Re: [time-nuts] Equipment question: OCXO versus GPSDO + XTAL

[Bob Camp]

Hi

Do you need 20 ps resolution / accuracy? If so at what time spans or gate times?

If the answer is > 100 sec then don't bother with any of the options you 
mentioned. They are not good enough. Plan on getting a Hydrogen Maser. It is 
the only thing you can easily get with adequate stability. If traceability is 
needed at the same level, that would need to be adressed as well. 

In the .01 to 10 second range the OCXO provides a lower noise floor than the 
TBolt. The TBolt provides better accuracy.

At 0.001 seconds your 20 ps is 2x10^-8. The OCXO may not have an advantage over 
the cheaper internal standard at this point.

 AVAR is not absolute error. That is the data most commonly seen on 
oscillators. Translating to absolute error is not simple. Thus the somedwhat 
general answers.

Bob


On Mar 17, 2011, at 11:41 PM, Mark Spencer  wrote:

> I'm inclined to agree.   (I'm not sure I'd want to use my Thunderbolt as the 
> reference oscillator for an instrument that had 20 ps of resolution, nor 
> would I trust the long term accuracy of an ocxo without being able to compare 
> it to a reference such as an gpsdo.)
> 
> 
> 
> Sent from my iPad
> 
> On 2011-03-17, at 7:30 PM, "J. L. Trantham"  wrote:
> 
>> Personally, I would get both.
>> 
>> Joe
>> 
>> -Original Message-
>> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
>> Behalf Of J. L. Trantham
>> Sent: Thursday, March 17, 2011 9:24 PM
>> To: 'Discussion of precise time and frequency measurement'
>> Subject: Re: [time-nuts] Equipment question: OCXO versus GPSDO + XTAL
>> 
>> 
>> Depends on what you want.  Stability or accuracy?  Bench or portable?  The
>> TBolt or another GPSDO will certainly be accurate.  Probably fairly stable
>> as well.  However, if you need portability, the OCXO is the only way to go.
>> You will have to look at the stability measurements of the OCXO versus the
>> GPSDO to choose that one
>> -Original Message-
>> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
>> Behalf Of Wolfgang
>> Sent: Thursday, March 17, 2011 8:51 PM f 
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Equipment question: OCXO versus GPSDO + XTAL
>> 
>> 
>> On Friday 18 March 2011, Greg Broburg wrote:
>>> I have a 53131 and 53181. There were several TB options.
>>> I dont have a manual for the 53230A. If you could, see what the option
>>> TB assembly PNs are, then go looking for these assemblies. Mine just 
>>> dropped in and did the autocal right off. I paid 300 to upgrade the 
>>> 53181. The autocal using a DAC works very well, no more tweaking Rs or 
>>> Cs and waiting a day for them to restabilize.
>>> 
>> Don't recall where I read this but IIRC: 
>> 
>> There are several other options for the 53230A which can be added lateron 
>> by the user ("kits") but the OCXO can only be installed lateron by sending 
>> the device to service. 
>> 
>> Thanks to the list for the answers - but: 
>> 
>> It seems like everybody is telling me "go for the cheaper, add the OCXO 
>> lateron if you need it" - but that's not what I'm after. What I'd really 
>> like to do is to make up my mind based on educated opinions on this list 
>> whether the built-in OXCO option offers any advantage at all compared 
>> to standard clock + good external reference. 
>> 
>> - Wolfgang, DL1SKY
>> 
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Re: [time-nuts] semi-OT: comparison of two 10x scope probes / cheap OCXO

[Bob Camp]

Hi

Some of the probes are pretty good. Others are a disaster fidelity wise. Always 
good to check one before buying a bunch of them. The tough part is that some of 
the bad ones look just like the good ones. 

Bob



On Mar 18, 2011, at 2:38 AM, Bruce Griffiths  wrote:

