[time-nuts] OT: xtal osc PN

francesco messineo francesco.messineo at gmail.com
Mon Sep 20 10:08:45 UTC 2010


Hi Piotr,

many thanks for the link, I didn't know that page!
Best regards

Frank IZ8DWF

On Mon, Sep 20, 2010 at 12:05 PM, Piotr Kolodziejczyk <sp3ukk at gmail.com> wrote:
> 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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