My apologize for the slow summary response to the email I sent way back
in April. We waited for a demo unit from Morris Instruments to be
delivered to us early this month before finally deciding to purchase a
more expensive HP network analyzer. I worried that the Morris unit,
which has some obvious utility for MRI labs, might not have sufficient
resolution for liquids work.
As it turned out, the Morris unit is very well built, and I had no
problems with its ability to tune probes accurately for liquids work at
500 MHz. A number of owners of Morris's equipment are overall quite
happy with the units; some are listed below, and I got positive comments
via phone from two companies not listed here. The primary problem from
our perspective with the Morris unit was the rather high cost for the
capability it provides. Although the HP unit we decided on is even more
expensive, it has capabilities that go well beyond simple sweeping and
filter bandwidth checks; we had the money and decided we could make good
use of the additional capability of the HP unit.
----------------------------------------------------------
Charlie Fry Tel: (608)262-3182
Director, MR Facility Fax: (608)262-0381
Chem. Dept., Univ. Wisconsin
Madison, WI 53706 USA email: fry@chem.wisc.edu
----------------------------------------------------------
*********************************************************************
>Date: Tue, 21 Apr 1998 11:21:41 -0500
>From: "Charles G. Fry" <fry@bert.chem.wisc.edu>
>Subject: sweepers for probe tuning
>To: ammrl@wwitch.unl.edu
>CC: marv@chem.wisc.edu, stringfe@chem.wisc.edu
>
>AMMRL'ers:
>
>I have seen previous posts on sweepers for probe tuning,
>but would like to get more specific information if possible.
>
>Morris Instruments (http://www.cyberplus.ca/~pmorris/) sells
>an LCD sweeper unit that looks like a good possibility, but
>I have concerns about its utility for tuning high resolution
>liquids probes.
>
>If any of you have the Morris unit, I would appreciate hearing
>how well it works for you.
>
>AEA makes a similar sweeper unit (http://www.mvangel.com/aea/),
>but we need 500 MHz, above what they offer.
>
>We are also looking at refurbished Waveteks and at HP's
>integrated (expensive) units.
>
>If you have other suggestions or know other suppliers that
>can provide sweep tuning facility for high res probes, please
>let me know.
>
>I will post a summary if I receive sufficient responses.
>
>Thanks for your help,
>
>
>----------------------------------------------------------
>Charlie Fry Tel: (608)262-3182
>Director, MR Facility Fax: (608)262-0381
>Chem. Dept., Univ. Wisconsin
>Madison, WI 53706 USA email: fry@chem.wisc.edu
>----------------------------------------------------------
>
*********************************************************************
Charlie:
The unit from pmorris certainly looks interesting.
I'm not sure the accuracy and frequency resolution
at 500 and 600 Mhz are good enough for critical
liquids (or solids) work.
Resolution of 100Khz may not be good enough. I
wonder what the absolute frequency accuracy is...
I've looked at the aea unit for some time - it's
clearly designed for radio amateur use and looks
a bit cheap in quality, and the resolution is quite
poor, as I remember. Also, the comercial units still
don't have a useful (for NMR) frequency coverage.
A demo and comparison of both would certainly be
informative. Also, how do they perform in a high
stray magnetic field? Some types of directional
couplers have toroidal inductors that saturate at
fairly low magnetic fields.
Both units would be useful in adjusting a broadband
coil (from 13C to 31P, etc), to "get it in the ballpark",
with final adjustment done with the spectrometer. And
two units might make tuning a Quad probe a breeze.
just my 2 cents, and it's OK to forward this to the group...
Cheers,
- Dennis
Dennis Edwards Currently Servicing 6.15GHZ of NMR
NMR Support Services edwards@chemistry.utah.edu
University of Utah TEL (801) 581-4208
Department of Chemistry FAX (801) 581-8433
315 S. 1400 E. RM Dock 40.45.717 N 111.50.940 W (GPS location)
Salt Lake City, Utah 84112 Altitude 4670 ft. (1420 meters)
USA Call KD7AMN
*********************************************************************
Charlie,
We have 3 of the Morris units and they are excellent for probe tuning
and they do have fine enough resolution for high res work. I can
recommend them highly.
You might want to also consider buying a used HP network analyzer. I
have seen them offered from various electronic rental/lease outfits for
around $5K.
HP also sells off their own leased equipment.The network analyzers are
excellent for determining match,plotting RF Fields and transmission
measurements as well
Regards
Scott Chesnick
In Vivo NMR
NIH/NHLBI/LCE
Bethesda MD
*********************************************************************
Charles: My unity500 tune mode is broken, so I rely on Morris's sweeper
exclusively. It works better than the 'tune mode' since I can rough in
with a broad range, then narrow it. I use it for any probe work on the
bench since I can sweep broad ranges easily and acurately.
Cheers, Lew
lew cary <lcary@chem.unr.edu>
*********************************************************************
Try a Bird wattmeter in line with the probe , set the AQ time to small
value,increase the pulse width , do a GO and tune for minimum reflected
power. Or if you have Bruker , Wobble. Put a sample in the probe for high
frequency nucleus. It does load the coil. Works for decouplers also.
=+=+=+=+=+=+=+=+=+=+=+=+=+=+=
Jim Breeyear
Univ of Vermont
Manager, Inst.
Chemistry Dept.
*********************************************************************
Charlie,
We have both a Morris 400 MHz and an AEA 135 MHz sweep
generator/tuning unit. The Morris sweeper has been a real workhorse and,
with the exception of its high price and relative bulkiness, has worked out
very well for tuning high resolution, solids, and imaging probes. The AEA,
on the other hand, is relatively hard to use due to its small screen and
slow refresh rate, although it was much less expensive than the Morris
sweeper.
One strategy that various people have used to build tuning devices
for high frequencies is to add a doubler to an existing lower-frequency
sweep generator. Alternatively, if you can find an old, surplus Wavetek
sweeper with a range up to 1000 MHz, this plus a reflection bridge and an
oscilloscope will give good results.
Finally, there was a fairly detailed posting regarding low-cost options for
RF tuning in the June 1996 AMMRL archives.
Regards,
Ken Fishbein
Facility Manager,
NMR Unit
NIH/NIA/GRC
Ph. (410) 558-8512
FAX (410) 558-8323 or 8173
E-mail: fishbein@vax.grc.nia.nih.gov
Address: Ken Fishbein
NIH/NIA/GRC
5600 Nathan Shock Drive
Baltimore, MD 21224 USA
----------------------------------------------------------
Charlie Fry Tel: (608)262-3182
Director, MR Facility Fax: (608)262-0381
Chem. Dept., Univ. Wisconsin
Madison, WI 53706 USA email: fry@chem.wisc.edu
----------------------------------------------------------