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

[ghf at hoffmann-hochfrequenz.de]

Am 2023-03-24 22:00, schrieb Christophe Huygens via time-nuts:
> 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've made a takeout from my 432 MHz -> 32 MHz transverter published in 
DUBUS 2 or 3
2022. It is just the ECS 100 MHz xtal oven, PLL to lock it to 10 MHz and 
further
multiplier to 300 or 400 MHz. My GPS delivers 10 MHz. I simply take the 
interesting
LVCMOS harmonic and dump it into a SAW or LC filter. There seem to be no 
SAWs for 300 MHz.

<  
https://www.digikey.de/de/products/filter/oszillatoren/172?s=N4IgTCBcDaIKYGMDOACRB7BKwFYwQF0BfIA 
   >

The 10->100 MHz PLL is 4046 + 74LVC161 1/10 divider. The 9046 is not 
available.
With a low enough filter corner, PN depends on the XO only.
I asked ECS for the phase noise plots of their 100 MHz oven and got them 
with
no NDA attached, so here it is. I think the layout can accommodate the 
CVHD-950
but this has never been tested. The entire takeout has not yet seen 
solder.

300 MHz is a more lucky choice WRT amplitude than 400. The oven already 
delivers
LVCMOS so there is not much to be lost by further buffering. 300/400 MHz 
happen to
be the fastest clock frequencies for the LMX2594 synthesizer in 
fractional/integer
mode.

> 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

My LVC161 prescaler created some spurs at frequencies one would never 
expect.
That's why it has it's own small house now.
I'm building stereo downconverters for my Timepod @100 MHz and X-band, 
but
day-time work takes precedence and my VNA is ill.
A few empty boards, Gerbers or Altium Designer files are available.
Outside EU, Gerber files for JLCPCB will be less ado than a leftover 
board.

regards,
Gerhard  DK4XP


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