[time-nuts] Re: Characterizing a 100M TCXO

[Ed Marciniak]

I think you might find some answers in your tolerance for potential spurs(how close in), and PLL loop bandwidths in figuring out how many loops are optimum, and which reference division ratios.

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________________________________
From: Christophe Huygens via time-nuts <time-nuts at lists.febo.com>
Sent: Friday, March 24, 2023 4:00:03 PM
To: time-nuts at lists.febo.com <time-nuts at lists.febo.com>
Cc: christophe.huygens at kuleuven.be <christophe.huygens at kuleuven.be>
Subject: [time-nuts] Characterizing a 100M TCXO

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.





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