Re: [time-nuts] When does NIST change to DST?

[Tom Van Baak]

Hi Andy,

No, there's nothing about 0200Z. Correct, WWVB doesn't know your local zone.

WWVB itself doesn't "switch" to/from DST. It always only transmits UTC. It is 
up to your receiver-clock to translate UTC to local time for the user display. 
This is why most of WWVB radio controlled clocks have a little PMCE (Pacific / 
Mountain / Central / Eastern) switch.

The WWVB data format also includes bits which announce if DST change will 
occur. It is up to the receiver-clock to decode these bits and make the 1 hour 
adjustment at the appropriate time (usually 2 am local time).

See also:
https://en.wikipedia.org/wiki/WWVB
http://tf.nist.gov/general/pdf/2422.pdf
http://www.nist.gov/pml/div688/grp40/radioclocks.cfm

/tvb

- Original Message - 
From: "Andy" 
To: "Discussion of precise time and frequency measurement" 
Sent: Sunday, March 13, 2016 7:21 PM
Subject: Re: [time-nuts] When does NIST change to DST?


> I wonder if WWVB switches to DST around 0200Z, maybe?  Since it can't
> tell where your local zone is.
> 
> Andy
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Re: [time-nuts] BG7TBL GPS Disciplined Source

[Joseph Gray]

There is a long thread over on the EEVblog forum about the various
versions made by BG7TBL. You can match the date and pictures with what
you have.

Joe Gray
W5JG


On Sun, Mar 13, 2016 at 9:47 PM, Gedas  wrote:
> Hello to the group. I am a new member and 1st wanted to say hello. I also
> wanted to say that I have been reading, with great interest, most of the
> posts here for the last 2-3 weeks.  I must say, I am quite ignorant of the
> majority of the information & terms being passed back and forth so this is a
> neat learning experience for me. I am a retired EE (had a prior life in the
> TEMPEST community for over 30 years) and I am slowly assembling my
> collection of test equipment here at home, purely for fun.
>
> This is where I really embarrass myself.sometime ago I purchased an
> inexpensive 10 MHz GPS based reference source (BG7TBL GPS Disciplined
> Source) for my various counters, transceivers, spectrum analyzers, etc and
> was wondering if it was a good purchase and if anyone else used a similar
> unit.  I guess in the end I am curious to know what the short & long term
> accuracy and stability of my unit may be?  I no longer have access to any
> accurate (known) frequency sources like I did while employed and I do not
> think I have the equipment here at home to measure my unit myself.
>
> Gedas, W8BYA
>
> Gallery at http://w8bya.com
> Light travels faster than sound
> This is why some people appear bright until you hear them speak.
>
>
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Re: [time-nuts] When does NIST change to DST?

[Glenn Little WB4UIV]

Does WWVB switch to DST, or, just set a bit in the data stream telling 
the device that receives the signal that DST is active?
I seam to remember (that is dangerous) that WWVB data has GMT time 
encoded into the data stream and that it is up to the receiving device 
to display the correct offset from GMT.


My buddy, Google, found the data WWVB transmits here:

http://www.nist.gov/pml/div688/grp40/wwvbtimecode.cfm

Hope this helps

73
Glenn
WB4UIV


On 3/13/2016 10:21 PM, Andy wrote:

I wonder if WWVB switches to DST around 0200Z, maybe?  Since it can't
tell where your local zone is.

Andy
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--
---
Glenn LittleARRL Technical Specialist   QCWA  LM 28417
Amateur Callsign:  WB4UIVwb4...@arrl.netAMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI LM   NRA LM   SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
---
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[time-nuts] BG7TBL GPS Disciplined Source

[Gedas]

Hello to the group. I am a new member and 1st wanted to say hello. I 
also wanted to say that I have been reading, with great interest, most 
of the posts here for the last 2-3 weeks.  I must say, I am quite 
ignorant of the majority of the information & terms being passed back 
and forth so this is a neat learning experience for me. I am a retired 
EE (had a prior life in the TEMPEST community for over 30 years) and I 
am slowly assembling my collection of test equipment here at home, 
purely for fun.


