Hi Ken,
Here are some other things I would look at:
Do you see the wiggles if you tune or wobb 15N? Does your instrument
still have a BB preamp? Is it cryoprobe compatible? If so, you
could try routing the 13C signal through that preamp instead. You'd
need to move the cables and change the cable connections in edprobe.
What's the voltage going into the console? If you have a multimeter
you can measure the voltage on the spare outlet on the top of the AQS rack.
It should be in the range that the black voltage selector is set to.
Having said that, you can make sure the voltage selector on the BSMS is also
set properly.
If you've got another probe that does 13C you can connect it to the thick RF
cable that connects to the prodigy probe and run wobb--you can see if you've
got the same wiggles with that probe. If you have a scope you can
look at the tuning signal going to the probe--there should be a steady 5V bias
and then the tuning frequency. If the bias isn't stable you could get
wiggles in the tuning dip. I'm going to see if I can calculate the
frequency of the wiggles and see if that points at anything useful.
Cheers,Mike
On Friday, May 31, 2024 at 10:04:02 AM MDT, Kenneth Sharp-Knott wrote:
Hi Mike,
I disconnected both of those connections (one at a time) and the result is
that the interference in still present, but weaker.
So the cross talk is coming from somewhere.... else....
Ken Sharp-Knott
Manager of Analytical Services and the NMR Facility
Department of Chemistry
Virginia Tech
(540)267-6502 (Cell)
(540)231-0885 (Office)
> From: main_at_ammrl.groups.io on behalf of Michael Groves via groups.io
> Sent: Thursday, May 30, 2024 5:45 PM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: Re: [AMMRL] Frequency ocillation in wobb curve on Prodigy TCI probe
If it shows up with both the RF cables disconnected from the probe then I'm
less likely to suspect the cold preamps. The next thing I might look at is
one of the lock blanking signals--there's a blanking signal that goes from
the L-TRX through the preamps to the probe and is not passed through the RF
cables--so when the input was disconnected from the 2H preamp and the signal
persisted it may point to this. If I recall correctly, this is the pulse
that switches the cold 2H preamp from transmit to receive mode.
I would reconnect the RF cables to the probe and preamp and then disconnect
the TP-F0 out from the L-TRX or the input from the PSM-A in the back of the
AQS rack. That blanking pulse goes from the L-TRX to one the PSM-A board
in the back of the AQS rack and then through one of the cables that goes to
the preamp. If I remember correctly. If that pulse is causing the
issues then disconnecting the TP-F0 cable should stop the wiggles in the tuning
signal as well. From there it might be a question of tracking where exactly
the cross-talk is happening.
Cheers,Mike
On Thursday, May 30, 2024 at 01:58:09 PM MDT, Bob Berno wrote:
Hi Ken,
Okay, just grasping at straws, but now I think that you might be getting
some crosstalk within the preamp stack itself. I don't know how this
can happen, but maybe a cable is loose or isn't properly grounded or something
like that. At the side of the preamp stack, there is a plastic cover on each of
the slices which you can easily pop-off. Once you have popped off those
pieces of plastic, that will expose a ribbon cable and several other wires
connecting each preamp slice to each other.
Take a photo before doing anything, so that you have a record of which cables go
where (it should be obvious, but you never know). Carefully check that all
of the cables are properly seated. Also, as you trace the "daisychain" of
cables, when you get to the last preamp slice you will probably see 50 ohm dummy
load resisters. Make sure that these are properly seated.
If it isn't a problem with the preamp stack next to the magnet, then maybe
it is a problem with the cold preamps in the probe.Let's hope that is not the case.
Bob.
Dr. Bob Berno
Manager: McMaster NMR Facility
Department of Chemistry & Chemical Biology
McMaster University, ABB-156
1280 Main Street West
Hamilton, ON L8S 4L9
(905) 525-9140 ext:24158
Fax: (905) 522-2509
http://macs.mcmaster.ca
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Received on Fri May 31 2024 - 10:29:26 MST