Tuning and matching - Revision history

Jma at 23:22, 4 December 2009

2009-12-04T23:22:12Z

← Older revision		Revision as of 23:22, 4 December 2009
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	== '''Probe Tuning and Matching''' ==		== '''Probe Tuning and Matching''' ==

	NMR probes come in various designs, but the typical triple-resonance HCN probe has two coils and four resonant circuits. The inner observe coil is connected to 1H and 2H circuits, and the outer decoupling coil is connected to 13C and 15N circuits.		NMR probes come in various designs, but the typical triple-resonance HCN probe has two coils and four resonant circuits. The inner observe coil is connected to 1H and 2H circuits, and the outer decoupling coil is connected to 13C and 15N circuits.

	In general, a resonant circuit can be tuned to the frequency of the corresponding nucleus and matched to the standard impedance of the connecting lines (50 Ohm). This is usually achieved by adjusting two variable capacitors in the circuit. Tuning and matching reduces reflected power and increases the quality factor Q, leading to shorter pulse widths and better sensitivity (and to stronger radiation damping).		In general, a resonant circuit can be tuned to the frequency of the corresponding nucleus and matched to the standard impedance of the connecting lines (50 Ohm). This is usually achieved by adjusting two variable capacitors in the circuit. Tuning and matching reduces reflected power and increases the quality factor Q, leading to shorter pulse widths and better sensitivity (and to stronger radiation damping).

	Often a circuit can only be tuned, but not matched. For example, cryogenic HCN probes typically allow both tuning and matching of the 1H circuit, but only allow tuning of the 15N, 13C or 2H circuits. The 2H circuit of room-temperature HCN probes can usually be neither tuned nor matched.		Often a circuit can only be tuned, but not matched. For example, cryogenic HCN probes typically allow both tuning and matching of the 1H circuit, but only allow tuning of the 15N, 13C or 2H circuits. The 2H circuit of room-temperature HCN probes can usually be neither tuned nor matched.

	=== '''Channel Setup''' ===		=== '''Channel Setup''' ===

	Tuning and matching can only be done for the nuclei assigned to a channel. To tune 1H, 15N, and 13C you can:		Tuning and matching can only be done for the nuclei assigned to a channel. To tune 1H, 15N, and 13C you can:
	* Load any triple-resonance or HSQC data set and type <tt>su</tt>
	* In any dataset define <tt>tn='H1' dn='C13' dn2='N15' su</tt>

	~~If you also want to tune the 2H channel add~~ <tt>~~dn3~~='H2' su</tt>		*Load any triple-resonance or HSQC data set and type <tt>su</tt>
			*In any dataset define <tt>tn='H1' dn='C13' dn2='N15' su</tt>

	=== ''~~'Cable Connection''' ===~~		If you also want to tune the 2H channel add <tt>dn3='H2' su</tt>

	To perform tuning and matching of a probe you have to re-cable the probe to connect it to the tuning bridge. The tuning bridge has a monitor displaying the amount of reflected power - the aim is to minimize its reading.		=== '''Cable Connection''' ===

			To perform tuning and matching of a probe you have to re-cable the probe to connect it to the tuning bridge. The tuning bridge has a monitor displaying the amount of reflected power - the aim is to minimize its reading.

	The cable connections depend on the probe type and the magnet leg configuration. For detailed desription consult these manuals:		The cable connections depend on the probe type and the magnet leg configuration. For detailed desription consult these manuals:
	* For room-temperature probes see '''Section 6.5''' of the [http://www.varianinc.com/image/vimage/docs/products/nmr/apps/pubs/manuals/0199916000b.pdf VNMR 6.1C Getting Started] manual.
	* For cryogenic probes see [http://www.varianinc.com/image/vimage/docs/products/nmr/apps/pubs/manuals/0199919600c.pdf Gen 1 HCN Cold Probe Manual] or [http://www.varianinc.com/image/vimage/docs/products/nmr/apps/pubs/manuals/0199930000c.pdf Gen 2 HCN Cold Probe Manual]

