[time-nuts] How far can I push a crystal?

Robert LaJeunesse rlajeunesse at sbcglobal.net
Wed Jan 23 09:22:17 EST 2013


Hi Ed,

Thanks, your explanation of single PLL helps. I see it now somewhat in the sense 
of "only have to BUILD a single PLL" to make things work. I can appreciate the 
simplified effort greatly. I also now think of the PLO as an oscillator locked 
to a tuned harmonic that (probably) comes from some sort of comb generator, so 
that's not a PLL in the more conventional sense, and the resulting system 
becomes a true "single PLL" design. I'll look forward to hearing how it works 
out.

Bob L.


----- Original Message ----
> From: Ed Breya <eb at telight.com>
> To: time-nuts at febo.com
> Sent: Tue, January 22, 2013 11:46:35 PM
> Subject: Re: [time-nuts] How far can I push a crystal?
> 
> I tried to send this message on Sunday, but for some reason it didn't go  
>through, so here it is again. Please excuse any redundancy if the original shows  
>up. I will have an update of the project soon.
> 
> Hi Bob L.,
> 
> Your  suggestion of the 300/953 scheme was inspiration for what hopefully will 
>be the  simplest solution of all - I've started building it. First, I should 
>clarify  more, that the original scheme actually has three phase-locked loops - 
>a 10.7  MHz, a 10.05944444 MHz, and the final one, 1207.1333333 MHz. The last 
>one is a  PLO brick that just multiplies any RF input by any n within reason to 
>phase lock  the microwave output (to nth harmonic of input). I wasn't counting 
>that one,  since it's more or less a fixed function, but it's a variable 
>(arbitrary n) in  the numbers game. So, when I was referring to getting rid of 
>one PLL, I meant  not needing to produce the intermediate 10.7 MHz, since the 
>"953" gives a  rational number solution directly from 1 or 10 MHz - this is the 
>"single PLL"  scenario.
> 
> I tested the PLO and microwave section with 15.883333333 MHz =  (10 
>MHz/600)*953 from a synthesizer, and it worked just fine. The PLO is tuned  near 
>1207 MHz, and uses whatever n lands it within lock range, so n=76 in this  case. 
>If you adjust the cavity, n can just as easily be 75 or 77, with different  
>output frequencies, or a number of numbers that satisfy the bounds of operation.  
>So, the trick is to produce that one "correct" frequency from the 10 MHz  
>reference, cleanly enough to get the job done, and feed it to the PLO - the n  
>value takes care of itself.
> 
> The way it's partitioned now, I will have one  can containing the 15.8833333 
>MHz VCXO (74HC86 and a 16 MHz ceramic resonator),  two LAN LPFs, a 74HC4020 
>feedback divider (1/953), and a CD4046B PLL. A second  can, which is needed 
>anyway for handling the various external and internal 10  and 1 MHz references, 
>will not only route and scale, but will also include the  divider to make the 
>16.66666 kHz (10 MHz/600) reference for the other  box.
> 
> So, the overall synthesis chain is (10 MHz/600)*953*76=1207.133333  MHz. Pretty  
>simple.
> 
> Ed
> 
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