[time-nuts] Characterizing a 100M TCXO

[Christophe Huygens]

Hi,

I am back on time-nuts after ... 15 years (kids etc...). I need some help in
characterizing a 100MHz TCXO (Crystek CVHD-950) which we used before
as a reference for a microwave PLL (ham project, see DUBUS 1/21). It worked
good from a PN perspective but uses multiple steps to get to the GPS-locked
100MHz used as the final reference.

I am trying to see if there is merit in locking the Crystek directly and 
therefore
would like to assess its short term time stability. We intend to make a 
bunch
of the above and simple is better here.

I dusted off and started my modest time lab and I *think* I have 
sensible results
with my setup. It may not be by the book: I am using a 5370B using a 
Symmetricom
TS3100 GPS-locked 10MHz as a the reference XO (on-time > 20 years), not the
internal 10811.

1. I guess I am seeing TS/HP5370B noise floor when measuring Z3801A 
10MHz in
frequency mode, since the results are not as good as those on 
leapsecond.com.
But still a lot better than the frequency results of 5370B on febo.com
(which I found confusing).
I am likely better of using the  Z3801A as a ref. for the 5370B but it
complicates my setup, one does get smarter with age and the lab is what 
it is.
I measured a NEO8M ublox 1pps using TI versus TB 1 pps  and that was as 
expected.

2. How do I go about for 100MHz measurements? Is frequency ok - it probably
will be for the Crystek? Or do I have to divide (MSI? prescaler? what s 
today's
simplest approach...) and then use  "pulsepuppy" next so I can get to TI?
Division has been asked before but a  definite answer has not come up imho.

My initial Crystek measurements certainly don t look great. 1PPS is already
better at tau way less than 10s and that is not the performance we want.

Any hints practical hints appreciated. Theory welcome too :-)

Xtof.