	~~====~~ '''~~1H Channel - Room-Temperature~~ HCN or ~~5NUC~~ Probe~~''' ====~~		*For room-temperature probes see '''Section 6.5''' of the [http://www.varianinc.com/image/vimage/docs/products/nmr/apps/pubs/manuals/0199916000b.pdf VNMR 6.1C Getting Started] manual.
			*For cryogenic probes see [http://www.varianinc.com/image/vimage/docs/products/nmr/apps/pubs/manuals/0199919600c.pdf Gen 1 HCN Cold Probe Manual] or [http://www.varianinc.com/image/vimage/docs/products/nmr/apps/pubs/manuals/0199930000c.pdf Gen 2 HCN Cold Probe Manual]

	# Locate the cable going from the '''1H''' or '''Observe''' port on the probe to an RF filter.		==== '''1H Channel - Room-Temperature HCN or 5NUC Probe''' ====
	# Disconnect it from the filter and connect it to the '''J5321''' port on the tune interface
	# If '''J5323 TUNE OUTPUT''' port is available, disconnect the cable from '''J5302 OUTPUT''' port on the 1H preamp and connect it to the '''J5323 TUNE OUTPUT''' port.		#Locate the cable going from the '''1H''' or '''Observe''' port on the probe to an RF filter.
	# Select channel 1 on the tune interface		#Disconnect it from the filter and connect it to the '''J5321''' port on the tune interface
	# Adjust tuning and matching using knobs		#If '''J5323 TUNE OUTPUT''' port is available, disconnect the cable from '''J5302 OUTPUT''' port on the 1H preamp and connect it to the '''J5323 TUNE OUTPUT''' port.
	# Return the cables to their original positions		#Select channel 1 on the tune interface
			#Adjust tuning and matching using knobs
			#Return the cables to their original positions

	==== '''1H Channel - Cryogenic HCN Probe''' ====		==== '''1H Channel - Cryogenic HCN Probe''' ====
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	[[Image:Tunebox2.jpg]]		[[Image:Tunebox2.jpg]]
	[[Image:Tunebox3.jpg]]		[[Image:Tunebox3.jpg]]

	''Fig. 1. 600 MHz at SUNY Buffalo: original cable position (left), 1H tuning and matching position (right).''		''Fig. 1. 600 MHz at SUNY Buffalo: original cable position (left), 1H tuning and matching position (right).''

	==== '''13C, 15N and 2H Channels - All Probes''' ====		==== '''13C, 15N and 2H Channels - All Probes''' ====
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	[[Image:Tunebox.jpg]]		[[Image:Tunebox.jpg]]

	''Fig. 2. 600 MHz SUNY Buffalo: cable to be reconnected for 13C and 15N matching (green arrows).''		''Fig. 2. 600 MHz SUNY Buffalo: cable to be reconnected for 13C and 15N matching (green arrows).''

	=== '''Additional Notes''' ===		=== '''Additional Notes''' ===
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	''Fig. 6. Tune interface.''		''Fig. 6. Tune interface.''



			== Tuning and Matching Bruker on Spectrometers ==

			On Bruker spectrometers equipped with TopSpin 2.0 and up, there are two methods for tuning and matching probes.

			=== Standard Probeheads ===

			For standard probeheads lacking the automatic tuning and matching functionality, tuning and matching is initiated for an experiment using the command:
			<pre>wobb
			</pre>
			A wobble page opens up (see Figure below):

			[[Image:Wobb.jpg\|600px]]

			According to the spectrometer set up in the current experiment (defined using the edasp command), the tuning display starts with lowest frequency nucleus in the experiment (for example, <sup>15</sup>N).  Proceed to the magnet and adjust the tuning and matching knobs for that nucleus.  Tuning moves the minumum in the display left or right, and matching moves it up and down.  The object is to center this "peak" and make it is low as possible.  At the same time, follow the relected power on the pre-ampliflier LED.

