may be in the NTP distribution, or 
Meinberg may have a copy.  At one time using the QueryPerfomanceCounter call 
was an option (look for "QPC").  With Windows-8 and later there is a much 
more precise GetSystemTime call which NTP uses.


I played a little with those calls (in a non-serious way) and wrote some 
code:


 http://www.satsignal.eu/ntp/TSCtime.html

based on:

 http://www.lochan.org/2005/keith-cl/useful/win32time.html

and just messing around!  Perhaps it's of interest or use?

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


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Re: [time-nuts] Dual GPSDO - any advantage?

[Dr. David Kirkby]

On 10 April 2018 at 16:23, Dr. David Kirkby 
wrote:

> On 10 April 2018 at 15:32, Clint Jay  wrote:
>
>> Ahh, I've found the listing, has anyone received one?
>>
>> I hate to say this but I'm highly sceptical that they will ever turn up,
>> looks and smells very much like the standard eBay scam to me.
>>
> --
>
>> Clint. M0UAW IO83
>>
>
>
> I'm VERY skeptical too of the item
>


The more I look at this, the more I think it is a scam.

* Description says orders shipped after April 2016 will be a new design,
yet the seller was not registered until 27th February 2018 - almost 2 years
later.
* Feedback is zero.

I phoned eBay. The guy I spoke too was highly suspicious too, and has past
it along to a team that deals with possible scams.

Dave
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Re: [time-nuts] Dual GPSDO - any advantage?

[Clint Jay]

Sad to say I think I was right, the listings have been pulled already and
the seller now has zero items for sale.

Get those paypal refund cases logged.

On 10 April 2018 at 15:13, gandalfg8--- via time-nuts 
wrote:

>
>
>
> Is this auction # 273145006434, actually showing at $9.77 here in the UK,
> and from a recently registered zero rated seller?
>
> If so, and given that the auction text, and perhaps the photos too, seem
> to be taken from one or more of Bob Mokia's
> auctions dating back a couple of years or so, and that this price is
> approximately $100 below the norm, perhaps
> a degree of caution might be worthwhile.
>
> It's either a very sad mistake, from the seller's point of view anyway, or
> perhaps something a little more devious!
>
> Nigel, GM8PZR
>
>
> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> error!] They are stated as being new, and use a Trimball dual oven OCXO. I
> plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
> been said that a man with two watches is never happy - unless, of course,
> they agree with each other ;-). Being identical the outputs should be
> coherent, unless one becomes faulty [one advantage of having two - any
> discrepancy and you know something must be wrong]], but is there some
> crafty way I can squeeze a little more "accuracy" out of two than if I only
> used one?
> TIA for your commentsDonald
> Brett Collie ZL4GX
>
> PS : I have no connection to the eBay seller. The US$9-50 seems to include
> a basic puck antenna, long downlead, and 4 interseries adaptors
>
>
>
> ___
> 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.
>



-- 
Clint. M0UAW IO83

*No trees were harmed in the sending of this mail. However, a large number
of electrons were greatly inconvenienced.*
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Re: [time-nuts] Dual GPSDO - any advantage?

[donald collie]

I have the Chinapost tracking numbers, so I don`t think it`s a scam - just
real good value. I have the eBay guarantee, anyway. I`m just looking for a
superior frequency standard at the moment, but the timenut bug might bight.
How could I take the average of two [now three]. A man with three watches.
. . . Cheers!... Don C.


Virus-free.
www.avg.com

<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

On Wed, Apr 11, 2018 at 2:32 AM, Clint Jay  wrote:

> Ahh, I've found the listing, has anyone received one?
>
> I hate to say this but I'm highly sceptical that they will ever turn up,
> looks and smells very much like the standard eBay scam to me.
>
>
>
>
>
> On 10 April 2018 at 14:52, Bob kb8tq  wrote:
>
> > Hi
> >
> > Simple answer is that the “simple” approaches don’t do much to improve
> > things.
> > Errors are indeed un-correlated, even off of the same antenna. You
> *could*
> > average the result off of the two. That might improve things by sqrt(2).
> My
> > experience is that the bumps and lumps (when they do occur) are not the
> > sort
> > of thing that averages out nicely…..
> >
> > Bob
> >
> > > On Apr 10, 2018, at 1:43 AM, donald collie 
> > wrote:
> > >
> > > I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> > > error!] They are stated as being new, and use a Trimball dual oven
> OCXO.
> > I
> > > plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s]
> > It`s
> > > been said that a man with two watches is never happy - unless, of
> course,
> > > they agree with each other ;-). Being identical the outputs should be
> > > coherent, unless one becomes faulty [one advantage of having two - any
> > > discrepancy and you know something must be wrong]], but is there some
> > > crafty way I can squeeze a little more "accuracy" out of two than if I
> > only
> > > used one?
> > > TIA for your comments..
> ..Donald
> > > Brett Collie ZL4GX
> > >
> > > PS : I have no connection to the eBay seller. The US$9-50 seems to
> > include
> > > a basic puck antenna, long downlead, and 4 interseries adaptors
> > > ___
> > > 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.
> >
>
>
>
> --
> Clint. M0UAW IO83
>
> *No trees were harmed in the sending of this mail. However, a large number
> of electrons were greatly inconvenienced.*
> ___
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> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>
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Re: [time-nuts] Cheap jitter measurements

