[time-nuts] 5065A phase noise

[Chris Caudle]

On Thu, October 15, 2020 12:11 am, AC0XU (Jim) wrote:
> I was able to borrow a Holzworth HA7062C phase noise
> analyzer recently and used it to measure phase noise for
> several oscillators.
>
> I have a few questions:
>
> 1) I noticed that ground loops can be a significant problem - generating
> noise peaks at multiples of 60Hz and/or multiples of 120Hz. If this were
> merely additive noise, then no noise peaks near the 5MHz or 10MHz carrier
> should result in the analyzer, so non-linearities must be involved. Where
> are those non-linearities arising and how can they be eliminated?

If you look at the block diagram of the instrument on page 3 of this
document:
https://www.holzworth.com/Portals/0/HA7062C_Web_Datasheet.pdf

You will notice that there is a mixer stage intrinsic to the instrument,
and the input signal to be measured is mixed with the local oscillator to
a lower frequency.  That is an inherently non-linear operation.


> 2) Using several 50 ohm baluns and disconnecting power
> supplies from ground eliminated some of the 60Hz-related
> noise in my tests but not all.

The devices under test were powered from the AC line?  Any device powered
from AC (at least with the AC to DC supply inside the chassis) will have
line frequency related electric and magnetic fields inside the chassis,
depending on what length the designers went to for containing those it is
not surprising to see some level leak through to the device output.

I am not familiar with the internal design of the 105 oscillator, I know
several here are so I will let someone else comment on likely source of
the 10kHz and 100kHz you saw.

-- 
Chris Caudle