Re: [time-nuts] GPSDO TC & Damping

[Steve Rooke]

Maybe this should be the subject of a separate thread but to enable
ordinary time-nuts to be able to test their ocxo's and gpsdo's for
phase stability at "home", what would it take as a minimum to be able
to perform something like an ADEV test? This would enable us (the
other half) to see the results of our experiments and tuning of the
gear we have otherwise it is a lot like working blind. I appreciate
that what is normally used is a counter which can continually
timestamp a dut as opposed to a gated counter but what would be the
cheapest way we could achieve this sort of setup?

Thanks and 73, Steve

2009/1/9 Bruce Griffiths :
> Richard Moore wrote:
>> On Jan 8, 2009, at 2:46 PM, time-nuts-requ...@febo.com wrote:
>>
>>
>>> Message: 1
>>> Date: Fri, 09 Jan 2009 10:28:35 +1300
>>> From: Bruce Griffiths 
>>> Subject: Re: [time-nuts] GPSDO TC
>>> To: Discussion of precise time and frequency measurement
>>>  
>>>
>>> Richard Moore wrote:
>>>
 On Jan 8, 2009, at 2:58 AM, time-nuts-requ...@febo.com wrote:



> Message: 6
> Date: Thu, 08 Jan 2009 11:51:50 +0100
> From: Magnus Danielson 
> Subject: Re: [time-nuts] GPSDO time constant
> To: Tom Van Baak , Discussion of precise
> time and
>frequency measurement 
>
> For ThunderBolt owners it is pretty straightforward to adjust the
> TC and
> damping, which is very nice. Use this oppertunity!
>
>
 So, Magnus (and Tom), what damping factor do you suggest for a TBolt?
 I'm running a verrry long TC now. If 1.2 is not actually critically
 damped, what value would be? Any guesses? BTW, I really like that
 plot of Tom's that tracks the oven and then gets better from the
 GPS...

 Dick Moore



>>> Richard
>>>
>>> As always, the problem is how do you know that the time constant
>>> you are
>>> using is anywhere near optimum?
>>>
>>>
>>> Bruce
>>>
>>
>> Well, like many here, I don't actually have the equipment, especially
>> the reference std., to do these MDEV, ADEV and other analyses, so,
>> since I use the GPSDO for a frequency standard and not for UTC, I
>> thought I'd get the expert opinions. Magnus has several times
>> indicated here that a TC laying somewhere in and around 100 to 1000
>> secs is probably optimum. When I enquired some time back about
>> damping in the TBolt, the consensus seemed to be "leave it at 1.2". I
>> have, but it just seems to me that won't be optimum for a fixed-
>> position, lab-located frequency standard -- at the moment, I'm
>> leaning toward the 0.7to 1.0 area.
>>
>>
> Why, since it has been demonstrated that a damping factor of 1.2 is
> better than one of 0.7 for a particular Thunderbolt this would tend to
> indicate that adjusting the damping without good justification is
> somewhat foolhardy.
> If in fact the phase noise characteristics of your OCXO are similar toi
> the one in the Thunderbolt that Tom measured this would degrade the
> performance.
>
> With no way of measuring the effect of such adjustments you are just
> hoping that your particular Thunderbolt is similar to the one Tom measured.
> Thats not engineering its more like witchcraft.
>
>> Tom's recent chart was quite helpful, especially the 1000 sec curve.
>> Now, I hope that Tom or someone else follows up on the suggestion to
>> track performance vs. damping factor. I do understand that the
>> results for any one GPSDO don't *necessarily* translate to other
>> devices, but they don't necessarily don't, either. At least for the
>> TBolts a lot of us are playing with, one good example (like Tom's)
>> may well put mine in a better ballpark than the ballpark the factory
>> wants it to play in, given the factors that you all have described.
>> Thx everyone for the comments. Look forward to the next round!
>>
>> Dick Moore
>>
> The probability that you will improve the performance significantly
> without a means of measuring the resultant performance is fairly low.
> You will never know if either an improvement or a degradation in
> performance has occurred.
> The one saving grace being that the factory defaults can always be restored.
>
> Bruce
>
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-- 
Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW
Omnium finis imminet

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Re: [time-nuts] 10 MHz Band-Pass Filter Needed

[Reeves Paul]

Try an old 10MBs Ethernet card - they have a nice packaged filter (contains
2 filters actually, 5 & 7 pole) which tidies up a 10MHz signal. Package is
'YCL 20F001N' but similar ones may exist. Essentially zero cost. Info from
the UHF-Satcom group.
 cheers,
Paul   G8GJA

-Original Message-
From: Richard W. Solomon [mailto:w1...@earthlink.net]
Sent: 08 January 2009 18:11
To: time-nuts@febo.com
Subject: [time-nuts] 10 MHz Band-Pass Filter Needed


The GPSDO I want to use has an output rich in harmonics. In some
cases that is good, but Murphy rules and in the application I have
today, it is not good.

I need a 10 MHz Band-Pass Filter, Bandwidth is not critical, something
small with SMA connectors would be ideal, but I can live with BNC.

Anyone have such a beast or know where I can get one ? I checked
Mini-Circuits
and choked on the price !!

Thanks, Dick, W1KSZ

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Re: [time-nuts] GPSDO TC & Damping

[Magnus Danielson]

Dick,

> Well, like many here, I don't actually have the equipment, especially  
> the reference std., to do these MDEV, ADEV and other analyses, so,  
> since I use the GPSDO for a frequency standard and not for UTC, I  
> thought I'd get the expert opinions. Magnus has several times  
> indicated here that a TC laying somewhere in and around 100 to 1000  
> secs is probably optimum.

I think you have misinterpreted my postings. I never claimed it was 
optimum, or at least never intended to. I think 100 secs is good for 
doing additional experiments with damping parameters. It would be 
interesting to see just how low the bulb may go. This only since it is 
obvious that it makes such a clear difference at 100 secs. It's a choice 
out of measurement and interpretation practicality, not optimum from a 
use perspective. If you consider my postings you would see that I rather 
promote the concept of adjusting the time constant dynamically to 
situations rather than say 1234.5678 seconds is the optimum.

Cheers,
Magnus

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Re: [time-nuts] GPSDO TC

[David C. Partridge]

 >But you might show up early or late for dinner, which could have dire
consequences.

I don't think my wife would notice if I arrived a few hundred pico-seconds
earlier or later!!!

Dave


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Re: [time-nuts] GPSDO TC

[Steve Rooke]

2009/1/9 David C. Partridge :
>  >But you might show up early or late for dinner, which could have dire
> consequences.
>
> I don't think my wife would notice if I arrived a few hundred pico-seconds
> earlier or later!!!

Wow! Your a lucky one!
-- 
Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW
Omnium finis imminet

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[time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Bruce Griffiths]

Steve

If we take TvB's measurements on a Thunderbolt as some guide as to what
to expect:
http://www.leapsecond.com/pages/tbolt-tc/

Then to make meaningful measurements on a Thunderbolt for example one needs:

1) An independent frequency standard with an MDEV better than 1E-12 or
so for  1 s  Maybe this should be the subject of a separate thread but to enable
> ordinary time-nuts to be able to test their ocxo's and gpsdo's for
> phase stability at "home", what would it take as a minimum to be able
> to perform something like an ADEV test? This would enable us (the
> other half) to see the results of our experiments and tuning of the
> gear we have otherwise it is a lot like working blind. I appreciate
> that what is normally used is a counter which can continually
> timestamp a dut as opposed to a gated counter but what would be the
> cheapest way we could achieve this sort of setup?
>
> Thanks and 73, Steve
>   


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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Bruce Griffiths]

Addendum:

Timestamping using a conventioanl gated counter is easily accomplished
using Greenhall's picket fence technique:
http://horology.jpl.nasa.gov/papers/picket_uffc.pdf

The Acam TDC ICs  (http://www.acam.de) have a resolution of a few tens
of ps and a range of up to 200ms or so depending on the chip.
These can easily be interfaced to most micros.


