[time-nuts] 1. Re: need recomendation for a portable 10mhz reference

Martyn Smith martyn at ptsyst.com
Fri Dec 14 15:03:10 EST 2007


Hi,

I saw the original message for the requirement of a portable reference 
needed to maintain an accuracy of 100 Hz at 47 GHz I think.

I know I'm a bit late, but there has been a lot of misguided advice, in my 
opinion.

If the user truly needs 100 Hz at 47 GHz, that is an accuracy of 2E-9.

Now, I supply the most stable oscillators from Wenzel and other suppliers as 
well as making my own oscillators.

There's no way of achieving an accuracy of 2E-9 unless you go to a rubidium 
oscillator.  At least not without a massive amount of work.

Although many crystal oscillators quote specs of 1E-10/day or even 
1E-11/day, this is only achieved after the crystal has been running for a 
long time.  A long time meaning weeks or months.

For example, Wenzel quote 1E-10/day but only after 30 days continuous use. 
Before that they drift by about 5E-8/day.  They need about 3 to six months 
before they start to age slowly.  Also an OXCO's retrace is usually very 
poor.  Typically 1E-7 to 1E-8.  Achieving 2E-9 accuracy is near on 
impossible for an OXCO.

However, a rubidium oscillator will achieve this in minutes.  My own range 
of rubidium oscillators has typically re-trace of 1E-10 in less than 10 
minutes.

Also my rubidium's have excellent Allan Variance  (<1E-11 in 1 sec for my 
units), equaling most OXCO'S oscillators, so there's no need to lock a OXCO 
to the rubidium, that was also suggested.

Simply use a good quality rubidium.

With some manufacturers selling rubidium oscillators for under $1000, the 
cost is not as much as what would be needed to keep an OXCO.

Best Regards

Martyn

This Email is from:

Martyn Smith
Precision Test Systems LTD
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Email: martyn at ptsyst.com
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----- Original Message ----- 
From: <time-nuts-request at febo.com>
To: <time-nuts at febo.com>
Sent: Tuesday, December 11, 2007 11:22 PM
Subject: time-nuts Digest, Vol 41, Issue 35


