[time-nuts] Odd-order multiplication of CMOS-output OCXO

[Bob kb8tq]

Hi

> On Jan 20, 2020, at 1:36 PM, Mark Haun <mark at hau.nz> wrote:
> 
> On Mon, 20 Jan 2020 13:13:00 -0500
> Bob kb8tq <kb8tq at n1k.org> wrote:
>> On Jan 20, 2020, at 1:01 PM, Mark Haun <mark at hau.nz> wrote:
>>> A fair question... in fact I was initially planning to use the
>>> ABLNO + a PLL.  The OCXOs I found, however, are CTS VFOV405's with
>>> phase noise claimed to be just as good as the ABLNO or CVHD VCXOs:
>>> https://www.ctscorp.com/wp-content/uploads/VFOV405.pdf  
>> 
>> If you are starting at 16 MHz and multiplying by 5, the phase noise
>> will degrade by 20 log (N). In this case, that will be 14 db. The
>> degradation may be more than that, but it can never be less.
>> 
>> Another issue is just how the spec’s actually apply. On any
>> oscillator that is spec’d over a range of frequencies, some may do a
>> bit better than others. Will this device at that frequency exceed the
>> spec by 6 db? Will another model at the same frequency “only” exceed
>> the spec by one db? Without testing a bunch of them …. no way to know.
> 
> Well, worse than that, the VFOV405 phase noise is a "typical" not a
> "max" spec ;)  On the other hand, I should have some leeway at only 80
> MSPS and no bandpass sampling.  (The main spectrum of interest is 5-20
> MHz.)  I am aware of the 20logN relationship and that there will be some
> residual extra phase noise from my multiplier on top of it.
> 
> The VFOV405 datasheet lists typical phase noise for 10- and 100-MHz
> units.  (Mine are 16.384 MHz.)  In comparing the two oscillators, I have
> used the 100-MHz "typical" numbers which they both state:
> 

So taking the 14 db from multiplication into account:


		VFO405		ABLNO		

1K 		-126			-141
10K		-146			-160
100K	-149			-161

Looking at the plots on the ABLNO data sheets, the wide band noise gets
down a bit below -161 on a “typical” basis. 

Locking an 80 MHz ABLNO to 16.384 is not going to be as easy as locking
one to 16.000. Getting an ABLNO with an EFC at 16.384 x 5 may be a bit of
a challenge.

Bob
	

> offset    VFOV405    ABLNO
> 10        -90        -88
> 100       -120       -118
> 1k        -140       -141
> 10k       -160       -160
> 100k      -163       -161
> 
> (The ABLNO also provides a worst-case spec which is 3-5 dB worse.)
> 
> Regards,
> Mark
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.