Making Cables for the 8-ch C13 Rat Array
8 coax cables for RF out from the preamps (black cables)
Single twisted-pair cable for 10V & gnd to power premps (white cable)
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Overview
Making JST Power Cables
Making Radiall SMP Coax Connections
Making Smiths/Hypertronics N series Mod K Coax Connections
Making Smiths/Hypertronics N series Mod V Signal Connections
Making Cable Traps
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Whether your scanner is a GE, Siemens, Philips, Bruker, etc., the far end of the cable that plugs into the scanner will
have proprietary connections. As a researcher at an institution that has access to proprietary information (one that
has signed a research agreement, a legal document), you have to be aware to not divulge any of those companies’
intellectual property.
Those companies typically buy their connectors from 3rd party connector companies and/or have special parts
made for them (of special non-magnetic, non-contaminated plating alloys, etc.). There are many such connector
companies (ODU, Smiths/Hypertronics, Huber & Suhner and so on.)
These slides won’t go over any proprietary connections, but rather simply go over the mechanics of making crimp
connections of a few types of relevant connectors, so that you can fix your cables if/when they break. When most
complicated pieces of equipment do break, it’s usually the connectors that have gone bad.
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A Typical MRI Scanner Connector
An ID chip (EEPROM), similar to the ID chips for printer toner cartridges
Coaxial connectors for RF out from each
coil in the array
Mechanical (only) guide posts for alignment
Single-wire connectors for
low-frequency control signals
and power/gnd
Plastic case is mostly cosmetic, but can be useful to
provide strain relief during handling
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Of course, on your end of the cable, you can design
with whatever connectors you like. Here we use JST
2-pin connectors for power/gnd, and Radiall’s SMP
miniature coax connectors for RF signals.
No connectors are used between the coil and the
preamp board. We simply solder/unsolder the coil
neck ends to two pads on each preamp board.
JST 2-pin power conns
Radiall SMP coax conns
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Overview
Making JST Power Cables
Making Radiall SMP Coax Connections
Making Smiths/Hypertronics N series Mod K Coax Connections
Making Smiths/Hypertronics N series Mod V Signal Connections
Making Cable Traps
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JST SFHR-02V-R
JST SSFH-001T-P0.5
JST WC-SFH1
JST SM02B-SFHRS-TF(LF)(SN)
Using 26 AWG stranded wire (Alpha Wire #3049), available from Mouser.
Contact JST to ask for crimping instructions and strip length. JST, like most
connector vendors, does not post crimping instructions on their web site.
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Important! Make
sure that whether
you choose #22, #24
and #26 wire, that
you choose one with
an outer diameter
less than 1.3 mm!
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Make sure to check the datasheet for the wire you use or measure the outer diameter. This Alpha Wire (#3049) 26
AWG wire’s outer diameter is just barely less than 1.3 mm. Similar 24 AWG wire that I tried was too large and the
crimp didn’t work (the cable fell apart). Check the manufacturer’s web site for datasheets, before you buy wire.
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Use diagonal cutters that have a flush backside and pointy tips: Xcelite (Digikey #MS543JV)...
...to snip the stripped length to 1.7 mm:
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1.7 mm
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A proper crimp should come out looking like this:
The stripped length should be precisely 1.7 mm so that the
wire strands end here, below where the mating pin will reach:
This upper tang should grab solely stripped metal.
This lower tang should grab the insulation.
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These bend-overs won’t be changed by the
crimp tool. This bend-over is what accepts
the mating pin that’s in the receptacle that
this plug will plug into.
The crimp tool is designed to crimp these
lower 2 tangs around your wire.
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If you simply hold your ~1.7 mm
length of stripped wire up to the
contact which is sitting in the back
flap, you can see if the strip length
is correct. The outer tang should
be able to grab onto the insulation,
so the outer tang should come to
about this position on your wire:
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Now, with the contact in the back flap’s hole marked 26
AWG, fold up the back flap ...
... from the front, the contact looks like this:
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Carefully, insert the wire all the way in, making sure the outer
tang will be able to grab the insulation. Then squeeze until the
handles spring back.
Notice, that as you gradually release, you can’t
actually get your crimped wire out now ...
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To get your crimped wire out, you now have to tilt the
back flap back a few degrees ...
... now you can pull it out.
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Top surface
These pins are positioned towards the top of this boardmount connector, so this contact has to have this part
that slides over that pin, oriented towards the top also,
when we slide it into the plug.