Bruce Griffiths wrote:
> Steve
>
> If we take TvB's measurements on a Thunderbolt as some guide as to what
> to expect:
> http://www.leapsecond.com/pages/tbolt-tc/
>
> Then to make meaningful measurements on a Thunderbolt for example one needs:
>
> 1) An independent frequency standard with an MDEV better than 1E-12 or
> so for  1 s 
> 2) A means of measuring MDEV with a resolution and internal noise <<
> 1E-12 1s < Tau < 1000 s
>
> If one relaxes the Tau range to say 100s < tau < 1000s, then a wider
> range of techniques that have adequate resolution are available.
> For most GPSDOs the relevant loop time constant will be somewhere within
> the (100 - 1000) s range.
>
> One point often missed when quoting/plotting MDEV, ADEV measures is the
> measurement system noise bandwidth.
> The ADEV and MDEV measures are, in general, dependent on the measurement
> system noise bandwidth.
> Different systems with different noise bandwidths measuring the relative
> ADEV or MDEV of the same pair of OCXOs will produce different results
> for ADEV, MDEV.
>
> Possible measurement systems:
>
> 1) Phase comparator directly comparing phases of the 2 (10MHz?) sources.
> The system can have a well defined noise bandwidth together with
> adequate resolution if the phase comparator output drives an ADC with a
> resolution of 12 bits or more ( a sigma delta ADC is perhaps the most
> suitable). However the frequencies of the 2 sources must match closely
> and in the case of digital phase detectors the non linearity at the ends
> of the range should be avoided.
>
> 2) Heterodyne system where a low noise offset oscillator is used to mix
> down to a beat frequency in the audio range.
> The beat frequency output is low pass filtered and amplified before
> driving either:
>
> A) a sound card  the samples from which are processed to  derive  the 
> phase  of the beat frequency.
>
> B) A well designed cascaded amplifier limiter low pass filter system
> that progressively amplifies the beat frequency signal. The output stage
> is a linear comparator and line driver which drives a conventional time
> interval counter with a resolution of 100ns or better. Using the beat
> frequency output to drive the counter directly results in excessive noise.
>
> 3) Dual mixer system with an offset oscillator the performance
> requirements of which are relaxed somewhat because only the differential
> phase shift between the 2 beat frequency outputs is of interest.
>
> Whilst in principle a high resolution (100ps or better) counter with
> interpolator could be employed to measure the phase of the divided down
> output of the UUT with respect to the standard, the system noise
> bandwidth is large and ill defined unless one resorts to crystal and/or
> passive RC or LC filters etc with their attendant phase stability problems.
>
> Lacking a suitable frequency standard the best you can do is log the
> phase and frequency errors of the thunderbolt when the OCXO is free
> running and plot the resultant MDEV.
> The best value for the loop time constant should be somewhere in the
> close to the value of Tau corresponding to the location of the minimum
> value of MDEV.
> Perhaps TvB can help by making measurements of the free running MDEV of
> a Thunderbolt as measured by the Thunderbolt itself to check the
> viability of this method of setting the loop TC.
>
> NOTES:
>
> 1) Assembling a high resolution timestamping counter with 100ps or so
> resolution should be reasonably practical.
>
> 2) Designing a optimised bandpass slope amplifier limiter cascade is
> relatively straightforward.
>
> 3) Optical or equivalent isolation is critical. Where mixers are used
> selecting one which allows the IF ports to be isolated at low
> frequencies is best - Minicircuits have several through-hole models that
> allow this.
>
> 4) The real stumbling block is obtaining a suitable reference.
> An FTS1200 or an OSA8607 may be suitable, however these are either rare
> or expensive.
> Some rubidium standards are also suitable.
> TvB only appears to have ADEV plots for the LPRO, however since MDEV is
> somewhat lower than ADEV an LPRO may well be suitable.
>
> 5) Using a sound card to timestamp beat frequency zero crossings or an
> equivalent technique is the most flexible and reliable provided that a
> high resolution sound card is used.
> Such a sound card can also be used for phase noise measurements for
> offset frequencies in the 20Hz to 20kHz range.
> Some care is required to keep mains related spurs sufficiently low. I
> have obtained mains related spur levels below 1uV rms by suitably
> arranging the 6m input cables for a bala

Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Steve Rooke]

Bruce,

Thanks for the detailed rundown. Looking at the picket-fence method,
this looks possible for me but I will have to get hold of the
reference standard. I have a Racal-Dana 1992 with IEEE488 but need to
get an interface card for the PC end. These are fairly cheap to buy.

You spoke about some types of rubidium standards being suitable, would
you care to elaborate on that please? Would something like an Efratom
FRS be suitable?  Generating the picket-fence itself should not be
hard as long as care is taken not to introduce noise. Do you have any
links to articles on the design for the
mixer/zero-crossing/square-wave beat circuit? One question, assuming
that I have a 10MHz reference standard and I'm measuring a 10MHz dut,
how do I arrange for them to be about 1Hz apart, given that we are
measuring for accuracy here? 1HZ different would make the accuracy
1E-7 out anyway, or am I missing something here?

So the real thing for the budget-conscious time-nut seems to be the
reference standard.  The ocxos you spoke about do seem to be on the
rare/expensive side and are an order of magnitude or two better than
the Option 4E I have in the 1992.

73, Steve

2009/1/9 Bruce Griffiths :
> Addendum:
>
> Timestamping using a conventioanl gated counter is easily accomplished
> using Greenhall's picket fence technique:
> http://horology.jpl.nasa.gov/papers/picket_uffc.pdf
>
> The Acam TDC ICs  (http://www.acam.de) have a resolution of a few tens
> of ps and a range of up to 200ms or so depending on the chip.
> These can easily be interfaced to most micros.
>
>
> Bruce Griffiths wrote:
>> Steve
>>
>> If we take TvB's measurements on a Thunderbolt as some guide as to what
>> to expect:
>> http://www.leapsecond.com/pages/tbolt-tc/
>>
>> Then to make meaningful measurements on a Thunderbolt for example one needs:
>>
>> 1) An independent frequency standard with an MDEV better than 1E-12 or
>> so for  1 s >
>> 2) A means of measuring MDEV with a resolution and internal noise <<
>> 1E-12 1s < Tau < 1000 s
>>
>> If one relaxes the Tau range to say 100s < tau < 1000s, then a wider
>> range of techniques that have adequate resolution are available.
>> For most GPSDOs the relevant loop time constant will be somewhere within
>> the (100 - 1000) s range.
>>
>> One point often missed when quoting/plotting MDEV, ADEV measures is the
>> measurement system noise bandwidth.
>> The ADEV and MDEV measures are, in general, dependent on the measurement
>> system noise bandwidth.
>> Different systems with different noise bandwidths measuring the relative
>> ADEV or MDEV of the same pair of OCXOs will produce different results
>> for ADEV, MDEV.
>>
>> Possible measurement systems:
>>
>> 1) Phase comparator directly comparing phases of the 2 (10MHz?) sources.
>> The system can have a well defined noise bandwidth together with
>> adequate resolution if the phase comparator output drives an ADC with a
>> resolution of 12 bits or more ( a sigma delta ADC is perhaps the most
>> suitable). However the frequencies of the 2 sources must match closely
>> and in the case of digital phase detectors the non linearity at the ends
>> of the range should be avoided.
>>
>> 2) Heterodyne system where a low noise offset oscillator is used to mix
>> down to a beat frequency in the audio range.
>> The beat frequency output is low pass filtered and amplified before
>> driving either:
>>
>> A) a sound card  the samples from which are processed to  derive  the
>> phase  of the beat frequency.
>>
>> B) A well designed cascaded amplifier limiter low pass filter system
>> that progressively amplifies the beat frequency signal. The output stage
>> is a linear comparator and line driver which drives a conventional time
>> interval counter with a resolution of 100ns or better. Using the beat
>> frequency output to drive the counter directly results in excessive noise.
>>
>> 3) Dual mixer system with an offset oscillator the performance
>> requirements of which are relaxed somewhat because only the differential
>> phase shift between the 2 beat frequency outputs is of interest.
>>
>> Whilst in principle a high resolution (100ps or better) counter with
>> interpolator could be employed to measure the phase of the divided down
>> output of the UUT with respect to the standard, the system noise
>> bandwidth is large and ill defined unless one resorts to crystal and/or
>> passive RC or LC filters etc with their attendant phase stability problems.
>>
>> Lacking a suitable frequency standard the best you can do is log the
>> phase and frequency errors of the thunderbolt when the OCXO is free
>> running and plot the resultant MDEV.
>> The best value for the loop time constant should be somewhere in the
>> close to the value of Tau corresponding to the location of the minimum
>> value of MDEV.
>> Perhaps TvB can help by making measurements of the free running MDEV of
>> a Thunderbolt as measured by the Thunderbolt itself to check the
>> viability of this method of setting the lo

[time-nuts] Sound cards

[Rex]

In the uber-thread "Sub Pico Second Phase logger", this exchange took 
place on 12/16:

Bruce Griffiths wrote:
 >
 > Joseph M Gwinn wrote:
 >>
 >> time-nuts-boun...@febo.com wrote on 12/15/2008 06:42:59 PM:
 >>>
 >>> I've also looked at the specs for several other high end sound cards.
 >>> Quite a few only have single ended inputs.
 >>> Maybe, I should document the various cards and highlight their
 >>> shortcomings etc for this application.
 >>>
 >> That would be very useful.
 >>  
 > I'll start on this shortly.

Maybe I lost track and missed something, but I don't think I ever saw 
more on the subject of specific high-end sound cards that might be 
useful for nutty measurements.

I'd be interested to hear what any of the group has to share about 
relative merits of current sound cards that can be interfaced for 
measurements like what was being discussed in that earlier thread. (And 
some before and since.)

 From my own point of view, I'd most like to hear about any that are 
external -- connected by USB or 1394, rather than an internal card. This 
makes it more portable and easier to move between different PC's.

Bruce or anyone, got more to share?



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Re: [time-nuts] 20Hz p-p / 24 hours with a Mini-T

[Mike Feher]

Mike -

You may want to mention that this requirement is to be met at 30.5 GHz.
Regards - Mike

 
 
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
 
 
-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Miguel Checa
Sent: Friday, January 09, 2009 1:34 AM
To: time-nuts@febo.com
Subject: [time-nuts] 20Hz p-p / 24 hours with a Mini-T

Hi group!

I need some opinions, counsel, help, whatever you can send my way:

I need to maintain the Mini-T within 20 Hz p-p in a 24 h period. I use 
T=450 and all is well until the thing starts to lose satellites one by 
one and goes into holdover and after a while, the VCO voltage jumps to 
the start value and with it the frequency (up to -150Hz).

The antenna is not in a good place and it can't be moved, but if I 
restart the Mini-T, all satellites that were grayed out come alive and 
strong. Any clues?

Thanks,

Miguel
W4/LU9AXC



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Re: [time-nuts] Sound cards

[John Ackermann N8UR]

Rex said the following on 01/09/2009 06:37 AM:

> Maybe I lost track and missed something, but I don't think I ever saw 
> more on the subject of specific high-end sound cards that might be 
> useful for nutty measurements.
> 
> I'd be interested to hear what any of the group has to share about 
> relative merits of current sound cards that can be interfaced for 
> measurements like what was being discussed in that earlier thread. (And 
> some before and since.)
> 
>  From my own point of view, I'd most like to hear about any that are 
> external -- connected by USB or 1394, rather than an internal card. This 
> makes it more portable and easier to move between different PC's.

[Shameless Plug]

One very interesting possibility is the HPSDR (High Performance Software 
Defined Radio) boards called Ozy and Janus.  Together with a passive 
backplane called Atlas, they provide an extremely high performance 
ADC/DAC that supports sampling to 192k and output via USB.  The system 
was designed for use as the interface between a PC and an SDR and 
special attention was paid to low noise and flat frequency response.  I 
am not certain, but I *think* that the inputs are DC coupled.

