[time-nuts] more is revealed about OCXO harmonics & level

walter shawlee 2 walter2 at sphere.bc.ca
Wed Jan 27 23:33:41 UTC 2016

I decided to rip the add-on board apart, and go right to the oscilloquartz 8633 
no surprise, >0dBm level, but alas, 20Mhz harmonics are only -35 dB down, and 
there's one at 30, etc..  hmm, what does this really mean?  well, when in doubt, 
go back and look at the data:


rats, *the spec is only -25dBc for harmonics*.  phase noise looks good, as does 
stability, but
now I understand why I am seeing these spurs, it's in spec!  it does look like 
my level is out of spec though, I cannot get +4dBm even right from the module, 
perhaps that's why these units became surplus.  the date code on my OCXO 8663-XS 
is 2008.  I cannot identify what the X part of the dash number means, maybe 
lower output with my luck?

to make the board a bit safer to use, I made up a resistive splitter with 2 51R 
carbon resistors, and slipped ferrite beads on the leads to help control high 
frequency harmonic content.  I can now run the counter and SA at the same time, 
and get maybe -2dBm outputs, closer to 0dBm if I use only one.
if I add my outboard 10MHz bandpass filter, harmonics drop into the grass at 
-60dBm, but level goes to -5dBm.

clearly not as nice as the FE5680A Rb unit, but I will leave it in there just 
for comparison. I think I will filter one output, and leave one raw, since I 
have 2 jacks already at the front for outputs. but this was very instructive, I 
really did not expect to see so much harmonic content from a precision OCXO 
sinewave crystal oscillator.  a quick cross check on some of my other hp/FE 
ovenized standards in the lab does not show this kind of unwanted content.

what kind of results does everyone else get?

all the best,

Walter Shawlee 2, President
Sphere Research Corporation
3394 Sunnyside Rd.,  West Kelowna,  BC
V1Z 2V4  CANADA  Phone: (250) 769-1834
walter2 at sphere.bc.ca
WS2: We're all in one boat, no matter how it looks to you.
Love is all you need. (John Lennon)
But, that doesn't mean other things don't come in handy. (WS2)

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