			Next, press the change nucleus icon at the top of the wobb display, and the system with move to the next highest frequency nucleus (i.e., <sup>13</sup>C).  Continue the process until <sup>1</sup>H tuning and matching is complete.



			=== ATM probeheads ===

			Bruker probeheads equipped with the automated tuning and matching (ATM) feature, do not have tuning/matching rods.  Instead the user tunes and matches using the automated tuning and matching dialog box initiated by the command:
			<pre>atmm
			</pre>
			Here an interactive dialog box (not shown) is opened analogous to the wobb display above, where the user can adjust tuning and matching by clicking buttons in the display.

			For completely automatic tuning and matching, the command is:
			<pre>atma
			</pre>
	<br>		<br>

	<br> -- GaohuaLiu - 24 Jan 2007		<br> -- GaohuaLiu - 24 Jan 2007

Alex: moved NESG:RFCoilTuningAndMatching to Tuning and matching

2009-12-04T19:53:49Z

moved NESG:RFCoilTuningAndMatching to Tuning and matching

← Older revision	Revision as of 19:53, 4 December 2009
(No difference)

Admin at 14:44, 22 October 2009

2009-10-22T14:44:46Z

← Older revision		Revision as of 14:44, 22 October 2009
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	<br>		<br>

	<br> -- ~~Main.~~GaohuaLiu - 24 Jan 2007		<br> -- GaohuaLiu - 24 Jan 2007

Admin at 14:44, 22 October 2009

2009-10-22T14:44:29Z

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	Tuning 2H is not required unless you have to pulse on 2H, but it may improve lock sensitivity. On the other hand, since experiments involving pulses on 2H, such as 2H-decoupling, are run very rarely, it is likely that the 2H circuit is mis-tuned.		Tuning 2H is not required unless you have to pulse on 2H, but it may improve lock sensitivity. On the other hand, since experiments involving pulses on 2H, such as 2H-decoupling, are run very rarely, it is likely that the 2H circuit is mis-tuned.

	~~<img src="%ATTACHURLPATH%/tune750~~.jpg~~" alt="tune750.jpg" width='556' height='422' />~~		[[Image:Tune750.jpg]]

	''Fig. 3. 750 MHz SUNY Buffalo: tuning knobs, room-temperature HCN probe.''		''Fig. 3. 750 MHz SUNY Buffalo: tuning knobs, room-temperature HCN probe.''

	~~<img src="%ATTACHURLPATH%/tune500~~.jpg~~" alt="tune500.jpg" width='556' height='415' />~~		[[Image:Tune500.jpg]]

	''Fig. 4. 500 MHz SUNY Buffalo: tuning knobs, room-temperature 5NUC probe.''		''Fig. 4. 500 MHz SUNY Buffalo: tuning knobs, room-temperature 5NUC probe.''

	~~<img src="%ATTACHURLPATH%/tune600a~~.jpg~~" alt="tune600a.jpg" width='612' height='480' />~~		[[Image:Tune600a.jpg]]

	''Fig. 5. 750 MHz SUNY Buffalo: tuning knobs, cryogenic HCN probe.''		''Fig. 5. 750 MHz SUNY Buffalo: tuning knobs, cryogenic HCN probe.''

	~~<img src="%ATTACHURLPATH%/tunebox4~~.jpg~~" alt="tunebox4.jpg" />~~		[[Image:Tunebox4.jpg]]

	''Fig. 6. Tune interface.''		''Fig. 6. Tune interface.''

	<br>		<br>

	<br> -- Main.GaohuaLiu - 24 Jan 2007		<br> -- Main.GaohuaLiu - 24 Jan 2007

Admin at 14:41, 22 October 2009

2009-10-22T14:41:51Z

← Older revision		Revision as of 14:41, 22 October 2009
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	''Fig. 1. 600 MHz at SUNY Buffalo: original cable position (left), 1H tuning and matching position (right).''		''Fig. 1. 600 MHz at SUNY Buffalo: original cable position (left), 1H tuning and matching position (right).''

