Hi Indeed, the output can never be better than the input with a DDS, but the Cy2302 is rated at a 90 to 100 ps jitter level. These days sub 1 ps jitter is a more reasonable spec for those sort of parts.
A lot depends on how wide a band you want to cover. A VCXO can pull +/- 1000 ppm and still do fairly well. That would give you +/- 14 KHz on 20 meters. For high(er) performance you could run over a 1.5 KHz range with a VCXO. Either way you still need to lock it up. An mix down and then compare architecture is probably the quick / easy way to go for sub 1 Hz steps and good spurs. Your synthesizer would be pretty band specific, but it could be quite low power. Bob On Aug 30, 2013, at 2:30 PM, "Collins, Graham" <[email protected]> wrote: > Hi Bob, > > Agreed. > > I was looking around for some different ideas on frequency multiplication and > stumbled across these "built in VCO" parts such as the CY2302. My first > thought was that they seem to be targeted to multiplying and synchronizing > clocks in digital systems rather than RF multiplication. > > Ultimate use of the DDS generated signal is as a high stability RF source for > a very low power transmitter for use with amateur radio QRSS modes. The > signals are typically frequency shift keyed or about 5 Hz and use slow data > keying to permit long integration at the reception location. Transmitted > Power levels are frequently 100 mW plus or minus, sometimes much lower. > Frequency stability is needed. The data keying is usually time synced as > well, commonly having a 10 minute frame rate, sometimes longer, sometimes > much longer. > > The more I think of it, the more it seems that the better choice is the > multiplier chain to get from 10 MHz to where I need to be. Perhaps I will > have a go at building an 80 MHz VCXO and phase locking that to my external 10 > MHz ref. > > There is another interesting chip, the SI-570, one version of which has a > Vcontrol input for FM'ing. Locking this device to an external 10 MHz > reference should not be much different than building a GPSDO. > > As I have discovered, with respect to these DDS chips, the signal out can > never any better quality than the refclock going in - GIGO. > > Cheers, Graham ve3gtc > > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Bob Camp > Sent: August-30-13 1:21 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] frequency multiplication > > Hi > > A discrete VCXO and PLL chip will always outperform the "buit in VCO" silicon > parts. The CY2302 is quite noisy even by silicon standards. Your doubler / > tripler will give you good close in noise, but poor performance broadband. A > lot depends on what the ultimate use for the DDS output is. The DDS it's self > likely has enough issues noise and spur wise to make the quality of the clock > driving it somewhat less important. > > Bob > > On Aug 30, 2013, at 12:56 PM, "Collins, Graham" <[email protected]> wrote: > >> >> >> Good day all, >> >> Lately I have been contemplating a variety of methods to take a high >> stability 10 MHz reference multiply it up to a suitable frequency for use a >> the reference clock for a DDS, for example 10 MHz to 80 MHz or 120 MHz (or >> whatever). >> >> On method is to use simple diode based doublers and triplers to get to where >> I want to be, that 10 x 2 x 2 x 2 = 80 or 10 x 3 x 2 x 2 = 120 or whatever >> combinations that would accomplish the same thing. >> >> Another is the use of something like the Cypress CY2302 frequency multiplier >> and zero delay buffer which uses a PLL to perform it's magic (i.e 2 or 4 or >> 8 or 16 times multiplication). >> >> My goal is to be able to use the DDS to generate a stable frequency close to >> the stability of the 10 MHz reference with good phase noise although the >> latter criteria is ill defined and of lesser importance than frequency >> stability at the moment. >> >> Anyone have any firsthand experience with the likes of the CY2302 and can >> comment on their suitability for this task? >> >> Cheers, Graham ve3gtc >> >> _______________________________________________ >> 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. > _______________________________________________ > 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.