The two boards, assembled and tested, run about $320, with a discount 
for TAPR members.  The backplane is a fairly simple kit (lots of 
connector pins to solder, but not much complexity) that sells for $28, 
also with a discount for TAPR members.  Bare boards, but not kits, for 
Ozy and Janus are also available for the adventurous.

I'm not aware of anyone using this system for T&F work, but it has some 
interesting possibilities.

[/Shameless Plug]

John

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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Tom Van Baak]

> 4) The real stumbling block is obtaining a suitable reference.
> An FTS1200 or an OSA8607 may be suitable, however these are either rare
> or expensive.
> Some rubidium standards are also suitable.

Bruce,

Note that my Tbolt time constant plots were made using just a
58503B GPSDO as the reference; not something more exotic.

/tvb



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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Magnus Danielson]

Bruce Griffiths skrev:
> Steve
> 
> If we take TvB's measurements on a Thunderbolt as some guide as to what
> to expect:
> http://www.leapsecond.com/pages/tbolt-tc/
> 
> Then to make meaningful measurements on a Thunderbolt for example one needs:
> 
> 1) An independent frequency standard with an MDEV better than 1E-12 or
> so for  1 s  
> 2) A means of measuring MDEV with a resolution and internal noise <<
> 1E-12 1s < Tau < 1000 s
> 
> If one relaxes the Tau range to say 100s < tau < 1000s, then a wider
> range of techniques that have adequate resolution are available.
> For most GPSDOs the relevant loop time constant will be somewhere within
> the (100 - 1000) s range.

I think it is of interest to measure the 10s - 10 ks range.

> One point often missed when quoting/plotting MDEV, ADEV measures is the
> measurement system noise bandwidth.
> The ADEV and MDEV measures are, in general, dependent on the measurement
> system noise bandwidth.
> Different systems with different noise bandwidths measuring the relative
> ADEV or MDEV of the same pair of OCXOs will produce different results
> for ADEV, MDEV.

There is another mistake being done regularly is not to compensate for 
frequency drift. ADEV, MDEV and TDEV measures is insensitive to phase 
offset and frequency offset, where as drift goes straigh thru, which is 
even very easy to show by manually insertion of a linear model into the 
respective formulas. On several occasions I have shown that the linear 
drift apparent in peoples measurements is where their naive ADEV 
calculations "floors out" where as a compensated dataset keeps going 
further down. When using a Rubidium as reference for longer taus, such 
considerations needs to be done, but it remains purely a post-processing 
aspect on the TIE data.

> Possible measurement systems:
> 
> 1) Phase comparator directly comparing phases of the 2 (10MHz?) sources.
> The system can have a well defined noise bandwidth together with
> adequate resolution if the phase comparator output drives an ADC with a
> resolution of 12 bits or more ( a sigma delta ADC is perhaps the most
> suitable). However the frequencies of the 2 sources must match closely
> and in the case of digital phase detectors the non linearity at the ends
> of the range should be avoided.
> 
> 2) Heterodyne system where a low noise offset oscillator is used to mix
> down to a beat frequency in the audio range.
> The beat frequency output is low pass filtered and amplified before
> driving either:
> 
> A) a sound card  the samples from which are processed to  derive  the 
> phase  of the beat frequency.
> 
> B) A well designed cascaded amplifier limiter low pass filter system
> that progressively amplifies the beat frequency signal. The output stage
> is a linear comparator and line driver which drives a conventional time
> interval counter with a resolution of 100ns or better. Using the beat
> frequency output to drive the counter directly results in excessive noise.
> 
> 3) Dual mixer system with an offset oscillator the performance
> requirements of which are relaxed somewhat because only the differential
> phase shift between the 2 beat frequency outputs is of interest.
> 
> Whilst in principle a high resolution (100ps or better) counter with
> interpolator could be employed to measure the phase of the divided down
> output of the UUT with respect to the standard, the system noise
> bandwidth is large and ill defined unless one resorts to crystal and/or
> passive RC or LC filters etc with their attendant phase stability problems.
> 
> Lacking a suitable frequency standard the best you can do is log the
> phase and frequency errors of the thunderbolt when the OCXO is free
> running and plot the resultant MDEV.
> The best value for the loop time constant should be somewhere in the
> close to the value of Tau corresponding to the location of the minimum
> value of MDEV.
> Perhaps TvB can help by making measurements of the free running MDEV of
> a Thunderbolt as measured by the Thunderbolt itself to check the
> viability of this method of setting the loop TC.

What I have been pondering over is what story does the time deviations 
of the ThunderBolt itself says. Just recording that over time and do the 
ADEV/MDEV dance would be kind of interesting.

> NOTES:
> 
> 1) Assembling a high resolution timestamping counter with 100ps or so
> resolution should be reasonably practical.
> 
> 2) Designing a optimised bandpass slope amplifier limiter cascade is
> relatively straightforward.
> 
> 3) Optical or equivalent isolation is critical. Where mixers are used
> selecting one which allows the IF ports to be isolated at low
> frequencies is best - Minicircuits have several through-hole models that
> allow this.

I migth add that it may not be apparent from their datasheets. I have 
Minicircuits mixers which is not documented to be isolated, but when 
looking at them closely you discover that they are isolated and that 
their foot-pattern is also very n

Re: [time-nuts] Sound cards

[Eric Williams]

I've been using a Edirol FA-66, a firewire box with two balanced inputs 
plus four more unbalanced.  I think it can handle 192ks/24bit on 4 
channels.  A lot of hams use it for software defined radios, but I just 
know it has better sound, especially the lows, for playing MP3s compared 
to most sound cards and iPods.

Rex wrote:
> I'd be interested to hear what any of the group has to share about 
> relative merits of current sound cards that can be interfaced for 
> measurements like what was being discussed in that earlier thread. (And 
> some before and since.)
>
>  From my own point of view, I'd most like to hear about any that are 
> external -- connected by USB or 1394, rather than an internal card. This 
> makes it more portable and easier to move between different PC's.
>   


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Re: [time-nuts] PCM61P

[EWKehren]

Does any one know where I can buy two PCM61P or AD1861? Thank you. Bert  
Kehren WB5MZJ
**New year...new news.  Be the first to know what is making 
headlines. (http://www.aol.com/?ncid=emlcntaolcom0026)
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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[WarrenS]

>> What would it take as a minimum for ordinary time-nuts  to be able  
>> to perform an ADEV test on their ocxo's and gpsdo's for phase stability at 
>> "home", 

I have noticed that Given enough expertise, anything can be made more 
complicated than need be.

For doing noise testing, there is an option to an expensive osc reference, that 
has been pointed out many times before. Its advantages is, that unlike other 
reference standards this one does not have a limit in how low it can measure, 
and most time-nuts seem to already one or more laying around. The alternative 
is to just use another one of the same things you are testing (or ANY thing 
better).
When comparing two independent noise sources, you get an answer that is the RMS 
sum of the two. That is the answer will be up to 1.414 times the noise of the 
worse one. It's not too hard to find which is the worse one if you need to with 
a few more test.

There are also some simple analog alternatives for measuring Phase noise that 
do not need high resolution Digital TIC, time stamp etc. and can give higher 
resolution results. I use a XOR phase detector, an analog filter and a radio 
shack multimeter with PC interface capability.

The ADEV, ODEV and MDEV can then be calculated from the text file data using 
any of the many great downloadable programs that are available .

The 2G test with a strip chart record of the EFC can be used as a simple way to 
measure the control loop Time constant and see how the control loop responses 
to an Osc step function error.

Another interesting and useful effect that can be used if one is careful 
interrupting the results is the fact that common errors will tend to cancel.
If you compare the noise of two different PLL controlled Osc driven by the SAME 
1PPS signal, you will see Just the effect of the control loops and Osc and NOT 
the effect of the 1pps GPS noise itself. Not what you really want to know when 
matching an OSC's noise to a GPS signal, but it can provide some interesting 
insights and results about the control loop and Osc.

I do acknowledge that there are limitations in any of the above and many ways 
that it can be done wrong, But it can provide a Simple usable test, and in some 
cases near state of the art testing, for the beginning time-nut that has not 
yet collected all the great test equipment that is so often referred to.

WarrenS
***

- Original Message - 
From: "Steve Rooke" 
To: "Discussion of precise time and frequency measurement" 
Sent: Friday, January 09, 2009 3:18 AM
Subject: Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]


> Bruce,
> 
> Thanks for the detailed rundown. Looking at the picket-fence method,
> this looks possible for me but I will have to get hold of the
> reference standard. I have a Racal-Dana 1992 with IEEE488 but need to
> get an interface card for the PC end. These are fairly cheap to buy.
> 
> You spoke about some types of rubidium standards being suitable, would
> you care to elaborate on that please? Would something like an Efratom
> FRS be suitable?  Generating the picket-fence itself should not be
> hard as long as care is taken not to introduce noise. Do you have any
> links to articles on the design for the
> mixer/zero-crossing/square-wave beat circuit? One question, assuming
> that I have a 10MHz reference standard and I'm measuring a 10MHz dut,
> how do I arrange for them to be about 1Hz apart, given that we are
> measuring for accuracy here? 1HZ different would make the accuracy
> 1E-7 out anyway, or am I missing something here?
> 
> So the real thing for the budget-conscious time-nut seems to be the
> reference standard.  The ocxos you spoke about do seem to be on the
> rare/expensive side and are an order of magnitude or two better than
> the Option 4E I have in the 1992.
> 
> 73, Steve
> 
> 2009/1/9 Bruce Griffiths :
>> Addendum:
>>
>> Timestamping using a conventioanl gated counter is easily accomplished
>> using Greenhall's picket fence technique:
>> http://horology.jpl.nasa.gov/papers/picket_uffc.pdf
>>
>> The Acam TDC ICs  (http://www.acam.de) have a resolution of a few tens
>> of ps and a range of up to 200ms or so depending on the chip.
>> These can easily be interfaced to most micros.
>>
>>
>> Bruce Griffiths wrote:
>>> Steve
>>>
>>> If we take TvB's measurements on a Thunderbolt as some guide as to what
>>> to expect:
>>> http://www.leapsecond.com/pages/tbolt-tc/
>>>
>>> Then to make meaningful measurements on a Thunderbolt for example one needs:
>>>
>>> 1) An independent frequency standard with an MDEV better than 1E-12 or
>>> so for  1 s >>
>>> 2) A means of measuring MDEV with a resolution and internal noise <<
>>> 1E-12 1s < Tau < 1000 s
>>>
>>> If one relaxes the Tau range to say 100s < tau < 1000s, then a wider
>>> range of techniques that have adequate resolution are available.
>>> For most GPSDOs the relevant loop time constant will be somewhere within
>>> the (100 - 1000) s range.
>>>
>>> One point of

Re: [time-nuts] 20Hz p-p / 24 hours with a Mini-T

[SAIDJACK]

Hi Miguel,
 
mike mentioned that this is for an 30.5GHz application?
 
