Re: [time-nuts] Atomic Watch

[John Allen]

It hurts to read this.   John K1AE

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Jim Palfreyman
Sent: Monday, October 17, 2016 9:46 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Atomic Watch

Well I think there's a mistake or two here...

https://www.inverse.com/article/20497-john-patterson-atomic-ce

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Re: [time-nuts] Atomic Watch

[Nick Sayer via time-nuts]

"Whereas other clocks fall victim to relativistic effects at high speeds, 
cesium clocks do not. The frequency remains the same, and so the time remains 
accurate.”

Well, to the wearer, it probably does. :)

It’s ironic they said that given that they flew cesium clocks in the 
Hafele–Keating experiment to demonstrate exactly those relativistic effects.

> On Oct 17, 2016, at 6:45 PM, Jim Palfreyman  wrote:
> 
> Well I think there's a mistake or two here...
> 
> https://www.inverse.com/article/20497-john-patterson-atomic-ce
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[time-nuts] Atomic Watch

[Jim Palfreyman]

Well I think there's a mistake or two here...

https://www.inverse.com/article/20497-john-patterson-atomic-ce
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Re: [time-nuts] Phase-noise through mixer?

[Richard (Rick) Karlquist]

Mixers also have the curious phenomenon of non-reciprocity

On 10/17/2016 4:13 PM, Bob Camp wrote:

Hi

Simple answer is yes.

More complex answer gets into things like the noise of the mixer (not just it’s 
floor),
the levels of the signals, noise being coherent rather than non-coherent, AM 
<-> PM
conversion and on and on ….

Bob




On Oct 17, 2016, at 4:45 PM, Anders Wallin  wrote:

Hi group!

Can someone help me with how phase-noise through a mixer is calculated?

Let's say I connect a 1 GHz signal with -80 dBc/Hz PN (wrt. 1GHz carrier)
at some offset to the RF port.
I then connect a 900 MHz signal with also -80dBc/Hz PN (wrt. 900MHz
carrier) at the same offset.
I'm interested in the 100 MHz IF signal (naively, will it have -77 dBc/Hz
PN wrt 100MHz? carrier?)

(ofcourse there might be a noise-figure through the mixer also)

thanks!
Anders
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Re: [time-nuts] Phase-noise through mixer?

[Bob Camp]

Hi

Simple answer is yes.

More complex answer gets into things like the noise of the mixer (not just it’s 
floor), 
the levels of the signals, noise being coherent rather than non-coherent, AM 
<-> PM
conversion and on and on ….

Bob



> On Oct 17, 2016, at 4:45 PM, Anders Wallin  
> wrote:
> 
> Hi group!
> 
> Can someone help me with how phase-noise through a mixer is calculated?
> 
> Let's say I connect a 1 GHz signal with -80 dBc/Hz PN (wrt. 1GHz carrier)
> at some offset to the RF port.
> I then connect a 900 MHz signal with also -80dBc/Hz PN (wrt. 900MHz
> carrier) at the same offset.
> I'm interested in the 100 MHz IF signal (naively, will it have -77 dBc/Hz
> PN wrt 100MHz? carrier?)
> 
> (ofcourse there might be a noise-figure through the mixer also)
> 
> thanks!
> Anders
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Re: [time-nuts] Phase-noise through mixer?

[Attila Kinali]

On Mon, 17 Oct 2016 23:45:23 +0300
Anders Wallin  wrote:

> Can someone help me with how phase-noise through a mixer is calculated?

Have you had a look at Enrico Rubiola's mixer tutorial[1]?
I think it contains all you need for noise calculation.


Attila Kinali

[1] 
http://rubiola.org/pdf-articles/archives/2006-arxiv-0608211v1-mixer-tutorial.pdf
-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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[time-nuts] Phase-noise through mixer?

[Anders Wallin]

Hi group!

Can someone help me with how phase-noise through a mixer is calculated?