[Dan Kemppainen]

Hi,

Yes, but isn't generating pulses OUT of a PC with low latency/jitter one 
of the difficult issues?


If we (somebody smarter than me...) flip this around and modify a copy 
NTP to grab the QueryPerformanceCounter value when it gets a PPS pulse 
and log that count, don't we now have a way to compare the high 
resolution uncorrected counter to NTP and the external PPS?


Agreed, not trivial. But maybe fun anyway!

Dan


On 4/10/2018 11:03 AM, time-nuts-requ...@febo.com wrote:

NTP already looks at incoming pulses and reports what it thinks is going on 
with them. The desire here
is to get a pulse*out*  of the device. Then you can toss it into a conventional 
set of gear. From the data
you can independently evaluate what’s going on.

So more or less:

1) Generate pulse
2) Work out when the pulse went out
3) Compare that to what NTP thinks is going on
4) Generate a message to describe the delta in time

No, not trivial ….

Bob



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Re: [time-nuts] Dual GPSDO - any advantage?

[Richard Solomon]

As we say in the world of DX'ing (Ham Radio) ...


"Work First Worry Later"


I just ordered two of them. If they are bogus, e-Bay will make good on them.


73, Dick, W1KSZ


Sent from Outlook

From: time-nuts  on behalf of gandalfg8--- via 
time-nuts 
Sent: Tuesday, April 10, 2018 7:13:28 AM
To: time-nuts@febo.com
Subject: [time-nuts] Dual GPSDO - any advantage?




Is this auction # 273145006434, actually showing at $9.77 here in the UK, and 
from a recently registered zero rated seller?

If so, and given that the auction text, and perhaps the photos too, seem to be 
taken from one or more of Bob Mokia's
auctions dating back a couple of years or so, and that this price is 
approximately $100 below the norm, perhaps
a degree of caution might be worthwhile.

It's either a very sad mistake, from the seller's point of view anyway, or 
perhaps something a little more devious!

Nigel, GM8PZR


I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
error!] They are stated as being new, and use a Trimball dual oven OCXO. I
plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
been said that a man with two watches is never happy - unless, of course,
they agree with each other ;-). Being identical the outputs should be
coherent, unless one becomes faulty [one advantage of having two - any
discrepancy and you know something must be wrong]], but is there some
crafty way I can squeeze a little more "accuracy" out of two than if I only
used one?
TIA for your commentsDonald
Brett Collie ZL4GX

PS : I have no connection to the eBay seller. The US$9-50 seems to include
a basic puck antenna, long downlead, and 4 interseries adaptors



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Re: [time-nuts] Dual GPSDO - any advantage?

[ewkehren via time-nuts]

Most likely but PayPal will have to get involved since there are more than one 
of usBert Kehren


Sent from my Galaxy Tab® A
 Original message From: Clint Jay  Date: 
4/10/18  10:32 AM  (GMT-05:00) To: Discussion of precise time and frequency 
measurement  Subject: Re: [time-nuts] Dual GPSDO - any 
advantage? 
Ahh, I've found the listing, has anyone received one?

I hate to say this but I'm highly sceptical that they will ever turn up,
looks and smells very much like the standard eBay scam to me.





On 10 April 2018 at 14:52, Bob kb8tq  wrote:

> Hi
>
> Simple answer is that the “simple” approaches don’t do much to improve
> things.
> Errors are indeed un-correlated, even off of the same antenna. You *could*
> average the result off of the two. That might improve things by sqrt(2). My
> experience is that the bumps and lumps (when they do occur) are not the
> sort
> of thing that averages out nicely…..
>
> Bob
>
> > On Apr 10, 2018, at 1:43 AM, donald collie 
> wrote:
> >
> > I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> > error!] They are stated as being new, and use a Trimball dual oven OCXO.
> I
> > plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s]
> It`s
> > been said that a man with two watches is never happy - unless, of course,
> > they agree with each other ;-). Being identical the outputs should be
> > coherent, unless one becomes faulty [one advantage of having two - any
> > discrepancy and you know something must be wrong]], but is there some
> > crafty way I can squeeze a little more "accuracy" out of two than if I
> only
> > used one?
> > TIA for your commentsDonald
> > Brett Collie ZL4GX
> >
> > PS : I have no connection to the eBay seller. The US$9-50 seems to
> include
> > a basic puck antenna, long downlead, and 4 interseries adaptors
> > ___
> > 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.
>



-- 
Clint. M0UAW IO83

*No trees were harmed in the sending of this mail. However, a large number
of electrons were greatly inconvenienced.*
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Re: [time-nuts] Dual GPSDO - any advantage?