If it is for the Government Ka-band Terminal application then you may not  be 
able to use Trimble for that. They apparently cannot meet the  spec due to 
crystal jumps on their units.
 
Sorry for the shameless promotion, but we have a product that  is qualified 
to meet that spec. Contact me offline if you are  interested.
 
bye,
Said
 
 
 
 
 
In a message dated 1/8/2009 22:35:23 Pacific Standard Time, m...@checa.us  
writes:

Hi  group!

I need some opinions, counsel, help, whatever you can send my  way:

I need to maintain the Mini-T within 20 Hz p-p in a 24 h period. I  use 
T=450 and all is well until the thing starts to lose satellites one by  
one and goes into holdover and after a while, the VCO voltage jumps to  
the start value and with it the frequency (up to -150Hz).

The  antenna is not in a good place and it can't be moved, but if I 
restart the  Mini-T, all satellites that were grayed out come alive and 
strong. Any  clues?

Thanks,

Miguel
W4/LU9AXC


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Re: [time-nuts] Sound cards

[Bruce Griffiths]

Eric Williams wrote:
> I've been using a Edirol FA-66, a firewire box with two balanced inputs 
> plus four more unbalanced.  I think it can handle 192ks/24bit on 4 
> channels.  A lot of hams use it for software defined radios, but I just 
> know it has better sound, especially the lows, for playing MP3s compared 
> to most sound cards and iPods.
>
> Rex wrote:
>   
>> I'd be interested to hear what any of the group has to share about 
>> relative merits of current sound cards that can be interfaced for 
>> measurements like what was being discussed in that earlier thread. (And 
>> some before and since.)
>>
>>  From my own point of view, I'd most like to hear about any that are 
>> external -- connected by USB or 1394, rather than an internal card. This 
>> makes it more portable and easier to move between different PC's.
>>   
>> 
>
>
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> and follow the instructions there.
>
>   
Like many external Firewire sound boxes it has +48V phantom power
available, which can be something of a hazard for this application
unless all external preamps etc are designed to survive accidental
application of +48V to their outputs.

It also has a relatively low maximum input (+4dBu ~1.2Vrms) making it
perhaps a little less robust than one with a

Bruce

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Re: [time-nuts] Sound cards

[Bruce Griffiths]

Rex wrote:
> In the uber-thread "Sub Pico Second Phase logger", this exchange took 
> place on 12/16:
>
> Bruce Griffiths wrote:
>  >
>  > Joseph M Gwinn wrote:
>  >>
>  >> time-nuts-boun...@febo.com wrote on 12/15/2008 06:42:59 PM:
>  >>>
>  >>> I've also looked at the specs for several other high end sound cards.
>  >>> Quite a few only have single ended inputs.
>  >>> Maybe, I should document the various cards and highlight their
>  >>> shortcomings etc for this application.
>  >>>
>  >> That would be very useful.
>  >>  
>  > I'll start on this shortly.
>
> Maybe I lost track and missed something, but I don't think I ever saw 
> more on the subject of specific high-end sound cards that might be 
> useful for nutty measurements.
>
> I'd be interested to hear what any of the group has to share about 
> relative merits of current sound cards that can be interfaced for 
> measurements like what was being discussed in that earlier thread. (And 
> some before and since.)
>
>  From my own point of view, I'd most like to hear about any that are 
> external -- connected by USB or 1394, rather than an internal card. This 
> makes it more portable and easier to move between different PC's.
>
> Bruce or anyone, got more to share?
>
>
>
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>
>   
I did start compiling info on sound cards and boxes that are suitable.
However I have yet to find a suitable simple way of presenting it.
A spreadsheet doesnt work that well.
I'll look at this again.

Bruce

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[time-nuts] Enrico Rubiola's new book

[John Miles]

Phase Noise and Frequency Stability in Oscillators:
http://www.amazon.com/gp/product/0521886775/

The UPS driver handed it to me 30 seconds ago, and I can already give it a
favorable review after opening it to a random page.  Exercise 6.2 on page
191: "Hack as many microwave oscillators as you can."

This book -- which I can immediately tell isn't long, dry, or
unreasonably-expensive -- seems like an effective marriage of math and
pragmatics, likely because it's based on the author's JPL tutorials and
industry lectures.  Looking through it, I'm seeing a lot of PN graphs which
are annotated with explanations of corner frequencies, slopes, and
comparisons with other sources, which are (IMHO) a great way to understand
what to expect from your own measurements.

Anyway: the book looks very approachable, relevant, and well-grounded in
hardware and processes often discussed on the list.  I'm looking forward to
spending some more time with it.

-- john, KE5FX


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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Bruce Griffiths]

Warren

WarrenS wrote:
>>> What would it take as a minimum for ordinary time-nuts  to be able  
>>> to perform an ADEV test on their ocxo's and gpsdo's for phase stability at 
>>> "home", 
>>>   
>
> I have noticed that Given enough expertise, anything can be made more 
> complicated than need be.
>
> For doing noise testing, there is an option to an expensive osc reference, 
> that has been pointed out many times before. Its advantages is, that unlike 
> other reference standards this one does not have a limit in how low it can 
> measure, and most time-nuts seem to already one or more laying around. The 
> alternative is to just use another one of the same things you are testing (or 
> ANY thing better).
> When comparing two independent noise sources, you get an answer that is the 
> RMS sum of the two. That is the answer will be up to 1.414 times the noise of 
> the worse one. It's not too hard to find which is the worse one if you need 
> to with a few more test.
>
>   

The critical requirement is that the 2 standards being compared are
statistically independent.
Comparing a pair of Thunderbolts GPSDOs with similar time constants and
damping will give optimistic results for Tau comparable with or greater
than the loop time constant.
Its is even better is to use 3 or more similar standards simultaneously
logging phase differences between the various pairs (0.5*N(N-1) pairs
for N standards).
It is then possible to obtain estimates for ADEV, MDEV etc for each
standard.
> There are also some simple analog alternatives for measuring Phase noise that 
> do not need high resolution Digital TIC, time stamp etc. and can give higher 
> resolution results. I use a XOR phase detector, an analog filter and a radio 
> shack multimeter with PC interface capability.
>
>   

Like all digital phase detectors its best to avoid, if possible, the
nonlinearity inherent at the ends of the range.

> The ADEV, ODEV and MDEV can then be calculated from the text file data using 
> any of the many great downloadable programs that are available .
>
> The 2G test with a strip chart record of the EFC can be used as a simple way 
> to measure the control loop Time constant and see how the control loop 
> responses to an Osc step function error.
>
> Another interesting and useful effect that can be used if one is careful 
> interrupting the results is the fact that common errors will tend to cancel.
> If you compare the noise of two different PLL controlled Osc driven by the 
> SAME 1PPS signal, you will see Just the effect of the control loops and Osc 
> and NOT the effect of the 1pps GPS noise itself. Not what you really want to 
> know when matching an OSC's noise to a GPS signal, but it can provide some 
> interesting insights and results about the control loop and Osc.
>
> I do acknowledge that there are limitations in any of the above and many ways 
> that it can be done wrong, But it can provide a Simple usable test, and in 
> some cases near state of the art testing, for the beginning time-nut that has 
> not yet collected all the great test equipment that is so often referred to.
>
> WarrenS
> ***
>
> - Original Message - 
> From: "Steve Rooke" 
> To: "Discussion of precise time and frequency measurement" 
> 
> Sent: Friday, January 09, 2009 3:18 AM
> Subject: Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]
>
>
>   
>> Bruce,
>>
>> Thanks for the detailed rundown. Looking at the picket-fence method,
>> this looks possible for me but I will have to get hold of the
>> reference standard. I have a Racal-Dana 1992 with IEEE488 but need to
>> get an interface card for the PC end. These are fairly cheap to buy.
>>
>> You spoke about some types of rubidium standards being suitable, would
>> you care to elaborate on that please? Would something like an Efratom
>> FRS be suitable?  Generating the picket-fence itself should not be
>> hard as long as care is taken not to introduce noise. Do you have any
>> links to articles on the design for the
>> mixer/zero-crossing/square-wave beat circuit? One question, assuming
>> that I have a 10MHz reference standard and I'm measuring a 10MHz dut,
>> how do I arrange for them to be about 1Hz apart, given that we are
>> measuring for accuracy here? 1HZ different would make the accuracy
>> 1E-7 out anyway, or am I missing something here?
>>
>> So the real thing for the budget-conscious time-nut seems to be the
>> reference standard.  The ocxos you spoke about do seem to be on the
>> rare/expensive side and are an order of magnitude or two better than
>> the Option 4E I have in the 1992.
>>
>> 73, Steve
>>
>> 2009/1/9 Bruce Griffiths :
>> 
>>> Addendum:
>>>
>>> Timestamping using a conventioanl gated counter is easily accomplished
>>> using Greenhall's picket fence technique:
>>> http://horology.jpl.nasa.gov/papers/picket_uffc.pdf
>>>
>>> The Acam TDC ICs  (http://www.acam.de) have a resolution of a few tens
>>> of ps and a range of up to 200ms or so dependi

Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Bruce Griffiths]

Tom Van Baak wrote:
>> 4) The real stumbling block is obtaining a suitable reference.
>> An FTS1200 or an OSA8607 may be suitable, however these are either rare
>> or expensive.
>> Some rubidium standards are also suitable.
>> 
>
> Bruce,
>
> Note that my Tbolt time constant plots were made using just a
> 58503B GPSDO as the reference; not something more exotic.
>
> /tvb
>
>   
Tom

Doesnt that introduce some correlations for larger tau as both the
Thunderbolt and the 58503B are both locked to GPS?

