Chapter 4. CRAMPS/Multipulse Module Operation
57
VNMR 6.1C User Guide: Solid-State NMR 01-999162-00 C0402
4.2 CRAMPS/Multipulse Module Hardware
Multipulse capability is available with all
UNITY
INOVA and UNITYplus spectrometers.
UNITY and VXR-S spectrometers require an additional Sync Module to improve pulse-
timing stability. The main CRAMPS/multipulse module hardware is the motor control box,
1-kW amplifier, sync module (UNITY and VXR-S systems only), and the CRAMPS probe.
The
1
H CRAMPS experiment requires the following:
•
1
H/
19
F 1-kW amplifier (see 2.1 “CP/MAS Solids Modules,” page 16)
• Fast ADC (2 MHz or 5 MHz)
• Solids high-power preamplifier
• Suitable MAS probe with pneumatics hardware
See 2.2 “Rotor Characteristics and Composition,” page 20 to 2.4 “Spinning the
Sample,” page 22 for information about MAS spinning.
1
H/
19
F 1-kW Amplifier
1
H/
19
F 1-kW amplifiers suitable for CRAMPS are described in section 2.1 “CP/MAS
Solids Modules,” page 16. The CRAMPS experiment generally requires more than 100
Watts of power. A very small-diameter rotor will facilitate running the experiments with a
100 Watt CP/MAS amplifier in some cases.
Amplifier Tuning
The CPI amplifier is tuned to either
1
H or
19
F. At 600 MHz only
1
H tuning is possible.
INPUT TUNING uses the 20-turn pot at the front of the amplifier chassis. The output tuning
uses the external Motor Control Box. A 3-position selector switch is used to choose
TUNE,
LOAD and STANDBY (AUX). The COARSE and FINE toggles are momentary contact and
can be pushed in two directions (designated
IN and OUT) to adjust either the TUNE or LOAD
depending upon the selection set on the 3-position selector switch.
A CMA amplifier is tuned to either
1
H or
19
F. INPUT TUNE and INPUT MATCH are 20 turn
pots at the bottom-front of the amplifier chassis.
OUTPUT TUNE and OUTPUT MATCH are
digital knobs at the center-front of the chassis.
Tune the Amplifier
1. Connect the amplifier output (the cable to the connection XMTR J5313 on the
preamplifier) through at least a 30 db attenuator to an oscilloscope or a power meter.
The attenuator must handle 50 Watts or more.
2. Do one of the following depending upon the type of amplifier:
• CMA amplifier only
Select the mode as either
GATE ACTIVE or CLASS C as required (see
“Amplifier and Receiver Blanking,” page 58).
• CMA or CPI amplifier
a. Set a single repeating pulse of pw = 300
µs with a d1=30 µs for either
1
H
or
19
F. Tune the input tuning pot(s) for maximum power or voltage.
b. Iteratively adjust the output tuning (tune and "load" or "match") for maximum
power or voltage.
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