[time-nuts] OXCO Spurious Output at Line Frequencies

Bob Camp kb8tq at n1k.org
Tue Jul 12 19:25:00 EDT 2016


Hi

Bottom line:

This is why you often see spur specs stated with a lower frequency limit (like 250Hz) or 
an exclusion for line related spurs. 

One really fun one not (yet) mentioned: 

All of those motors in the building are rotating at line frequency. You don’t just have an 
electromagnetic field. You can have an acoustic / vibration field as well. Probably not a big 
deal, but it’s there ….

Bob

> On Jul 12, 2016, at 6:45 PM, Alan Melia <alan.melia at btinternet.com> wrote:
> 
> Bob the VLF guys in Europe can receive the 60Hz signal over here! so you probably needed a test site on the far side of the Moon :-))
> Alan
> G3NYK
> 
> ----- Original Message ----- From: "Bob Camp" <kb8tq at n1k.org>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Sent: Tuesday, July 12, 2016 10:53 PM
> 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 <martyn at 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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