This is where I really embarrass myself.sometime ago I purchased an 
inexpensive 10 MHz GPS based reference source (BG7TBL GPS Disciplined 
Source) for my various counters, transceivers, spectrum analyzers, etc 
and was wondering if it was a good purchase and if anyone else used a 
similar unit.  I guess in the end I am curious to know what the short & 
long term accuracy and stability of my unit may be?  I no longer have 
access to any accurate (known) frequency sources like I did while 
employed and I do not think I have the equipment here at home to measure 
my unit myself.


Gedas, W8BYA

Gallery at http://w8bya.com
Light travels faster than sound
This is why some people appear bright until you hear them speak.


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Re: [time-nuts] When does NIST change to DST?

[Andy]

I wonder if WWVB switches to DST around 0200Z, maybe?  Since it can't
tell where your local zone is.

Andy
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Re: [time-nuts] HP 5065A repair

[Bob Camp]

Hi

Some math:

5x10^-11 over 50C

You have 1x10^-13 / C

If you have pretty good HVAC you get 2C cycles. On a typical home system, you 
get 2X that or more. 

Net is a bump at 2x10^-13 (or more). 

That assumes no hysteresis. (Hint: there always is hysteresis). 

That assumes you have no rate dependent effects. (… they almost always are 
present ..). 

If you are at 10X the data sheet level, the bump is more like 2x10^-12 (or 
more). Either one will likely show up on a good test plot.

Can you take care of all this? Of course you can. Does modeling and correcting 
all this fall into the “quick and easy fix” category? Nope, not at all. The 
thread is about a request for a simple approach to an Rb setup. That sort of 
thing does not include fancy models and all sorts of corrections. 

Bob



> On Mar 13, 2016, at 5:10 PM, Poul-Henning Kamp  wrote:
> 
> 
> In message , cdel...@juno.com writes:
> 
>> As far a tempco goes, unless your lab swings tens of degrees will you
>> really see it?
> 
> Well, I do...
> 
> My air-con is far from optimal, but it clearly makes a very obvious
> bump in my AVAR plots.
> 
> 
> -- 
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
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[time-nuts] HP Catalogs

[Perry Sandeen via time-nuts]

List,
I have 5 HP Test and Measurements catalogs which I will send for postage from 
92220.
The years are 1982, 1985 (2), 1987, and 1991.
These are heavy suckers (bound books.  I estimate postage to be $10 per book.
Please reply off list if interested.
Regards,
Perrier

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Re: [time-nuts] Best Rubidium Frequency Standard

[Charles Steinmetz]

Poul-Henning wrote:


At least some of the firmware versions do not allow you to change the
PPSIN offset second by second, so you cannot compensate for the
"negative sawtooth", and the resulting "hanging bridges" means that
you have to us a very unoptimal PLL time constant.


The cure for that is to use a GPS that has a clock synchronous with 
PPS -- like a TBolt.  (Why anyone does it any other way baffles me 
completely, but they do.)


And the long time constant is not "unoptimal" -- it is optimized for 
best stability.  GPS stability (not including any uncorrected 
sawtooth) is about 5x10e-9 at tau = one second, improving by 10x per 
decade at longer averaging times.  Most oscillators a time-nut would 
be interested in start at around e-11 at one second, improving for 2 
to 5 decades (OCXO and Rb, respectively -- generally improving as a 
root per decade), then worsening at longer tau.  At some point, these 
stability curves cross.  The whole point of GPS discipline is, at 
each tau, to follow whichever curve is more stable by crossing over 
from one to the other.  This results in a TC of typically 100-1000 
seconds for disciplined OCXOs, or 1000-100k seconds for disciplined Rbs.


So, the TC that is optimum for a disciplined OCXO is NOT optimum for 
a disciplined Rb, assuming what one wants is the best possible 
stability, at all tau, that the particular GPS and oscillator can 
provide.  The long TC needed to average out an uncorrected sawtooth 
in the GPSDRb would be chosen as the optimum TC for stability anyway.


Best regards,

Charles


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Re: [time-nuts] HP 5065A repair

[Poul-Henning Kamp]

In message , cdel...@juno.com writes:

>As far a tempco goes, unless your lab swings tens of degrees will you
>really see it?

Well, I do...

My air-con is far from optimal, but it clearly makes a very obvious
bump in my AVAR plots.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] When does NIST change to DST?

[Bill Byrom]

The NIST web page at http://nist.time.gov is rather complex. It appears to use 
the discontinued OpenLaszlo[1] programming techniques. As far as I can tell, 
the determination of the time zone and Earth image are all done using 
javascript in your browser. So the solution of your issue is probably going to 
be closing your browser and re-opening at NIST page. If that fails, you may 
need to clear your browser cache.
 
