In a previous life I once traveled to Paris to sort out similar issues
in a lab with a 500 and 600 sitting beside each other. The 500 was fine
and the 600 behaved badly in a fashion similar to what you describe.
The subway ran under the building so it was the likely culprit. After a
few false starts it was found that a nearby FM radio station switched
power massively with a schedule close to the subway.. midnight power
went down 6 am back up. Our problem was the lock frequency in the 600
matched the radio station! Better shielding on the VT setup fixed the issue.
Since you see issues with lock off I doubt a similar case in your case
but thought the mystery story worth repeating. Best luck with a
solution and please let us know the answer!
Best,
Ron Crouch
On 5/29/2015 2:17 AM, Christophe Farès wrote:
> Dear AMMRLers,
>
> I've seen some amazingly fast and helpful crowd-problem-solving on the
> AMMRWe oneL network lately, and so I thought I would share my own
> issue hoping for a similar response ;)
>
> We have a relatively newly installed AVIII Nanobay 300MHz system (with
> an older ultrashield magnet) used in open-access for routine 1D NMR.
> The 2D experiments are however plagued with horrible T1-noise streaks
> and we identified some major field instabilities as the most probable
> source of the problem. If we run a 1D 1H continuously without lock, we
> see erratic field jumps of up to +/-30 Hz! Curious however is that
> this phenomenon does not seem to occur completely randomly. For
> instance: it seems that there are periods of 5-8 minutes every 25-35
> minutes where they are more intense. And nights between approx 11pm
> and 4am, the interferences are almost completely gone. To illustrate
> what I mean, I've attached a printout of the 2d stacks (each column
> represents 2048 1D 1H measured every 2 seconds)...
>
> This is not observed on 400, 2x 500 and 600MHz spectrometers sitting
> only a few tens of meters away.
>
> Of course, the night relative calmness and "regular" more intense
> periods made us look into public transport schedules. The closest
> streetcar stop is 400m away, but the schedule correlates quite
> wellwith this phenomenon (for instance, the first one runs at 4:30,
> intervals are 20-30 minutes).
>
> So my questions are: what could be causing these disturbances and how?
> And of course, what can we do about it?
>
> best regards
>
> Chris
>
--
Ron
Received on Fri May 29 2015 - 14:01:02 MST