Let's say I connect a 1 GHz signal with -80 dBc/Hz PN (wrt. 1GHz carrier)
at some offset to the RF port.
I then connect a 900 MHz signal with also -80dBc/Hz PN (wrt. 900MHz
carrier) at the same offset.
I'm interested in the 100 MHz IF signal (naively, will it have -77 dBc/Hz
PN wrt 100MHz? carrier?)

(ofcourse there might be a noise-figure through the mixer also)

thanks!
Anders
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[time-nuts] Moving GPSDO

[Mark Sims]

A lot of the telecom GPSDOs that speak SCPI have no way of running except in a 
"position hold" mode.   The Trimble Thunderbolt and telecom GPSDOs (like the 
NTBW, NTPX, etc) units can run in a dynamic environment... how well they do 
that is left as an exercise for the user to determine.  They also have commands 
for specifying the movement environment to expect.

All the GPS timing receivers that I have can work in either a dynamic or fixed 
position mode.  Most also have a way of specifying the movement environment / 
dynamics.

> In addition to TimeNuts, there are actually *are* people who get nutty about 
> measuring 
changes in gravity.

Hey!   I resemble that remark!  I have a Worden gravity meter around here... 
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Re: [time-nuts] Moving GPSDO

[Bob Camp]

Hi

Survey is pretty much a bad thing while in motion :)

Some (but not all) GPS modules allow you to set up in a “mobile / do not 
survey” mode. This is one area that the 
newer ( = not 1997 era) devices do much better at. It also is something that 
SBAS / EGNOS / WAAS may indeed
help you out on. You may be changing *many* settings on the part to make it 
behave in a mobile setting. There
are a few bugs you just may turn up while doing this ….

Bob


> On Oct 17, 2016, at 1:38 PM, Nick Sayer via time-nuts  
> wrote:
> 
> Speaking for my GPSDOs specifically, you can’t disable the survey mode with 
> the Venus838 receiver (well, you can, but it requires you to talk to the 
> module with SkyTraq’s software, which requires disabling the GPSDO’s 
> controller - possible to do, but annoying). I haven’t attempted to see what 
> it would do if it were moved after the survey is completed (if you move 
> during the survey, then the survey will fail and repeat).
> 
> The older GPSDOs that had PA6H receivers were navigation receivers that 
> didn’t have a survey mode.
> 
> In either case, without a surveyed position, PPS stability will suffer 
> if/when the constellation degrades due to poor reception, which can happen 
> if, say, the unit is in a moving vehicle in interesting terrain. Poor PPS 
> stability will have an impact on the PLL, obviously.
> 
>> On Oct 16, 2016, at 9:19 PM, Joseph Gray  wrote:
>> 
>> I'm curious to know how accurately a GPSDO will keep its 10 MHz output
>> while moving. No initial survey to set a position would be done. I
>> don't care about the UTC time.
>> 
>> Joe Gray
>> W5JG
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Re: [time-nuts] Moving GPSDO

[Nick Sayer via time-nuts]

Speaking for my GPSDOs specifically, you can’t disable the survey mode with the 
Venus838 receiver (well, you can, but it requires you to talk to the module 
with SkyTraq’s software, which requires disabling the GPSDO’s controller - 
possible to do, but annoying). I haven’t attempted to see what it would do if 
it were moved after the survey is completed (if you move during the survey, 
then the survey will fail and repeat).

The older GPSDOs that had PA6H receivers were navigation receivers that didn’t 
have a survey mode.

In either case, without a surveyed position, PPS stability will suffer if/when 
the constellation degrades due to poor reception, which can happen if, say, the 
unit is in a moving vehicle in interesting terrain. Poor PPS stability will 
have an impact on the PLL, obviously.

> On Oct 16, 2016, at 9:19 PM, Joseph Gray  wrote:
> 
> I'm curious to know how accurately a GPSDO will keep its 10 MHz output
> while moving. No initial survey to set a position would be done. I
> don't care about the UTC time.
> 
> Joe Gray
> W5JG
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[time-nuts] Improved Symmetricom ET-6000...