The web page uses a bit of javascript in the HTML page itself, with an 
additional long javascript library file which is downloaded to your browser. If 
you are using Firefox, see the HTML code at:
view-source:http://nist.time.gov/
 
With any browser, see the javascript library code at:
http://nist.time.gov/nist_time.lzx.js
 
Your browser reveals the timezone you are in to the javascript code
running in your browser, and this local code determines the daylight
saving time status and timezone.
 
In addition, the javascript code running in your browser actually solves 
Kepler's equation to get the ecliptic latitude and longitude, then converts 
this to equatorial latitude and longitude. These values are used to select a 
xearth image[2] from a NIST server. The image shows the illumination of the 
Earth at various points in the Earth's orbit and rotation (time). For example:
http://www.time.gov/images/xearths/1S/96S.jpg
http://www.time.gov/images/xearths/23N/180N.jpg
 
 --
Bill Byrom N5BB
 
 
 
On Sun, Mar 13, 2016, at 01:50 PM, James Flynn wrote:
>  writes:
>
>>
>> I noticed that NIST, at http://nist.time.gov/, is still sending 
> standard time. When do they change?
>>
>> John  WA4WDL
>>
>>
>
> As of 1849Z it was reporting DST.
>
>
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Links:

  1. https://en.wikipedia.org/wiki/OpenLaszlo
  2. http://xearth.org/
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Re: [time-nuts] When does NIST change to DST?

[Richard (Rick) Karlquist]

On 3/13/2016 10:39 AM, Nick Sayer via time-nuts wrote:

Our WWVB clock switched way, way early last night - like 20:00 or so (PST).

but that clock hasn’t exhibited any whacky behavior as long as I can remember.


Same here with my clock.

Rick
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Re: [time-nuts] When does NIST change to DST?

[Nick Sayer via time-nuts]

Our WWVB clock switched way, way early last night - like 20:00 or so (PST).

It’s conceivable that it’s a coincidence and it switched because of a parity 
error or something like that, but that clock hasn’t exhibited any whacky 
behavior as long as I can remember.

> On Mar 13, 2016, at 7:48 AM, Jim Harman  wrote:
> 
> WWVB has sent the signal to switch to DST but the website has not changed
> yet.
> 
> On Sun, Mar 13, 2016, 10:11 AM  wrote:
> 
>> I noticed that NIST, at http://nist.time.gov/ , is still sending standard
>> time. When do they change?
>> 
>> John  WA4WDL
>> 
>> 
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Re: [time-nuts] When does NIST change to DST?

[James Flynn]

  writes:

> 
> I noticed that NIST, at http://nist.time.gov/ , is still sending 
standard time. When do they change?
> 
> John  WA4WDL
> 
> 

As of 1849Z it was reporting DST. 


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[time-nuts] HP 5065A repair

[cdelect]

I'm changing the topic from best rubidium frequency standard for this
post.

Most repairs I make to the 5065A run well below $250.00, sometimes as low
as $100.00.

A "crazy bad" repair might run $400.00 or so but out of over 50 repairs
only two needed that level of help.

As far a tempco goes, unless your lab swings tens of degrees will you
really see it?

Short term stability scales with cell size and is also proportional to
the design temperature.

Also separate filter and resonance cells perform better than an
"integrated" cell.

The 5065A cell is the largest available today and the 66 degree C is the
lowest temp around these days.

The 5065A cell also has a temperature regulated stem to stabilize the
Rubidium level.

These combine to give a typical STS of  1.5X10-13 at a Tau of 100
Seconds.

Unfortunately as others have noted, it is easily the most expensive
Rubidium standard out there.

A few members are looking into improving the tempco and I hope testing
the barometric pressure performance.

Cheers,


Corby

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Re: [time-nuts] Best Rubidium Frequency Standard

[Poul-Henning Kamp]

In message , Bob Camp writes:

>Even if they do take the correction, do they want it before or after the 
>PPS comes along? If you have a destination device that wants it before 
>the pps and a GPS that gives it to you after the PPS ... that's a bit of
>a problem. 

The Oncore GPS gives it to you before, and if the PRS10 has new enough
firmware to support it, you have plenty of time to send it over there
before the PPS pulse.

