[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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