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
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
. 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
µ
s
with a
d1=30
µ
s
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.