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

[Bob Camp]

Hi

Even if they do take the correction, do they want it before or after the PPS 
comes along? If you have a destination device that wants it before the pps and 
a GPS that gives it to you after the PPS … that’s a bit of a problem. 

Bob


> On Mar 13, 2016, at 12:07 PM, Poul-Henning Kamp  wrote:
> 
> 
> In message <1e2b85.da47c0.4416d...@aol.com>, KA2WEU--- via time-nuts writes:
> 
>> what is wrong with   the Standford Research  Rubidium  standard with a 1 
>> sec sync pulls form a GPS satellite ?" 
> 
> At least some of the firmware versions do not allow you to change the
> PPSIN offset second by second, so you cannot compensate for the
> "negative sawtooth", and the resulting "hanging bridges" means that
> you have to us a very unoptimal PLL time constant.
> 
> 
> -- 
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] Best Rubidium Frequency Standard

[Poul-Henning Kamp]

In message <1e2b85.da47c0.4416d...@aol.com>, KA2WEU--- via time-nuts writes:

>what is wrong with   the Standford Research  Rubidium  standard with a 1 
>sec sync pulls form a GPS satellite ?" 

At least some of the firmware versions do not allow you to change the
PPSIN offset second by second, so you cannot compensate for the
"negative sawtooth", and the resulting "hanging bridges" means that
you have to us a very unoptimal PLL time constant.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] When does NIST change to DST?

[Jim Harman]

WWVB has sent the signal to switch to DST but the website has not changed
yet.

On Sun, Mar 13, 2016, 10:11 AM  wrote:

> I noticed that NIST, at http://nist.time.gov/ , is still sending standard
> time. When do they change?
>
> John  WA4WDL
>
>
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Re: [time-nuts] Best Rubidium Frequency Standard

[Bob Camp]

Hi

> On Mar 13, 2016, at 10:22 AM, ka2...@aol.com wrote:
> 
> Good morning ,
>  
> what is wrong with   the Standford Research  Rubidium standard with a 1 sec 
> sync pulls form a GPS satellite ?” 

The second to second variation in the pps from a normal GPS receiver is in the 
> 20 ns range. If you lock directly to it with a short time constant loop (say 
< 500 seconds) your Rb probably can’t even keep up with the changes. 

The daily swing in the GPS signal at L1 is in the 10 to >50 ns range (sunrise 
and sunset). That’s worse than the stability of these Rb’s over the same time 
period. In order to average things out you need a loop with a time constant out 
in the “many days” range. 

The normal way to take care of all this in a GPSDO is to track the lock in 
process and adjust the loop as it progresses (or does not progress).  The unit 
may switch between two or three filter settings even after it has fully 
“settled in”. Some days will be >50 ns days, other days will be 10 ns days ….

Bob


>  
> Ulrich
>  
> In a message dated 3/13/2016 10:16:11 A.M. Eastern Daylight Time, 
> kb...@n1k.org writes:
> Hi
> 
> With “real” (who knows how real) Rb based GPSDO’s selling below $250, it’s 
> not clear that running an Rb in a lash up that makes it look like a TBolt is 
> a worthwhile exercise. Unless you can get the time constants out into the 
> “several days” range, a manual adjust is a much better way to go. Since we 
> are talking about a “I just want to plug it all in” sort of approach here, 
> anything more than “set and forget” appears to be out of the question. 
> 
> Bob
> 
> 
> > On Mar 12, 2016, at 10:48 PM, Charles Steinmetz  
> > wrote:
> > 
> > I wrote:
> > 
> >> With the right settings, a PRS10 *does* work extremely well with the PPS 
> >> input from a GPS.  They do generally take several days or more to lock, 
> >> because of the long time constants involved.
> > 
> > Bob replied:
> > 
> >> I would call having to wait a few days for it to lock a bit of a 
> >> disadvantage. Even more so for those with an antenna challenged 
> >> environment that gives them dropouts every few hours.
> > 
> > Well, one is certainly free to use shorter time constants to achieve lock 
> > faster.  The very long TCs simply allow one to exploit the exemplary 
> > stability of the PRS10 for performance much better than what an OCXO-based 
> > GPSDO can deliver.  If you are content with the stability of, say, a TBolt, 
> > you can replicate that performance by adjusting the PRS10 loop to match 
> > TBolt dynamics -- in which case it will lock in a comparable time.
> > 
> > WRT holdover, the long TC and the inherent stability of the PRS10 mean that 
> > it will stay very close to the GPS PPS even over long holdover periods, so 
> > re-acquiring lock does not take nearly as long as acquiring it initially.  
> > For the same reason, a PRS10 set up for maximum stability can acquire lock 
> > even if there are holdover periods during the acquisition process (in both 
> > cases, assuming that the GPS does not output "bad" PPS pulses when it is 
> > not locked to GPS).
> > 
> > In principle, one might be able to begin the process by setting the PRS10 
> > loop "tighter," then changing the loop constants in one or more steps after 
> > it achieves initial lock.  I have not tried this, and do not know if 
> > changing the loop programming on the fly upsets the PRS10 phase.  If not, 
> > it should work (and one could even program a BBB, 'uino, or other small 
> > processor to do it automatically).
> > 
> > Best regards,
> > 
> > Charles
> > 
> > 
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Re: [time-nuts] Best Rubidium Frequency Standard