Bruce

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Re: [time-nuts] Enrico Rubiola's new book

[Lux, James P]

I like how you can get *Used* copies from Amazon for more than twice the brand 
new price (even from the exact same seller!).  Surely some sort of artifact of 
the used book sellers' pricing algorithms.  (or, maybe, you're paying for 
someone to buy the book new, open it up, scuff the covers a bit, page through 
it while sipping a Caffe Latte, and then putting into the box)

http://www.amazon.com/gp/offer-listing/0521886775/ref=dp_olp_used?ie=UTF8&condition=used

Jim

> -Original Message-
> From: time-nuts-boun...@febo.com
> [mailto:time-nuts-boun...@febo.com] On Behalf Of John Miles
> Sent: Friday, January 09, 2009 1:09 PM
> To: time-nuts@febo.com
> Subject: [time-nuts] Enrico Rubiola's new book
>
> Phase Noise and Frequency Stability in Oscillators:
> http://www.amazon.com/gp/product/0521886775/
>
>

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Re: [time-nuts] Enrico Rubiola's new book

[Jeffrey Pawlan]

I had hoped to meet him at the UFFC last Spring but he cancelled at the last 
moment owing to a family emergency.

Take a look at his webpage:

http://www.femto-st.fr/~rubiola/



Jeffrey Pawlan  WA6KBL
sr member IEEE UFFS & MTT


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Re: [time-nuts] Sound cards

[Bruce Griffiths]

John

John Ackermann N8UR wrote:
> Rex said the following on 01/09/2009 06:37 AM:
>
>   
>> Maybe I lost track and missed something, but I don't think I ever saw 
>> more on the subject of specific high-end sound cards that might be 
>> useful for nutty measurements.
>>
>> I'd be interested to hear what any of the group has to share about 
>> relative merits of current sound cards that can be interfaced for 
>> measurements like what was being discussed in that earlier thread. (And 
>> some before and since.)
>>
>>  From my own point of view, I'd most like to hear about any that are 
>> external -- connected by USB or 1394, rather than an internal card. This 
>> makes it more portable and easier to move between different PC's.
>> 
>
> [Shameless Plug]
>
> One very interesting possibility is the HPSDR (High Performance Software 
> Defined Radio) boards called Ozy and Janus.  Together with a passive 
> backplane called Atlas, they provide an extremely high performance 
> ADC/DAC that supports sampling to 192k and output via USB.  The system 
> was designed for use as the interface between a PC and an SDR and 
> special attention was paid to low noise and flat frequency response.  I 
> am not certain, but I *think* that the inputs are DC coupled.
>
>   
Not according to the circuit schematic.
The input coupling is 10uF + 10K with a corresponding low frequency 3dB
cutoff of 1.6Hz.
Default inputs are single ended, balanced inputs are accessible via a
pair of headers.
Input full scale is that of the AKM5394 ADC chip (1.7Vrms nominal).
There is a small dc offset between the differential inputs to the
AKM5394 to eliminate an idle tone related spurious output.

> The two boards, assembled and tested, run about $320, with a discount 
> for TAPR members.  The backplane is a fairly simple kit (lots of 
> connector pins to solder, but not much complexity) that sells for $28, 
> also with a discount for TAPR members.  Bare boards, but not kits, for 
> Ozy and Janus are also available for the adventurous.
>
> I'm not aware of anyone using this system for T&F work, but it has some 
> interesting possibilities.
>
> [/Shameless Plug]
>
> John
>
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>
>   
Bruce

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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[John Miles]

I'd like to see a similar test conducted against a local Cs clock (and/or
maser), just to get everything on one graph.

-- john, KE5FX

> -Original Message-
> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on
> Behalf Of Bruce Griffiths
> Sent: Friday, January 09, 2009 1:26 PM
> To: Tom Van Baak; Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]
>
>
> Tom Van Baak wrote:
> >> 4) The real stumbling block is obtaining a suitable reference.
> >> An FTS1200 or an OSA8607 may be suitable, however these are either rare
> >> or expensive.
> >> Some rubidium standards are also suitable.
> >>
> >
> > Bruce,
> >
> > Note that my Tbolt time constant plots were made using just a
> > 58503B GPSDO as the reference; not something more exotic.
> >
> > /tvb
> >
> >
> Tom
>
> Doesnt that introduce some correlations for larger tau as both the
> Thunderbolt and the 58503B are both locked to GPS?
>
> Bruce
>
>


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Re: [time-nuts] Enrico Rubiola's new book

[GandalfG8]

 
In a message dated 09/01/2009 21:09:51 GMT Standard Time, jmi...@pop.net  
writes:

Phase  Noise and Frequency Stability in  Oscillators:
http://www.amazon.com/gp/product/0521886775/


---
 
Thanks John for the information, that looks like a very worthwhile  
investment..
 
Apologies if what follows is common knowledge but, whilst performing a  
Google search on the current title, I discovered  that this supersedes a 2005 
draft 
version, "The Leeson effect - Phase  noise in quasilinear oscillators", 
copies of which are  freely, and legally:-), available online.
 
One link to that is...
 
_http://arxiv.org/abs/physics/0502143_ (http://arxiv.org/abs/physics/0502143) 
 
Another interesting link, and where I found the reference to the  earlier 
work, offers some supplementary material to the current book in the  form of 
seminar texts
 
_http://www.femto-st.fr/~rubiola/indexx-oscillator-noise.html_ 
(http://www.femto-st.fr/~rubiola/indexx-oscillator-noise.html) 
 
regards
 
Nigel
GM8PZR
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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Bruce Griffiths]

Steve

The Efratom FRS may be OK, its hard to say without some MDEV measurements.
The specifications only give ADEV for 1s, 10s and 100s.

One way to find out is to compare 3 of them in a 3 cornered hat arrangement.

Bruce

Steve Rooke wrote:
> Bruce,
>
> Thanks for the detailed rundown. Looking at the picket-fence method,
> this looks possible for me but I will have to get hold of the
> reference standard. I have a Racal-Dana 1992 with IEEE488 but need to
> get an interface card for the PC end. These are fairly cheap to buy.
>
> You spoke about some types of rubidium standards being suitable, would
> you care to elaborate on that please? Would something like an Efratom
> FRS be suitable?  Generating the picket-fence itself should not be
> hard as long as care is taken not to introduce noise. Do you have any
> links to articles on the design for the
> mixer/zero-crossing/square-wave beat circuit? One question, assuming
> that I have a 10MHz reference standard and I'm measuring a 10MHz dut,
> how do I arrange for them to be about 1Hz apart, given that we are
> measuring for accuracy here? 1HZ different would make the accuracy
> 1E-7 out anyway, or am I missing something here?
>
> So the real thing for the budget-conscious time-nut seems to be the
> reference standard.  The ocxos you spoke about do seem to be on the
> rare/expensive side and are an order of magnitude or two better than
> the Option 4E I have in the 1992.
>
> 73, Steve
>
> 2009/1/9 Bruce Griffiths :
>   
>> Addendum:
>>
>> Timestamping using a conventioanl gated counter is easily accomplished
>> using Greenhall's picket fence technique:
>> http://horology.jpl.nasa.gov/papers/picket_uffc.pdf
>>
>> The Acam TDC ICs  (http://www.acam.de) have a resolution of a few tens
>> of ps and a range of up to 200ms or so depending on the chip.
>> These can easily be interfaced to most micros.
>>
>>
>> Bruce Griffiths wrote:
>> 
>>> Steve
>>>
>>> If we take TvB's measurements on a Thunderbolt as some guide as to what
>>> to expect:
>>> http://www.leapsecond.com/pages/tbolt-tc/
>>>
>>> Then to make meaningful measurements on a Thunderbolt for example one needs:
>>>
>>> 1) An independent frequency standard with an MDEV better than 1E-12 or
>>> so for  1 s >>
>>> 2) A means of measuring MDEV with a resolution and internal noise <<
>>> 1E-12 1s < Tau < 1000 s
>>>
>>> If one relaxes the Tau range to say 100s < tau < 1000s, then a wider
>>> range of techniques that have adequate resolution are available.
>>> For most GPSDOs the relevant loop time constant will be somewhere within
>>> the (100 - 1000) s range.
>>>
>>> One point often missed when quoting/plotting MDEV, ADEV measures is the
>>> measurement system noise bandwidth.
>>> The ADEV and MDEV measures are, in general, dependent on the measurement
>>> system noise bandwidth.
>>> Different systems with different noise bandwidths measuring the relative
>>> ADEV or MDEV of the same pair of OCXOs will produce different results
>>> for ADEV, MDEV.
>>>
>>> Possible measurement systems:
>>>
>>> 1) Phase comparator directly comparing phases of the 2 (10MHz?) sources.
>>> The system can have a well defined noise bandwidth together with
>>> adequate resolution if the phase comparator output drives an ADC with a
>>> resolution of 12 bits or more ( a sigma delta ADC is perhaps the most
>>> suitable). However the frequencies of the 2 sources must match closely
>>> and in the case of digital phase detectors the non linearity at the ends
>>> of the range should be avoided.
>>>
>>> 2) Heterodyne system where a low noise offset oscillator is used to mix
>>> down to a beat frequency in the audio range.
>>> The beat frequency output is low pass filtered and amplified before
>>> driving either:
>>>
>>> A) a sound card  the samples from which are processed to  derive  the
>>> phase  of the beat frequency.
>>>
>>> B) A well designed cascaded amplifier limiter low pass filter system
>>> that progressively amplifies the beat frequency signal. The output stage
>>> is a linear comparator and line driver which drives a conventional time
>>> interval counter with a resolution of 100ns or better. Using the beat
>>> frequency output to drive the counter directly results in excessive noise.
>>>
>>> 3) Dual mixer system with an offset oscillator the performance
>>> requirements of which are relaxed somewhat because only the differential
>>> phase shift between the 2 beat frequency outputs is of interest.
>>>
>>> Whilst in principle a high resolution (100ps or better) counter with
>>> interpolator could be employed to measure the phase of the divided down
>>> output of the UUT with respect to the standard, the system noise
>>> bandwidth is large and ill defined unless one resorts to crystal and/or
>>> passive RC or LC filters etc with their attendant phase stability problems.
>>>
>>> Lacking a suitable frequency standard the best you can do is log the
>>> phase and frequency errors of the thunderbolt when the OCXO is free
>>> running an