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> Today's Topics:
>
>   1. Re: need recomendation for a portable 10mhz reference
>      oscilator (Magnus Danielson)
>   2. Re: is there a "best bet" advanced hobbyist buildable
>      GPSDOdesign? (Bruce Griffiths)
>   3. Re: need recomendation for a portable 10mhz reference
>      oscilator (John Ackermann N8UR)
>   4. Re: need recomendation for a portable 10mhz reference
>      oscilator (Bruce Griffiths)
>   5. Re: need recomendation for a portable 10mhz reference
>      oscilator (Bruce Griffiths)
>   6. Re: Fury Interface Board simulation results (Bruce Griffiths)
>   7. Re: need recomendation for a portable 10mhz reference
>      oscilator (Hal Murray)
>   8. Re: need recomendation for a portable 10mhz reference
>      oscilator (Alan Melia)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 11 Dec 2007 21:52:55 +0100 (CET)
> From: Magnus Danielson <magnus at rubidium.dyndns.org>
> Subject: Re: [time-nuts] need recomendation for a portable 10mhz
> reference oscilator
> To: time-nuts at febo.com, eric.fort at gmail.com
> Message-ID: <20071211.215255.-743699540.cfmd at bredband.net>
> Content-Type: Text/Plain; charset=us-ascii
>
> From: "Eric Fort" <eric.fort at gmail.com>
> Subject: [time-nuts] need recomendation for a portable 10mhz reference 
> oscilator
> Date: Tue, 11 Dec 2007 11:38:40 -0800
> Message-ID: <2ad2af430712111138q23eb4dfm76d9a138d76365fc at mail.gmail.com>
>
> Eric,
>
>> I'm looking for a fairly basic, relatively simple 10 Mhz PORTABLE
>> reference (probably quartz based) with enough stability over a period
>> of a week of outdoor temp extremes to keep a 47Ghz transmitter locked
>> within 100hz  while mountaintop contesting.  Suggestions are
>> appreciated.  something that is small and ran off 12 volts dc (car
>> battery) would be a definite plus.
>
> Have a look at the Oscilloquartz 8711/8712 (G option, you would need
> < 3E-10/day, so 2E-10/day fits your needs, but maybe you can live with the
> 164,5 Hz the standard 5E-10/day would give you) for instance.
> Hook up a DAC and a small PIC or AVR to keep the DAC easilly controlable 
> when
> calibrating the frequency in the home lab.
>
> There are many similar oscillators which will do the same trick. A 10811 
> would
> also do the same thing, but it requires a higher voltage but a switcher 
> would
> double up the 12V.
>
> Cheers,
> Magnus
>
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 12 Dec 2007 09:53:36 +1300
> From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
> Subject: Re: [time-nuts] is there a "best bet" advanced hobbyist
> buildable GPSDOdesign?
> To: Tom Van Baak <tvb at leapsecond.com>, Discussion of precise time and
> frequency measurement <time-nuts at febo.com>
> Message-ID: <475EF8D0.7030400 at xtra.co.nz>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Tom Van Baak wrote:
>>> Hi,
>>>
>>> Like many, I've acquired a fair amount of surplus test equipment off of 
>>> Ebay
>>> which could use the services of good master frequency standard.  So I'm
>>> looking to discipline an HP 10811 VXCO to provide this.
>>>
>>> Any general consensus about the best design for a hobbyist to build?
>>> I'm familiar with the Brooks Shera design, the G4JNT Jupiter-T design,
>>> the TAC-2 circuit, and the VE2ZAZ design.  I take it from discussions
>>> I've seen in the archives of this list that the VE2ZAZ design makes a
>>> number of simplification/performance tradeoffs.
>>>
>>> Is there a design I haven't listed which is "better" than the others?
>>> I'm quite familiar with microcontrollers, FPGAs, spinning my own
>>> PCBs, etc, so I'll roll my own if I have to, but I'd prefer to build
>>> a variation on someone's tried and true design.
>>>
>>> I'm aware of products like the Fury, but I'd like something I could 
>>> tinker
>>> with, and the cost is hard to justify for a hobbyist.
>>>
>>> Scott
>>>
>>
>> Scott,
>>
>> Hard to say which is better at this point; there are a number
>> of variables, not the least of which is the intrinsic short-term
>> stability of the OCXO you use.
>>
>> Do have a close look at James Miller's GPSDO:
>>
>> http://www.jrmiller.demon.co.uk/projects/freqstd/frqstd.htm
>>
>> I recently tested one and it makes it to 1e-13 at one day, which
>> is really nice for a simple, cheap, homebrew GPSDO.
>>
>> /tvb
>>
>>
>> _______________________________________________
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>> To unsubscribe, go to 
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>>
>>
> Tom
>
> What about the short term performance?
