power, the experiment can be performed in the inverse mode using the decoupler as the frequency source (Exp. 2.4). Load standard ¹H NMR parameters, record a normal ¹H NMR spectrum, and note the offset of CHCl₃. You have to set:

td	4 k
sw	500 Hz
o1	on resonance of ¹H signal
p1	90° ¹H transmitter pulse, to be determined for each attenuation level
d1	60 s
ns	1
transmitter attenuation	0 dB initial value, to be increased in 3 dB steps

Determine the 90° pulse-width at 0 dB attenuation. Then change the attenuation in 3 dB steps and redetermine the 90° pulse-width for each attenuation level by varying p1. If available, measure with an oscilloscope the peak-to-peak voltage of your pulse (for this, set ns to 64 k, d1 to 10 ms, p1 to 40 μs and td to 256 points in order to obtain rapid pulsing; connect the transmitter cable to an external attenuator and an oscilloscope with 50 ohm impedance).

5. Processing

Use standard 1D processing (see Exp. 3.1) applying an exponential window with a line-broadening factor lb = 1 Hz. From the 90° pulse duration calculate the radiofrequency field using Equation (3). Verify that the expected values correspond to the attenuation. Note the large power range, from 0 to 90 dB, required in different types of NMR experiments.

6. Result

The table lists results obtained with an ARX-200 spectrometer.

Attenuation [dB]	90° Pulse-width [μs]	γB₁ [Hz]	U_pp [V]	P [W]
0	7.8	32051	107	28.6
3	10.3	24271	82	16.8
6	13	19230	59	8.7
9	19.5	12820	41	4.2
12	27.5	9090	29	2.1
15	39.5	6329	20	1.
18	55	4545	15	0.56
21	75	3333	11	0.30
24	105	2380	7.9	0.16
27	145	1724	5.9	0.087
30	200	1250	4.3	0.046
33	290	862	3.3	0.027
36	425	588	2.2	0.012