[time-nuts] question Alan deviation measured with Timelab and counters
steph.rey at wanadoo.fr
Mon Jan 19 10:44:14 EST 2015
Actually I'm working in the RF department of a big lab, designing RF
electronics mainly in microwaves range. I'm luckilly having some tools
around to play with and a lot of components like
mixers/amplifiers/couplers/splitters/attenuators, ... almost whatever
the frequency is up to several tens of GHz.
At home since the last 20 years I could as well get nice instruments.
The next two measuring tools really missing and for which I'm limited
are the phase noise and stability measurement and possibly a good
standard. My Effratom FRK Rb is old and probably not the best from a
phase noise and stability point of view but until now has never been
characterized. Otherwise I've almost everything I need up to 40 GHz I
I'm doing further measurement right now which sounds much much more
consistent. I will share tonight.
On Mon, 19 Jan 2015 08:59:58 -0500, Bob Camp <kb8tq at n1k.org> wrote:
>> On Jan 18, 2015, at 5:12 PM, Stéphane Rey <steph.rey at wanadoo.fr>
>> Bonsoir Magnus (Are you in Sweeden ?)
>> Being able to measure high stability and low phase noise is
>> definitely a need for me as I'm trying to design low noise
>> synthesizers and I'm already reaching the limits of my current tools
>> for phase noise and I can't afford an E5052 for my own. At work I've
>> one but I will probably not stay after august. And anyway I need such
>> tools in my lab at home…
> If you have tools at work, the best possible thing to do is to get
> some oscillators / standards characterized. If you *know* what this
> that oscillator is doing in terms of ADEV or phase noise at this Tau
> or frequency offset, it’s much easier to figure a lot of this out.
> The most basic way to do phase noise in the basement is with a single
> mixer setup running into some sort of audio FFT device. A sound card
> can be used or an audio spectrum analyzer. Parts are < $100 to get
> setup once you can do the audio measurements.
> For ADEV, a DMTD or it’s cousin, the single mixer is the easy way to
> go. The single mixer does not get a lot of discussion these days. It
> is much easier to set up than a DMTD. It does require an offset
> oscillator. Once you have a single mixer phase noise setup, you are
> about half way to a single mixer ADEV setup. Cost for one is < $100
> parts. You already have a counter to collect the data out of it.
> In both cases you are running a comparison device. Having a
> characterized OCXO to compare to is a really nice thing.
>> As low-noise and stable synthetizers depends on the standard used, I
>> need as well to measure them as well...
>> Let's start with this simple experiments and once I will understand
>> the ins and outs I will try to improve. I know techniques of
>> cross-correlations and you've already talked about DMTD that for sure
>> I will have to come to...
>> Good night
>> -----Message d'origine-----
>> De : Magnus Danielson [mailto:magnus at rubidium.se]
>> Envoyé : dimanche 18 janvier 2015 22:46
>> À : Stéphane Rey; 'Discussion of precise time and frequency
>> Cc : magnus at rubidium.se
>> Objet : Re: [time-nuts] question Alan deviation measured with
>> Timelab and counters
>> Bonsoir Stéphane,
>> On 01/18/2015 10:34 PM, Stéphane Rey wrote:
>>> Thanks a lot Bob and Magnus for your very helpful comments.
>>> The HP5370a was indeed in TI mode. By the way what is the
>>> difference with +/-TI, the button just aside...
>>> But I guess I understand where I've missed something : I've tried
>>> to put the Rb on channel A and the DUT on channel B but result was
>>> always the same but I do understand now that there is indeed a switch
>>> to change from COMmon to SEParate and it was always on COM meaning I
>>> believe that channel B wasn't used. This explains a lot of things I
>>> did not understand. I'm sorry for these so basic issues that might
>>> have been solved if I had read carefully the HP5370a manual first.
>> Good. This confirmation makes sense to be and Bob, now we can relax
>> as the mystery is solved.
>>> So possible conclusions until now are that I have actually measured
>>> the ADEV floor of the system rather than my DUT... which is already
>>> nice. The second conclusion from these oscillations seen with the
>>> GPSDO under test is that there is very likely in this GPSDO design a
>>> systemic noise added to the 10 MHz output (power supply, PCB
>>> coupling, ... I'll make further investigations on it later on).
>> It's a great opportunity to learn the tools, and once you have the
>> tools, you can see if you can't improve things.
>>> I will experiment all the suggestions you made and will come back.
>>> For information the 1PPS from the HP58503b has a positive pulse width
>>> that is only few us length.
>> This only makes it hard to view on a scope, but long enough to
>> reliably trigger your counter and scope.
>>> Now, when considering that the method is to compare the DUT to an
>>> other source, I assume then that the other source shall be at least 1
>>> order of magnitude better than the DUT. Otherwise this will be
>>> impossible to distinguish who is the instability contributor between
>>> the source and DUT, right ?
>> For a simple setup, yes. But then we are the time-nuts, we have ways
>> of handling these things. :) Let's get you started with the basic
>> measurement, it will be a good start.
>>> Then the second question is what kind of very stable source can be
>>> used to measure DUT which could be Rb or GPSDO which are already in
>>> the range of 10E-10 to 10E-12 < 100s ?
>> Time-nuts tend to spend their time and money getting even more
>> stable clocks and tools. If you have the right tool, you can measure
>> near and
>> *under* the noise-level of your reference, but not without running
>> into issues. One such trick is called cross-correlation, while another
>> is to use three-corner hat techniques.
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