[time-nuts] Measuring ADEV using TBolt-Tic tester
John Ackermann N8UR
jra at febo.com
Fri Oct 7 17:13:58 EDT 2011
In that test I was just capturing the ADEV table from the TSC-5120 so don't have raw phase data.
I'm curious where you got the noise data for the TBolt gps engine -- that's far better than I've seen quoted before. The Trimble data sheet that I found specs the system PPS accuracy at 20 nanoseconds one sigma; they don't separately spec the GPS engine. (The data sheet for the current Thunderbolt E data sheet says 15 nanoseconds.)
The USNO says that their filtered, linear fit time transfer measurements over a two day period, over the entire constellation, have an RMS residual of 4 to 10 nanoseconds without SA (http://tycho.usno.navy.mil/gpstt.html). That may not be apples-to-apples methodology, but it implies that sub-nanosecond results may be difficult to obtain.
On Oct 7, 2011, at 4:16 PM, "ws at Yahoo" <warrensjmail-one at yahoo.com> wrote:
> What was the RMS and PP phase noise for your 8e-14 test?
> Something to keep in mind is that although the Z3801 has a better Osc than the typical Tbolt.
> Long term, really low noise is all about the quality of the GPS signal and engine.
> The Z3801's GPS engine is far inferior and not even close to the 10 to 100 ps, 1 sec noise that a Tbolt engine has.
> So how much does that effect the mid term GPS Phase noise which is highly dominated by how good of antenna system one has.
> Sounds like comparison is needed.
> Some test like these are on my list for this winter. I am planning to look at a Z3801A versus a couple of 5061 class units: one with a high stability tube that I think is in very good condition, and another with an FTS replacement tube of probably typical surplus quality. I can also add a TBolt into the mix. I'm hoping to lash up multiple 5334 counters in TIC mode so I can do several comparisons simultaneously.
> In an early test of the 004 tube vs. Z3801A over a week or so, I saw what looked like a floor in the 8e14 range.
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