[Bob Camp]

Hi

> On Mar 13, 2016, at 4:37 AM, Iain Young  wrote:
> 
> Hi,
> 
> OK, so I'm about to show the limitations of my knowledge :)
> 
> Bob Wrote:
> 
> On 11/03/16 22:51, Bob Camp wrote:
> 
>> If your target is something like a microwave radio, many Rb’s are
> > “challenged” in terms of phase noise and/or spurs. Some sort of
> > cleanup will be needed for almost all of them.
> 
> Are some models particularly better than others at either phase noise
> or spurs ? If so, do we know which ones ? Or is it more a case by case
> basis (damage/maltreatment not with standing...) ?

Hi

None of them are what I would call “good” for phase noise or spurs. Even a 
cheap OCXO will beat them all. The “least awful” that is commonly available on 
surplus is the PRS-10.

> 
> Also, are we "simply" talking LPF/HPF/BPF precautions here ?

No, not at all, the phase noise and spurs are all over the place. 

> Or would
> folks advise doing other things as well ?

You need a good clean OCXO and a very narrowband clean up loop. How narrow 
depends on how good your radio needs to be. 

> The microwave radio isn't
> going to care about delay through any filter [assuming that delay stays
> constant of course] (Different on the timing side of course)

You would need a filter with a 30 db bandwidth of < 1 Hz to even begin to clean 
up some of these. 

> 
> (I looked at the 10MHz output from the KS24361 boxes that Bob posted
> on here, with all the multiples, and brain simply screamed LPF.

That’s a *much* cleaner output than most of these Rb’s. 


> Saw
> the sub harmonic, and it shouted HPF at me!)

Most microwave radio setups are going to ignore stuff like sub-harmonics. Their 
multiplier chains are plenty narrow enough to take them out.

Bob

> 
> 
> Iain
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Re: [time-nuts] Best Rubidium Frequency Standard

[Bob Camp]

Hi

Ok, so I can spend $2,500 on a working 5065A if I can find one. I can spend the 
same money on five working FRK’s at $500 (if I can find them). I can spend the 
same money on 10 working PRS-10’s (if they show up). I can spend that money on 
40 working with a warranty telecom Rb’s right at $125 each now any day of the 
week. I can get 200 of the “repair” grade telecom Rb’s for the same money. 

Yes that neglects shipping and it also does not include your time spending a 
year or two shopping for this or that. 

Let’s say that the buyer is 65 years old. Let’s also guess that by age 95 this 
stuff isn’t going to be of much interest. 

Based on their history, the 5065A will need a pretty major rebuild over the 
course of 30 years. 

The FRK’s each would need to run for 6 years to keep you going for the time 
period. That’s a reasonable bet, but not a slam dunk based on my data here.

The PRS-10’s would need to work for about 3 years to last you that amount of 
time. None of mine have run that long and I do not seem to be the only one who 
has seen that. 

The telecom Rb’s would need to run for less than a year to make it. That’s a 
slam dunk. In fact it’s a slam dunk with 15 of them. 

The repair units are a bit of an unknown. If you get 120 working units, they 
need to each last 3 months. That is indeed a slam dunk. If they each run for 2 
years (the unknown) you are back to 15 units. 

Can I call up and get a PRS-10 repaired today for the same cost as a 
replacement unit on eBay? Maybe I can. If so how long does it run after the 
repair compared to the eBay part. If it’s no better than the eBay unit, the 
math does not change. If in 10 years they stop doing that, the math changes a 
bit. 

