[time-nuts] Trueposition Antenna Location

[Bob kb8tq]

Hi
 
Well, what you are coming up with as a result simply is not correct. Properly 
calculated ADEV does not do what you show it doing. TimeLab has been around
long enough to be considered “correct” in this regard. The normal input to an 
ADEV calculation is phase rather than frequency. 

Bob

> On Dec 3, 2018, at 8:58 PM, Mark Goldberg <marklgoldberg at gmail.com> wrote:
> 
> I am starting with what should be a frequency measurement at the sample
> rate. Timelab can import that and should be able to determine ADEV from
> that. I agree that something is not right though. I unfortunately am trying
> to measure with what I already have. I don't have a TIC.
> 
> Regards,
> 
> Mark
> 
> 
> On Mon, Dec 3, 2018 at 5:10 PM Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> Hi
>> 
>> Let’s back up a bit:
>> 
>> The input to an ADEV calculation is a record of phase (time between wide
>> spaced
>> edges). Often this is from a PPS output on a device. It could equally well
>> be from
>> 10 MHz edges spaced a count of 10,000,000 edges apart.
>> 
>> The first part of the formula takes the difference between adjacent
>> samples.
>> 
>> The next step puts that difference into a standard deviation calculation.
>> 
>> If you are starting with something else, then you likely are not
>> calculating ADEV.
>> 
>> Bob
>> 
>>> On Dec 3, 2018, at 11:21 AM, Mark Goldberg <marklgoldberg at gmail.com>
>> wrote:
>>> 
>>> I have looked at it multiple times and so far cannot see a discrepancy.
>> The
>>> ration of the ADEVs for the two sample rates is very close to 2 for a
>> wide
>>> range of Tau in the 10-200 sec range. That can't be a coincidence. It's
>>> between 2 and 3 for higher Tau but that may be due to temperature
>> changes.
>>> 
>>> Basically, the Perseus SDR, clocked by my Bodnar GPSDO is sampling the 10
>>> MHz from my TruePosition and using the DDC to down convert to 48 kHz. I
>>> then do either a 32768 or 262144 point FFT, resulting in window times of
>>> 0.6816 or 5.453 sec and use a built in function in Spectrum Lab that as I
>>> understand it interpolates the peak frequency from the highest two bins.
>>> That calculated peak frequency is saved every 0.6816 or 5.453 seconds.
>> That
>>> data is fed to Timelab.
>>> 
>>> I could do the same size FFT for both and decimate the input by 1 and 8
>>> respectively, which should result in the same FFT window time and check
>>> that.
>>> 
>>> I'm scratching my head here.
>>> 
>>> Regards,
>>> 
>>> Mark
>>> 
>>> 
>>> On Mon, Dec 3, 2018 at 6:28 AM Bob kb8tq <kb8tq at n1k.org> wrote:
>>> 
>>>> Hi
>>>> 
>>>> ADEV is pretty well documented and the results should *not* be dependent
>>>> on the
>>>> sample rate. The proper approach to dropping the sample rate is
>> decimation
>>>> of the
>>>> data. I think you may want to look at the way you are doing ADEV.
>>>> 
>>>> Bob
>>>> 
>>>>> On Dec 3, 2018, at 12:30 AM, Mark Goldberg <marklgoldberg at gmail.com>
>>>> wrote:
>>>>> 
>>>>> I ran them again today and the results are almost identical. The slower
>>>>> sample rate still shows a lower ADEV. I am not sure what the algorithm
>> to
>>>>> determine the peak frequency is but it is described as a linear
>>>>> interpolation between the two highest peaks on the FFT.  I could see
>> how
>>>>> that could be subject to math errors. For the slower sample rate, the
>>>>> frequency bins are smaller. I have not researched how all this could
>>>> affect
>>>>> the peak frequency and possibly introduce noise (or by truncation
>> remove
>>>>> small amounts of noise).
>>>>> 
>>>>> I will run it a few times in the next few days and will also try to
>> move
>>>>> the antennas to a location with lower multipath.
>>>>> 
>>>>> Thanks for the suggestions,
>>>>> 
>>>>> Mark
>>>>> 
>>>>> 
>>>>> On Sun, Dec 2, 2018 at 2:16 PM Bob kb8tq <kb8tq at n1k.org> wrote:
>>>>> 
>>>>>> Hi
>>>>>> 
>>>>>> Looking at the data, I’m guessing the slower sample rate was done
>> last.
>>>> If
>>>>>> so,
>>>>>> you may not be letting the GPSDO’s “warm up” long enough. Most designs
>>>>>> take days (if not weeks) to get to their ultimate stability.
>>>>>> 
>>>>>> Bob
>>>>>> 
>>>>>>> On Dec 2, 2018, at 11:16 AM, Mark Goldberg <marklgoldberg at gmail.com>
>>>>>> wrote:
>>>>>>> 
>>>>>>> I broke down and drilled a couple holes in the wall and moved the
>>>>>> antennas
>>>>>>> for both GPSDOs outside with a better view of the sky, but still
>>>> somewhat
>>>>>>> shielded by the house and a metal RV cover. The number of sats is way
>>>> up
>>>>>>> and the TruePosition is in normal mode most of the time. The ADEV is
>>>> not
>>>>>>> improved and actually measured worse. I took data for twice as long
>> at
>>>>>> two
>>>>>>> sample rates, 0.6816 sec and 5.453 sec. The ADEV from the slower
>> sample
>>>>>>> rates is lower, possibly due to the measurement method, but they all
>>>> are
>>>>>> in
>>>>>>> the same order of magnitude. I've named the Heather screen captures
>> for
>>>>>> the
>>>>>>> inside and outside locations and shown one combined Timelab capture.
>>>>>>> 
>>>>>>> Regards,
>>>>>>> 
>>>>>>> Mark
>>>>>>> 
>>>>>> 
>>>> 
>> <TruePos_Outside_Ant_Heather.png><TruePos_Inside_Outside_Compare_Ant_Allan.png><TruePos_Inside_Ant_Heather.png>_______________________________________________
>>>>>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>>>>>> To unsubscribe, go to
>>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>>>>>> and follow the instructions there.
>>>>>> 
>>>>>> 
>>>>>> _______________________________________________
>>>>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>>>>> To unsubscribe, go to
>>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>>>>> and follow the instructions there.
>>>>>> 
>>>>> _______________________________________________
>>>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>>>> To unsubscribe, go to
>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>>>> and follow the instructions there.
>>>> 
>>>> 
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>>> To unsubscribe, go to
>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>>> and follow the instructions there.
>>>> 
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>> To unsubscribe, go to
>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>> and follow the instructions there.
>> 
>> 
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com
>> To unsubscribe, go to
>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
>> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.