[Dr. David Kirkby]

On 10 April 2018 at 15:32, Clint Jay  wrote:

> Ahh, I've found the listing, has anyone received one?
>
> I hate to say this but I'm highly sceptical that they will ever turn up,
> looks and smells very much like the standard eBay scam to me.
>
--

> Clint. M0UAW IO83
>


I'm VERY skeptical too of the item

https://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-sine-and-square-wave/273145006434

I have bought 10, on the assumption if they don't show up, I will get my
money back. Note the seller has a feedback of zero, and had not been
registered that long. So I'm thinking there's a 95% chance its a scam.

Also listed by the same seller is a rubidium source

https://www.ebay.com/itm/New-FE-5650A-OPTION-58-RUBIDIUM-FREQUENCY-STD-FREQUENCY-ELECTRONICS-INC/273145001650

which looking nothing like one.

Perhaps with hindsight, I wish I had not ordered 10, but then I would kick
myself if I did not order them, and find out later they are genuine.

Dave
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Re: [time-nuts] Dual GPSDO - any advantage?

[Bob kb8tq]

Hi

I certainly would not pay with anything other than PayPal. There is a very
real risk …..

Bob

> On Apr 10, 2018, at 10:32 AM, Clint Jay  wrote:
> 
> Ahh, I've found the listing, has anyone received one?
> 
> I hate to say this but I'm highly sceptical that they will ever turn up,
> looks and smells very much like the standard eBay scam to me.
> 
> 
> 
> 
> 
> On 10 April 2018 at 14:52, Bob kb8tq  wrote:
> 
>> Hi
>> 
>> Simple answer is that the “simple” approaches don’t do much to improve
>> things.
>> Errors are indeed un-correlated, even off of the same antenna. You *could*
>> average the result off of the two. That might improve things by sqrt(2). My
>> experience is that the bumps and lumps (when they do occur) are not the
>> sort
>> of thing that averages out nicely…..
>> 
>> Bob
>> 
>>> On Apr 10, 2018, at 1:43 AM, donald collie 
>> wrote:
>>> 
>>> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
>>> error!] They are stated as being new, and use a Trimball dual oven OCXO.
>> I
>>> plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s]
>> It`s
>>> been said that a man with two watches is never happy - unless, of course,
>>> they agree with each other ;-). Being identical the outputs should be
>>> coherent, unless one becomes faulty [one advantage of having two - any
>>> discrepancy and you know something must be wrong]], but is there some
>>> crafty way I can squeeze a little more "accuracy" out of two than if I
>> only
>>> used one?
>>> TIA for your commentsDonald
>>> Brett Collie ZL4GX
>>> 
>>> PS : I have no connection to the eBay seller. The US$9-50 seems to
>> include
>>> a basic puck antenna, long downlead, and 4 interseries adaptors
>>> ___
>>> 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.
>> 
> 
> 
> 
> -- 
> Clint. M0UAW IO83
> 
> *No trees were harmed in the sending of this mail. However, a large number
> of electrons were greatly inconvenienced.*
> ___
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> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

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Re: [time-nuts] Cheap jitter measurements

[Bob kb8tq]

Hi


> On Apr 10, 2018, at 9:59 AM, Dan Kemppainen  wrote:
> 
> Hi,
> 
> Don't know how good they are, but there are two functions in the kernel32 lib 
> in windows that are related to a cpu performance counter, 
> QueryPerformanceCounter and QueryPerformanceFrequency. (Maybe Linux has 
> similar?)
> 
> Anyway, on most systems the frequency reported is the raw cpu clock. (Couple 
> of Ghz Range numbers, My current system is reporting 3,320,458 Hz, windows7.) 
> Supposedly these are low latency functions. It may not offer a perfect 
> solution, but at least it gives you 'low latency' access to a high speed 
> counter.
> 
> Maybe it's possible to timestamp incoming PPS pulses with this (assuming 
> they're triggering an interrupt), and learn something neat.
> 
> Some of this is subject to change with windows versions:
> 
> https://msdn.microsoft.com/en-us/library/windows/desktop/dn553408(v=vs.85).aspx
>  
> 

NTP already looks at incoming pulses and reports what it thinks is going on 
with them. The desire here 
is to get a pulse *out* of the device. Then you can toss it into a conventional 
set of gear. From the data
you can independently evaluate what’s going on. 

