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 <[email protected]> > To: [email protected] > 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 > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