[Burt I. Weiner]

Erik,

For what it may be worth...  I have two DATUM 
9390-52054 GPS Frequency and Time Standards.  A 
few years ago I had to replace the original 
Vectron oscillators in one of the units and 
eventually in the other one.  In my case I used a 
McCoy VCXO that's in an oven.  This McCoy 
oscillator, being about 1/4 the size of the 
Vectron did not match the original wholes in the 
circuit board, so like you, I had to extend the 
wires from the circuit board to the oscillator 
module, which I mounded upside down in the same 
location that the Vectron occupied.  I also 
mounted it inside of a foam block that I cut out 
to enclose the McCoy and trimmed to fit in the 
same space as the original oscillator and as tall 
as the vertical real estate would allow.  The top 
cover of my DATUM's push down on the top half of 
the foam giving it a pretty good seal.


I found that while the EFC control voltage for 
the McCoy was in the right direction and and the 
desired tuning voltage center very close to the 
center that the original Vectron used, the McCoy 
was much more sensitive to EFC voltage change and 
what the Vectron seemed to be happy with would 
drive the McCoy out of range into never-never 
land.  I needed a bigger "Flywheel."  In my case 
I wound up adding a series 18k resistor in series 
with the EFC source to the EFC terminal on the 
oscillator and a 47uf capacitor from the EFC 
terminal to the ground terminal on the 
McCoy.  This made for a much larger "Flywheel" 
and tamed things down quite nicely.  You may have 
a similar issue.  Since doing this on my two 
units I have had no further problems, even when 
powering them down and doing a cold reset on 
them, they come back up nicely and behave 
well.  Normally they are connected to a UPS.


I documented this all in this 
group.  See:  https://www.mail-archive.com/time-nuts@febo.com/msg73790.html


I took a bunch of pictures of what I did and I'd 
be happy to share them.  I'll be out of town for 
about two weeks so if I'm slow in answering, that's why.


I hope this offers some help based on my experience.

Have fun,

Burt, K6OQK


From: Erik Thomassen 

Subject: [time-nuts] Improved Symmetricom ET-6000
Good evening/morning -depending, group :-)
 For the perfectionists of you, pass this post 
;-)Â  For the rest, here are my results in 
improving an Symmetricom Exacttime ET-6000.  My 
problem was that the supposedly stable 10MHz, off 
the programmable outputs just wandered "all over 
the place" with the supplied TCXO. Refered to any 
free running OCXO or rubidium the output was useless even in the locked state.


There was an upgrade-set avaliable that also 
involved a software change but that was not an option for me.


The original TCXO is relatively easy to remove. 
The solder holes are left alone, better 
connection points for experiments exists on the 
PCB. Check for connectivity the 10MHz output, and 
Vcorr.  The 5V connection i left alone.Before 
this project arose i had a 5V/10MHz Bliley OCXO 
unit previously bought off Ebay from China for 
some USD20.-Â  I did not think about the output 
being square wave The main thing however is 
that this OCXO matches the Vref range of the TCXO.


Yesterday was the day:Â  Took out the original 
TCXO.  The new Bliley unit, for the sake of the 
experiment, was set outside the main PCB with 
long wires soldered between the units.  Due to 
the higher current drain on the OCXO i decided to 
supply it via an external simple 7805 regulator. 
This was mounted directly to the bottom of the 
chassis for good heat dispersal during warmup. 12V was taken from the main PCB.


After power-up things looked usable - but did not 
work  No lock, the system searching up to+/- 
200Hz trying to find a lock point. Setting the 
DAC-value to "zero beat" with a similar standard 
did not help.The combination of quite higher 
output voltage from the OCXO combined with a very 
distorted waveform (due to the square-wave 
output) made the 6000-unit to discard the OCXO.Â


To improve the waveform I used an old trick: A 
10MHz crystal in series with the signal.  This 
improved things a bit, I now can see a distorted 
sinus wave on the output  A 50k 10-turn 
potmeter in series with the crystal solved the level problem -.