> The cheap probes probably lack the resistive inner conductor in their 
> interconnecting coaxial cables.
> This results in a poorly damped transient response.
> 
> Bruce
> 
> Eric Garner wrote:
>> I too, fell for the siren song of cheap Chinese probes. 2 years after
>> I bought 4 of them, only one has not failed. However, my 1980's
>> vintage probes from Tek still work dandily.
>> 
>> 
>> 
>> On Thu, Mar 17, 2011 at 12:47 PM, beale  wrote:
>>   
>>> Yes, I am controlling the OCXO frequency with a voltage input (center tap 
>>> of 10k trimpot from +5V to ground). I hooked up my custom 26 MHz PIC 
>>> divider* and was able to trim the OCXO to match the output of my GPS 1pps 
>>> signal to better than 1E-9 (at least for short periods of time).
>>> 
>>> These parts draw about 60 mA at +5V in operation in a 23 C ambient 
>>> environment, after a brief one-time warmup pulse of about 200 mA. The can 
>>> gets a bit warm if left open. I taped a small thermistor against the case, 
>>> and made a little styrofoam box to nest snugly over it and measured the can 
>>> case temp to reach about 50 C when thus insulated.
>>> 
>>> I am accumulating some performance data on the two units I have and can 
>>> post it online if anyone is interested.  (actually, I was thinking of 
>>> buying a bunch more before posting the data, because the price seems too 
>>> good to be true).
>>> 
>>> * http://www.bealecorner.org/best/measure/time/source/
>>> 
>>> Scott Newell wrote:
>>> 
 That's a great price for any OCXO. Do they have EFC? (I can't tell from 
 the part number in the auction photo.)
   
>>> At 01:41 PM 3/17/2011, beale wrote:
>>>output of a 26 MHz Pletronics OCXO in a 14DIP can (by the way these go 
>>> for $2 online, the cheapest OCXO I've seen).
>>> 
>>> 
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>>> 
>> 
>> 
>>   
> 
> 
> 
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Re: [time-nuts] Result of Earth Quake speeds up earth?

[jimlux]

On 3/17/11 12:30 PM, Chris Albertson wrote:

On Wed, Mar 16, 2011 at 11:00 PM, jimlux  wrote:



Synchronizing the several receivers that are spread aroud is not
really even required.  Many years ago astronomers would mail magnetic
tapes and the data would be combined days after the observations
After all if both receivers are looking at the same distant
transmitters you should be able search for a solution.  But of course
having good time tags reduces the search space.


Since the goal of this BYMLBI (Back Yard Medium LBI) is to measure the 
change in the earth's rotation rate, one would at the least need a time 
code recorded on those tapes, since you want to know the instant when 
the source crosses some reference plane.  It's not quite like a classic 
interferometer application where you're looking for high resolution in a 
small region, but don't need high absolute position accuracy.






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Re: [time-nuts] Result of Earth Quake speeds up earth?

[jimlux]

A 10-12m diameter dish is probably close to the minimum feasible aperture.
A 4m dish can be made to work in conjunction with a mauch larger dish
(eg 30m).



The original speculation was for measuring the small change in earth 
rotation rate, for which some sort of interferometric measurement of a 
stellar source could be used.


The source has to be bright (so you can detect it with a practical 
antenna.. not everyone has a 30m dish in their back yard)
The source has to be small angle (or at least something that you could 
accurately determine the centroid of)
The source has to be "not moving"  (which I think leaves out using 
something like jupiter)
The frequency of measurement has to be somewhere that the atmosphere 
won't dominate the uncertainty (leaving out optical, I think)



SO what's the brightest small angular radio source out there?


As someone else has pointed out, measuring the earth surface position 
relative to spacecraft orbits, e.g. GPS, would be another technique.  In 
fact, a high resolution measurement of the position of a geosync sat 
might do.. If the earth's rotation rate changes you'd have to adjust the 
height of the satellites in Clarke orbit to keep them stationary.


Unfortunately, for earth orbiters, there's enough other perturbations 
that you probably can't see it.  They already have to move satellites 
around to compensate for things like solar wind, air drag (for LEO), etc.


But maybe for a spacecraft in deep space, between planets, which is on a 
well understood trajectory?


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[time-nuts] lower cost Rb, GPS OCXO with -110dBc/Hz@1Hz & GPS Rb

[Clive Green]

We just made a breakthrough with 2" x "2 OCXO size Rb for $666:00 with 3
year warranty. This enables a low cost GPS-Rb one board with 1us holdover,
NMEA or NTP. Our standard GPS OCXO has -110dBc/Hz@1Hz Phase Noise. Available
from mid 2011 in quantity.not even on our web site yet.

 

Clive Green

CEO 

Quartzlock 

+ Gothic, Plymouth Road, Totnes, Devon. TQ9 5LH England

(: +44 (0) 1803 862 062 7: +44 (0) 1803 867 962

š:   cgr...@quartzlock.com ü:
 www.quartzlock.com

Skype: clive.green.skype Messenger: cgr...@quartzlock.com

Registered office: Gothic, Plymouth Road, Totnes, Devon. TQ9 5LH England
Registered in England

 P Think Environment, print only if necessary.

