[time-nuts] Close in phase noise of microwave VCOs

Bob Camp kb8tq at n1k.org
Sat Jun 20 14:25:08 EDT 2015


HI

> On Jun 20, 2015, at 9:25 AM, Jim Lux <jimlux at earthlink.net> wrote:
> 
> On 6/19/15 9:30 PM, Bob Camp wrote:
>> Hi
>> 
>> One of the most interesting things about the last paper mentioned:
>>> On Jun 19, 2015, at 8:57 PM, Charles Steinmetz <csteinmetz at yandex.com> wrote:
>>> 
>>> Rick wrote:
>>> 
>>>> However, a better tutorial would be the one written by
>>>> HP's Dieter Scherer which was published in Microwaves
>>>> & RF Magazine (or possibly Microwave Journal).  I believe
>>>> the same content was available from HP as an Ap Note or
>>>> something.
>>> 
>>> I suspect the paper you are referring to is:
>>> 
>>> Design Principles and Test Methods for Low Phase Noise RF and Microwave Sources (Scherer, 1978)
>>> 
>>> It is available on Didier's site at:
>>> 
>>> <http://www.ko4bb.com/manuals/download.php?file=03_App_Notes_-_Proceedings/Scherer_Low_noise_source_design_and_test.pdf>
>>> 
>>> There are two other Scherer papers there:
>>> 
>>> Generation of Low Phase Noise Microwave Signals (Scherer, 1981)
>>> <http://www.ko4bb.com/manuals/download.php?file=03_App_Notes_-_Proceedings/Scherer_Low_PN_Signal_Generation.pdf>
>>> 
>>> The "Art" of Phase Noise Measurement (Scherer, 1985)
>>> <http://www.ko4bb.com/manuals/download.php?file=03_App_Notes_-_Proceedings/Scherer_Art_of_PN_measurement.pdf>
>>> 
>> ^^^^^^^^^ this one
>> 
>>> Best regards,
>>> 
>>> Charles
>>> 
>> 
>> is that it has a phase noise plot on an open loop microwave source down to 10 Hz. Not quite the VCO Jim
>> was looking for, but close ….
>> 
>> 
> 
> page 25 shows down to 100 Hz, "Typical Free-Running Source at 10 GHz". Eyeballing it it looks like 20dB/decade from 10-100k, a bit more from 1-10k, and almost 30 dB/decade from 100Hz to 1k. I wonder what the source was?
> 
> The SAW is definitely in the 30dB/decade bucket
> 
> 
> This makes a good case for the "30dB/decade very close in”


I think that (unless something is *very* wrong) the 30 db / decade number is a safe bet. I have seen 40 db / decade happen on devices. It’s rare. In the cases I’ve seen it was an indication of something wrong in the design. It’s also rare to see anything that is an oscillator stay at 20 db / decade as it gets close in.

The other thing that the plots pretty clearly show is that the “dbc” can go into the positive region (it’s above carrier not below) on some of what you are looking at.  

Bob

> 
> 
> 
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