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Transmission line probes take advantage of larger bore sizes because losses in coaxial lines are minimized with increase in diameters of their conductors and with ability to maintain ratio of these diameters as close to optimal as possible.
This compact TxL circuit design has been described in [1] and is based loosely on traditional transmission line circuits by McKay-Shaefer [2] and by Rienstra [3].
A sleeve balun is employed in the 1H channel to electrically balance the sample coil and to prevent RF field from becoming inhomogeneous due to wavelength effects at very high 1H frequency.
This probe is built around Varian 3.2 mm PencilTM MAS stator, which is capable of spinning speeds up to 25 kHz.
Low temperature applications are planned down to 123K once the upgrades are made to external heat exchangers and transfer lines.
(As of January 1, 2007)
| 1H |
B1 = 135 kHz @ 330 W |
20 ms pulses every 2 s |
| X=13C |
B1 > 100 kHz @ 140 W |
10 ms pulses every 2 s |
| X=15N |
B1 = 80 kHz @ 520 W |
2 ms pulses every 2 s |
Nuclei are switched by replacing chip in the probehead next to the stator and by switching the RF component at the end of the threaded wand, which is inserted at the bottom of the probe (black knob labeled "X WAND").
Use tuning table below to replace the chip in the probehead, visible in the top photo (insert chip from right to left). Then unscrew the the black wand and take it out of the probe.
The tip of the wand has snap-in component plug, which must be replaced according to the tuning table.
Replace it as needed. Do not over-tighten when threading the wand back into the probe's base.
| Isotope |
Removeable chip
inside probehead |
Plug for wand
inserted at base |
| 15N, 35Cl |
82 pF |
39 pF chip |
| 207Pb |
12 pF |
6.8 pF chip |
| 13C |
10 pF |
empty blank plug |
| 11B |
5.6 |
inductor |
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If your isotope is not in the above table, contact Peter Gor'kov to arrange new tuning plugs.
[1] R.Fu et al., J. Magn. Reson. 177 1-8 (2005) [ read online]
[2] J. Schaefer, R.A. McKay, US Patent: 5,861,748 (1999)
[3] C.M. Rienstra, Thesis, in Chemistry, MIT (1999)
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