John, Your hunch is correct. For most modern TIC devices, measurement noise is white. That is, if you do a self-test using a common DUT & REF you get a nice clean Gaussian plot. But the TICC is not like that. The TICC is based on a ring counter and so there is a *high* degree of quantization. This is not bad, per se, but it does impact how one should perform, or interpret, a noise floor test.
Take a look at: http://leapsecond.com/pages/ticc/ And in particular: http://leapsecond.com/pages/ticc/ticc-log5342-hist-1.gif What this means is that a noise floor measurement made with the same chA and chB and REF could be quite wrong. This is not an indictment against the TICC. I have several, and use them all. But because of the strong quantization effects you can't just feed in a common DUT and REF and expect that to represent all possible real-life phase measurements. Those quantized "camel humps" are really quite extreme with the TICC. /tvb ----- Original Message ----- From: "John Ackermann N8UR" <j...@febo.com> To: <time-nuts@lists.febo.com> Sent: Tuesday, January 08, 2019 10:48 AM Subject: Re: [time-nuts] Short term 10MHz source > Hi Luciano -- > > Thanks for posting that. There's a subtle point about the noise floor > that's forever been on my list of things to investigate: the noise floor > should be lower in timestamp mode than in time interval (A->B) mode. > > That's because in timestamp mode there is jitter contribution only from > a single measurement, whereas in time interval mode there is a > measurement from each channel so you have two jitter components. So a > guess is that the floor should be about sqrt(2) lower in timestamp mode. > Someday I will test that theory. > > John > ---- > On 1/8/19 12:38 PM, tim...@timeok.it wrote: >> >> .gif of the TICC noise floor. >> Luciano >> >> >> Da "time-nuts" time-nuts-boun...@lists.febo.com >> A time-nuts@lists.febo.com >> Cc >> Data Tue, 8 Jan 2019 18:31:02 +0100 >> Oggetto Re: [time-nuts] Short term 10MHz source >> >> Hi Paul, >> here the TICC noise floor. >> Regarding the GPS/TICC versus a good Rubidium standard like the HP5065A >> , you cannot apreciate the Rubidium ADEV stability lower than 10Kseconds. >> Luciano >> >> >> Da "time-nuts" time-nuts-boun...@lists.febo.com >> A "Discussion of precise time and frequency measurement" >> time-nuts@lists.febo.com >> Cc >> Data Sat, 5 Jan 2019 12:35:26 -0000 >> Oggetto Re: [time-nuts] Short term 10MHz source >> Hi All sorry for a new be question but what is a TICC regards Paul B UK >> >> -----Original Message----- >> From: time-nuts [mailto:time-nuts-boun...@lists.febo.com] On Behalf Of >> Chris >> Burford >> Sent: 02 January 2019 03:56 >> To: Time Nuts List >> Subject: [time-nuts] Short term 10MHz source >> >> I have a situation in which I have access to a GPSDO 10MHz source but for >> only about 10-12 hours at a time. My current residence does not allow a >> permanent GPS antenna therefore I am limited in its use. >> >> I do realise that the long term stability of the GPSDO is somewhat >> superior >> to a Rubidium source. I'm planning on using my TICC to validate both my >> GPSDO and RFS. I'm aware that such a short "power on" period is somewhat >> counterproductive but I have no other options. I'd like to know if a 6-8 >> hour window for the GPSDO is sufficient for use as a 10MHz source for the >> TICC. >> >> I appreciate any and all comments. >> >> Regards, Chris
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