[time-nuts] Trueposition Antenna Location

[Bob kb8tq]

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>_______________________________________________
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