I can't seem to get the line related spurs much below -170dBc/Hz for the
fundamental and -180dBc/Hz for the line frequency related harmonics. Everything
was bolted down to a 12mm thick aluminium slab. Avoiding an Earth loop by
isolating the Timepod Ch0 and CH2 inputs from the aluminium plate seemed to
help.
Unfortunately I don't have a cornfield or equivalent readily available,
although there is a carpark and paddock at the local zoo to which I have access
after hours should I want.
Bruce
From: Bob Camp <kb...@n1k.org>
To: Discussion of precise time and frequency measurement <time-nuts@febo.com>
Sent: Wednesday, 13 July 2016 9:53 AM
Subject: Re: [time-nuts] OXCO Spurious Output at Line Frequencies
Hi
The “practical” solution often is to ship it to an office of the same company
that happens
to have 60 Hz power. The spur moves to 60 / 120 / 180 and they move on with
their
evaluation.
I have also played the “let’s do it with batteries" approach. Screen rooms were
of little benefit.
Simply running test gear on batteries did not do the job. Ultimately we wound
up in the
middle of an Illinois corn field with a bunch of gear modified to run purely on
batteries. The
spur did go down, but it never fully went away. It’s been 40 years since that
adventure so I
really could not say just how far down we got it ….
Anything past -120 db at line frequency is in the “don’t bother” category.
Bob
> On Jul 12, 2016, at 6:44 AM, Martyn Smith <mar...@ptsyst.com> wrote:
>
> Hello,
>
> I have a customer who is measuring the phase noise of my 10 MHz ultra-low
> phase noise frequency standard.
>
> He is seeing spurious signals at line frequencies (50 and 100 Hz as we are in
> Europe) at a level around -130 dBc.
>
> My opinion is that it's impossible to get much better than that. Even
> running on batteries make little difference, since the equipment is in a test
> rack with AC signals everywhere.
>
> Even the £50k R&S test set he is using only quotes a spurious spec of -90 dBc.
>
> What experience does anyone have here?
>
> Best Regards
>
> Martyn
>
>
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