[time-nuts] Sine or TTL signal transmission for low phase noise?

John Miles john at miles.io
Mon Jan 20 03:19:50 EST 2014


> Hi!
> 
> Taking a 10MHz signal from a rubidium clock to an external device it is
better
> to use 0.5-1Vrms sine wave or TTL? A 75 ohm coaxial cable will be used
with
> just 1 meter long. In any case the receiver will be made around a
unbuffered
> gate with self biasing (it seems that the 74AC type has better phase noise
> performance, as stated on http://www.ham-radio.com/sbms/LPRO-101.pdf.
> Circuit behaviour with other series like VHC, LV are unkown, at least for
> me!). Anyone have experience on EMI/RFI issues and phase noise
> performance under these circumstances?
> 

I'd bring the 10 MHz sine out of the rubidium standard and convert it at the
destination, if that's what you're asking.  There wouldn't be much upside to
moving the line receiver or comparator to the source end of the cable.   

If you want to see some quantified measurements of the 74AC04 buffer, check
out http://www.ke5fx.com/ac.htm .  The ones in the LPRO-101.pdf document
don't appear to be true residual measurements (plus, their suggested
circuits leave some room for improvement.)

-- john, KE5FX
Miles Design LLC



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