A new connector mounted on the rear for 24VDC 
supply and an surplus Rifa 24V to 5/12/-12V 
converter module from a Instrument Landing System 
transmitter solved the mains problem No more power surges :-)


Inserting a jumper (J27) told at least the 
display that there is an OCXO in place.
After some 6 hours of use now, the internal 
monitoring system claims that output accuracy for 
the time beeing is +/- 40 e-12, almost two 
decades better than the original TCXO, for all what that statement is worth
The next question coming up: Why not use a simple 
12V supply, sinus output OCXO? Yes, why not try 
that?  With the level problems sorted out - a 
simple potentiometer, the only 

Re: [time-nuts] Moving GPSDO

[Attila Kinali]

On Mon, 17 Oct 2016 07:25:34 -0600
"Cube Central"  wrote:

> I had run across this just yesterday:  
> https://www.youtube.com/watch?v=zILwgQhjC_Q
> 
> He talks about how crystal oscillators are sensitive to movement and changes 
> in gravity.  An interesting watch!

As usual with EEVblog, there are several things wrong with what he presents.

1) As Bob wrote, the acceleration sensitivity of crystals vary a lot more
than the rough number Dave gave.

2) The acceleration sensitivity has very little to do with the cut.
Even though there is some cut related effect on acceleration, it is
very very small. The by far most dominant effect comes from the
mechanical stress of the holder onto the crystal. It is probably
obvious that the crystal and the holders bend upon acceleration.
This bending will cause the crystal to change its frequency due
to stress on the lattice. Now, why are AT cuts worse than SC cuts?
The reason is simple, SC cuts are usually ment for high stability
applications and people tend to take more care with the mounting
and the crystal shape, than for regular AT cuts.

3) Rb vapor standards have very low acceleration effects. As Dave
said, the control loop will kill most of the effects inside the
loop frequency. The loop frequency is relatively fast, in the
order of couple of 100Hz to a couple of 10kHz, depending on the
exact build of the Rb standard and what type of crystal they used.
Contrary to what he says, there are no acceleration dependent
diffusion effects. The vapor cell is is heated and the gas atoms
in there are pretty fast, any acceleration of them will be negligible
compared to what they do upon collision. The relativistic red shift due
to acceleration is way too low to measure (much lower than the intrinsic 
noise). The only mechanical effect that is possible, is bending of
the microwave cavity or the parts inside. But given that the cavity
is several mm thick aluminium and everything is mounted rigidly,
I very much doubt that there is any significant effect.

4) If you think that the tilting your frequency counter will have
a significant effect, you are severly underestimating temperature
and aging effects. Just in comparison, a good SC cut DOCXO has an
aging of a few parts in 10^-9. So each week will affect on your crystal
more than a 1g of acceleration. And that's with a slow aging DOCXO.
Temperature effects are in the order of 1x10^-10/°C to 1x10^-7/°C.
So depending on how good the OCXO is, a single degree of temperature
will cause a larger shift than 1g of acceleration. Etc.pp.


Attila Kinali

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

[Bob Camp]

Hi

In addition to TimeNuts, there are actually *are* people who get nutty about 
measuring 
changes in gravity. That’s a bit different than what he’s talking about in the 
video. Local
variations in the earth’s mass cause variations in gravity (think mountains or 
similar…). 
They also are one of the things that cause GPS orbits to be “bumpy” rather than 
the nice
smooth curves we tend to think of them as being. 