Plug top surface
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... or here’s another way of saying it:
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On the preamp board and on the
power distribution ribbon, I defined
the leftside pin as ground.
Here we’ll use black as the color of
the wire to be connected to ground.
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Plug bottom surface
This tang orients towards the bottom and latches.
Plug top surface (top is
flatter than the bottom)
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This front lead and the one on the far side are just for mechanical
attachment to the board. They aren’t connected to the internal pins.
The board footprint is laid out for this lead to be +10 V.
Ground
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On the power distribution ribbon, the
yellow connector is where the cable will
bring 10 V and ground to this power
ribbon.
Then the power distribution ribbon has a
separate red power connector for each
preamp board. For each preamp board,
we need to make a power cable to
connect here and here:
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Think first, before inserting the contacts into the other plug. The way the boards are laid out, we need this way:
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Always ohm-out power and ground connections after you make power cables. Make sure ground and one
board is connected to ground on another board. Check 10 V locations on each board. Make sure a 10 V
location is not connected to ground, etc. Don’t skip this step. It’s not worth it (the preamps are $145 each
and have a 6-week lead time).
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Overview
Making JST Power Cables
Making Radiall SMP Coax Connections
Making Smiths/Hypertronics N series Mod K Coax Connections
Making Smiths/Hypertronics N series Mod V Signal Connections
Making Cable Traps
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SMP coaxial connectors:
Once the plug and receptacle are mated, we need a special SMP separation tool to get them apart.
SMP separation tool
To scanner
SMP right-angle plug
To probe coil
SMP surface-mount receptacle
(sends RF_out from the preamp to the scanner cable)
First though, we need to attach the SMP right-angle plug to a piece of coax cable ...
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How do we attach the SMP right-angle plug (this SMP plug is made for RG-316 coax) to the cable?
When you buy this connector (Radiall #R222.900.357W), it comes with a ferrule and a cap:
ferrule
cap
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Radiall R222.900.357W SMP (non magnetic) right angle plug
http://www.radiall.com/media/files/NonMagnetic%20D1C004XEe.pdf
First, strip the (non-magnetic) RG-316 coax
to these dimensions:
1.3 mm
1.5 mm
5 mm
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Elspec non-magnetic RG316 coaxial cable:
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Kingsing KS-09S coax stripper
www.kingsing.sh
Parameters for coax stripping RG316 for SMP plugs:
Step 1:
Strip length
Wire dia
Wire drawback
Blade wayback
Cut time
Rotary twist
2.8 mm
1.25 mm
4 mm
0.1 mm
1 sec
0 (no)
Step 2:
Strip length
Wire dia
Wire drawback
Blade wayback
Cut time
Rotary twist
1.3 mm
0.5 mm
4 mm
0.1 mm
1 sec
1 (yes)
Step 3:
Strip length
Wire dia
Wire drawback
Blade wayback
Cut time
Rotary strip
7.8 mm
2.15 mm
10 mm
0.1 mm
1 sec
0 (no)
Hint: use a vise grips (Quick-Grip with rubber jaws) to hold onto
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Radiall R222.900.357W SMP (non magnetic) right angle plug
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Note: slide the ferrule onto the wire before flaring the braid! Don’t forget this step!
I use a sharp scalpel’s point to gently flare the
braid. Since this particular coax cable from
Elspec has an inner foil, sometimes you need
to slice it in order to flare it out.
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Inner conductor slides over top this
gold post inside the plastic insulator:
Outer conductor goes outside the
knurled shaft of the SMP plug
Plastic insulation
surrounding gold post
Inner conductor
The crazy part is that we actually need to solder the inner conductor to that gold piece ... But that’s a later step.
First, we need to crimp the outer conductor ...
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Radiall R222.900.357W SMP (non magnetic) right angle plug
Daniels crimp frame HX4
Daniels die set Y196, cavity A
...for the outer crimp of the Emerson SMA bulkhead-cable jack, #142-9303-411
Y196 cavity A
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Slide the ferrule down over the outer braid. The ferrule is what we’re crimping to the knurled shaft:
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Now that we’ve connected the outer braid of the cable to the
outer shell of the SMP plug, we next have to connect the cable’s
inner conductor to the SMP plug’s signal pin. This means we
have to solder this inner conductor to this gold post:
The only chance of soldering this sucessfully is if
you have a beveled tip like this. The “bevel”
means is has a flat edge here:
We’ll put that flat edge so it contacts both the
inner conductor and the gold post, so as to heat
them simultaneously.