[time-nuts] Z3805A

[James Robbins]

Does anyone have any links to any materials on the Z3805A receiver,
especially as to the RS422 pinouts?  I'm having trouble getting the receiver
to talk with a Sealevel RS232 to USB converter (which works fine with the
Z3801A).  Thanks much.  Jim Robbins, N1JR
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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[WarrenS]

>Bruce said:
> The critical requirement is that the 2 standards being compared are 
> statistically independent.
> Comparing a pair of Thunderbolts GPSDOs with similar time constants and
> damping will give optimistic results for Tau comparable with or greater than 
> the loop time constant.
> Its is even better is to use 3 or more similar standards simultaneously
> logging phase differences between the various pairs (0.5*N(N-1) pairs for N 
> standards).
> It is then possible to obtain estimates for ADEV, MDEV etc for each standard.

The optimistic results at and above the loop time constant, that results even 
when 3 or more units are used, 
is because the noise is then mostly due to the GPS signal itself and NOT the 
local oscillators in the GPSDO.
In effect you are then using the same 1PPS signal into each unit, and any 
common noise on the 
GPS 1PPS signal will cancel and not be seen.
So I think what Bruce is saying is that you can not (or is it should not?) use 
the GPS signal to 
measure the GPS's noise.
But the point is, if you want to compare your GPSDO with different settings, or 
compare it to 
another OCXO, It can be done this way, if you do not have a better ref to use.
You could then add the noise of the GPS nose above the control loop time to 
your 
optimistic results if you want true results at high Tau values.

Also note that having the GPS noise cancle is not necessary a bad thing,  It 
can be a good thing 
especially if the GPS noise is not what it is that you want to measure. 

> Like all digital phase detectors its best to avoid, if possible, the 
> nonlinearity inherent at the ends of the range.

Using a phase detector near its end point (or at its crossover point if there 
is any deadband) 
is something that needs to be avoided. 
The two basic standard ways to insure that just the center of the phase 
detector's range is use:
1) Divide the signals down just enough before sending them to the phase 
detector so that 
the end points is not an issue.  This works when both signals are from devices 
that are 
locked to a common signal such as the GPS.

2) When one of signals is from a non locked source such as a OCXO whose phase 
can drift 
any amount overtime, One of ways to limit phase detector issues, and use just 
the very accurate zero phase point, is to use the Phase detector's output to 
lock the OCXO in a fast control loop and then by knowing the gain of the EFC 
input, the filtered EFC voltage can be use as freq drift information to find 
the ADEV's.

WarrenS

*:
>>> What would it take as a minimum for ordinary time-nuts  to be able  
>>> to perform an ADEV test on their ocxo's and gpsdo's for phase stability at 
>>> "home", 

>Warren wrote:
>> I have noticed that Given enough expertise, anything can be made more 
>> complicated than need be.
>>
>> For doing noise testing, there is an option to an expensive osc reference, 
>> that has been pointed out many times before. Its advantages is, that unlike 
>> other reference 
>> standards this one does not have a limit in how low it can measure, and most 
>> time-nuts seem 
>> to already one or more laying around. 
>> The alternative is to just use another one of the same things you are 
>> testing (or ANY thing better).
>> When comparing two independent noise sources, you get an answer that is the 
>> RMS sum of the two. 
>> That is the answer will be up to 1.414 times the noise of the worse one. 
>> It's not too hard to find 
>> which is the worse one if you need to with a few more test.
>>
>>   
> The critical requirement is that the 2 standards being compared are 
> statistically independent.
> Comparing a pair of Thunderbolts GPSDOs with similar time constants and
> damping will give optimistic results for Tau comparable with or greater than 
> the loop time constant.
> Its is even better is to use 3 or more similar standards simultaneously
> logging phase differences between the various pairs (0.5*N(N-1) pairs for N 
> standards).
> It is then possible to obtain estimates for ADEV, MDEV etc for each standard.

>> There are also some simple analog alternatives for measuring Phase noise 
>> that do not need high 
>> resolution Digital TIC, time stamp etc. and can give higher resolution 
>> results. 
>> I use a XOR phase detector, an analog filter and a radio shack multimeter 
>> with PC interface capability.

> Like all digital phase detectors its best to avoid, if possible, the 
> nonlinearity inherent at the ends of the range.
> 

>> The ADEV, ODEV and MDEV can then be calculated from the text file data using 
>> any of the 
>> many great downloadable programs that are available .
>>
>> The 2G test with a strip chart record of the EFC can be used as a simple way 
>> to measure 
>> the control loop Time constant and see how the control loop responses to an 
>> Osc step function error.
>>
>> Another interesting and useful effect that can be used if one is careful 
>> interrupting the results is the 
>> fact that common

Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Tom Van Baak]

> I'd like to see a similar test conducted against a local Cs clock (and/or
> maser), just to get everything on one graph.
> 
> -- john, KE5FX

It's on the list.

One earlier idea was to measure tc=1 10 100 1000 10k
simultaneously with 5 Thunderbolts, but I suspected that
unit to unit variations among the GPSDO would partially
cloud the results. So that's why I did back-to-back runs
using the same TBolt, same reference, and same TIC for
each run. All I changed was the TC in the GUI, figuring
that was the safest thing to do.

/tvb


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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Tom Van Baak]

> Tom
> 
> Doesnt that introduce some correlations for larger tau as both the
> Thunderbolt and the 58503B are both locked to GPS?
> 
> Bruce

Correct, the choice of reference often has some impact on the plots.

Since I used a GPSDO (a nice one), if the plot extended well
past 10^4 or 10^5 the GPS correlation effects would show up in
the long-term, I think. In that case the plots would start to appear
slightly optimistic.

On the other hand, because I used a GPSDO instead of a maser
reference, the plot I posted appears slightly pessimistic in the
short- and mid-term.

So the main thing about the plot was just how well the difference
between tc=10, 100, 1000 showed up, regardless if the reference
was a maser or a GPSDO. A nice Rb might work too.

That the TC setting was so visible using (only) a GPSDO as a
reference is promising. It means normal time-nuts (oxymoron?)
who don't have cesium or masers lying around have a good
chance to investigate the optimal TC for their GPSDO. Looks
like a 5370 or SR620 would also work for the TI counter.

/tvb


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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Bruce Griffiths]

Warren

Another limitation of such phase detectors is that the 2 frequencies
being compared have to be within a small fraction of 1Hz of one another.
This rules out using a low noise reference that happens to have
drifted/aged out of the adjustment range but which is otherwise OK.

Bruce

WarrenS wrote:
>> Bruce said:
>> The critical requirement is that the 2 standards being compared are 
>> statistically independent.
>> Comparing a pair of Thunderbolts GPSDOs with similar time constants and
>> damping will give optimistic results for Tau comparable with or greater than 
>> the loop time constant.
>> Its is even better is to use 3 or more similar standards simultaneously
>> logging phase differences between the various pairs (0.5*N(N-1) pairs for N 
>> standards).
>> It is then possible to obtain estimates for ADEV, MDEV etc for each standard.
>> 
>
> The optimistic results at and above the loop time constant, that results even 
> when 3 or more units are used, 
> is because the noise is then mostly due to the GPS signal itself and NOT the 
> local oscillators in the GPSDO.
> In effect you are then using the same 1PPS signal into each unit, and any 
> common noise on the 
> GPS 1PPS signal will cancel and not be seen.
> So I think what Bruce is saying is that you can not (or is it should not?) 
> use the GPS signal to 
> measure the GPS's noise.
> But the point is, if you want to compare your GPSDO with different settings, 
> or compare it to 
> another OCXO, It can be done this way, if you do not have a better ref to use.
> You could then add the noise of the GPS nose above the control loop time to 
> your 
> optimistic results if you want true results at high Tau values.
>
> Also note that having the GPS noise cancle is not necessary a bad thing,  It 
> can be a good thing 
> especially if the GPS noise is not what it is that you want to measure. 
>
>   
>> Like all digital phase detectors its best to avoid, if possible, the 
>> nonlinearity inherent at the ends of the range.
>> 
>
> Using a phase detector near its end point (or at its crossover point if there 
> is any deadband) 
> is something that needs to be avoided. 
> The two basic standard ways to insure that just the center of the phase 
> detector's range is use:
> 1) Divide the signals down just enough before sending them to the phase 
> detector so that 
> the end points is not an issue.  This works when both signals are from 
> devices that are 
> locked to a common signal such as the GPS.
>
> 2) When one of signals is from a non locked source such as a OCXO whose phase 
> can drift 
> any amount overtime, One of ways to limit phase detector issues, and use just 
> the very accurate zero phase point, is to use the Phase detector's output to 
> lock the OCXO in a fast control loop and then by knowing the gain of the EFC 
> input, the filtered EFC voltage can be use as freq drift information to find 
> the ADEV's.
>
> WarrenS
>
> *:
>   
Bruce
 What would it take as a minimum for ordinary time-nuts  to be able  
 to perform an ADEV test on their ocxo's and gpsdo's for phase stability at 
 "home", 
 