Bob


> On Oct 17, 2016, at 9:25 AM, Cube Central  wrote:
> 
> I had run across this just yesterday:  
> https://www.youtube.com/watch?v=zILwgQhjC_Q
> 
> He talks about how crystal oscillators are sensitive to movement and changes 
> in gravity.  An interesting watch!
> 
>   -Randal
>   (at CubeCentral)
> 
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp
> Sent: Monday, 17 October, 2016 05:48
> To: Discussion of precise time and frequency measurement 
> Subject: Re: [time-nuts] Moving GPSDO
> 
> Hi
> 
> Is the OCXO in your GPSDO acceleration compensated? If not then the 
> acceleration involved in your “moving around” will get into the OCXO at 
> around 1x10^-9 / g. Some OCXO’s are compensated to the 1x10^-11 / g level. 
> Some low cost crystals are up around 2x10^-8. Often vibration is an issue as 
> well, since it is an acceleration, the same stuff applies. 
> 
> How well temperature controlled is your moving environment? Your oscillator 
> can have all sorts of temperature coefficients,. It will respond to dynamic 
> change as well as static change. The sensitivity can be just about anything 
> over the 1x10^-12 / C up to 1x10^-7 / C depending on the part. 
> 
> None of that has anything at all to do with GPS, all of it is something the 
> GPSDO will have to deal with in addition to any GPS errors. Unless you want a 
> very coarse output
> (1x10^-9 to 2x10^-8 / second) you will need some sort of loop filter. If it 
> is in the traditional 
>> 200 seconds range, the stuff above can become very apparent in the 
>> output.  The loop
> does not eliminate error at the (say) 200 seconds point, it only gets going 
> by then. 
> 
> Does your moving around include tunnels? If so, how long will you be in a 
> tunnel? Urban canyons also count in this respect. Once you go down to < 3 
> sats, you are in big trouble for timing in motion. Even with 3, your fix and 
> time performance is degraded. Chugging in and out of holdover has it’s 
> impact. 
> 
> Do you want to use multiple systems? If you are running a mixed mode system, 
> you can go from 100% GPS to 100% GLONASS to 100% BEID0U due to viewing angle. 
>  That tosses a whole *bunch* of issues into the mix. 
> 
> How fast are you going? Moving around can involve move 100’, stop and wait 
> for a day or it can involve something moving at mach 3. By far the most 
> common for a GPSDO is some sort of car, truck, or military vehicle on the 
> highway. There are many other possibilities.  
> 
> Lots of variables. Lots of things to get into the mix in addition to the 
> basic nav math.
> 
> Bob
> 
> 
>> On Oct 17, 2016, at 12:19 AM, Joseph Gray  wrote:
>> 
>> I'm curious to know how accurately a GPSDO will keep its 10 MHz output 
>> while moving. No initial survey to set a position would be done. I 
>> don't care about the UTC time.
>> 
>> Joe Gray
>> W5JG
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Re: [time-nuts] Moving GPSDO

[Cube Central]

I had run across this just yesterday:  
https://www.youtube.com/watch?v=zILwgQhjC_Q

He talks about how crystal oscillators are sensitive to movement and changes in 
gravity.  An interesting watch!

-Randal
(at CubeCentral)

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp
Sent: Monday, 17 October, 2016 05:48
To: Discussion of precise time and frequency measurement 
Subject: Re: [time-nuts] Moving GPSDO

Hi

Is the OCXO in your GPSDO acceleration compensated? If not then the 
acceleration involved in your “moving around” will get into the OCXO at around 
1x10^-9 / g. Some OCXO’s are compensated to the 1x10^-11 / g level. Some low 
cost crystals are up around 2x10^-8. Often vibration is an issue as well, since 
it is an acceleration, the same stuff applies. 

How well temperature controlled is your moving environment? Your oscillator can 
have all sorts of temperature coefficients,. It will respond to dynamic change 
as well as static change. The sensitivity can be just about anything over the 
1x10^-12 / C up to 1x10^-7 / C depending on the part. 

None of that has anything at all to do with GPS, all of it is something the 
GPSDO will have to deal with in addition to any GPS errors. Unless you want a 
very coarse output
(1x10^-9 to 2x10^-8 / second) you will need some sort of loop filter. If it is 
in the traditional 
> 200 seconds range, the stuff above can become very apparent in the 
> output.  The loop
does not eliminate error at the (say) 200 seconds point, it only gets going by 
then. 