Can I call up somebody and get a 5065A rebuilt? I suspect that there is *some* 
amount of cash I can throw at him to do so. Expecting him to do if for free … 
that’s crazy. Is somebody still rebuilding the 5065’s in 15 years … who knows. 
I’d bet it does not get cheaper.

Can I call somebody and get any of the other stuff repaired? I suppose I can if 
I was offering $5,000 for the repair. (No I’m not offering so no need to email 
me). Once you get past the simple stuff, it’s not easy to fix this stuff. 

===

So based on a “bang for the buck” estimate:

The rebuild units come out on top

The working telecom units come in second

The FRK’s come in third

The others come in someplace further back than that.

===

Even simple repairs on theses are far more complex that manually setting an Rb 
on frequency against GPS. The more involved repairs are way more complex that a 
manual frequency set. To me that makes a “auto locking” unit that likely needs 
complex troubleshooting a much less attractive thing. Yes, that goes into the 
numbers above. 


Bob



> On Mar 13, 2016, at 1:18 AM, Mark Sims  wrote:
> 
> In many ways the 5065A is the probably the most repairable of all the units 
> (closely followed by the FRK family and the M100).   They all use parts that 
> are mostly still available and the circuitry is accessible.  You can assume 
> that the lamp (and maybe some of the microwave parts) in any Rb oscillator is 
> unobtainium.  
> Most failures seen in these systems tend to be in the power related parts 
> (electrolytic caps and heater / lamp driver transistors).  Total rubidium 
> lamp failures are rare.  Lamps with degraded output due to rubidium 
> depositing on the lamp walls can usually be refurbished with a heat gun.
> If you don't need the ultimate in performance the telecom Rb's are a very 
> good value.   They can be had for prices where repair is not an issue... just 
> replace them.  At one time LPROs could be had for less than $50 and they were 
> usually in good operating condition.   The bulk packs of the TEMIC units on 
> Ebay approach that level today.  As time has passed the availability has gone 
> down,  prices have gone up,  and the quality what is available had gone down. 
>   
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Re: [time-nuts] Best Rubidium Frequency Standard

[KA2WEU--- via time-nuts]

Good morning ,
 
what is wrong with   the Standford Research  Rubidium  standard with a 1 
sec sync pulls form a GPS satellite ?" 
 
Ulrich 
 
 
In a message dated 3/13/2016 10:16:11 A.M. Eastern Daylight Time,  
kb...@n1k.org writes:

Hi

With “real” (who knows how real) Rb based GPSDO’s selling  below $250, it’
s not clear that running an Rb in a lash up that makes it look  like a 
TBolt is a worthwhile exercise. Unless you can get the time constants  out into 
the “several days” range, a manual adjust is a much better way to go.  
Since we are talking about a “I just want to plug it all in” sort of approach  
here, anything more than “set and forget” appears to be out of the 
question.  

Bob


> On Mar 12, 2016, at 10:48 PM, Charles Steinmetz   
wrote:
> 
> I wrote:
>  
>> With the right settings, a PRS10 *does* work extremely well with  the 
PPS input from a GPS.  They do generally take several days or more to  lock, 
because of the long time constants involved.
> 
> Bob  replied:
> 
>> I would call having to wait a few days for it to  lock a bit of a 
disadvantage. Even more so for those with an antenna  challenged environment 
that 
gives them dropouts every few hours.
>  
> Well, one is certainly free to use shorter time constants to achieve  
lock faster.  The very long TCs simply allow one to exploit the exemplary  
stability of the PRS10 for performance much better than what an OCXO-based  
GPSDO can deliver.  If you are content with the stability of, say, a  TBolt, 
you 
can replicate that performance by adjusting the PRS10 loop to match  TBolt 
dynamics -- in which case it will lock in a comparable time.
>  
> WRT holdover, the long TC and the inherent stability of the PRS10  mean 
that it will stay very close to the GPS PPS even over long holdover  periods, 
so re-acquiring lock does not take nearly as long as acquiring it  
initially.  For the same reason, a PRS10 set up for maximum stability can  
acquire 
lock even if there are holdover periods during the acquisition process  (in 
both cases, assuming that the GPS does not output "bad" PPS pulses when it  
is not locked to GPS).
> 
> In principle, one might be able to  begin the process by setting the 
PRS10 loop "tighter," then changing the loop  constants in one or more steps 
after it achieves initial lock.  I have  not tried this, and do not know if 
changing the loop programming on the fly  upsets the PRS10 phase.  If not, it 
should work (and one could even  program a BBB, 'uino, or other small 
processor to do it  automatically).
> 
> Best regards,
> 
>  Charles
> 
> 
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Re: [time-nuts] Best Rubidium Frequency Standard