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Also, there is absolutely no chance to be successful unless you apply flux. Flux is the magical chemical
that makes soldering work. The soldering process is a highly engineered system – flux is corrosive and
gets rid of the oxide, allowing the two metal surfaces to get soldered together:
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After applying flux, heat both the inner conductor and the gold post at the same time:
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Then bring in a bit of solder (if you’re using lead-free solder, you need to use flux made for lead-free solder).
There is no chance to get this to work unless you sit down and fixture your arms and hands against the desk, and
the vise, using your palms and wrists to wrap around the vise:
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It should end up like this – a solder fillet on top of the gold post,
with no solder shorting to the sides of the aluminum cavity:
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Verify that there is no solder shorting the inner conductor to the outer shell, by ohming them out. You can also ohm
out the opposite end of the cable to check.
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Next, press-fit the SMP plug’s cap:
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With the cap on, there is no danger that a piece of dirt will fall in there and short the inner conductor to the cavity:
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SMP plugs have this moveable ring that has a slot. When
you push this plug into its mating receptacle, this ring
gets forced upwards (by the mating receptacle) towards
the aluminum block and tightens, making a very good
connection, yet allows for rotation:
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When inserting the plug into its mating receptacle on a board, be careful. You don’t want to break or bend this pin.
The goal of a good coax connection is to have a perfect 50 ohm transmission line, without any reflections of the
wave when it sees the connector. Check for dirt or dust in the receptacle. Blow out with clean dry air. Also, use a
gage on both the plug and the receptacle after you’ve crimped the plug and soldered the receptacle (to check that
they connectors weren’t mangled during the assembly processes).
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These SMP connectors are precision, expensive, high-quality connectors. Put them together carefully. Make sure the
board is resting on a flat surface, and orient the top of the plug exactly perpendicular to the mating receptacle. Then
push down with exactly an axial force (a lot of force, carefully applied), until they go together.
Apply force vertically
Hold horizontally
The non-magnetic surface-mount mating receptacle is Radiall #R222941324w.
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Push straight down until fully seated.
Now the tricky part is getting them apart. These are such
good connectos, getting them apart is not straightforward...
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Radiall R222.900.357W SMP (non magnetic) right angle plug
The extraction tool to remove this plug from its mating receptacle, R222941324w is:
R282.918.210
You have to use this special tool, and you
have to sharpen it first...
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This pry-bar edge looks like this when you buy the
tool new. It’s not nearly sharp enough to pry the
plug ring’s top edge down from the plug’s
aluminum block.
You have to file the edge of this tool. Hold it in a
vise and file the angled edge until it’s sharp.
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Not filed sharp enough:
This edge needs to be *very* sharp, like this ...
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... because you need to insert the sharp tip into a difficult, tight space ...
You *must* hold onto the plug’s
aluminum block (with your
opposite hand):
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The pry-bar tip needs to go flush
against the plug’s aluminum block,
between the aluminum block and the
top of the plug’s ring.
Not between the plug’s ring and the mating receptacle!
The idea is to force down the plug’s ring using the thickness of the pry-bar,
which in turn pushes the mating receptacle away from the plug.
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Here’s another view of what you’re trying to do:
It’s an indirect separation technique. You don’t even
touch the mating receptacle!
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Only after you’ve separated the plug ring away from the plug’s aluminum
block, do put the tool away and now gently (applying a vertical force) pull the
mating receptacle away from the plug:
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If the pry-bar wasn’t sharp enough, you’ll just be pushing against both surfaces and gouging them up.
And they won’t come apart. The whole trick is to make a very sharp tool.
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Overview
Making JST Power Cables
Making Radiall SMP Coax Connections
Making Smiths/Hypertronics N series Mod K Coax Connections
Making Smiths/Hypertronics N series Mod V Signal Connections
Making Cable Traps
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N series Module K
Single-conductor (not coax) signal pins
These crimp contacts accept
22 AWG through 26 AWG
stranded wire
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Google for the crimping instructions, S50063:
(Also ask for the extraction instructions.
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T1970
You can use the insertion tool to first push the pin
all the way in, in this downward direction ...
Then use the extraction tool, sliding its tubular end
over the pin’s tangs to squeeze the tangs together
so they no longer catch on the latching bump.
