Jeff;
Baker Chemical in Houston, TX had a similar RF problem with the AC300. I
had a AF300 at Rice University and did not have the issue. I had 3 feet of
1920's type walls that block 90 MHz signals from radios statios and Radio
Shack remote control toys. (That is another old-timer story for another
days). Baker on the other had to insulate their rf co-ax cables with
glass beads. Talk to the Bruker engineers in the Woodlands Office, they
may have a solution for you since they helped Baker 10 years ago.
Alan Kook
Dell Computer Corp
alan_kook_at_dell.com
P.S. Yes, even though I'm not in the business anymore I still follow the
NMR trends
----- Original Message -----
From: "Jeff Walton" <jhwalton_at_ucdavis.edu>
To: <ammrl_at_wwitch.unl.edu>
Cc: "LAWRENCE BYRNES" <numare_at_eclipse.net>
Sent: Tuesday, December 19, 2000 1:55 PM
Subject: RF Interference
> Dear All,
>
> Thanks to all who replied before. I FINALLY figured out where this
> interference is coming from. It turns out that it is the campus
> radio station at 90.3 FM. The interference was so bad one day that I
> was able to hear it (the radio station) over the console speaker by
> turning the gain way up.
>
> This system, and I believe all the old GE systems, use an IF at 58.25
> MHz. The difference between 90.3 and 58.25 is very close to the
> difference between 58.25 and 26. Both signals beat against the IF
> and produce THE SAME DIFFERANCE FREQUENCY! For now the problem is
> particularly bad for one particular imaging coil. I can only imagine
> that there something about this coil which interacts with the to
> setup some sort of resonance at 90 MHz. Apparently, between this and
> because the station is relatively close, we are picking it up.
>
> I have never heard of this occurring before. I don't know how we are
> going to get rid of this aside from changing fields. We run this
> magnet at 0.6 Tesla rather than its design field of 2 Tesla due to
> environmental reasons (very tight space), so this is an unusual
> situation. Please let me know if any of you have run across something
> like this. I don't know if this has has anything to do with Lawrence
> Byrnes' problem on his Aspect 3000, but he may want to consider this
> as a possible source.
>
> Thanks Again!
>
> Jeff
>
>
> ******* Original Message *************
>
> Dear All,
>
> We have a 45 cm horizontal bore imaging system operating at 26 MHz (0.6
> Tesla). The spectrometer is an old GE 2T CSI system (we are running on the
> lowband) retrofit with a Tecmag Libra. Recently, radio frequency
> interference has plagued us. The amplitude of the interference depends on
> which coil we use. The interference appears to be frequency modulated.
It
> appears whether or not there is sample in the coil and appears over the
> entire tuning range of the coil, 25.5 MHz to 26.1 MHz. I can terminate
the
> coax with a 50 ohm resistor instead of the coil and it disappears. Thus,
> it appears we are picking something up through the air.
>
> Question: Does anyone know if there are any commercial, two-way hand held,
> or ham radios that regularly transmit around 26 MHz? Also, if anyone can
> think of another mechanism by which we might get this sort of
interference,
> I am open to suggestions.
>
> Thanks!
>
> Jeff
>
> ******* Original Message *************
> Jeffrey H. Walton
> Associate Research Physicist
> One Shields Ave.
> UCD NMR Facility, Bldg. MS1-D
> University of California
> Davis, CA 95616
> (530) 752-7794 (office)
> (530) 752-6480 (MS1-D lab)
> (530) 754-9064 (Cruess Hall lab)
> (530) 752-8109 (FAX)
> jhwalton_at_ucdavis.edu
> NMR Facility URL http://www.nmr.ucdavis.edu
>
Received on Thu Dec 21 2000 - 09:20:14 MST