[time-nuts] True Position GPSDP + Rb X72

Bob kb8tq kb8tq at n1k.org
Fri Sep 22 11:50:29 EDT 2017


Given the noise levels of typical Rb’s - use XOR gates as the mixers. 

Do a either a simple LPF on the output or ignore the HF component 
(each approach is a bit of a tradeoff). 

Once you have the beat notes, feed them into timer inputs on your uC
chip of choice. 

If you do the filters as R/C’s they are cheap. If you just re-clock, you
maybe add a flip flop or two to each channel. Total BOM for the DMTD
part of it would be < $1 not counting the OCXO. 

All of the previous comments about “why would you want to do this?” 
still apply. Most of the small Rb’s we can get our hands on have really 
awful phase noise and spurs. That’s not true of all small Rb’s, but buying
them new in small volume at $2K each is not something most of us 
are interested in doing ….

Lots of fun


> On Sep 22, 2017, at 9:37 AM, Attila Kinali <attila at kinali.ch> wrote:
> On Wed, 20 Sep 2017 10:21:51 -0400
> Bob kb8tq <kb8tq at n1k.org> wrote:
>> An alternative is to add an offset oscillator to the mix and look at beat 
>> notes. It does not have to be ultra close. An 11 MHz offset signal would take the 
>> 12 ns down to an effective 1.2 ns. Odd frequency OCXO’s sell cheap on
> I considered the DMTD approach as well, but couldn't come up with a
> good idea how to make it easy and reliable to implement.
> How would you approach this?
> 				Attila Kinali
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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