> Its relatively easy to achieve a stability of 1E-13 for an averaging
> time of 1 day, achieving good short or medium term stability is more
> difficult.
>
> If you want simplicity and higher performance you can do far better with
> fewer parts,
> An expensive high resolution DAC can be replaced with a software
> sigma-delta DAC that has higher resolution.
> The complex phase detector can be replaced with a D flipflop.
> Add a microprocessor plus an opamp or 2 to filter and scale the EFC
> voltage and thats about all thats required in addition to a good GPS
> timing receiver.
> For improved performance a hardware circuit to correct the PPS sawtooth
> error will improve the medium term stability significantly when using a
> high performance GPS timing receiver that provides an estimate of this
> error.
>
> Both the Brooks Shera and the James Miller designs have inadequate phase
> error measurement resolution to achieve good short and medium term
> stability.
> However, this is only noticeable when using high performance GPS timing
> receivers (M12+T, M12MT etc) and a high quality OCXO (10811A etc).
>
> Bruce
>
>
>
> ------------------------------
>
> Message: 3
> Date: Tue, 11 Dec 2007 15:56:42 -0500
> From: John Ackermann N8UR <jra at febo.com>
> Subject: Re: [time-nuts] need recomendation for a portable 10mhz
> reference oscilator
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Message-ID: <475EF98A.6010207 at febo.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Hal Murray wrote:
>> I'm picturing an open hill top at night with clear skies so there would 
>> be
>> lots of radiation cooling.  Of course, with an open hill top, GPS 
>> recption
>> would be easy.
>
> As great as GPSDO are, the problem with using them in a portable
> environment is the time it takes to do a survey and then get to final
> lock; mountain-toppers may not be in one place long enough.
>
> One thought I've had is to use a cheap Rubidium for long term stability,
> and phase lock a good OCXO to it for short term stability and phase
> noise (ie, use a loop time constant of perhaps 100 seconds).  That would
> make a portable package that would meet both the short and long term
> stability requirements.
>
> John
>
>
>
> ------------------------------
>
> Message: 4
> Date: Wed, 12 Dec 2007 10:05:49 +1300
> From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
> Subject: Re: [time-nuts] need recomendation for a portable 10mhz
> reference oscilator
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Message-ID: <475EFBAD.7000708 at xtra.co.nz>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hal Murray wrote:
>>> A good (and well-aged) double-oven OCXO with aging compensation should
>>> be able to provide that type of performance. The problem is: how
>>> much physical movement will the unit experience? What are the
>>> temperature extremes that are expected, and how fast does the
>>> ambient move between the temp extremes? Can it be GPS locked during
>>> that time?
>>>
>>
>> Assuming you don't GPS lock it...
>>
>> How well will two units from the same manufacturer/batch track?
>>
>> I'm assuming they will see roughly the same temperature profile and that 
>> you
>> start with them running at the same frequency.
>>
>>
>> Has anybody made a triple oven setup?  I'm thinking of a big box with a 
>> few
>> holes and a temperature controlled fan.  The idea is to let the oven (and
>> electronics) keep itself warm when the ambient temperature gets very 
>> cold.
>>
>> I'm picturing an open hill top at night with clear skies so there would 
>> be
>> lots of radiation cooling.  Of course, with an open hill top, GPS 
>> recption
>> would be easy.
>>
>>
>>
>>
> Hal,
>
> A triple oven is a particularly bad idea, its just too difficult to
> achieve a wide operating temperature range without losing temperature
> control or cooking everything in the innermost oven unless one uses a
> watercooled peltier device to control the outer oven temperature.
>
> A well designed single oven with feedforward (or the outer oven of a
> dual oven system if you cant redesign/rebuild the inner oven) can easily
> achieve a thermal gain of more than 1E5 see:
>
> http://tf.nist.gov/timefreq/general/pdf/595.pdf
>
>
>
> A bootstrapped oven design like that used by Wenzel (not as new as he'd
> have you believe - its been in use in one form or another for the better
> part of a century) will also help in improving performance. The optimum
> solution is of course to combine the 2 techniques.
>
> http://www.wenzel.com/documents/Sub-pico%20Multiplier.pdf
>