>
>   
>> Warren wrote:
>> 
>>> I have noticed that Given enough expertise, anything can be made more 
>>> complicated than need be.
>>>
>>> For doing noise testing, there is an option to an expensive osc reference, 
>>> that has been pointed out many times before. Its advantages is, that unlike 
>>> other reference 
>>> standards this one does not have a limit in how low it can measure, and 
>>> most time-nuts seem 
>>> to already one or more laying around. 
>>> The alternative is to just use another one of the same things you are 
>>> testing (or ANY thing better).
>>> When comparing two independent noise sources, you get an answer that is the 
>>> RMS sum of the two. 
>>> That is the answer will be up to 1.414 times the noise of the worse one. 
>>> It's not too hard to find 
>>> which is the worse one if you need to with a few more test.
>>>
>>>   
>>>   
>> The critical requirement is that the 2 standards being compared are 
>> statistically independent.
>> Comparing a pair of Thunderbolts GPSDOs with similar time constants and
>> damping will give optimistic results for Tau comparable with or greater than 
>> the loop time constant.
>> Its is even better is to use 3 or more similar standards simultaneously
>> logging phase differences between the various pairs (0.5*N(N-1) pairs for N 
>> standards).
>> It is then possible to obtain estimates for ADEV, MDEV etc for each standard.
>> 
>
>   
>>> There are also some simple analog alternatives for measuring Phase noise 
>>> that do not need high 
>>> resolution Digital TIC, time stamp etc. and can give higher resolution 
>>> results. 
>>> I use a XOR phase detector, an analog filter and a radio shack multimeter 
>>> with PC interface capability.
>>>   
>
>   
>> Like all digital phase detectors its best to avoid, if possible, the 
>> nonli

Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Bruce Griffiths]

Tom Van Baak wrote:
>> Tom
>>
>> Doesnt that introduce some correlations for larger tau as both the
>> Thunderbolt and the 58503B are both locked to GPS?
>>
>> Bruce
>> 
>
> Correct, the choice of reference often has some impact on the plots.
>
> Since I used a GPSDO (a nice one), if the plot extended well
> past 10^4 or 10^5 the GPS correlation effects would show up in
> the long-term, I think. In that case the plots would start to appear
> slightly optimistic.
>
> On the other hand, because I used a GPSDO instead of a maser
> reference, the plot I posted appears slightly pessimistic in the
> short- and mid-term.
>
> So the main thing about the plot was just how well the difference
> between tc=10, 100, 1000 showed up, regardless if the reference
> was a maser or a GPSDO. A nice Rb might work too.
>
> That the TC setting was so visible using (only) a GPSDO as a
> reference is promising. It means normal time-nuts (oxymoron?)
> who don't have cesium or masers lying around have a good
> chance to investigate the optimal TC for their GPSDO. Looks
> like a 5370 or SR620 would also work for the TI counter.
>
> /tvb
>
>
>   
Tom

What does the MDEV plot for the particular Thunderbolt look like when
the Thunderbolt itself measures the phase error of the its unlocked OCXO
against GPS?

In other words how reliable a guide is setting the loop TC to coincide
with the value of Tau at the minimum of such an MDEV plot?


Bruce

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[time-nuts] ADEV test setup [was GPSDO TC & Damping]

[WarrenS]

Bruce

True, but not a problem for me, because I don't have any like that.
I know you have brought this up many times. Is it a real problem that 
exist enough to even think about? What kind of Osc are you referring to
that is worth keeping even though it can not be adjusted to be on freq. 
How far off is it? 
How do you know it is good enough?
Trick question, why not just continue to use what it is that you tested it 
with? 
Maybe could use the dual 90 deg phase detector system, 
so there is at least one phase signal near the center of the range at all times.
There is probable some simpler solution also.


WarrenS

*

Warren

Another limitation of such phase detectors is that the 2 frequencies
being compared have to be within a small fraction of 1Hz of one another.
This rules out using a low noise reference that happens to have
drifted/aged out of the adjustment range but which is otherwise OK.

Bruce
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Re: [time-nuts] 20Hz p-p / 24 hours with a Mini-T (Mike Feher)

[Miguel Checa]

Mike,

Yes, sorry. 10MHz x 2900 for the LO, +/- 10Hz at 29GHz.

In fact, the mini-t has good stability, it goes down to +/- 6Hz 
---EXCEPT--- when it loses the last satellite and we don't know why it 
does that. With Time constant=3600sec the unit can do +/-3Hz.

As I said, the satellites are there but it uses the best for time, the 
monitor reports all the others as tracked but not used, funny thing is 
the signal (AMU) reported is either 0.8 or 1.0 for all those, my guess 
is the unit ignores them and forgets all about them and when the one in 
use goes down, the mini-t goes to bed...

Trimble said today they have a solution...we'll see. Regards,

Miguel
W4/LU4AXC
> --
>
> Message: 1
> Date: Fri, 9 Jan 2009 08:00:24 -0500
> From: "Mike Feher" 
> Subject: Re: [time-nuts] 20Hz p-p / 24 hours with a Mini-T
> To: "'Discussion of precise time and frequency measurement'"
>   
> Message-ID: 
> Content-Type: text/plain; charset="us-ascii"
>
> Mike -
>
> You may want to mention that this requirement is to be met at 30.5 GHz.
> Regards - Mike
>
>  
>  
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>  
>   
>   

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Re: [time-nuts] GPSDO TC & Damping

[Richard Moore]

On Jan 9, 2009, at 12:10 AM, time-nuts-requ...@febo.com wrote:

> Message: 4
> Date: Fri, 09 Jan 2009 19:18:57 +1300
> From: Bruce Griffiths 
> Subject: Re: [time-nuts] GPSDO TC & Damping

>> Well, like many here, I don't actually have the equipment, especially
>> the reference std., to do these MDEV, ADEV and other analyses, so,
>> since I use the GPSDO for a frequency standard and not for UTC, I
>> thought I'd get the expert opinions. Magnus has several times
>> indicated here that a TC laying somewhere in and around 100 to 1000
>> secs is probably optimum. When I enquired some time back about
>> damping in the TBolt, the consensus seemed to be "leave it at 1.2". I
>> have, but it just seems to me that won't be optimum for a fixed-
>> position, lab-located frequency standard -- at the moment, I'm
>> leaning toward the 0.7to 1.0 area.
>>
>>
> Why, since it has been demonstrated that a damping factor of 1.2 is
> better than one of 0.7 for a particular Thunderbolt this would tend to
> indicate that adjusting the damping without good justification is
> somewhat foolhardy.
> If in fact the phase noise characteristics of your OCXO are similar  
> toi
> the one in the Thunderbolt that Tom measured this would degrade the
> performance.
>
> With no way of measuring the effect of such adjustments you are just
> hoping that your particular Thunderbolt is similar to the one Tom  
> measured.
> Thats not engineering its more like witchcraft.
>
>> Tom's recent chart was quite helpful, especially the 1000 sec curve.
>> Now, I hope that Tom or someone else follows up on the suggestion to
>> track performance vs. damping factor. I do understand that the
>> results for any one GPSDO don't *necessarily* translate to other
>> devices, but they don't necessarily don't, either. At least for the
>> TBolts a lot of us are playing with, one good example (like Tom's)
>> may well put mine in a better ballpark than the ballpark the factory
>> wants it to play in, given the factors that you all have described.
>> Thx everyone for the comments. Look forward to the next round!
>>
>> Dick Moore
>>
> The probability that you will improve the performance significantly
> without a means of measuring the resultant performance is fairly low.
> You will never know if either an improvement or a degradation in
> performance has occurred.
> The one saving grace being that the factory defaults can always be  
> restored.
>
> Bruce

Bruce, thx for the reminder -- my friend and mentor Paul W. Klipsch  
was fond of saying that "You can't make what you can't measure 'cause  
you don't know when you've got it made!" At the same time, all sorts  
of wonderful things have come about thru just fooling around. Again,  
I remark that for all the reasons Tom enumerated -- er, listed -- the  
manufacturer's choice of settings may not be the best choice for a  
particular use. When in a strange country, local enquiry is usually  
recommended. For GPSDOs, a strange country to me, what better place  
to enquire than here?

Dick Moore

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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Bruce Griffiths]

Warren

Yes its a real problem several of us have such OCXOs.
They are typically a few Hz off.
If they can be shown to have low noise and low drift they are worth keeping.
Its a pity to discard such OCXOs just because ones measurement system
cant verify their performance.

The only way to know if such an OCXO is still good enough is to compare
it with a better standard or with a pair of low noise OCXOs using a 3
cornered hat technique.
Unfortunately one can't easily use 3 digital phase detectors plus ADCs
for this unless the associated low pass filter cutoff frequency is
increased.
One would then also need to use something like a sigma delta ADC rather
than a cheap DVM to ensure that the low pass filter output sampling rate
is high enough.
An ADC with an input multiplexer could also be used (several
microprocessor have such ADCs built in).

Such a setup is not that much simpler than using an array of timestamp
counters based on a suitable microprocessor.
A dual mixer scheme would require 6 timestamp counters or 6 simultaneous
sound card inputs.

In principle one could use 3 dividers setup so that the output
transitions of each divider are well separated from the output
transitions of the other dividers.
A standard time interval counter with an external input multiplexer
could then be used in a variation of the picket fence technique to
sequentially time stamp the divider output transitions.