 

This is an e-mail from Quartzlock (UK) Limited, its contents (including all
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for any loss or damage arising in any way from the receipt or use thereof.

 

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Re: [time-nuts] lower cost Rb, GPS OCXO with -110dBc/Hz@1Hz & GPS Rb

[Greg Broburg]

Here Here! Excellent, Clive. Thanks for the heads up.

Now the HP 53230A is likely to have an internal DAC
generated tuning Voltage control which is tied to the
autocal through firmware. Any idea if your little box
could use the internal HP autocal idea to control the
C field?? I believe that it is likely -10V to +10V range.

Maybe this is a cue for you to make a drop in assembly
for the 53230A.

Thank you

Greg

On 3/18/2011 8:09 AM, Clive Green wrote:

We just made a breakthrough with 2" x "2 OCXO size Rb for $666:00 with 3
year warranty. This enables a low cost GPS-Rb one board with 1us holdover,
NMEA or NTP. Our standard GPS OCXO has -110dBc/Hz@1Hz Phase Noise. Available
from mid 2011 in quantity.not even on our web site yet.



Clive Green

CEO

Quartzlock

+ Gothic, Plymouth Road, Totnes, Devon. TQ9 5LH England

(: +44 (0) 1803 862 062 7: +44 (0) 1803 867 962

š:  cgr...@quartzlock.com ü:
  www.quartzlock.com

Skype: clive.green.skype Messenger: cgr...@quartzlock.com

Registered office: Gothic, Plymouth Road, Totnes, Devon. TQ9 5LH England
Registered in England

  P Think Environment, print only if necessary.



This is an e-mail from Quartzlock (UK) Limited, its contents (including all
attachments) and any files transmitted with it are confidential and intended
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[time-nuts] BYMLBI (Back Yard Medium LBI)

[Brooke Clarke]

Hi:

For a number of decades I've tried to figure out a way to measure the 
period of the Earth's rotation accurate to at least 1 ms.
For some thoughts (since I don't think it will work) on doing it 
optically see:

http://www.prc68.com/I/StellarTime.shtml

Is it possible to do it using a radio method in my (large) back yard?

--
Have Fun,

Brooke Clarke
http://www.PRC68.com


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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[Bruce Griffiths]

Brooke Clarke wrote:

Hi:

For a number of decades I've tried to figure out a way to measure the 
period of the Earth's rotation accurate to at least 1 ms.
For some thoughts (since I don't think it will work) on doing it 
optically see:

http://www.prc68.com/I/StellarTime.shtml

Is it possible to do it using a radio method in my (large) back yard?



1ms corresponds to an angle of 15 milliarcsec or 73 nrad for 0 
declination objects.


15 milliarc sec positioning accuracy is just within the capability of an 
7" aperture transit circle or PZT equipped with a CCD camera.
This accuracy was close to that achievable with a video camera equipped 
transit circle in the late 1980's.


A 2900 km diameter dish or equivalent has a resolution of about 73 nrad 
at 1420MHz.
Position accuracy for a point source can be somewhat higher than the 
resolution if the SNR is sufficiently high.
However an antenna system of several hundred km in extent is likely to 
be necessary.


Just how large is your backyard?

Bruce


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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[Brooke Clarke]

Hi Bruce:

From what I can learn about "seeing" the atmosphere instability is too 
great to allow making measurements optically in the 1 ms area.


It's a couple of acres.

Have Fun,

Brooke Clarke
http://www.PRC68.com


Bruce Griffiths wrote:

Brooke Clarke wrote:

Hi:

For a number of decades I've tried to figure out a way to measure the 
period of the Earth's rotation accurate to at least 1 ms.
For some thoughts (since I don't think it will work) on doing it 
optically see:

http://www.prc68.com/I/StellarTime.shtml

Is it possible to do it using a radio method in my (large) back yard?



1ms corresponds to an angle of 15 milliarcsec or 73 nrad for 0 
declination objects.


15 milliarc sec positioning accuracy is just within the capability of 
an 7" aperture transit circle or PZT equipped with a CCD camera.
This accuracy was close to that achievable with a video camera 
equipped transit circle in the late 1980's.


