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 Tue Dec 19 2000 - 20:00:24 MST