	==== '''13C, 15N and 2H Channels - All Probes''' ====		==== '''13C, 15N and 2H Channels - All Probes''' ====

	# Locate the cable going from the respective 13C, 15N or 2H port on the probe to an RF filter.		#Locate the cable going from the respective 13C, 15N or 2H port on the probe to an RF filter.
	# Disconnect it from the filter and connect it to the '''J5321''' port on the tune interface		#Disconnect it from the filter and connect it to the '''J5321''' port on the tune interface
	# If '''J5323 TUNE OUTPUT''' port is available, disconnect the cable from '''J5312 OUTPUT''' port on the broadband preamp and connect it to the '''J5323 TUNE OUTPUT''' port.		#If '''J5323 TUNE OUTPUT''' port is available, disconnect the cable from '''J5312 OUTPUT''' port on the broadband preamp and connect it to the '''J5323 TUNE OUTPUT''' port.
	# Select the corresponding channel (2, 3 or 4) on the tune interface		#Select the corresponding channel (2, 3 or 4) on the tune interface
	# Adjust tuning and matching using knobs		#Adjust tuning and matching using knobs
	# Return the cables to their original positions		#Return the cables to their original positions

	~~<img src="%ATTACHURLPATH%/tunebox~~.jpg~~" alt="tunebox.jpg" />~~		[[Image:Tunebox.jpg]]

	''Fig. 2. 600 MHz SUNY Buffalo: cable to be reconnected for 13C and 15N matching (green arrows).''		''Fig. 2. 600 MHz SUNY Buffalo: cable to be reconnected for 13C and 15N matching (green arrows).''

Admin at 14:39, 22 October 2009

2009-10-22T14:39:05Z

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	#Return the cables to their original positions		#Return the cables to their original positions

	[[~~image~~:~~tunebox2~~.jpg]]		[[Image:Tunebox2.jpg]]
	[[~~image~~:~~tunebox3~~.jpg]]		[[Image:Tunebox3.jpg]]

	''Fig. 1. 600 MHz at SUNY Buffalo: original cable position (left), 1H tuning and matching position (right).''		''Fig. 1. 600 MHz at SUNY Buffalo: original cable position (left), 1H tuning and matching position (right).''

Admin at 14:36, 22 October 2009

2009-10-22T14:36:13Z

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	# Return the cables to their original positions		# Return the cables to their original positions

	==== '''1H Channel - Cryogenic HCN Probe''' ====		==== '''1H Channel - Cryogenic HCN Probe''' ====

	# Disconnect the cable from the '''J5303 HB XMTR''' port on the 1H preamp		#Disconnect the cable from the '''J5303 HB XMTR''' port on the 1H preamp
	# Take a short cable and connect it to the '''J5303 HB XMTR''' port and the '''J5321''' port on the tune interface.		#Take a short cable and connect it to the '''J5303 HB XMTR''' port and the '''J5321''' port on the tune interface.
	# If '''J5323 TUNE OUTPUT''' port is available, disconnect the cable from '''J5302 OUTPUT''' port on the 1H preamp and connect it to the '''J5323 TUNE OUTPUT''' port.		#If '''J5323 TUNE OUTPUT''' port is available, disconnect the cable from '''J5302 OUTPUT''' port on the 1H preamp and connect it to the '''J5323 TUNE OUTPUT''' port.
	# Select channel 1 on the tune interface		#Select channel 1 on the tune interface
	# Adjust tuning and matching using knobs		#Adjust tuning and matching using knobs
	# Return the cables to their original positions		#Return the cables to their original positions

	~~<img src="%ATTACHURLPATH%/~~tunebox2.jpg~~" alt="tunebox2.jpg" /> <img src="%ATTACHURLPATH%/tunebox3.jpg" alt="~~tunebox3.jpg~~" />~~		[[image:tunebox2.jpg]]
			[[image:tunebox3.jpg]]

	''Fig. 1. 600 MHz at SUNY Buffalo: original cable position (left), 1H tuning and matching position (right).''		''Fig. 1. 600 MHz at SUNY Buffalo: original cable position (left), 1H tuning and matching position (right).''