A 2900 km diameter dish or equivalent has a resolution of about 73 
nrad at 1420MHz.
Position accuracy for a point source can be somewhat higher than the 
resolution if the SNR is sufficiently high.
However an antenna system of several hundred km in extent is likely to 
be necessary.


Just how large is your backyard?

Bruce


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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[Bruce Griffiths]

The Naval Observatory and others have been doing this for years albeit 
averaged over several observations and by fitting curves to the stellar 
transit path in the transit circle focal plane eg:


http://adsabs.harvard.edu/full/1986IAUS..109..483H

The setup with Heidenhain elevation encoders etc was impressive when I 
visited the facility in the 1980's.
The accomodation etc was in stark contrast to the Observatory a little 
further up the hill where we only had underfloor heating and didnt 
obseve from the comfort of a temperature controlled computer room.


Bruce

Brooke Clarke wrote:

Hi Bruce:

From what I can learn about "seeing" the atmosphere instability is too 
great to allow making measurements optically in the 1 ms area.


It's a couple of acres.

Have Fun,

Brooke Clarke
http://www.PRC68.com


Bruce Griffiths wrote:

Brooke Clarke wrote:

Hi:

For a number of decades I've tried to figure out a way to measure 
the period of the Earth's rotation accurate to at least 1 ms.
For some thoughts (since I don't think it will work) on doing it 
optically see:

http://www.prc68.com/I/StellarTime.shtml

Is it possible to do it using a radio method in my (large) back yard?



1ms corresponds to an angle of 15 milliarcsec or 73 nrad for 0 
declination objects.


15 milliarc sec positioning accuracy is just within the capability of 
an 7" aperture transit circle or PZT equipped with a CCD camera.
This accuracy was close to that achievable with a video camera 
equipped transit circle in the late 1980's.


A 2900 km diameter dish or equivalent has a resolution of about 73 
nrad at 1420MHz.
Position accuracy for a point source can be somewhat higher than the 
resolution if the SNR is sufficiently high.
However an antenna system of several hundred km in extent is likely 
to be necessary.


Just how large is your backyard?

Bruce


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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[Brooke Clarke]

Hi Bruce:

Thanks for the link.  I learned after I moved here that our town of 
Ukiah, Calif. was one of a handful of locations to have a Latitude 
observatory.

http://www.prc68.com/I/UkiahObs.shtml
The Zenith Telescope that's over 100 years old has angular accuracy 
that's maybe 100 times better than the Paramount ME mount.
It's interesting that the Photographic Zenith Tube (PZT) was compared to 
the Zenith Telescope and the results were essentially the same.  NBS 
used the PZT to set it's pendulum clocks for some time.
I have a feeling that the 7 inch transit circle is a very expensive 
instrument and that there's no low cost commercial equivalent.


Have Fun,

Brooke Clarke
http://www.PRC68.com


Bruce Griffiths wrote:
The Naval Observatory and others have been doing this for years albeit 
averaged over several observations and by fitting curves to the 
stellar transit path in the transit circle focal plane eg:


http://adsabs.harvard.edu/full/1986IAUS..109..483H

The setup with Heidenhain elevation encoders etc was impressive when I 
visited the facility in the 1980's.
The accomodation etc was in stark contrast to the Observatory a little 
further up the hill where we only had underfloor heating and didnt 
obseve from the comfort of a temperature controlled computer room.


Bruce

Brooke Clarke wrote:

Hi Bruce:

From what I can learn about "seeing" the atmosphere instability is 
too great to allow making measurements optically in the 1 ms area.


It's a couple of acres.

Have Fun,

Brooke Clarke
http://www.PRC68.com


Bruce Griffiths wrote:

Brooke Clarke wrote:

Hi:

For a number of decades I've tried to figure out a way to measure 
the period of the Earth's rotation accurate to at least 1 ms.
For some thoughts (since I don't think it will work) on doing it 
optically see:

http://www.prc68.com/I/StellarTime.shtml

Is it possible to do it using a radio method in my (large) back yard?



1ms corresponds to an angle of 15 milliarcsec or 73 nrad for 0 
declination objects.


15 milliarc sec positioning accuracy is just within the capability 
of an 7" aperture transit circle or PZT equipped with a CCD camera.
This accuracy was close to that achievable with a video camera 
equipped transit circle in the late 1980's.


A 2900 km diameter dish or equivalent has a resolution of about 73 
nrad at 1420MHz.
Position accuracy for a point source can be somewhat higher than the 
resolution if the SNR is sufficiently high.
However an antenna system of several hundred km in extent is likely 
to be necessary.