[Bob Camp]

Hi

With “real” (who knows how real) Rb based GPSDO’s selling below $250, it’s not 
clear that running an Rb in a lash up that makes it look like a TBolt is a 
worthwhile exercise. Unless you can get the time constants out into the 
“several days” range, a manual adjust is a much better way to go. Since we are 
talking about a “I just want to plug it all in” sort of approach here, anything 
more than “set and forget” appears to be out of the question. 

Bob


> On Mar 12, 2016, at 10:48 PM, Charles Steinmetz  wrote:
> 
> I wrote:
> 
>> With the right settings, a PRS10 *does* work extremely well with the PPS 
>> input from a GPS.  They do generally take several days or more to lock, 
>> because of the long time constants involved.
> 
> Bob replied:
> 
>> I would call having to wait a few days for it to lock a bit of a 
>> disadvantage. Even more so for those with an antenna challenged environment 
>> that gives them dropouts every few hours.
> 
> Well, one is certainly free to use shorter time constants to achieve lock 
> faster.  The very long TCs simply allow one to exploit the exemplary 
> stability of the PRS10 for performance much better than what an OCXO-based 
> GPSDO can deliver.  If you are content with the stability of, say, a TBolt, 
> you can replicate that performance by adjusting the PRS10 loop to match TBolt 
> dynamics -- in which case it will lock in a comparable time.
> 
> WRT holdover, the long TC and the inherent stability of the PRS10 mean that 
> it will stay very close to the GPS PPS even over long holdover periods, so 
> re-acquiring lock does not take nearly as long as acquiring it initially.  
> For the same reason, a PRS10 set up for maximum stability can acquire lock 
> even if there are holdover periods during the acquisition process (in both 
> cases, assuming that the GPS does not output "bad" PPS pulses when it is not 
> locked to GPS).
> 
> In principle, one might be able to begin the process by setting the PRS10 
> loop "tighter," then changing the loop constants in one or more steps after 
> it achieves initial lock.  I have not tried this, and do not know if changing 
> the loop programming on the fly upsets the PRS10 phase.  If not, it should 
> work (and one could even program a BBB, 'uino, or other small processor to do 
> it automatically).
> 
> Best regards,
> 
> Charles
> 
> 
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[time-nuts] When does NIST change to DST?

[jmfranke]

I noticed that NIST, at http://nist.time.gov/ , is still sending standard time. 
When do they change?

John  WA4WDL


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Re: [time-nuts] Best Rubidium Frequency Standard

[Iain Young]

Hi,

OK, so I'm about to show the limitations of my knowledge :)

Bob Wrote:

On 11/03/16 22:51, Bob Camp wrote:


If your target is something like a microwave radio, many Rb’s are

> “challenged” in terms of phase noise and/or spurs. Some sort of
> cleanup will be needed for almost all of them.

Are some models particularly better than others at either phase noise
or spurs ? If so, do we know which ones ? Or is it more a case by case
basis (damage/maltreatment not with standing...) ?

Also, are we "simply" talking LPF/HPF/BPF precautions here ? Or would
folks advise doing other things as well ? The microwave radio isn't
going to care about delay through any filter [assuming that delay stays
constant of course] (Different on the timing side of course)

(I looked at the 10MHz output from the KS24361 boxes that Bob posted
on here, with all the multiples, and brain simply screamed LPF. Saw
the sub harmonic, and it shouted HPF at me!)


Iain
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Re: [time-nuts] HP 5065A flaws and improvements

[Poul-Henning Kamp]

In message , Bob Camp writes:

>> That's the first I've heard of any drawbacks to the 5065.  Can you give
>> more details on this?
>
>The manual talks about a 5x10^-11 temperature stability over 0-50C.
>Various members have reported data that suggests a stability about
>10X worse than this.

I'm pretty sure that is easily fixable, it's Zener in the power-supply
which has become temperature sensitive.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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