> With a thermal gain of 1E5 for the outer oven temperature fluctuations
> at the outer shell of the inner oven will only be a 1 millikelvin or so
> (assuming the ambient temperature range is less than 100K).
>
> Bruce
>
>
>
> ------------------------------
>
> Message: 5
> Date: Wed, 12 Dec 2007 10:11:51 +1300
> From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
> Subject: Re: [time-nuts] need recomendation for a portable 10mhz
> reference oscilator
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Message-ID: <475EFD17.3070500 at xtra.co.nz>
> Content-Type: text/plain; charset=ISO-8859-1
>
> John Ackermann N8UR wrote:
>> Hal Murray wrote:
>>
>>> I'm picturing an open hill top at night with clear skies so there would 
>>> be
>>> lots of radiation cooling.  Of course, with an open hill top, GPS 
>>> recption
>>> would be easy.
>>>
>>
>> As great as GPSDO are, the problem with using them in a portable
>> environment is the time it takes to do a survey and then get to final
>> lock; mountain-toppers may not be in one place long enough.
>>
>> One thought I've had is to use a cheap Rubidium for long term stability,
>> and phase lock a good OCXO to it for short term stability and phase
>> noise (ie, use a loop time constant of perhaps 100 seconds).  That would
>> make a portable package that would meet both the short and long term
>> stability requirements.
>>
>> John
>>
> John
>
> Why not lock it to a GPS timing receiver output when its at home, and
> allow the controller to learn the aging and tempco characteristics etc
> of the oscillator being disciplined and use this information to correct
> for temperature variations etc at the remote site?
>
> The model used can be as complex as required to achieve the desired
> performance and a PC can be used to derive optimum correction
> coefficients, the micro only has to perform the simpler task of applying
> these corrections.
>
> Bruce
>
>
>
> ------------------------------
>
> Message: 6
> Date: Wed, 12 Dec 2007 11:10:38 +1300
> From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
> Subject: Re: [time-nuts] Fury Interface Board simulation results
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Message-ID: <475F0ADE.1050505 at xtra.co.nz>
> Content-Type: text/plain; charset=ISO-8859-1
>
> xaos wrote:
>> Bruce Griffiths wrote:
>>
>>> George
>>>
>>> In the JFET frequency doubler:
>>> 1) Surely the 50 ohms should be is series with the the voltage source V3
>>> for the simulation?
>>>
>>>
>> Correct. I did a cut and paste "without rotate" there.
>>
>>> 2) Usually a 1:4 impedance ratio step up transformer on the input is
>>> about right with a similar transformer used to step down the output
>>> (perhaps an even higher impedance ratio transformer (8:1, 9:1?? may be
>>> better). The maximum turns ratio depends somewhat on the maximum
>>> allowable drain voltage swing which in turn is limited by the drain
>>> supply voltage.
>>>
>>>
>> I will re-run with the this in mind and will repost.
>>
> The idea is that the FETs are not operated in the square law region but
> are actually switched off alternately so that the combined drain current
> waveform is a rectified sinewave with a small dc offset.
> With a well balanced circuit the odd harmonic amplitudes (including the
> fundamental) at the output will be small with the 20MHz 4th harmonic of
> the fundamental being the largest component.
> Achieving low distortion isnt the aim, but achieving low phase noise is.
> Any residual harmonics and subharmonics can be removed with tuned
> circuit traps (dont use a high Q bandpass filter as it will inevitably
> have a high phase shift tempco and may add flicker phase noise depending
> on the components used). A relatively broadband low pass filter
> contributes little phase shift (and associated flicker phase noise as
> well as little phase shift tempco) at 10MHz as do a series of relatively
> high Q LC traps. High performance is rarely achieved by the
> simplest/obvious solution.
> If you have difficulty finding suitable JFETs a high impedance bipolar
> junction transistor (BJT) implementation is also possible however
> biasing is a little trickier and requires a couple of extra BJTs to
> ensure reasonable thermal stability of the bias currents.
>>> In the voltage offset circuit:
>>>
>>> 1) The junction of R9 and R12 should be connected to the offset source
>>> (+5V??).
>>>
>>>
>> This is what I didn't get about the original circuit.  I was scratching
>> my head as to the purpose of a variable R9 when
>> the only value that made sense was when it was set to the "0" position.
>>
>>