Just how large is your backyard?

Bruce


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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[Hal Murray]

> From what I can learn about "seeing" the atmosphere instability is too
> great to allow making measurements optically in the 1 ms area. 

There has been some interesting amateur work done on taking lots of 
short-exposure pictures and sifting through them to find the good ones.  (I 
can't find a good URL right now.)

I don't know if any stars are bright enough to make that practical.


> The source has to be "not moving"  (which I think leaves out using
> something like jupiter) 

We know where Jupiter is.  It should be possible to correct for that motion.  
It's just another layer of software. :)


> As someone else has pointed out, measuring the earth surface position
> relative to spacecraft orbits, e.g. GPS, would be another technique.

That's an interesting idea, but I think all the orbit data for GPS satellites 
is Earth relative rather than star relative.  I wonder if the group that 
drives the GPS satellites even knows their location relative to the stars.  
I'll bet not.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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[time-nuts] EPROMS

[Rob Kimberley]

Have just listed 49 assorted EPROMS on EBay - 320673010061.

These are all ex-equipment, some of it Datum. Not planning on splitting or
sorting them. 
WYSIWYG
:-)

Rob Kimberley





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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[Chris Albertson]

On Fri, Mar 18, 2011 at 8:36 AM, Brooke Clarke  wrote:
> Hi:
>
> For a number of decades I've tried to figure out a way to measure the period
> of the Earth's rotation accurate to at least 1 ms.


The US Navel observatory at Flagstaff was an 8 inch transit telescope.
 You can Google "FASTT" and read more.

You can measure to 1ms optically actually you can do 1000 times
better.  The trick is to look at many, not just one star and to use a
very accurate star catalog.   You don't really measure the position of
one star, you measure the position of a patch of sky that contains
many stars who's positions are known to great accuracy and then you
solve to find a best solution for the entire frame.They measure
thousands of stars every  night and have been doing so for 30 years.

The result of this is that they know the local optical reference
frames is not stationary withing the frame defined by distant quasars.

One of the things to know is that an optical telescope can measure
position of a star to maybe 10x better than it's resolving powerYes
the stars look like little blurs but you can use some analytic methods
to find the pear of the blur.  The simplest method is just to take the
centroid.   You avoid issues with resolving close stars by ignoring
them and using only the "best" isolated stars.

There is MUCH detail to worry about if you want to match FASST's
results but person working at home can still do better then 1ms if you
set u a good program with automated data reduction and run it long
enough.   Almost all of the software you need to free although you'd
need to do considerable integration.   And that there is the learning
curve.
-- 
=
Chris Albertson
Redondo Beach, California

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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[Chris Albertson]

On Fri, Mar 18, 2011 at 12:29 PM, Hal Murray  wrote:
>
>> From what I can learn about "seeing" the atmosphere instability is too
>> great to allow making measurements optically in the 1 ms area.
>
> There has been some interesting amateur work done on taking lots of
> short-exposure pictures and sifting through them to find the good ones.  (I
> can't find a good URL right now.)

Video is used for imaging planets.  They are bright because like earth
they are lit by the sun.   But measurement is different from imaging.
 For this job we don't need pictures.   The method using by FASST is
called "drift scan".  The images of the sky is allowed to move over a
large CCD sensor.  The telescope does not track the sky so the stars
images drift.CCD sensors are read out one row at a time then the
entire images is shifted down and the next ros is read.   It a drift
scan camers the charge shifting in the CCD is synchronized to the
motion  of the image.   The result is a very. long image.Think of
it as like a flat bad scanner ony the image moves not the sensor.
This allows for some longer exposures and also covers a lot of the
sky.  One BIG advantage of drift scan is that the telescope is bolted
down solid and never moves, so uncertainty in pointing is greatly
reduced.

The FASST camera continously  a large part of the sky as it drifts
overheadand they match that data to a catalog of stars and then know
the rate the sky is drifting and thenthe rate the Earth turns

I worked on a drift scan camera project a few years back.  We were
able to generate the wave forms to control the CCD in software.  The
Earth does not really turn all that fast  I had a prtottype camera
mounted on my Garage roof for a long time,  It used a chaep telephoto
lens (135mm f/2.8) as the telescopes and we were getting surprizing
accuracy for a "junk box" optical system.   An example of one of the
prototypes is the white tripple lens unit here
http://www.tass-survey.org/. Software ran under a rel-time version
of Linux with timming by NTP but later re-calibratd by the stars
themselves.  Our system not not nearly as good as FASST, not even
close but used many of the same techniques



-- 
=
Chris Albertson
Redondo Beach, California

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Re: [time-nuts] Thunderbolt setup

[Shawn Tayler]

Thanks Bob!  Alot to digest but a good starting point!

