Hi all, I'm fairly new here and might not fully understand things.
Earlier in this thread it was suggested that one lock an 8Mhz signal to a 10 Mhz signal by analogue methods. To quote A Plummer: "and it is relative easy to make 10MHz from 8MHz with analog frequency manipulation, which generates less jitter 73" and H Poetzi asked the same thing as I am: "On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote: > and it is relative easy to make 10MHz from 8MHz with analog > frequency manipulation, which generates less jitter Could you elaborate on this a little if time permits? I'm more a 'digital person' but it sounds interesting. Thanks in advance, Herbert" I have not seen how that is done as suddenly the signals are 24Mhz and 10 Mhz and digital dividers and multipliers are used. One other point. Attila mentioned using "LEA-M8T". I assume the T suffix relates to Time rather than the plain GPS. What is the difference? Apart from 50% higher cost. Cheers Will ZL1TAO > Sent: Sunday, April 10, 2016 at 7:00 AM > From: "Bob Camp" <kb...@n1k.org> > To: ewkeh...@aol.com, "Discussion of precise time and frequency measurement" > <time-nuts@febo.com> > Subject: Re: [time-nuts] Advise on building a DIY GPSDO? > > Hi > > Averaged over a long enough time (and without any hanging bridges) the > frequency accuracy > will be fine. The frequency accuracy of a 1 pps output on a GPS is “fine” on > the same basis. Since > 200 KHz is a “round division” off of any of the likely TCXO’s you will not > have any jitter or spurs in the “static” > case. > > Bob > > > > On Apr 9, 2016, at 10:07 AM, Bert Kehren via time-nuts <time-nuts@febo.com> > > wrote: > > > > I do not know what U blox does but I know when we use 200 KHz out of the 1 > > pps output on a $ 10 ublox 6 we consistently get better than 1 E-10 closer > > to 1 E-11 out of the Morion have the data > > Bert Kehren > > > > > > In a message dated 4/9/2016 10:01:05 A.M. Eastern Daylight Time, > > kb...@n1k.org writes: > > > > Hi > > > >> On Apr 8, 2016, at 9:39 PM, time...@metachaos.net wrote: > > > >> > >> Hello Bob, > >> > >> Friday, April 8, 2016, 6:13:07 PM, you wrote: > >> > >>> Hi > >> > >>> If you start from a 24 MHz TCXO (different modules use different TCXO’ > > s): > >> > >>> On an 8 MHz output, most of the time you divide by three. > >> > >>> On a 10 MHz output, you need to divide by 2.4. The net result is that > > you > >>> divide by 2 sometimes and 3 other times. > >> > >>> In the 10 MHz case, there is a *lot* of energy at 12 MHz and 8 MHz, > > along with > >>> the 10 MHz output. > >> > >>> In the 8 MHz case, most of the RF energy is at 8 MHz. > >> > >>> ==== > >> > >>> To correct the output by 1 ppm on the 8 MHz output, you need to either > > drop or > >>> add one pulse out of every million pulses. Effectively you divide the > > 24 MHz by > >>> 2 or by 4 when you do that. You get a bit of 12 MHz or a bit of 6 MHz > > as a result. > >> If you know you are doing a 24Mhz and a 10Mhz, why not divide the first > > by 12 > >> and the second by 5 and then phase lock the resulting 2Mhz? Or divide by > > 24 > >> and 10, respectively and lock the 1Mhz? That way, everything is exact. > > > > The bigger problem is that the 24 MHz is *not* exact. It is simply a free > > running TCXO > > that happens to be in a GPS module. It has a basic accuracy of +/- 1 ppm > > or something > > similar. It is no better or worse than any other TCXO you could buy. > > > > To make it accurate they have two choices: > > > > 1) Put a voltage control input on the TCXO and turn it into a TCVCXO, then > > lock it up > > with a loop. > > > > 2) Let the oscillator free run and “fix up” the output. > > > > For a variety of reasons, none of the small GPS modules go with option > > number 1. They > > all go with option number 2. The 24 Hz error on the (maybe) 24 MHz gets > > taken out by dropping > > 24 edges every second. That’s not a lot of edges, it’s not going to turn > > the output into