Hi
Just in case anybody else has missed the uBlox "magic code":
A LEA-6 is a nav receiver *unless* it is a LEA-6T. The LEA-6T is a timing receiver. The same convention applies to other parts in their lineup in the same fashion.
The "T" enables a number of features. It is *not* clear that it changes the basic function of the unit. The features it enables make it much easier to use in a GPSDO or other precise timing (sawtooth corrected) application. The net result is that you are below 1x10^-9 at one second rather than up around 1x10^-8 at 1 second.
I enclose two charts showing my results with NEO-6M (naviagation only and about 10USD on ebay) and LEA-6T (about 30USD on ebay). I have tested both with a patch antenna in-house that gave about 30db C/N (=int on chart) and an small patch antenna on the roof that gave about 50dB C/N (=ext). For the LEA-6T I also have set mode 0 that is mobile mode (=nf on chart) and also done a survey and set mode 2 fixed (=f on chart). A note: I have default mask angle 5 degrees and maybe a higher value should have given better results especially as I am in Sweden that is quite far north.
If you use the GPS module standalone the ADEV give a good indication of what you can get if you test for example a counter. If you have 1E-8 at 1sec you can get about 8digits average and 7digits with normal measurement confidence at 1sec gate time (Frequency plots often seems to jump about a factor ten more than the ADEV). At 100 sec ADEV is 1E-10 and for 100sec gate time you get 10digits average and 9digits with confidence.
For using a GPS module standalone I haven´t seen any DIY designs of hardware sawtooth correction. Otherwise sawtooth correction probably gives an extra digit.
I enclosed the MDEV chart as I think MDEV is useful to see possible limits when designing GPSDO controllers with PI-loops and a Pre-filter that take away part of the sawtooth errors.
At short time constants (10-100secs) sawtooth correction probably is very useful for a GPSDO. At long time constants (1000-10000secs) a pre-filter probably is nearly as efficient I think. I have never seen a hanging bridge longer than 300secs. Also at Tau longer than 1000sec the GPS errors (changing satellites, ionosphere etc) starts to get in the same region as the filtered GPS module errors I think.
My own rule of thumb is also that AT cut OCXO´s (and good VCTCXO as DOT050V) need time constants in the GPSDO of about 10-100secs, SC cut OCXO 100-1000secs and Rubidium 5000-20000secs to match good GPS receivers.
Lars