Does your moving around include tunnels? If so, how long will you be in a 
tunnel? Urban canyons also count in this respect. Once you go down to < 3 sats, 
you are in big trouble for timing in motion. Even with 3, your fix and time 
performance is degraded. Chugging in and out of holdover has it’s impact. 

Do you want to use multiple systems? If you are running a mixed mode system, 
you can go from 100% GPS to 100% GLONASS to 100% BEID0U due to viewing angle.  
That tosses a whole *bunch* of issues into the mix. 

How fast are you going? Moving around can involve move 100’, stop and wait for 
a day or it can involve something moving at mach 3. By far the most common for 
a GPSDO is some sort of car, truck, or military vehicle on the highway. There 
are many other possibilities.  

Lots of variables. Lots of things to get into the mix in addition to the basic 
nav math.

Bob


> On Oct 17, 2016, at 12:19 AM, Joseph Gray  wrote:
> 
> I'm curious to know how accurately a GPSDO will keep its 10 MHz output 
> while moving. No initial survey to set a position would be done. I 
> don't care about the UTC time.
> 
> Joe Gray
> W5JG
> ___
> time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to 
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

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Re: [time-nuts] Moving GPSDO

[Bob Camp]

Hi

Is the OCXO in your GPSDO acceleration compensated? If not then the acceleration
involved in your “moving around” will get into the OCXO at around 1x10^-9 / g. 
Some
OCXO’s are compensated to the 1x10^-11 / g level. Some low cost crystals are up
around 2x10^-8. Often vibration is an issue as well, since it is an 
acceleration, the same
stuff applies. 

How well temperature controlled is your moving environment? Your oscillator can 
have
all sorts of temperature coefficients,. It will respond to dynamic change as 
well as static
change. The sensitivity can be just about anything over the 1x10^-12 / C up to 
1x10^-7 / C 
depending on the part. 

None of that has anything at all to do with GPS, all of it is something the 
GPSDO will 
have to deal with in addition to any GPS errors. Unless you want a very coarse 
output 
(1x10^-9 to 2x10^-8 / second) you will need some sort of loop filter. If it is 
in the traditional 
> 200 seconds range, the stuff above can become very apparent in the output.  
> The loop
does not eliminate error at the (say) 200 seconds point, it only gets going by 
then. 

Does your moving around include tunnels? If so, how long will you be in a 
tunnel? Urban
canyons also count in this respect. Once you go down to < 3 sats, you are in 
big trouble 
for timing in motion. Even with 3, your fix and time performance is degraded. 
Chugging 
in and out of holdover has it’s impact. 

Do you want to use multiple systems? If you are running a mixed mode system, 
you can go 
from 100% GPS to 100% GLONASS to 100% BEID0U due to viewing angle.  That tosses
a whole *bunch* of issues into the mix. 

How fast are you going? Moving around can involve move 100’, stop and wait for 
a day or
it can involve something moving at mach 3. By far the most common for a GPSDO 
is some 
sort of car, truck, or military vehicle on the highway. There are many other 
possibilities.  

Lots of variables. Lots of things to get into the mix in addition to the basic 
nav math.

Bob


> On Oct 17, 2016, at 12:19 AM, Joseph Gray  wrote:
> 
> I'm curious to know how accurately a GPSDO will keep its 10 MHz output
> while moving. No initial survey to set a position would be done. I
> don't care about the UTC time.
> 
> Joe Gray
> W5JG
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Re: [time-nuts] Moving GPSDO

[Magnus Danielson]

Joe,

In T-mode, the location in X, Y and Z is assumed known so those values 
is used as constants in producing the T difference between a satellite 
and the GPSDO. As you now move your receiver from the original X, Y and 
Z those location errors will translate into time errors. The worst of 
this will the T-RAIM hopefully clip out, but for the remaining the 
errors might drive the receiver all over the place, and as it shifts 
around so will the frequency. It won't be a pretty picture.


What you should do, if you can, is to go out of T-mode into normal 
tracking. Choosing the speed-grade of your movement can be worth some 
effort. Far from all GPSDOs can do this, since they typically is 
intended for fixed locations.