	==== '''13C, 15N and 2H Channels - All Probes''' ====		==== '''13C, 15N and 2H Channels - All Probes''' ====

Admin at 15:28, 13 October 2009

2009-10-13T15:28:00Z

← Older revision		Revision as of 15:28, 13 October 2009
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	''Fig. 2. 600 MHz SUNY Buffalo: cable to be reconnected for 13C and 15N matching (green arrows).''		''Fig. 2. 600 MHz SUNY Buffalo: cable to be reconnected for 13C and 15N matching (green arrows).''

	=== '''Additional Notes''' ===		=== '''Additional Notes''' ===

	There is often some cross-talk between tuning and matching capacitors of the same circuit. The effect is negligible near the tuning optimum, and the two capacitors can be adjusted in an interleaved fashion with a few iterations. But the cross-talk makes it more difficult to tune a badly mis-tuned probe, getting you stuck in a local minimum. If this happens, one has to "undo" one of the capacitors and adjust the other one, aiming to find the global minimum by trial and error.		There is often some cross-talk between tuning and matching capacitors of the same circuit. The effect is negligible near the tuning optimum, and the two capacitors can be adjusted in an interleaved fashion with a few iterations. But the cross-talk makes it more difficult to tune a badly mis-tuned probe, getting you stuck in a local minimum. If this happens, one has to "undo" one of the capacitors and adjust the other one, aiming to find the global minimum by trial and error.

	A cross-talk can also exist between different circuits, however, it has not yet been observed with our probes. To minimize this cross-talk it is recommended to tune the low gyromagnetic ratio channels first: 15N -> 2H -> 13C -> 1H.		A cross-talk can also exist between different circuits, however, it has not yet been observed with our probes. To minimize this cross-talk it is recommended to tune the low gyromagnetic ratio channels first: 15N -> 2H -> 13C -> 1H.

	As a general rule, 1H tuning and matching depends strongly on the ionic strength of the sample, and usually differs for aqueous samples and those in organic solvents. 13C and 15N tuning shows much weaker dependence on the ionic strength.		As a general rule, 1H tuning and matching depends strongly on the ionic strength of the sample, and usually differs for aqueous samples and those in organic solvents. 13C and 15N tuning shows much weaker dependence on the ionic strength.

	Tuning 2H is not required unless you have to pulse on 2H, but it may improve lock sensitivity. On the other hand, since experiments involving pulses on 2H, such as 2H-decoupling, are run very rarely, it is likely that the 2H circuit is mis-tuned.		Tuning 2H is not required unless you have to pulse on 2H, but it may improve lock sensitivity. On the other hand, since experiments involving pulses on 2H, such as 2H-decoupling, are run very rarely, it is likely that the 2H circuit is mis-tuned.

	<img src="%ATTACHURLPATH%/tune750.jpg" alt="tune750.jpg" width='556' height='422' />		<img src="%ATTACHURLPATH%/tune750.jpg" alt="tune750.jpg" width='556' height='422' />
	~~''Fig. 3. 750 MHz SUNY Buffalo: tuning knobs, room-temperature HCN probe.''~~

	~~<img src="%ATTACHURLPATH%/tune500.jpg" alt="tune500.jpg" width='556' height='415' />~~		''Fig. 3. 750 MHz SUNY Buffalo: tuning knobs, room-temperature HCN probe.''
	''Fig. 4. ~~500~~ MHz SUNY Buffalo: tuning knobs, room-temperature ~~5NUC~~ probe.''