So more or less:

1) Generate pulse
2) Work out when the pulse went out
3) Compare that to what NTP thinks is going on
4) Generate a message to describe the delta in time

No, not trivial ….

Bob


> 
> Dan
> 
> 
> 
> 
> On 4/10/2018 8:01 AM, time-nuts-requ...@febo.com wrote:
>> kb...@n1k.org  said:
>>> The kernel clock comes from the CPU clock. That CPU clock is phase locked to
>>> a crystal. If you have a CPU that is driven by a VCXO that is a*very*
>>> unusual CPU board.  The crystal runs at an arbitrary frequency. That gives
>>> you edges that are unlikely to happen ���right on the second���.
>> I was assuming the CPU clock was fast enough that reading a cycle-count
>> register and converting to ns would be within a ns which is the resolution of
>> the clock.
>> That's obviously not true for low end SOC type setups.  A Pi-1 runs at 700
>> MHz.  The Pi 3 is up to 1.4 GHz.
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] Dual GPSDO - any advantage?

[Clint Jay]

Ahh, I've found the listing, has anyone received one?

I hate to say this but I'm highly sceptical that they will ever turn up,
looks and smells very much like the standard eBay scam to me.





On 10 April 2018 at 14:52, Bob kb8tq  wrote:

> Hi
>
> Simple answer is that the “simple” approaches don’t do much to improve
> things.
> Errors are indeed un-correlated, even off of the same antenna. You *could*
> average the result off of the two. That might improve things by sqrt(2). My
> experience is that the bumps and lumps (when they do occur) are not the
> sort
> of thing that averages out nicely…..
>
> Bob
>
> > On Apr 10, 2018, at 1:43 AM, donald collie 
> wrote:
> >
> > I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> > error!] They are stated as being new, and use a Trimball dual oven OCXO.
> I
> > plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s]
> It`s
> > been said that a man with two watches is never happy - unless, of course,
> > they agree with each other ;-). Being identical the outputs should be
> > coherent, unless one becomes faulty [one advantage of having two - any
> > discrepancy and you know something must be wrong]], but is there some
> > crafty way I can squeeze a little more "accuracy" out of two than if I
> only
> > used one?
> > TIA for your commentsDonald
> > Brett Collie ZL4GX
> >
> > PS : I have no connection to the eBay seller. The US$9-50 seems to
> include
> > a basic puck antenna, long downlead, and 4 interseries adaptors
> > ___
> > 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.
>



-- 
Clint. M0UAW IO83

*No trees were harmed in the sending of this mail. However, a large number
of electrons were greatly inconvenienced.*
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[time-nuts] Dual GPSDO - any advantage?

[gandalfg8--- via time-nuts]

Is this auction # 273145006434, actually showing at $9.77 here in the UK, and 
from a recently registered zero rated seller?

If so, and given that the auction text, and perhaps the photos too, seem to be 
taken from one or more of Bob Mokia's
auctions dating back a couple of years or so, and that this price is 
approximately $100 below the norm, perhaps
a degree of caution might be worthwhile.

It's either a very sad mistake, from the seller's point of view anyway, or 
perhaps something a little more devious!

Nigel, GM8PZR


I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
error!] They are stated as being new, and use a Trimball dual oven OCXO. I
plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
been said that a man with two watches is never happy - unless, of course,
they agree with each other ;-). Being identical the outputs should be
coherent, unless one becomes faulty [one advantage of having two - any
discrepancy and you know something must be wrong]], but is there some
crafty way I can squeeze a little more "accuracy" out of two than if I only
used one?
TIA for your commentsDonald
Brett Collie ZL4GX

PS : I have no connection to the eBay seller. The US$9-50 seems to include
a basic puck antenna, long downlead, and 4 interseries adaptors



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Re: [time-nuts] Cheap jitter measurements

[Tom Van Baak]

Dan,

I wrote a PC-based time-stamping counter (TSC) tool that uses a serial port and 
QueryPerformanceCounter:

www.leapsecond.com/tools/pctsc.exe (Win32)
www.leapsecond.com/tools/pctsc.c (source)

Give it a try.

/tvb

- Original Message - 
From: "Dan Kemppainen" 
To: 
Sent: Tuesday, April 10, 2018 6:59 AM
Subject: Re: [time-nuts] Cheap jitter measurements


Hi,

Don't know how good they are, but there are two functions in the 
kernel32 lib in windows that are related to a cpu performance counter, 
QueryPerformanceCounter and QueryPerformanceFrequency. (Maybe Linux has 
similar?)

