[time-nuts] Lucent RFTG-XO performance...

John Ackermann N8UR jra at febo.com
Sun Feb 3 20:18:07 EST 2008

Has anyone here done any performance measurements of the Lucent RFTG-XO
unit?  I am testing one now and getting extremely unimpressive results,
and wonder if anyone else has looked closely at these things.

What I'm seeing is almost flat ADEV in the low to mid 10s from 1 second
out to 40,000 seconds.  At 100,000 seconds, it drops to the high 11s.*
To this point I haven't seen anything that looks like the normal GPSDO
characteristic of a rapid ADEV improvement from around 1000 seconds or
so.  In fact, this is about the flattest ADEV plot I've ever seen from
an oscillator.

The frequency difference plot** shows a bang-bang effect of about
1.6x10e-9 over the course of a few minutes.  This seems to go on
continuously (at least over the 4 days of data so far).  That certainly
explains the mediocre ADEV performance.

The thing does appear to be locked to GPS, but if my unit is working
properly, it's about the worst performing GPSDO I've seen.

By the way -- to do this test, I started with both the -XO and -RB units
online and interconnected the way they were supposed to be.  After a
couple of days of operation, I pulled the interconnect cable and the -RB
went off line, while the -XO came on.  I then started data collection.
After I'm satisfied with the amount of XO data I have, I'll reconnect
the cable and do the same test on the -RB side.  The full set of plots
is at http://www.febo.com/pages/oscillators/rftg/ and will be updated as
I get more data.


* http://www.febo.com/pages/oscillators/rftg/rftg-xo_cs1-adevplot.png
** http://www.febo.com/pages/oscillators/rftg/rftg-xo_cs1-freqdiff.png

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