>>> I dont understand what the 7812 does in this circuit.
>>>
>>>
>> It was there in the original circuit so I modeled accordingly. Actually
>> I ran some simulations with PS voltage variation
>> to see the effect as well. In that case I removed the 7812.
>>
>>> Isolation amplifier looks OK.
>>>
>>> Bruce
>>>
>>>
>> This is a very nice design and the AC analysis shows a bandpass around
>> 10 MHz with 20 MHz BW.
>>
>> The only issue I see there is that it needs 50 parts of 6 different 
>> values.
>>
>> This might be difficult to implement on a small board and would be prone
>> to error for people trying to
>> assemble their own board.
>>
>> The way I see the final product is a bare board and possibly a kit. It
>> has to be easy to assemble and minimize
>> errors.
>>
>> Actually, I was looking at the isolation amplifier provided in the C.M.
>> Felton Paper:
>>
>> http://www.darksmile.net/ee/Superimposing_Low-Phase-Noise_Low-Drift_Instrumentation_Techniques_On_RF_Design.pdf
>>
>> It is relatively simple and would use similar devices as the Frequency
>> doubler.
>>
> The trouble with this design is that it has a low input impedance and
> thus is unsuitable for OCXOs that require a high impedance load (eg 
> 10544A).
> Its gain isnt adjustable and its difficult to obtain suitable dual JFETS
> (you would have to use a couple of J310's to achieve similar performance
> since U431 isnt readily obtainable, the LS840 is definitely unsuitable
> as its minimum Idss isnt high enough ), it also has relatively low
> reverse isolation. Simplicity isnt the key to high performance.
>> I will upload more info as I compile it.
>>
>> George
>>
>
>
>
>
> ------------------------------
>
> Message: 7
> Date: Tue, 11 Dec 2007 14:57:38 -0800
> From: Hal Murray <hmurray at megapathdsl.net>
> Subject: Re: [time-nuts] need recomendation for a portable 10mhz
> reference oscilator
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Message-ID: <20071211225739.00A28BE31 at ip-64-139-1-69.sjc.megapath.net>
> Content-Type: text/plain; charset=us-ascii
>
>
>> As great as GPSDO are, the problem with using them in a portable
>> environment is the time it takes to do a survey and then get to final
>> lock; mountain-toppers may not be in one place long enough.
>
> What if you use a navigation GPS unit rather than a timing unit?
>
> How long does a survey take (in good conditions) and what sort of time
> constant would you want to use with a navigation box?
>
> Does anybody have graphs of the PPS wander from a navigation unit?
>
>
> I like the lock-to-rubidium suggestion.
>
>
> -- 
> These are my opinions, not necessarily my employer's.  I hate spam.
>
>
>
>
>
>
> ------------------------------
>
> Message: 8
> Date: Tue, 11 Dec 2007 23:21:47 -0000
> From: "Alan Melia" <alan.melia at btinternet.com>
> Subject: Re: [time-nuts] need recomendation for a portable 10mhz
> reference oscilator
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Message-ID: <009301c83c4c$9be64680$0900a8c0 at Lark>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi John, Andy Talbot G4JNT developed the a Jupiter based GPSDO for just 
> this
> purpose, several are used by hill-toppers in the UK.
> http://www.scrbg.org/g4jnt/freqlock.htm
> The idea was that it would settle and be accurate in the time it took to
> seet up the microwave part of the station.
>
> I hope that helps/
> Alan G3NYK
>
> ----- Original Message -----
> From: "John Ackermann N8UR" <jra at febo.com>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Sent: Tuesday, December 11, 2007 8:56 PM
> Subject: Re: [time-nuts] need recomendation for a portable 10mhz reference
> oscilator
>
>
>> Hal Murray wrote:
>> > I'm picturing an open hill top at night with clear skies so there would
> be
>> > lots of radiation cooling.  Of course, with an open hill top, GPS
> recption
>> > would be easy.
>>
>> As great as GPSDO are, the problem with using them in a portable
>> environment is the time it takes to do a survey and then get to final
>> lock; mountain-toppers may not be in one place long enough.
>>
>> One thought I've had is to use a cheap Rubidium for long term stability,
>> and phase lock a good OCXO to it for short term stability and phase
>> noise (ie, use a loop time constant of perhaps 100 seconds).  That would
>> make a portable package that would meet both the short and long term
>> stability requirements.
>>
>> John
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
>
>
> ------------------------------
>
> _______________________________________________
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