Anyway, on most systems the frequency reported is the raw cpu clock. 
(Couple of Ghz Range numbers, My current system is reporting 3,320,458 
Hz, windows7.) Supposedly these are low latency functions. It may not 
offer a perfect solution, but at least it gives you 'low latency' access 
to a high speed counter.

Maybe it's possible to timestamp incoming PPS pulses with this (assuming 
they're triggering an interrupt), and learn something neat.

Some of this is subject to change with windows versions:

https://msdn.microsoft.com/en-us/library/windows/desktop/dn553408(v=vs.85).aspx

Dan




On 4/10/2018 8:01 AM, time-nuts-requ...@febo.com wrote:
> kb...@n1k.org  said:
>> The kernel clock comes from the CPU clock. That CPU clock is phase locked to
>> a crystal. If you have a CPU that is driven by a VCXO that is a*very*
>> unusual CPU board.  The crystal runs at an arbitrary frequency. That gives
>> you edges that are unlikely to happen ���right on the second���.
> I was assuming the CPU clock was fast enough that reading a cycle-count
> register and converting to ns would be within a ns which is the resolution of
> the clock.
> 
> That's obviously not true for low end SOC type setups.  A Pi-1 runs at 700
> MHz.  The Pi 3 is up to 1.4 GHz.
> 
> 
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Re: [time-nuts] Cheap jitter measurements

[Dan Kemppainen]

Hi,

Don't know how good they are, but there are two functions in the 
kernel32 lib in windows that are related to a cpu performance counter, 
QueryPerformanceCounter and QueryPerformanceFrequency. (Maybe Linux has 
similar?)


Anyway, on most systems the frequency reported is the raw cpu clock. 
(Couple of Ghz Range numbers, My current system is reporting 3,320,458 
Hz, windows7.) Supposedly these are low latency functions. It may not 
offer a perfect solution, but at least it gives you 'low latency' access 
to a high speed counter.


Maybe it's possible to timestamp incoming PPS pulses with this (assuming 
they're triggering an interrupt), and learn something neat.


Some of this is subject to change with windows versions:

https://msdn.microsoft.com/en-us/library/windows/desktop/dn553408(v=vs.85).aspx

Dan




On 4/10/2018 8:01 AM, time-nuts-requ...@febo.com wrote:

kb...@n1k.org  said:

The kernel clock comes from the CPU clock. That CPU clock is phase locked to
a crystal. If you have a CPU that is driven by a VCXO that is a*very*
unusual CPU board.  The crystal runs at an arbitrary frequency. That gives
you edges that are unlikely to happen ���right on the second���.

I was assuming the CPU clock was fast enough that reading a cycle-count
register and converting to ns would be within a ns which is the resolution of
the clock.

That's obviously not true for low end SOC type setups.  A Pi-1 runs at 700
MHz.  The Pi 3 is up to 1.4 GHz.



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Re: [time-nuts] Dual GPSDO - any advantage?

[Bob kb8tq]

Hi

Simple answer is that the “simple” approaches don’t do much to improve things. 
Errors are indeed un-correlated, even off of the same antenna. You *could* 
average the result off of the two. That might improve things by sqrt(2). My 
experience is that the bumps and lumps (when they do occur) are not the sort
of thing that averages out nicely…..

Bob

> On Apr 10, 2018, at 1:43 AM, donald collie  wrote:
> 
> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> error!] They are stated as being new, and use a Trimball dual oven OCXO. I
> plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
> been said that a man with two watches is never happy - unless, of course,
> they agree with each other ;-). Being identical the outputs should be
> coherent, unless one becomes faulty [one advantage of having two - any
> discrepancy and you know something must be wrong]], but is there some
> crafty way I can squeeze a little more "accuracy" out of two than if I only
> used one?
> TIA for your commentsDonald
> Brett Collie ZL4GX
> 
> PS : I have no connection to the eBay seller. The US$9-50 seems to include
> a basic puck antenna, long downlead, and 4 interseries adaptors
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Re: [time-nuts] Cheap jitter measurements

[Bob kb8tq]

Hi

> On Apr 10, 2018, at 6:58 AM, Hal Murray  wrote:
> 
> 
> kb...@n1k.org said:
>> The kernel clock comes from the CPU clock. That CPU clock is phase locked to
>> a crystal. If you have a CPU that is driven by a VCXO that is a *very*
>> unusual CPU board.  The crystal runs at an arbitrary frequency. That gives
>> you edges that are unlikely to happen “right on the second”.  
> 
> I was assuming the CPU clock was fast enough that reading a cycle-count 
> register and converting to ns would be within a ns which is the resolution of 
> the clock.
> 
> That's obviously not true for low end SOC type setups.  A Pi-1 runs at 700 
> MHz.  The Pi 3 is up to 1.4 GHz.


