20 (327) BRUKER BIOSPIN User Manual Version 002
General Hardware Setup
Figure 3.5. Matching Box Setup for High Power X-BB Preamplifiers
The frequency of the observed nucleus must be within the bandwidth of the
matching box (the matching box contains a low pass filter to suppress frequencies
above the X-nucleus frequency range (
1
H,
19
F) and a passive diode multiplexer,
which directs the RF pulse into the probe, and the NMR signal into the preamplifi-
er). High resolution preamplifiers use actively switched pin diodes for this purpose
and are therefore broadbanded, so there is no exchangeable box.
Pulsing with high power into an RF circuit which is not properly set up to pass this
frequency may result in damage to the RF circuit (in this case, the “matching box”)
or to the transmitter. This applies to filters, preamplifiers and matching boxes. Es-
pecially, if liquids preamps are used for solids work, as well power limitations as
frequency limitations must be strictly observed!
RF Connections Between Preamplifier and Probe 3.2
These connections must be done with high quality cable, with suitable length. It
should be short, but not too short so that the cable must not be severely bent.
Higher quality cable is fairly stiff; the flexible ones are of less quality.
N.B.: It is extremely important that RF cables are not bent to a radius of less than
30 cm, and that no force is exerted on the RF connectors. Adapters should be
avoided; since every connector may change the impedance to deviate from the
required 50 Ω. Cables with loose connectors should be discarded, unless they
1. Pulse from TX
2. Pulse pathway to probe
3. To probe
4. Signal from probe
5. Signal to preamplifier
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