Potentially can aiding by IMU help some, but very few GPSDOs come close 
to support it. When moving you have to consider other factors of a 
dynamic environment.


I know of only a handful of GPSDOs for dynamic platforms.

Cheers,
Magnus

On 10/17/2016 08:02 AM, Joseph Gray wrote:

Bill,

My question was more generally about any GPSDO, but it's good to know
about the Motorola/Lucent.

What about this scenario - the GPSDO has a fixed position on initial
powerup, but then it is moved periodically or even continuously,
without updating the GPS coordinates. The distance from the original
coordinates could be anywhere from close by, to across the state.
Periodically, a new survey could be run to keep things from getting
too far out in left field.

At some point, I'll have to do some field testing, but I wanted to get
the list wisdom first.

Joe Gray
W5JG


On Sun, Oct 16, 2016 at 11:08 PM, Bill Hawkins  wrote:

The Motorola receivers in Lucent gear won't output a time signal if they
don't have an initial survey.

I make this assertion because the RFTG I had would not lock. The
Motorola bag of bits decodes to say there's no position fix because
enough satellites have not been acquired. Too bad I lived in a valley.

Let us know how this turns out, starting from an initial survey.

Bill Hawkins

-Original Message-
From: Joseph Gray
Sent: Sunday, October 16, 2016 11:20 PM

I'm curious to know how accurately a GPSDO will keep its 10 MHz output
while moving. No initial survey to set a position would be done. I don't
care about the UTC time.

Joe Gray
W5JG

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Re: [time-nuts] Moving GPSDO

[Hal Murray]

jg...@zianet.com said:
> What about this scenario - the GPSDO has a fixed position on initial
> powerup, but then it is moved periodically or even continuously, without
> updating the GPS coordinates. The distance from the original coordinates
> could be anywhere from close by, to across the state. Periodically, a new
> survey could be run to keep things from getting too far out in left field. 

Most commercial GPSDOs assume they are running at a fixed location and won't 
work very well unless they are near their surveyed location.  Near is 
measured in feet, not miles.  That allows them to work with fewer satellites 
which was important with the GPS receivers in old gear like the TBolt and 
Z3801A.

But that's all software/firmware.  If you build your own GPSDO you can use 
whatever GPS receiver you like as long as it puts out a PPS or something that 
you can lock to.

I think Jackson Labs makes some non-survey GPSDOs.
http://www.jackson-labs.com/index.php/products/lte_lite
The FAQ says there is a non-survey mode.

You might find something interesting in time-nuts archives from about 2 years 
ago.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Moving GPSDO

[Joseph Gray]

Bill,

My question was more generally about any GPSDO, but it's good to know
about the Motorola/Lucent.

What about this scenario - the GPSDO has a fixed position on initial
powerup, but then it is moved periodically or even continuously,
without updating the GPS coordinates. The distance from the original
coordinates could be anywhere from close by, to across the state.
Periodically, a new survey could be run to keep things from getting
too far out in left field.

At some point, I'll have to do some field testing, but I wanted to get
the list wisdom first.

Joe Gray
W5JG


On Sun, Oct 16, 2016 at 11:08 PM, Bill Hawkins  wrote:
> The Motorola receivers in Lucent gear won't output a time signal if they
> don't have an initial survey.
>
> I make this assertion because the RFTG I had would not lock. The
> Motorola bag of bits decodes to say there's no position fix because
> enough satellites have not been acquired. Too bad I lived in a valley.
>
> Let us know how this turns out, starting from an initial survey.
>
> Bill Hawkins
>
> -Original Message-
> From: Joseph Gray
> Sent: Sunday, October 16, 2016 11:20 PM
>
> I'm curious to know how accurately a GPSDO will keep its 10 MHz output
> while moving. No initial survey to set a position would be done. I don't
> care about the UTC time.
>
> Joe Gray
> W5JG
>
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> 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.
>
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