S/DEM1.0060
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Use squeeze-n-strip wire strippers:
Strip 0.173” (4.4 mm)
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The AFM8 tool frame works with a variety of positioners. The positioners hold different crimp pins at different
depths in the backside of the tool:
Crimp tool frame
Pin positioners
(want the K547)
Remove the clip to swap positioners
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Note listings here. The listings tell which setting of the crimp squeeze to use for different wire gauges. For 24 AWG,
we want setting #4:
Pull out this clip and rotate the black dial to setting #4.
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Squeeze-n-strip ...
... and snip to 4.4 mm length
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Flip the crimp frame over and insert the pin into
the positioner:
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Squeeze the handles lightly – don’t crimp all the way. You can see where the crimp teeth will bite into the pin:
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Insert the stripped end of the wire into the pin,
squeeze the handles until they spring back, and
then remove the crimped pin:
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Next, insert the pin into the plug’s insulating housing. Refer back to the crimping instructions and note the flats
on the housing’s holes:
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These flats on the left and right edges of the gold pin go into the
black plastic rectangular holes in this orientation:
These flats on the left and right edges of the gold pin go into the
black plastic rectangular holes in this orientation:
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Overview
Making JST Power Cables
Making Radiall SMP Coax Connections
Making Smiths/Hypertronics N series Mod K Coax Connections
Making Smiths/Hypertronics N series Mod V Signal Connections
Making Cable Traps
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Hypertronics (now
Smiths Connectors)
Modular N series:
N series Module V male
coax connectors
Ferrule
Heat shrink tubing
Contact
Male pin
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Hypertronics catalog
N series, Module V, NVMRTH w/male contacts, (magnetic version) YCX0315-004: p. 4/34.
Crimping Datasheet Number is listed on p. 4/35
of the catalog:
-female
-male
These are the standard catalog part numbers (magnetic version).
Call Hypertronics for the non-magnetic version.
Also ask for the crimping
instructions.
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To extract a Mod V contact, you need this tool
... and any 1/8” dia rod:
T1982
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Push the back side of the contact all the way forward, and then slip the tube over the front of the contact, so that it
pushes in the
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If the tube has successfully pushed down the latches, then pushing on the plunger should push the contact
out easily:
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Smiths/Hypertronics’ ClearImage line of connectors are the non-magnetic versions of the N series modular connectors:
http://www.hypertronics.com/en/Technology/HypertacTechnologies/ClearImage.aspx
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For assembling the Mod V connector, you use 2 crimp tools, one for the inner conductor, and one for the
outer conductor:
Daniels AFM8
crimp tool frame
Daniels K1246
positioner
Daniels HX3
crimp tool frame
Daniels 101
die set (crosses with the
T1958 called out). Use
cavity A.
Use setting #5
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2.54 mm
3.94 mm
5.59 mm
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Elspec non-magnetic RG316 coaxial cable:
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Kingsing KS-09S coax stripper
www.kingsing.sh
Parameters for coax stripping for Hypertronics N series Mod V:
Step 1:
Strip length
Wire dia
Wire drawback
Blade wayback
Cut time
Rotary twist
6.5 mm
1.3 mm
10 mm
0.2 mm
1 sec
0 (no)
Step 2:
Strip length
Wire dia
Wire drawback
Blade wayback
Cut time
Rotary twist
2.5 mm
0.5 mm
4 mm
0.1 mm
1 sec
1 (yes)
Step 3:
Strip length
Wire dia
Wire drawback
Blade wayback
Cut time
Rotary strip
12.1 mm
2.01 mm
15 mm
0.2 mm
1 sec
0 (no)
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Use the AFM8 crimp frame with the T1957 (K1246) positioner. T1957 is the MIL-Spec standard number and K1246 is
the manufacturer’s (Daniels Manufacturing) part number. Set the black dial to Setting #5:
The gold pin sits all the way
down in the aluminum
positioner:
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Squeeze the handles lightly – don’t crimp all the way.
You can see where the crimp teeth will bite into the pin:
With your RG-316 coax cable stripped to the correct
length, insert the inner conductor all the way in, and
crimp:
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Release the handle and take out the crimped pin.
If you look carefully, you can see where the teeth
dug into the gold pin to crimp it. If you inserted
the coax correctly into the positioner, the gold pin
should butt up directly against the clear insulation:
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Now, before moving on to crimping the outer conductor, don’t forget this step:
Slide the heat shrink tubing and the ferrule onto the cable first!
Ferrule
Heat shrink tubing
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The contact has been inserted into the T2040 alignment tool.
