[time-nuts] Centering ocxo

Don Latham djl at montana.com
Wed Oct 3 13:14:39 EDT 2012


Please don't adjust the dampening, you might find it floating...
adjust the damping if you need to change the settling time.
Yours in pedantry-one of my hot buttons :-)
Don

Bill Dailey
> ok..  So that may very well be true of this unit.  Electrical tuning is
> 3E-7  0 - 5v (+/-).  It also lists a digital tuning range of +- 3Hz at
> 10MHz.  Correct me if I am wrong but that appears to mean 3Hz electrical
> and 6Hz digital tuning range.   I am not doing digital tuning but
> thought I
> would throw that out there.
>
> I have been trying to "optimize" parameters on this Fury board but it
> seems
> my "optimization" has just been increasing the deviation.  Running 1.8
> ns
> sd overnight with an average TI of about 26ns (was with my "optimized"
> settings)...the original settings were giving me a much lower
> deviation...I
> didnt log it but looking at the graph of frequency in excel I would say
> probably between 0.1-0.6 ns.  I just put it back on the original
> settings
> and am letting it settle now.  Was adjusting Dampening, EFCSCALE and DAC
> gain.  My observations reveal dampening makes it a bit slower to respond
> and perhaps settles it some, The efcscale seems to act as pure gain on
> top
> of the baseline dac gain which is essentially determined by the tuning
> range as you referred to.  What I saw with a low efcscale is that the TI
> was higher but the SD lower... with efc scale higher the TI was lower
> but
> the SD suffered.
>
> Since my goal here is low noise and very good short term stability I
> prefer
> the lower efcscale  (low gain with low SD).
>
> Let me know if I have any gross conceptual errors here or if I am
> looking
> at this properly.
>
> Doc
> KX0O
>
>
> On Tue, Oct 2, 2012 at 11:54 PM, Hal Murray <hmurray at megapathdsl.net>
> wrote:
>
>>
>> docdailey at gmail.com said:
>> > I am ok for awhile but how do you center the efc of an ocxo?  I
>> understand
>> > there is something (screw) to adjust the ocxo so it is approximately
>> on
>> freq
>> > with 2.5v efc.
>>
>> > Specific oscillator datum-1111c. I have he datasheet but doesn't say
>> "coarse
>> > frequency adjust this screw" or some such.
>>
>> There may not be a coarse adjustment.  If the tuning range is big
>> enough to
>> cover the aging over your design life, you don't need one.
>>
>>
>> There is a tradeoff between adjustment range and the number of bits
>> you
>> need
>> in a DAC to get a required accuracy.
>>
>> Suppose I have an adjustment range of 1 Hz (peak to peak) on a 10 MHz
>> oscillator.  That's 1 part is 10^7.  If I have a 10 bit DAC, I can
>> adjust
>> to
>> 1 part is 10^10.  A 20 bit DAC can get to 1 part is 10^13.
>>
>> But if the tuning range is 10 Hz, the same 20 bit DAC setup only gets
>> you
>> to
>> 1 part is 10^12.
>>
>>
>>
>> --
>> These are my opinions.  I hate spam.
>>
>>
>>
>>
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>
>
>
> --
> Doc
>
> Bill Dailey
> KXØO
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>


-- 
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
De Erroribus Medicorum, R. Bacon, 13th century.
"If you don't know what it is, don't poke it."
Ghost in the Shell


Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com






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