absolute > > garbage you can see on a scope. It is plenty of nonsense to mess up a > > radio or a piece of test gear. > > > > One easy way to look at it: You have ~1 ppm jitter on the output (in the > > example of 1 ppm of error). A > > phase locked GPSDO with only simple filtering of a 1 pps would get you > > down to 0.01 ppm of jitter. > > A sawtooth corrected 1 pps would get you to 0.01 ppm. A good filter would > > get you to <0.00001 ppm. > > Yes, I’m using a very hand waving definition of jitter here, but it does > > illustrate the point. You could > > look at the jitter on the pulse drop as 0.04 ppm. > > > > Bob > > > >> > >> > >> Mike > >> > >>> That can be filtered out with a RF filter. The same is true with a > > (somewhat more > >>> complex) filter on the 10 MHz output. > >> > >>> In addition to the “big” RF spurs, you get a low frequency component > > to the output > >>> modulation. You are “phase hitting” the output eight times a second. > > That gives you > >>> an 8 Hz sideband along with the further removed stuff. Since it’s not > > simple / clean > >>> phase modulation, there are more sidebands than just the few mentioned > > above. > >> > >>> What messes things up even more is that you never are quite doing one > > ppm. You are doing > >>> corrections like 0.12356 ppm this second and 0.120201 ppm the next > > second. > >>> The pattern of pulse drop and add is not as simple as you might hope. > > The low > >>> frequency part of the jitter (and it will be there) is no different > > than the noise on > >>> a 1 pps output. You still need to do very long time constant (or very > > narrow band) > >>> filtering to take it out. > >> > >>> Bob > >> > >>>> On Apr 8, 2016, at 7:06 AM, Herbert Poetzl <herb...@13thfloor.at> > > wrote: > >>>> > >>>> On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote: > >>>>> and it is relative easy to make 10MHz from 8MHz with analog > >>>>> frequency manipulation, which generates less jitter > >>>> > >>>> Could you elaborate on this a little if time permits? > >>>> I'm more a 'digital person' but it sounds interesting. > >>>> > >>>> Thanks in advance, > >>>> Herbert > >>>> > >>>>> 73 > >>>> > >>>>> On 4/4/2016 4:27 PM, Attila Kinali wrote: > >>>>>> On Mon, 4 Apr 2016 17:56:29 -0400 > >>>>>> Bob Camp <kb...@n1k.org> wrote: > >>>> > >>>>>>> The variable frequency output on the uBlox (and other) GPS > >>>>>>> receivers has come up many times in the past. > >>>> > >>>>>>> If you dig into the archives you can find quite a bit of > >>>>>>> data on the (lack of) performance of the high(er) frequency > >>>>>>> outputs from the various GPS modules. They all depend on > >>>>>>> cycle add / drop at the frequency of their free running TCXO. > >>>>>>> Regardless of the output frequency, that will put a *lot* of > >>>>>>> jitter into the output. > >>>>>> That's why you should put the output frequency of the ublox modules > >>>>>> to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz. > >>>> > >>>>>> Attila Kinali > >>>> > >>>> > >>>>> _______________________________________________ > >>>>> time-nuts mailing list -- time-nuts@febo.com > >>>>> To unsubscribe, go to > >>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >>>>> and follow the instructions there. > >>>> _______________________________________________ > >>>> time-nuts mailing list -- time-nuts@febo.com > >>>> To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >>>> and follow the instructions there. > >> > >>> _______________________________________________ > >>> time-nuts mailing list -- time-nuts@febo.com > >>> To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >>> and follow the instructions there. > >> > >> > >> > >> -- > >> Best regards, > >> Timenut mailto:time...@metachaos.net > >> > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@febo.com > >> To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> and follow the instructions there. > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.