[time-nuts] OT: xtal osc PN

[Piotr Kolodziejczyk]

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 <mfeher at 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-bounces at febo.com [mailto:time-nuts-bounces at 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 <mfeher at 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
>
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