Sent from my iPhone

On Mar 16, 2011, at 4:51, Bob Camp  wrote:

> Hi
> 
> If you only have one sat to look at, horizon view is worse than overhead. 
> With multiple sats you want them spaced out over the sky to get a benefit 
> from triangulation.
> 
> More TBolt opinions (there are lots of us and we all have them ...)
> 
> The wonderful thing about a TBolt is that it can use foam core TV satellite 
> coax. Since 75 ohms is lower loss than 50 ohm (all else being constant) you 
> can get away with quite a bit of the stuff. F connectors are easy to do 
> wrong, so get some good ones and a proper crimp tool.  Most antennas are TNC 
> or N, so you will need an adapter. Again - get a good one. 
> 
> Keeping the antenna away from traffic is your first goal. Up in the air is 
> one way to do that, far from the house is another way. Last choice would be 
> near the dinner table. Good view of the sky down to about 20 degrees off the 
> horizon is ok. A view to 10 degrees is slightly better. Don't worry a lot 
> about a view towards the north pole if you are in the northern hemisphere. 
> 
> Run the unit constantly. The OCXO will settle down that way. The holdover 
> training will work best that way. The power required is pretty modest. 
> Mounting the unit in some sort of enclosure is an excellent idea simply to 
> minimize accidents. The power connector needs some protection from bumps and 
> snags. 
> 
> Where ever you mount the unit, consider that they tend to multiply. You may 
> soon have three or even more than twenty. 
> 
> So much fun.
> 
> Bob
> 
> 
> On Mar 16, 2011, at 5:15 AM, li...@lazygranch.com wrote:
> 
>> I thought for timing a view of the horizon was bad. 
>> 
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Re: [time-nuts] Thunderbolt setup

[Bob Camp]

Hi

It's not all that crazy. Unless you are going to buy a new home, there are a 
limited number of antenna locations possible. With almost any antenna, higher 
is better, and higher is harder to do. GPS is no different than most things in 
that respect. People do get TBolts working with living room antennas. 

The biggest issue is the "keep it on all the time". I'm not sure a UPS is worth 
the money in this case, but a dedicated supply certainly is.

It's a hobby - have fun!

Bob

 
On Mar 18, 2011, at 8:43 PM, Shawn Tayler wrote:

> Thanks Bob!  Alot to digest but a good starting point!
> 
> Sent from my iPhone
> 
> On Mar 16, 2011, at 4:51, Bob Camp  wrote:
> 
>> Hi
>> 
>> If you only have one sat to look at, horizon view is worse than overhead. 
>> With multiple sats you want them spaced out over the sky to get a benefit 
>> from triangulation.
>> 
>> More TBolt opinions (there are lots of us and we all have them ...)
>> 
>> The wonderful thing about a TBolt is that it can use foam core TV satellite 
>> coax. Since 75 ohms is lower loss than 50 ohm (all else being constant) you 
>> can get away with quite a bit of the stuff. F connectors are easy to do 
>> wrong, so get some good ones and a proper crimp tool.  Most antennas are TNC 
>> or N, so you will need an adapter. Again - get a good one. 
>> 
>> Keeping the antenna away from traffic is your first goal. Up in the air is 
>> one way to do that, far from the house is another way. Last choice would be 
>> near the dinner table. Good view of the sky down to about 20 degrees off the 
>> horizon is ok. A view to 10 degrees is slightly better. Don't worry a lot 
>> about a view towards the north pole if you are in the northern hemisphere. 
>> 
>> Run the unit constantly. The OCXO will settle down that way. The holdover 
>> training will work best that way. The power required is pretty modest. 
>> Mounting the unit in some sort of enclosure is an excellent idea simply to 
>> minimize accidents. The power connector needs some protection from bumps and 
>> snags. 
>> 
>> Where ever you mount the unit, consider that they tend to multiply. You may 
>> soon have three or even more than twenty. 
>> 
>> So much fun.
>> 
>> Bob
>> 
>> 
>> On Mar 16, 2011, at 5:15 AM, li...@lazygranch.com wrote:
>> 
>>> I thought for timing a view of the horizon was bad. 
>>> 
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>> 
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Re: [time-nuts] Equipment question: OCXO versus GPSDO + XTAL

[Wolfgang Wieser]

Hello all,

first, thanks for all the answers!

