Hi Frank, SM5BSZ has interesting article about measuring low PN oscillators.
http://www.sm5bsz.com/osc/osc-design.htm He also describes there his NEWREF which achieved -179.5 dBc/Hz. You could use it as practical design example. Regards, Piotr, sp3ukk On Sun, Sep 19, 2010 at 10:40 PM, Mike Feher <mfe...@eozinc.com> wrote: > Frank - > > DBMs are extremely cheap in the frequency range you are talking about. The > rest, well, you just have to try. I think you are way overcomplicating > this. > I am still not sure why you feel you need a xtal filter. It is not going to > help with the 100 Hz away stuff. Using simple BJTs common base > configuration > would give you more than enough isolation for what you are doing. Besides, > I > believe you will only be using one output at any given time. Sounds like > you > need to experiment and learn. Else just do it and see what you get. That is > what all of us did when we needed something special, and then that way > learned what to do and what not. As I said, nothing about your approach > seems magical or even difficult. I have been a ham for almost 50 years. > While in HS everything I built worked just fine. The more education I > received the greater my expectations became, however, it did not need to > over complicate matters. 73 - Mike > > Mike B. Feher, N4FS > 89 Arnold Blvd. > Howell, NJ, 07731 > 732-886-5960 > > > > > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of francesco messineo > Sent: Sunday, September 19, 2010 4:12 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] OT: xtal osc PN > > Hi Mike, > > On 9/19/10, Mike Feher <mfe...@eozinc.com> wrote: > > Frank - > > > > Great idea, so obvious I did not think of it. If you mix the 20 and 22 > you > > will only get 3 dB degradation or still very close to the -131 dBc/Hz > > relative to the 10811A. As I mentioned before the architecture is > relevant. > > I have found that mixing does not cause any noticeable degradation, and I > > used to go all the way up to 45 GHz on military programs where it was > very > > critical. At the frequencies you are talking about I doubt if the > amplifiers > > will have any appreciable degradation either. Of course you have to keep > > levels in perspective, as you will not do better than kT. I also do not > > believe that dividers will have much impact. After all, a DDS is a > > divider/counter and accumulator, and PN is usually considered to be very > > close to 20logN better at the output than the reference, however, DDS > does > > have spurious at most frequencies, but that is a discussion for another > > time. I still think your original thought is your best approach. Fast, > easy > > and less than $100, even if you do use a used 10811A. 73 - Mike > > this approach as I said has a lot of unkown to me, for example, how to > divide by 5 (ttl or cmos or maybe synchronous or something else?), > then there's the doubler (diodes? jfet?), then the mixers: need them > to be diode mixers (a classic double balanced? can be homebrewed or > better use ready-made?) or I can get away with something cheaper like > fet mixer or something else? > Finally the xtal filters, those need to be ordered, where? what > exactly do I need as filter here in terms of poles or number of xtals? > Not to mention I need to "reuse" many of the signals, this means a few > isolation amplifiers with good isolation. > After posing myself these questions I thought I might evaluate other > approaches :-) > > Best regards > Frank > > _______________________________________________ > 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.