Except that’s not the way most timers run. The silicon needed to get a 
programable 
divider to work at 2.4 GHz is expensive. If you dig into the hardware 
descriptions, 
the clock tree feeds something much slower to the “top end” of the typical timer
in a CPU or MCU. The exception is the high perf timers in some of the Intel 
chips. 
There the issue is getting them to relate to anything “outside” the chip. 

> 
> 
>> And the kernel does the “adjust” by dropping or adding clock cycles to the
>> count.
> 
> I was expecting the kernel to do the clock arithmetic with lots of fractional 
> bits.
> You get things like:
>  This is a 2.4 GHz system.  That's 0.41666 ns per cycle
>  But the crystal is 12 ppm fast, so we actually use 0.416661666
>  It's been 123456 cycles since we last checked.
>  That's 51439.382637696 ns

That may be what the kernel does, but it implements the result as a drop / add
to a counter. 


> Internally, the current time has to remember the fractional bits.
> 
> If anybody is looking carefully, most PC clocks are spread spectrum.  We 
> should do some back-of-envelope work on how significant that is.
> 
> 
>> Being able to read the kernel time is only part of the process. You need to
>> generate an edge. That gets you into timers and (likely) a different set of
>> limitations as the 
> 
> If you want an output pulse, I was thinking of generating it from userland at 
> roughly the right time but recording the actual time.  That would require a 
> fixup pass in software before analyzing the data recorded by traditional 
> hardware approaches.

…… and it would require some sort of correction message out to the user to
tell them how far off that edge that just went out was ….

Bob


> 
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 

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Re: [time-nuts] Dual GPSDO - any advantage?

[ewkehren via time-nuts]

I have run 2 Tbolts from thee same antenna  in to my Tracor and see the 
corrections are in no way correlated.Bert Kehren


Sent from my Galaxy Tab® A
 Original message From: Florian Teply  Date: 
4/10/18  7:00 AM  (GMT-05:00) To: time-nuts@febo.com Subject: Re: [time-nuts] 
Dual GPSDO - any advantage? 
Am Tue, 10 Apr 2018 17:43:25 +1200
schrieb donald collie :

> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> error!] They are stated as being new, and use a Trimball dual oven
> OCXO. I plan to run these in parallel [2 antennas, 2 feedlines, and 2
> GPSDO`s] It`s been said that a man with two watches is never happy -
> unless, of course, they agree with each other ;-). Being identical
> the outputs should be coherent, unless one becomes faulty [one
> advantage of having two - any discrepancy and you know something must
> be wrong]], but is there some crafty way I can squeeze a little more
> "accuracy" out of two than if I only used one?
> TIA for your
> commentsDonald Brett
> Collie ZL4GX

well, my experience in that regard is very limited, not to say
nonexisting, thus take the following with a grain of salt.

Assuming a system with two antenna locations where one device would
be fed both antennas, one could potentially employ some extra
correction based on extra knowledge from these two antennas. Even
though the antenna location usually is known with limited accuracy
(error on the order of 1m), the relative location of two antennas can
be known to a much greater accurracy (order of centimetres or better).
If the system can take that extra information into account, one could
maybe gain some extra accuracy for the solution of time/location.
For example, if the antennas are mounted 1m apart, and everything else
being equal, it is a priori clear, that the calculated position for
both antennas should also be 1m apart. As the signal received by both
antennas should be correlated, while their respective noise
contribution is not, one should gain some SNR. If on top of that time
resolution of the receiver system is very high, one could even take the
phase shift between signals received from both signals into account
similar to the way beam steering is done with phased antenna arrays,
just on receive side, again improving SNR. 
So far for an integrated system, where all signals arew processed in
one place. Now, as I read it you'll rather have two entirely separate
receiver systems. Here, depending on how it is implemented in the
receivers, one could potentially  still gain something extra over a
single unit, but I'd bet this can only be done in postprocessing.
After all, receiver A has no access to the signals as received by
receiver B and vice versa, therefore the spatial relationship can not
be used while deriving the timing solution. Maybe the independent
position solutions could be used to correct the timing solutions after
the fact.

Best regards,
Florian
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Re: [time-nuts] Dual GPSDO - any advantage?

[ewkehren via time-nuts]

Looking at the pictures it is the same unit I bought. It is not dual oven bit 
trimble works with LH right now shows tracking 10 satelites.Attached  is data 
that made  me buy a second one for Jürg for $ 129  and one more for me for 
$9.50.What you see is highly filtered data to see long time changes to better 
understand if analog filtering os possible. Planning on using Wenzel 600 sec. 
Filter maybe up to 2000 seconds. Board is ready for order.Top plot is my data 
against my Cs 5061B bottom is original Tbolt against his FTS  Cs. We use 53132 
counters.I think  the new one lends it self better for filtering looking at 
both  with my Tracor, Trimble uses a  much shorter time constant and no short 
1E-10 changes you see on our standard units.Will keep you posted         Bert 
Kehren

Sent from my Galaxy Tab® A
 Original message From: Tim Shoppa  Date: 
4/10/18  6:46 AM  (GMT-05:00) To: Discussion of precise time and frequency 
measurement  Subject: Re: [time-nuts] Dual GPSDO - any 
advantage? 
Most of the Chinese cheapo units have been frequency, not phase locked.