	<img src="%ATTACHURLPATH%/~~tune600a~~.jpg" alt="~~tune600a~~.jpg" width='~~612~~' height='~~480~~' />		<img src="%ATTACHURLPATH%/tune500.jpg" alt="tune500.jpg" width='556' height='415' />
	~~''Fig. 5. 750 MHz SUNY Buffalo: tuning knobs, cryogenic HCN probe.''~~

	~~<img src="%ATTACHURLPATH%/tunebox4.jpg" alt="tunebox4.jpg" />~~		''Fig. 4. 500 MHz SUNY Buffalo: tuning knobs, room-temperature 5NUC probe.''
	''Fig. 6. ~~Tune interface~~.''

	%~~COMMENT~~%		<img src="%ATTACHURLPATH%/tune600a.jpg" alt="tune600a.jpg" width='612' height='480' />

			''Fig. 5. 750 MHz SUNY Buffalo: tuning knobs, cryogenic HCN probe.''

	-- Main.GaohuaLiu - 24 Jan 2007		<img src="%ATTACHURLPATH%/tunebox4.jpg" alt="tunebox4.jpg" />

			''Fig. 6. Tune interface.''

			<br>

			<br> -- Main.GaohuaLiu - 24 Jan 2007

Admin: Created page with '== '''Probe Tuning and Matching''' == NMR probes come in various designs, but the typical triple-resonance HCN probe has two coils and four resonant circuits. The inner observe …'

2009-10-08T14:49:04Z

Created page with '== '''Probe Tuning and Matching''' == NMR probes come in various designs, but the typical triple-resonance HCN probe has two coils and four resonant circuits. The inner observe …'

New page

== '''Probe Tuning and Matching''' ==

NMR probes come in various designs, but the typical triple-resonance HCN probe has two coils and four resonant circuits. The inner observe coil is connected to 1H and 2H circuits, and the outer decoupling coil is connected to 13C and 15N circuits.

In general, a resonant circuit can be tuned to the frequency of the corresponding nucleus and matched to the standard impedance of the connecting lines (50 Ohm). This is usually achieved by adjusting two variable capacitors in the circuit. Tuning and matching reduces reflected power and increases the quality factor Q, leading to shorter pulse widths and better sensitivity (and to stronger radiation damping).

Often a circuit can only be tuned, but not matched. For example, cryogenic HCN probes typically allow both tuning and matching of the 1H circuit, but only allow tuning of the 15N, 13C or 2H circuits. The 2H circuit of room-temperature HCN probes can usually be neither tuned nor matched.

=== '''Channel Setup''' ===

Tuning and matching can only be done for the nuclei assigned to a channel. To tune 1H, 15N, and 13C you can:
* Load any triple-resonance or HSQC data set and type <tt>su</tt>
* In any dataset define <tt>tn='H1' dn='C13' dn2='N15' su</tt>

If you also want to tune the 2H channel add <tt>dn3='H2' su</tt>

=== '''Cable Connection''' ===

To perform tuning and matching of a probe you have to re-cable the probe to connect it to the tuning bridge. The tuning bridge has a monitor displaying the amount of reflected power - the aim is to minimize its reading.

The cable connections depend on the probe type and the magnet leg configuration. For detailed desription consult these manuals:
* For room-temperature probes see '''Section 6.5''' of the [http://www.varianinc.com/image/vimage/docs/products/nmr/apps/pubs/manuals/0199916000b.pdf VNMR 6.1C Getting Started] manual.
* For cryogenic probes see [http://www.varianinc.com/image/vimage/docs/products/nmr/apps/pubs/manuals/0199919600c.pdf Gen 1 HCN Cold Probe Manual] or [http://www.varianinc.com/image/vimage/docs/products/nmr/apps/pubs/manuals/0199930000c.pdf Gen 2 HCN Cold Probe Manual]

==== '''1H Channel - Room-Temperature HCN or 5NUC Probe''' ====

# Locate the cable going from the '''1H''' or '''Observe''' port on the probe to an RF filter.
# Disconnect it from the filter and connect it to the '''J5321''' port on the tune interface
# If '''J5323 TUNE OUTPUT''' port is available, disconnect the cable from '''J5302 OUTPUT''' port on the 1H preamp and connect it to the '''J5323 TUNE OUTPUT''' port.
# Select channel 1 on the tune interface
# Adjust tuning and matching using knobs
# Return the cables to their original positions

