Reflectance Bridges Summary

From: Roger Kautz <rkautz_at_lynx.dac.neu.edu>
Date: Fri, 12 Oct 2001 12:14:42 -0400

Reflectance Bridges Summary


The Wiltron SWR bridges looked right for the job, I think the 5400 6NF50 is
has the right connectors and RF range, check
http://www.wiltron.com/products/showProd.asp?prod=206

Mini-circuits directional couplers are also recommended - see note below.

Other bridges mentioned were:
The Wavetec FB40-50
And the Anzac H-1-4 (5-1000 MHz) that I couldn't find.

Clearly this list is incomplete, e.g. no HP (agilent) products made it.

                                        -- Roger

========== Peter Lundberg <peterl_at_raf.liu.se>

I purchased an 'rf-sweeper' (i.e., includes a swept frequency generator)
from Morris Instruments Inc in Canada. The model number is 405NV+, with
background light. I find it very easy to use also in low light conditions
near the magnet.
Have a look at http://www.netrover.com/~pmorris/sweeper.html for more details
73, Peter

---
[Roger's note: These units look great - advertise they can even be used 
inside an imaging magnet.  Costs were
1. Model 405NV+ 1.3 to 405MHz  $3,300.00 U.S.
2. Model 505NV+: 1.6 to 505MHz $3,800.00 U.S.
3. Model 610NV+: 2.0 to 610MHz $4,300.00 U.S.  ]
==========  Robert Santini <rsantini_at_purdue.edu>
I have been using reflectance bridges from a company called Wiltron for 
many years. There are various models, but the relatively low-cost units 
(about $100 the last time I looked) are excellent. I prefer the versions 
with the built-in reference impedance. The last time I bought one was about 
5 years ago, so they hold up. My model types may no longer be in 
production. If you can't find catalog or web-based data, I will send you 
the model numbers. These units cost a bit more than most, but the 
performance justifies the expense.
Regards,
-- Bob Santini
===========  From: "Kalisker, Thomas R" <thomas_kalisker_at_merck.com>
I have occasionally been tuning probes using
a Tektronix Spectrum Analyzer equipped with a tracking generator.
I have had good results used the mini-circuits directional couplers
that Varian uses in their tuning circuit.
The older systems used ZDC-10-1
The newer Inovas are using ZFSC-2-2
and most recently ZFDC-20-5
The devices are bandwidth limited so you might want to
look up the specs.
Bird-Electronics and HP are also good sources for this
type of RF part.
regards,
Tom Kalisker
[ Also  ZFDC-10-2 or  ZFDC-10-2.  All are about $50, 
www.minicircuits.com.  Mini-Circuits comes recommended by an RF engineer I 
consulted.  He suggested I connect my sweeper to "out", my 
detector/oscilloscope to "in", and my probe to "cpl".  An alternative 
connection is given at 
http://nmrsg1.chem.indiana.edu/NMRguide/misc/wavetek.html.
				-- Roger]
[Some advice on why I was having trouble with my test setup, since the 
bridge should be OK was:  ]
===========  Jeff Walton <jhwalton_at_ucdavis.edu>
Did you make sure the scope was on high impedance input and not 50 ohms?
Jeff
==========   jim breeyear <jbreeyea_at_zoo.uvm.edu>
make sure your have it terminated correctly and you have good cables.
========== Original Query
 >In setting up my electronics bench I am having trouble finding a reflectance
 >bridge for tuning NMR probes.   There was some good discussion of this in
 >the AMMRL archives some years ago.  But I can't find the same vendors and
 >models, and there are sooo many different kinds of bridges out there.  I'd
 >be grateful (and will post a summary) if those who have one could tell me:
 >
 >What make & model number reflectance bridge do you use?    Do you recommend
 >it as good, economical, or both?
 >
 >
 >`					-- Roger
 >
 >
 >This would be the "magic tee" that you put between your swept frequency
 >generator and oscilloscope (via an RF detector), with the probe on one side
 >and a 50 ohm load on the other side.
 >
 >If folks can say what RF detector they use that would be a useful list, too.
 >And any good references (web pages) on tuning (or making) probes.
 >
 >Some people in the earlier summary used a directional coupler from
 >Mini-Circuits.
 >When I tried this I found a large background signal, much larger than a
 >probe that tuned well on the spectrometer - I could see slight movement only
 >if I knew where to look.  Is there a trick to this anyone knows?
 >

Received on Fri Oct 12 2001 - 19:43:44 MST