It would be great if you could put the GPSDO outputs into a 2 Channel scope and 
eyeball them for a while to see if they appear in phase (say plus-minus 20ns) 
over a few hours.

Tim N3QE

> On Apr 10, 2018, at 1:43 AM, donald collie  wrote:
> 
> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> error!] They are stated as being new, and use a Trimball dual oven OCXO. I
> plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
> been said that a man with two watches is never happy - unless, of course,
> they agree with each other ;-). Being identical the outputs should be
> coherent, unless one becomes faulty [one advantage of having two - any
> discrepancy and you know something must be wrong]], but is there some
> crafty way I can squeeze a little more "accuracy" out of two than if I only
> used one?
> TIA for your commentsDonald
> Brett Collie ZL4GX
> 
> PS : I have no connection to the eBay seller. The US$9-50 seems to include
> a basic puck antenna, long downlead, and 4 interseries adaptors
> ___
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Filter 500 Tb + Tb2.pdf
Description: Adobe PDF document
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Re: [time-nuts] Dual GPSDO - any advantage?

[Mike Feher]

Sounds to me like you have two independent systems. I do not believe they can 
ever be “coherent”. Regards – Mike 

 

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

848-245-9115

 

-Original Message-
From: time-nuts  On Behalf Of donald collie
Sent: Tuesday, April 10, 2018 1:43 AM
To: Discussion of precise time and frequency measurement 
Subject: [time-nuts] Dual GPSDO - any advantage?

 

I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an error!] 
They are stated as being new, and use a Trimball dual oven OCXO. I plan to run 
these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s been said that 
a man with two watches is never happy - unless, of course, they agree with each 
other ;-). Being identical the outputs should be coherent, unless one becomes 
faulty [one advantage of having two - any discrepancy and you know something 
must be wrong]], but is there some crafty way I can squeeze a little more 
"accuracy" out of two than if I only used one?

TIA for your commentsDonald

Brett Collie ZL4GX

 

PS : I have no connection to the eBay seller. The US$9-50 seems to include a 
basic puck antenna, long downlead, and 4 interseries adaptors 
___

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Re: [time-nuts] Dual GPSDO - any advantage?

[Florian Teply]

Am Tue, 10 Apr 2018 17:43:25 +1200
schrieb donald collie :

> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> error!] They are stated as being new, and use a Trimball dual oven
> OCXO. I plan to run these in parallel [2 antennas, 2 feedlines, and 2
> GPSDO`s] It`s been said that a man with two watches is never happy -
> unless, of course, they agree with each other ;-). Being identical
> the outputs should be coherent, unless one becomes faulty [one
> advantage of having two - any discrepancy and you know something must
> be wrong]], but is there some crafty way I can squeeze a little more
> "accuracy" out of two than if I only used one?
> TIA for your
> commentsDonald Brett
> Collie ZL4GX

well, my experience in that regard is very limited, not to say
nonexisting, thus take the following with a grain of salt.

Assuming a system with two antenna locations where one device would
be fed both antennas, one could potentially employ some extra
correction based on extra knowledge from these two antennas. Even
though the antenna location usually is known with limited accuracy
(error on the order of 1m), the relative location of two antennas can
be known to a much greater accurracy (order of centimetres or better).
If the system can take that extra information into account, one could
maybe gain some extra accuracy for the solution of time/location.
For example, if the antennas are mounted 1m apart, and everything else
being equal, it is a priori clear, that the calculated position for
both antennas should also be 1m apart. As the signal received by both
antennas should be correlated, while their respective noise
contribution is not, one should gain some SNR. If on top of that time
resolution of the receiver system is very high, one could even take the
phase shift between signals received from both signals into account
similar to the way beam steering is done with phased antenna arrays,
just on receive side, again improving SNR. 
So far for an integrated system, where all signals arew processed in
one place. Now, as I read it you'll rather have two entirely separate
receiver systems. Here, depending on how it is implemented in the
receivers, one could potentially  still gain something extra over a
single unit, but I'd bet this can only be done in postprocessing.
After all, receiver A has no access to the signals as received by
receiver B and vice versa, therefore the spatial relationship can not
be used while deriving the timing solution. Maybe the independent
position solutions could be used to correct the timing solutions after
the fact.