Maybe let me ask the more fundamental question: Completely independent 
of use scenarios and so on: Assume device A uses standard reference tied 
to ultra-stable zero-drift magic 10 MHz refclock. Device B uses TXCO option. 

Is there any measurement type with any strange setup that you could imagine 
where B outperforms A just because the combo "standard XO + refclock" 
is inferior in any respect compared to "TXCO". (Lab/shop equipment, 
no portability needed.)

I mean - not necessarily for this particular Agilent 53230A but for anything 
of this type and class. 

@Bill: 
thanks - exactly the type of advice/opinion I was hoping to get. 

@Paul Swed: 
> Unfortunately in the first round of the thread you did not say what you are
> actually doing with the system and whats important to you.
Measuring time and frequency? Maybe there are some unknown issues that I am 
not aware of but what I would like to know is whether for any usual 
measurement made with a timer/freq counter the choice of XO+refclock could 
be inferior to TXCO. If there are significantly different scenarios in 
your mind - it would be nice to let me know for what type of measurement 
you think that the one is better and for what not. 
Anything except portability issues?

> The last answers actually the best considering the base system initial
> investment. 
Well, once a year I buy something more expensive...
However, while 2500 EUR seems reasonable for the counter, additional 
1000 EUR seems a bit much for the OCXO option. 

@Joe
> You will have to look at the stability measurements of the OCXO versus the
> GPSDO to choose that one.
OK, do you have an educated guess about the outcome of that?
Because acutally doing this comparison exceeds my scope ATM. 

@Greg
> My opinion is that first you need to tell more about how you
> are going to use this counter. For work in the shop where
> a distributed reference is always available (...)
>
Hm.. OK.. I re-formulated into the question on the top. 

> I am suspicious of the note that this OCXO upgrade can only
> be done at the factory.  See if you can get the control sequence
> to cause reference autocal.
I've got a test unit ATM and there actually is a security code to 
unlock the calibration. I don't know the code right now. 

- Wolfgang, DL1SKY

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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[jimlux]

That's an interesting idea, but I think all the orbit data for GPS satellites
is Earth relative rather than star relative.  I wonder if the group that
drives the GPS satellites even knows their location relative to the stars.
I'll bet not.



I'll bet they do. Lots of earth orbiting satellites use star trackers 
for position determination.


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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[Wolfgang]

On Friday 18 March 2011, Brooke Clarke wrote:
> For a number of decades I've tried to figure out a way to measure the
> period of the Earth's rotation accurate to at least 1 ms.
>
> [...]
> 
> Is it possible to do it using a radio method in my (large) back yard?
>
1 ms / day = 1.2e-8 = 460um position accuracy on the ground. 

If the measurement takes more than a couple of days, continental drift 
may need to be considered. 

- Wolfgang, DL1SKY

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Re: [time-nuts] Equipment question: OCXO versus GPSDO + XTAL

[Wolfgang]

Hi Bob,

thanks very much; this is actually the type of answer I was hoping 
to find!

On Friday 18 March 2011, Bob Camp wrote:
> In the .01 to 10 second range the OCXO provides a lower noise floor than
> the TBolt. The TBolt provides better accuracy.
>
...although the TBolt itself has an OCXO built-in...

- Wolfgang, DL1SKY

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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[lists]

http://www.astronomycast.com

Episode 211 was a good primer on celestial navigation. It covers time piece 
construction. 

Building your own backyard continental drift hardware would be high on the 
coolness scale. 
 
 
--Original Message--
From: Wolfgang
Sender: time-nuts-boun...@febo.com
To: Discussion of precise time and frequency measurement
ReplyTo: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] BYMLBI (Back Yard Medium LBI)
Sent: Mar 18, 2011 8:58 PM

On Friday 18 March 2011, Brooke Clarke wrote:
> For a number of decades I've tried to figure out a way to measure the
> period of the Earth's rotation accurate to at least 1 ms.
>
> [...]
> 
> Is it possible to do it using a radio method in my (large) back yard?
>
1 ms / day = 1.2e-8 = 460um position accuracy on the ground. 