==== '''1H Channel - Cryogenic HCN Probe''' ====

# Disconnect the cable from the '''J5303 HB XMTR''' port on the 1H preamp
# Take a short cable and connect it to the '''J5303 HB XMTR''' port and the '''J5321''' port on the tune interface.
# If '''J5323 TUNE OUTPUT''' port is available, disconnect the cable from '''J5302 OUTPUT''' port on the 1H preamp and connect it to the '''J5323 TUNE OUTPUT''' port.
# Select channel 1 on the tune interface
# Adjust tuning and matching using knobs
# Return the cables to their original positions

<img src="%ATTACHURLPATH%/tunebox2.jpg" alt="tunebox2.jpg" /> <img src="%ATTACHURLPATH%/tunebox3.jpg" alt="tunebox3.jpg" />

''Fig. 1. 600 MHz at SUNY Buffalo: original cable position (left), 1H tuning and matching position (right).''

==== '''13C, 15N and 2H Channels - All Probes''' ====

# Locate the cable going from the respective 13C, 15N or 2H port on the probe to an RF filter.
# Disconnect it from the filter and connect it to the '''J5321''' port on the tune interface
# If '''J5323 TUNE OUTPUT''' port is available, disconnect the cable from '''J5312 OUTPUT''' port on the broadband preamp and connect it to the '''J5323 TUNE OUTPUT''' port.
# Select the corresponding channel (2, 3 or 4) on the tune interface
# Adjust tuning and matching using knobs
# Return the cables to their original positions

<img src="%ATTACHURLPATH%/tunebox.jpg" alt="tunebox.jpg" />

''Fig. 2. 600 MHz SUNY Buffalo: cable to be reconnected for 13C and 15N matching (green arrows).''

=== '''Additional Notes''' ===

There is often some cross-talk between tuning and matching capacitors of the same circuit. The effect is negligible near the tuning optimum, and the two capacitors can be adjusted in an interleaved fashion with a few iterations. But the cross-talk makes it more difficult to tune a badly mis-tuned probe, getting you stuck in a local minimum. If this happens, one has to "undo" one of the capacitors and adjust the other one, aiming to find the global minimum by trial and error.

A cross-talk can also exist between different circuits, however, it has not yet been observed with our probes. To minimize this cross-talk it is recommended to tune the low gyromagnetic ratio channels first: 15N -> 2H -> 13C -> 1H.

As a general rule, 1H tuning and matching depends strongly on the ionic strength of the sample, and usually differs for aqueous samples and those in organic solvents. 13C and 15N tuning shows much weaker dependence on the ionic strength.

Tuning 2H is not required unless you have to pulse on 2H, but it may improve lock sensitivity. On the other hand, since experiments involving pulses on 2H, such as 2H-decoupling, are run very rarely, it is likely that the 2H circuit is mis-tuned.

<img src="%ATTACHURLPATH%/tune750.jpg" alt="tune750.jpg" width='556' height='422' />
''Fig. 3. 750 MHz SUNY Buffalo: tuning knobs, room-temperature HCN probe.''

<img src="%ATTACHURLPATH%/tune500.jpg" alt="tune500.jpg" width='556' height='415' />
''Fig. 4. 500 MHz SUNY Buffalo: tuning knobs, room-temperature 5NUC probe.''

<img src="%ATTACHURLPATH%/tune600a.jpg" alt="tune600a.jpg" width='612' height='480' />
''Fig. 5. 750 MHz SUNY Buffalo: tuning knobs, cryogenic HCN probe.''

<img src="%ATTACHURLPATH%/tunebox4.jpg" alt="tunebox4.jpg" />
''Fig. 6. Tune interface.''

%COMMENT%

-- Main.GaohuaLiu - 24 Jan 2007