[time-nuts] SE880 GPSDO

[Bob Camp]

Hi


> On Apr 25, 2016, at 7:36 PM, Attila Kinali <attila at kinali.ch> wrote:
> 
> On Mon, 25 Apr 2016 23:34:52 +0200
> Ilia Platone <info at iliaplatone.com> wrote:
> 
>> I selected this because of the CMOS output, since I didn't find any 
>> Connor Winfield osc with these levels yet.
> 
> To get to CMOS levels, you usually add a simple inverter, with an
> capacitor in front and a 1M resistor across the inverter (from input
> to output).


If you set up a modern (74AC or faster) inverter with a resistor from input to 
output, you are very likely to get it running as an oscillator all on it’s own. That
oscillation may or may not add to the desired output. 

Stick with a two resistor bias on the input … it’s a lot safer.


> 
> 
>> Actually  want to achieve less than around 78ps jitter at 125MHz. (this 
>> should be achievable using this also: 
>> http://www.digikey.it/product-detail/it/fox-electronics/FVXO-HC53B-125/FVXO-HC53B-125-ND/2153894)
> 
> I think you are mixing up a few things here:
> 
> Your logger might have very relaxed jitter requirements, but the
> GPS module needs a low noise reference signal. If you feed it with
> the noisy HC53 output, you will degrade your GPS receivers performance
> severely. At the minimum, you should use a normal XO for the GPS modul.
> You can of corse use a HC53 as the reference for your logger if its
> jitter is ok for you.
> 
> And for comparison, for a XO you usually talk about jitter in the
> order of 100fs to 1ps (10kHz-20MHz)
> 
> 
> 
> 			Attila Kinali
> -- 
> Reading can seriously damage your ignorance.
> 		-- unknown
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Bob