[time-nuts] OT: xtal osc PN

[Mike Feher]

Well, if one just looks at the spec of the 10811A for relative performance,
it is -140 dBc/Hz at 100 Hz offset at 10 MHz. Realistically, probably a
little better. From that it would be real easy to generate the frequencies
Frank is looking for, obviously 20 would be easy but would be only -134
dBc/Hz at 100 Hz away. 22 would be easy by diving the 10 and mixing it with
the 20, assuming the divide by 5 has a very small contribution, the PN of
the resultant at 2 MHz is also theoretically 20logN better, so, mixing will
also give close to -134 dBc at 100 Hz away. 42 can easily be generated by
doubling the 20, to get -128 dBc at 100 Hz and then mixing with the same 2
MHz to get the 42 MHz, still resulting in almost -128 dBc/Hz at 42 MHz.
Obviously filters will have to be used to get rid of the unwanted lower
mixing products. Depending on the architecture used, as stated below,
further multiplications will again decrease these numbers by 20logN.
Filtering at the IF with a 250 to 500 Hz filter is not going to do anything
to the 100 Hz numbers. I assume the mode of communications here is CW, hence
the narrow filter at IF. 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 jimlux
Sent: Sunday, September 19, 2010 2:03 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] OT: xtal osc PN

francesco messineo wrote:
> Hi Mike,
> 
> as I said, current plans are for a few frequencies in the 20-50 MHz
> range. The current project needs 20, 22 and 42 MHz oscillators.
> 


But you're multiplying that up, it will be 20log(N) worse...

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