[time-nuts] OT: xtal osc PN

Mike Feher mfeher at eozinc.com
Sun Sep 19 20:40:08 UTC 2010


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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