However, before inserting the crimped center pin, we’ll need to flare out the stripped outer braid ...
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Flare back the outer braid and its aluminum-foil shield (you might need to use a sharp surgeon’s scalpel to slice
foil so that you can flare it back. This outer conductor needs to go outside the gold, knurled shaft of the contact:
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Hold the cable right here, to gently (but firmly) push in the pin:
Verify you’ve pushed the pin in all the way by
looking at the tip of the pin from this angle. There is
no gage kit for this connector, so you have to use this
tool to confirm you’ve got the center pin at the
correct depth. You’ll feel a snap-like latch when the
center pin seats correctly into the contact. The pin
should touch
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The crimp instructions a few slides back called out the
MIL-Spec standard part numbers for the appropriate
crimp tool frame and die set to use for the outer contact’s
crimp. The corresponding part numbers from the vendor
are Daniel’s HX3 crimp frame and X101 die set. The crimp
instructions also called out to use “Cavity A” for our RG316 cable:
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Slide the ferrule down over the outer braid which is now on top of the contact’s knurled shaft. The ferrule is
what we actually crimp:
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Now it’s crimped:
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Now slide the heat shrink tubing over the crimped ferrule:
...and shrink the heat shrink tubing
with a hot air gun:
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Then label the cable and put it into the connector:
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Once you’ve made the electrical connections for your cables, you need to add mechanical strain reliefs ...
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Here’s a home-brew strain relief for a home-brew cable: machine a plastic ring, slide it over your cables and
then shring heat shrink tubing over it. Carve out a slot in the housing where the shrink-covered plastic ring
can sit:
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That is, put thin heat shrink around the cable
bundle, followed by the nylon spacer ring ... then
put 4:1 shrinkable fabric heat shrink on the
outside of the nylon spacer ring, and slip the
whole spacer fin assembly into the milled slot.
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Now you can tug in this direction all you want, and
no stress gets applied to the electrical contacts.
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Do something similar on the rat cylinder ... create a feature on the rat cylinder that serves the same purpose as the
milled slot shown in the previous slides:
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... and machine another plastic ring that you can pass over this far end of your cable. You’ll heat shrink this
ring over the cable bundle and let it sit in this slot:
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Move the heat-shrinked plastic ring
over to sit in this pocket.
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Then screw on the upper half of the bracket and you’ll have a
good strain relief for this end of the cable.
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•
•
•
•
•
•
Overview
Making JST Power Cables
Making Radiall SMP Coax Connections
Making Smiths/Hypertronics N series Mod K Coax Connections
Making Smiths/Hypertronics N series Mod V Signal Connections
Making Cable Traps
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To make a cable trap, find some plastic tubing
(easy to slice if you have a laser cutter). Then
design and 3D-print a simple spool that will fit in
the tube. Wind your coax cable around the spool
and slip the tube over the spool.
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Then remove a small slice of the coax cable’s outer jacket on
each end.
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You can use a wire stripper to (gently) make the correct
diameter cut, as shown on the previous slide ... or you
can use a surgeon’s scalpel (put on a new sharp blade).
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After stripping slices of the outer jacket, wrap the spool
in copper tape.
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Copper tape usually comes with a conductive adhesive on the back, but it’s best to add some solder to make a good
contact. Always, always, always apply flux when soldering. Flux is the magic ingredient that makes solder work. If
you use lead-free solder (what we typically use, since all components these days are plated with lead-free solder),
make sure to use a flux designed for lead-free solder. The combination is a heavily-engineered systems by
metallurgists.
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To make a cable trap, one end of the spool’s
RF shield gets soldered directly to the outer
braid. Apply copper tape from the shield
up to, and touching the braid.
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The other end of the spool gets a capacitor soldered between the RF
shield and the copper braid. Here, 256 pF made the outer braid’s
inductance create a parallel resonance at the frequency for C13
imaging at 3 T (32 MHz). We used two non-magnetic ATC (series 100B)
capacitors in parallel: 200 pF + 56 pF. Hold the two together in a pair
of tweezer, apply flux and solder their ends together.
Then solder the capacitors onto the other end of the spool.
Hint: Tin the copper tape (apply flux first!) with some solder first. Then you can solder one
end of the capacitor pair to that tined surface.
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Then solder the other end of the capacitor pair to the outer braid:
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Then measure the parallel resonance on a |S11| trace on
the network analyzer, using a sniffer coil attached to Port 1.
Sniffer coil.
Ferrite cable trap for bench top testing.
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