Re: [AMMRL] 19F and 1H single channel HOESY (Varian)

From: Spin-Doc <bert.heise_at_spin-doc.net>
Date: Thu, 24 Jul 2025 23:55:26 +0200
Hi Shawn,


I have a dual tuned 1H and 19F probe which is currently on a VNMRS system (I do have a MR400 but that has a OneProbe). After consideration of using a spitter/combiner I realized that it is no viable because of the high power at the probe and I don't have one that can handle more than a couple of watts.

Now do you want to run the H/F experiments on your VNMRS-400? I thought I remembered you wanted to run them on your 400MR…
Does your VNMRS-400 have two highband channels (like 3-channel hi-lo-hi or 4-channel hi-lo-hi-lo)? Then it’s much better to run the experiments in true dual-highband fashion - but this requires:
- the splitter-combiner, with both Ch1 & Ch3 directional couplers connected in series at the output (probe side) of the combiner
- set up the probeConnect global variable as probeConnect=‚H1 X F19‘ (in latest OpenVnmrJ there is a graphical interface for this on the Probe popup).

Not sure what you mean with „not viable because of higher power“ - you are much more limited in terms of decoupling because of all the time-sharing. Of course you still shouldn’t exceed more than about 1 W of CW power. Plus less artifacts from the chopping.


By default, for the H-F sequence in VnmrJ, Channel 1 is set for 1H and Channel 2 for 19F. If I assume this is true when the sequence runs then the power for 19F is going to be on the probe low band channel that is tuned to 13C.

No - all 1H as well as 19F are both going to the double-tuned highband channel. 
That’s indeed the opposite to what most Bruker probes do, where most times (there are exceptions) 19F is tuned on the low-band channel.

If accrurate, I need to alter the sequence to use Channel 1 for both.

Absolutely not: in dual-highband VNMRS this is handled by probeConnect (see above) and in single-highband systems PSG will set up everythin g for you (withon boundaries).

(Bert, I don't know if you have any insight on how the VNMRS is going to handle that sequence). I would guess the easiest check is to load the sequence and set it up then check the PTS frequency and see if the Channel 1 frequency is altered while running the sequence.

If I remember correctly this frequency switching during the pulse sequence isn’t produced by the PTS/VFS synthesizer (too fast for it to switch the base frequency) but instead by shifting the frequency inside the transmitter boards - similar to what frequency-swept adiabatic shaped pulses do.
If you want to see what’s going on then connect the scope to the -30 dB side output of the highband directional coupler (bit more finicky inside a 400MR which is pretty crammed near the exit).

Cheers
Bert



From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> on behalf of Baas, Sander via groups.io <sander.baas=wur.nl_at_groups.io>
Sent: Thursday, July 24, 2025 6:15 AM
To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
Subject: Re: [AMMRL] 19F and 1H single channel HOESY (Varian)
 
Hi Shawn, If I understand correctly, your probe's high freq channel can be either tuned to 1H or 19F, but not double tuned to both at the same time? That would mean you would be either not matched at the 1H or 19F frequency (nor tuned), which
Hi Shawn,
 
If I understand correctly, your probe's high freq channel can be either tuned to 1H or 19F, but not double tuned to both at the same time? That would mean you would be either not matched at the 1H or 19F frequency (nor tuned), which could damage the equipment. We sometimes run non-tuned experiments with homebuilt microcoils and have not blown anything up (yet), but caveat emptor. If you would attempt this, you don't need to run any external combiners, the VNMRS takes care of this as Bert explained.
 
Best,
 
Sander
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Received on Thu Jul 24 2025 - 16:54:33 MST

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