Best regards,
Florian
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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

kb...@n1k.org said:
> The kernel clock comes from the CPU clock. That CPU clock is phase locked to
> a crystal. If you have a CPU that is driven by a VCXO that is a *very*
> unusual CPU board.  The crystal runs at an arbitrary frequency. That gives
> you edges that are unlikely to happen “right on the second”.  

I was assuming the CPU clock was fast enough that reading a cycle-count 
register and converting to ns would be within a ns which is the resolution of 
the clock.

That's obviously not true for low end SOC type setups.  A Pi-1 runs at 700 
MHz.  The Pi 3 is up to 1.4 GHz.


> And the kernel does the “adjust” by dropping or adding clock cycles to the
> count.

I was expecting the kernel to do the clock arithmetic with lots of fractional 
bits.
You get things like:
  This is a 2.4 GHz system.  That's 0.41666 ns per cycle
  But the crystal is 12 ppm fast, so we actually use 0.416661666
  It's been 123456 cycles since we last checked.
  That's 51439.382637696 ns
Internally, the current time has to remember the fractional bits.

If anybody is looking carefully, most PC clocks are spread spectrum.  We 
should do some back-of-envelope work on how significant that is.


> Being able to read the kernel time is only part of the process. You need to
> generate an edge. That gets you into timers and (likely) a different set of
> limitations as the 

If you want an output pulse, I was thinking of generating it from userland at 
roughly the right time but recording the actual time.  That would require a 
fixup pass in software before analyzing the data recorded by traditional 
hardware approaches.



-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Dual GPSDO - any advantage?

[Tim Shoppa]

Most of the Chinese cheapo units have been frequency, not phase locked.

It would be great if you could put the GPSDO outputs into a 2 Channel scope and 
eyeball them for a while to see if they appear in phase (say plus-minus 20ns) 
over a few hours.

Tim N3QE

> On Apr 10, 2018, at 1:43 AM, donald collie  wrote:
> 
> I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
> error!] They are stated as being new, and use a Trimball dual oven OCXO. I
> plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
> been said that a man with two watches is never happy - unless, of course,
> they agree with each other ;-). Being identical the outputs should be
> coherent, unless one becomes faulty [one advantage of having two - any
> discrepancy and you know something must be wrong]], but is there some
> crafty way I can squeeze a little more "accuracy" out of two than if I only
> used one?
> TIA for your commentsDonald
> Brett Collie ZL4GX
> 
> PS : I have no connection to the eBay seller. The US$9-50 seems to include
> a basic puck antenna, long downlead, and 4 interseries adaptors
> ___
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Re: [time-nuts] Dual GPSDO - any advantage?

[ewkehren via time-nuts]

I bought one too, is a mistake, I am holding my breath  supposedly shipped I 
previously bought two one for Jürg because it's performance, easier to clean up 
            Bert Kehren


Sent from my Galaxy Tab® A
 Original message From: donald collie  
Date: 4/10/18  1:43 AM  (GMT-05:00) To: Discussion of precise time and 
frequency measurement  Subject: [time-nuts] Dual GPSDO - 
any advantage? 
I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
error!] They are stated as being new, and use a Trimball dual oven OCXO. I
plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
been said that a man with two watches is never happy - unless, of course,
they agree with each other ;-). Being identical the outputs should be
coherent, unless one becomes faulty [one advantage of having two - any
discrepancy and you know something must be wrong]], but is there some
crafty way I can squeeze a little more "accuracy" out of two than if I only
used one?
TIA for your commentsDonald
Brett Collie ZL4GX

PS : I have no connection to the eBay seller. The US$9-50 seems to include
a basic puck antenna, long downlead, and 4 interseries adaptors
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Re: [time-nuts] Cheap jitter measurements

[Andy ZL3AG via time-nuts]

There's a "realtime" kernel available for Linux that improves timing - no idea 
if this would help in this situation.

See: linux-image-rt-amd64 in debian, for instance




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[time-nuts] Dual GPSDO - any advantage?

[donald collie]

I`ve just bought two GPSDO`s from China @ US$9-50 each [This is not an
error!] They are stated as being new, and use a Trimball dual oven OCXO. I
plan to run these in parallel [2 antennas, 2 feedlines, and 2 GPSDO`s] It`s
been said that a man with two watches is never happy - unless, of course,
they agree with each other ;-). Being identical the outputs should be
coherent, unless one becomes faulty [one advantage of having two - any
discrepancy and you know something must be wrong]], but is there some
crafty way I can squeeze a little more "accuracy" out of two than if I only
used one?
TIA for your commentsDonald
Brett Collie ZL4GX

PS : I have no connection to the eBay seller. The US$9-50 seems to include
a basic puck antenna, long downlead, and 4 interseries adaptors
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