If the measurement takes more than a couple of days, continental drift 
may need to be considered. 

- Wolfgang, DL1SKY

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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[Wolfgang]

On Saturday 19 March 2011, Wolfgang wrote:
> 1 ms / day = 1.2e-8 = 460um position accuracy on the ground.
>
...oops sorry, 460mm, not um...   (I should find some sleep)

- Wolfgang, DL1SKY

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Re: [time-nuts] BYMLBI (Back Yard Medium LBI)

[jimlux]

On 3/18/11 9:20 PM, li...@lazygranch.com wrote:

http://www.astronomycast.com

Episode 211 was a good primer on celestial navigation. It covers time piece 
construction.

Building your own backyard continental drift hardware would be high on the 
coolness scale.




good gps measurements processed through GIPSY at JPL would probably do 
that quite nicely.  Where I live, about 2 cm/year motion generally 
northwards on pacific plate.  And about 1 cm/year vertical motion


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Re: [time-nuts] Equipment question: OCXO versus GPSDO + XTAL

[WB6BNQ]

Well Wolfgang,

You’re A/B scenario does not make sense to me.  I am getting the impression that
you think there is a third oscillator in the “Timebase” selection.  From reading
the manual I only see two selections; the first is the standard supplied
oscillator which is the “TCXO” and the only selectable option is the high 
quality
OCXO.  BUT, as you stated the question, NO, I cannot think of a scenario where
“B” would exceed “A.”  Cases do exist where having an oscillator wander around a
bit can be used as a dither function, but the circumstances where I seen it used
would negate having 12 digits of resolution.

In reviewing the specification of the 53230A, the internal 53230A timebase is
phase locked by the external reference source when using the external or auto
modes.  So you do not have a “direct-drive” function when using the external
reference (i.e., a distinctly separate source).  I wonder about the added noise
the PLL circuitry could possibly add.  I would suspect it to be worse with the
TCXO compared to the OCXO option.  After buying such a sophisticated instrument,
it would be a shame to settle for the cheap hubcaps.

Just my two cents !  I could be all wet.  Maybe we all will lucky and Bruce will
chime in here and give us a well educated response.  If he does it would be 
worth
paying attention to.

73BillWB6BNQ



Wolfgang Wieser wrote:

> Hello all,
>
> first, thanks for all the answers!
>
> Maybe let me ask the more fundamental question: Completely independent
> of use scenarios and so on: Assume device A uses standard reference tied
> to ultra-stable zero-drift magic 10 MHz refclock. Device B uses TXCO option.
>
> Is there any measurement type with any strange setup that you could imagine
> where B outperforms A just because the combo "standard XO + refclock"
> is inferior in any respect compared to "TXCO". (Lab/shop equipment,
> no portability needed.)
>
> I mean - not necessarily for this particular Agilent 53230A but for anything
> of this type and class.
>
> @Bill:
> thanks - exactly the type of advice/opinion I was hoping to get.
>
> @Paul Swed:
> > Unfortunately in the first round of the thread you did not say what you are
> > actually doing with the system and whats important to you.
> Measuring time and frequency? Maybe there are some unknown issues that I am
> not aware of but what I would like to know is whether for any usual
> measurement made with a timer/freq counter the choice of XO+refclock could
> be inferior to TXCO. If there are significantly different scenarios in
> your mind - it would be nice to let me know for what type of measurement
> you think that the one is better and for what not.
> Anything except portability issues?
>
> > The last answers actually the best considering the base system initial
> > investment.
> Well, once a year I buy something more expensive...
> However, while 2500 EUR seems reasonable for the counter, additional
> 1000 EUR seems a bit much for the OCXO option.
>
> @Joe
> > You will have to look at the stability measurements of the OCXO versus the
> > GPSDO to choose that one.
> OK, do you have an educated guess about the outcome of that?
> Because acutally doing this comparison exceeds my scope ATM.
>
> @Greg
> > My opinion is that first you need to tell more about how you
> > are going to use this counter. For work in the shop where
> > a distributed reference is always available (...)
> >
> Hm.. OK.. I re-formulated into the question on the top.
>
> > I am suspicious of the note that this OCXO upgrade can only
> > be done at the factory.  See if you can get the control sequence
> > to cause reference autocal.
> I've got a test unit ATM and there actually is a security code to
> unlock the calibration. I don't know the code right now.
>
> - Wolfgang, DL1SKY
>
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