Luis On the second one at 50 MHz compare you will be able to do 25 Hz steps at 18 GHZ since this is fractional. They will not be exactly 25 Hz because of the fractional nature but if exact steps are required you use a reference that is a binary multiple, nothing major, I have done it to get exact 1 Hz steps. Takes an AD4157 with a Xtal VCXO, in my case 134.217728 MHz which actually gives me .33333 Hz steps. You should be able to get better than -90 dbc phase noise 20 KHz off. If you want to go that way I will be glad to get you data for your requirement. Bert In a message dated 10/15/2009 8:56:31 A.M. Eastern Daylight Time, cup...@mail.ua.pt writes:
Hi Bert, Thanks for the input. briefly; -Phase noise is not too important -It is to make just a few (and cost is not a major issue) The suggestions using prescalers or any other high speed digital chips may bring simplicity while compared with the design using multiple loops and harmonic mixers and samplers that is something I had in mind when I place the question out. I was wondering if recent technology would make possible to have a simpler approach. I like your first suggestion but I fear the spurious... I have no clue how bad it will be, but I guess I can only be sure if I make a prototype of that. The second one I must check how small would be the step... 1 MHz would be enough for a start. Thanks Luis Cupido. ewkeh...@aol.com wrote: > Luis > There is not really enough information to make a good recommendation. Is > this a one off or is the plan to make multiple units, what are the phase > noise requirements, what are the cost limitations? If cost is a major issue > there are in my opinion only two options. > In both cases a VCO has to be used presetting with a fast D/A. In the > first case you pre scale by 16 and feed an AD 9910 DDS as a programmable > divider using a 100 MHz output in to a Hittite HNC 439 phase comparator with > all the shortcomings of a DDS multiplied by the total divider ratio. > The second option is a Hittite HMC 700 fractional PLL and use 50 or 60 MHZ > compare frequency. You have to pre scale by 2 . Having used the all the > above components I can tell you the DDS works reliable at 1200 MHz in and the > 700 works great at 9 GHz. > I have not gone for switching speed but in my case emphasis is on phase > noise and resolution. As a matter of fact a friend of mine and I are doing a > low cost signal generator from 100KHz to 26 GHz in one Hz resolution using > the Hittite 700 part. Phase noise goal at 8 GHz is -100 dbc, 10 KHz offset. > We use surplus yigs. > Bert Kehren WB5MZJ > > > In a message dated 10/14/2009 3:25:33 P.M. Eastern Daylight Time, > cup...@mail.ua.pt writes: > > Hi, > > I'm looking for the schemes used on the > frequency synthesizers that change frequency > in few microseconds time (or less) > at microwaves lets say circa 12-18Ghz) > Obviously with some resolution (let's say 100Khz step > or in that order)(otherwise it would > be a trivial exercise in the BW of the PLL loop filter) > > Does anyone know of some paper or tech notes from > some instrument or modules that show block diagrams > of such? > > I have many info on mw synthesizers but all fall into > microwave radio style of things with much higher > resolution (khz and less) and much longer > switching times (millisencods or more). > Info on fast stuff I can't really find. > > > I'm thinking of experimenting on something along those > lines so... all comments are welcome. > > Thanks. > > Luis Cupido. > ct1dmk. > > _______________________________________________ > 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.