Bruce

WarrenS wrote:
> Bruce
>
> True, but not a problem for me, because I don't have any like that.
> I know you have brought this up many times. Is it a real problem that 
> exist enough to even think about? What kind of Osc are you referring to
> that is worth keeping even though it can not be adjusted to be on freq. 
> How far off is it? 
> How do you know it is good enough?
> Trick question, why not just continue to use what it is that you tested it 
> with? 
> Maybe could use the dual 90 deg phase detector system, 
> so there is at least one phase signal near the center of the range at all 
> times.
> There is probable some simpler solution also.
>
>
> WarrenS
>
> *
>
> Warren
>
> Another limitation of such phase detectors is that the 2 frequencies
> being compared have to be within a small fraction of 1Hz of one another.
> This rules out using a low noise reference that happens to have
> drifted/aged out of the adjustment range but which is otherwise OK.
>
> Bruce
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Re: [time-nuts] GPSDO TC & Damping

[Richard Moore]

On Jan 9, 2009, at 2:24 AM, time-nuts-requ...@febo.com wrote:

> Message: 2
> Date: Fri, 09 Jan 2009 10:27:05 +0100
> From: Magnus Danielson 
> Subject: Re: [time-nuts] GPSDO TC & Damping
>
> Dick,
>
>> Well, like many here, I don't actually have the equipment, especially
>> the reference std., to do these MDEV, ADEV and other analyses, so,
>> since I use the GPSDO for a frequency standard and not for UTC, I
>> thought I'd get the expert opinions. Magnus has several times
>> indicated here that a TC laying somewhere in and around 100 to 1000
>> secs is probably optimum.
>
> I think you have misinterpreted my postings. I never claimed it was
> optimum, or at least never intended to. I think 100 secs is good for
> doing additional experiments with damping parameters. It would be
> interesting to see just how low the bulb may go. This only since it is
> obvious that it makes such a clear difference at 100 secs. It's a  
> choice
> out of measurement and interpretation practicality, not optimum from a
> use perspective. If you consider my postings you would see that I  
> rather
> promote the concept of adjusting the time constant dynamically to
> situations rather than say 1234.5678 seconds is the optimum.
>
> Cheers,
> Magnus

Sorry, Magnus, I didn't mean to put words in your mouth. I was  
remembering last Fall, when you suggested that people look at your  
ADEV plot and to be mindful of the of the bounding slopes of the  
curves. If I've mis-remembered the emphasis or the facts, I do  
apologize. I thought your argument then, as I remember it, was strong  
and valuable. Seems like it gave a good range of possible values to  
use for Tau in the measurements.

I probably won't go far beyond the capabilities of the TBolt, such as  
implementing a PID controller with dynamic control of variables using  
a microcontroller and LPGAys and writing my own software, but I love  
it when you talk that way.

Best,
Dick Moore


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Re: [time-nuts] GPSDO TC & Damping

[Bruce Griffiths]

Richard Moore wrote:
> On Jan 9, 2009, at 12:10 AM, time-nuts-requ...@febo.com wrote:
>
>   
>> Message: 4
>> Date: Fri, 09 Jan 2009 19:18:57 +1300
>> From: Bruce Griffiths 
>> Subject: Re: [time-nuts] GPSDO TC & Damping
>> 
>
>   
>>> Well, like many here, I don't actually have the equipment, especially
>>> the reference std., to do these MDEV, ADEV and other analyses, so,
>>> since I use the GPSDO for a frequency standard and not for UTC, I
>>> thought I'd get the expert opinions. Magnus has several times
>>> indicated here that a TC laying somewhere in and around 100 to 1000
>>> secs is probably optimum. When I enquired some time back about
>>> damping in the TBolt, the consensus seemed to be "leave it at 1.2". I
>>> have, but it just seems to me that won't be optimum for a fixed-
>>> position, lab-located frequency standard -- at the moment, I'm
>>> leaning toward the 0.7to 1.0 area.
>>>
>>>
>>>   
>> Why, since it has been demonstrated that a damping factor of 1.2 is
>> better than one of 0.7 for a particular Thunderbolt this would tend to
>> indicate that adjusting the damping without good justification is
>> somewhat foolhardy.
>> If in fact the phase noise characteristics of your OCXO are similar  
>> toi
>> the one in the Thunderbolt that Tom measured this would degrade the
>> performance.
>>
>> With no way of measuring the effect of such adjustments you are just
>> hoping that your particular Thunderbolt is similar to the one Tom  
>> measured.
>> Thats not engineering its more like witchcraft.
>>
>> 
>>> Tom's recent chart was quite helpful, especially the 1000 sec curve.
>>> Now, I hope that Tom or someone else follows up on the suggestion to
>>> track performance vs. damping factor. I do understand that the
>>> results for any one GPSDO don't *necessarily* translate to other
>>> devices, but they don't necessarily don't, either. At least for the
>>> TBolts a lot of us are playing with, one good example (like Tom's)
>>> may well put mine in a better ballpark than the ballpark the factory
>>> wants it to play in, given the factors that you all have described.
>>> Thx everyone for the comments. Look forward to the next round!
>>>
>>> Dick Moore
>>>
>>>   
>> The probability that you will improve the performance significantly
>> without a means of measuring the resultant performance is fairly low.
>> You will never know if either an improvement or a degradation in
>> performance has occurred.
>> The one saving grace being that the factory defaults can always be  
>> restored.
>>
>> Bruce
>> 
>
> Bruce, thx for the reminder -- my friend and mentor Paul W. Klipsch  
> was fond of saying that "You can't make what you can't measure 'cause  
> you don't know when you've got it made!" At the same time, all sorts  
> of wonderful things have come about thru just fooling around. Again,  
> I remark that for all the reasons Tom enumerated -- er, listed -- the  
> manufacturer's choice of settings may not be the best choice for a  
> particular use. When in a strange country, local enquiry is usually  
> recommended. For GPSDOs, a strange country to me, what better place  
> to enquire than here?
>
> Dick Moore
>
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>   
Dick

What does the plot of ADEV vs tau look like when the Thunderbolt OCXO is
unlocked and one just logs the Thunderbolt's own measurements of the
phase and frequency errors.
It should exhibit a minimum at a value of certain value of tau.

Setting the loop TC to somewhere near this vlue of Tau is perhaps a good
start in the absence of any other data.
No other equipment other than the Thunderbolt and a PC is required to do
this.

Bruce

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Re: [time-nuts] ADEV test setup [was GPSDO TC & Damping]

[Bruce Griffiths]

Steve

Steve Rooke wrote:
> Bruce,
>
> Thanks for the detailed rundown. Looking at the picket-fence method,
> this looks possible for me but I will have to get hold of the
> reference standard. I have a Racal-Dana 1992 with IEEE488 but need to
> get an interface card for the PC end. These are fairly cheap to buy.
>
> You spoke about some types of rubidium standards being suitable, would
> you care to elaborate on that please? Would something like an Efratom
> FRS be suitable?  Generating the picket-fence itself should not be
> hard as long as care is taken not to introduce noise. Do you have any
> links to articles on the design for the
> mixer/zero-crossing/square-wave beat circuit? One question, assuming
> that I have a 10MHz reference standard and I'm measuring a 10MHz dut,
> how do I arrange for them to be about 1Hz apart, given that we are
> measuring for accuracy here? 1HZ different would make the accuracy
> 1E-7 out anyway, or am I missing something here?
>
>   
The best article I've come across on zero-crossing detector design is:

The Design of Low Jitter Hard Limiters" Oliver Collins, IEEE
transactions on Communications, Vol 44 No 5, May 1996 pp 601-608

Unfortunately its not free, however you may be able to access it via a
Library.

However if you only want to use the technique described in the paper, I
have a couple of spreadsheets that calculate the stage gains and low
pass filter time constants both for the simplified analysis in the paper
and the more general case where the input noise spectral density differs
for each stage.
Some pointers on what to include in the noise calculations for each
stage can be found at:

http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html


Some care is required, in that if the spreadsheet predicts a gain of
less than unity for the input stage, it is in fact better to use a
passive RC low pass filter in front of the first amplifier limiter stage
(without a clamp as typically the IF signal amplitude at the mixer
output is insufficient to cause the clamp diodes to conduct - more
complex clamps are too noisy).
The amplifier limiter chain is then redesigned to accommodate this change.

Don't be taken in by those who would insist that everything should be
linear as long as possible, the resultant deign is suboptimal.
Such comments sprang from the fact that no one at that time had worked
out how to include the effect of the clamps on the performance.
Oliver Collins solved that problem, so there is no longer a valid excuse
for such misguided recommendations.

> So the real thing for the budget-conscious time-nut seems to be the
> reference standard.  The ocxos you spoke about do seem to be on the
> rare/expensive side and are an order of magnitude or two better than
> the Option 4E I have in the 1992.
>
> 73, Steve
>   
Bruce

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[time-nuts] GPSDO TC & Damping

[Mark Sims]

The good Lady Heather's GPS Disciplined Oscillator Controller Program 
calculates and plots  (also writes the results to the log file) ADEV and OADEV 
of the Thunderbolt's reported error estimates.  My comparison of these 
"auto-ADEVs" to the values generated from a Tek DC5010 counter showed they 
agreed within a factor of two.  

Note that the DC5010 was measuring the Thunderbolt 10 MHz signal against a 1 
MHz cesium reference.  The data had to be massaged some where the phase rolled 
over (the DC5010 counter has a 5 nsec or so bogus zone where the time interval 
is wrapping).  The counter was set up to calculate time intervals over 10 
seconds (to get picosecond resolution) so ADEVs below 10 seconds were not 
available.



-

What does the plot of ADEV vs tau look like when the Thunderbolt OCXO is
unlocked and one just logs the Thunderbolt's own measurements of the
phase and frequency errors.
It should exhibit a minimum at a value of certain value of tau.


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Re: [time-nuts] GPSDO TC & Damping

[Bruce Griffiths]

Mark Sims wrote:
> The good Lady Heather's GPS Disciplined Oscillator Controller Program 
> calculates and plots  (also writes the results to the log file) ADEV and 
> OADEV of the Thunderbolt's reported error estimates.  My comparison of these 
> "auto-ADEVs" to the values generated from a Tek DC5010 counter showed they 
> agreed within a factor of two.  
>
> Note that the DC5010 was measuring the Thunderbolt 10 MHz signal against a 1 
> MHz cesium reference.  The data had to be massaged some where the phase 
> rolled over (the DC5010 counter has a 5 nsec or so bogus zone where the time 
> interval is wrapping).  The counter was set up to calculate time intervals 
> over 10 seconds (to get picosecond resolution) so ADEVs below 10 seconds were 
> not available.
>
>
>
> -
>
> What does the plot of ADEV vs tau look like when the Thunderbolt OCXO is
> unlocked and one just logs the Thunderbolt's own measurements of the
> phase and frequency errors.
> It should exhibit a minimum at a value of certain value of tau.
>
>
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>   
Mark

Where these results obtained when the Thunderbolt OCXO was locked?

Bruce

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