I think some one put up a link with photos but here's what I do: Sorry about
the extra spacing but I just switched to open office and this is what I get
when I paste it into OE.
Installing N-Type crimp connectors for LMR-400 such as the RF-Connections
type RF Parts
This is how I derived how much to cut and where.
NOTE: Measure as you may find some slight differences.
The tip which solders to the center connector has a hole 6 mm in depth.
When installed in the connector (pressed into the insulator) the bottom of
this hole is 16mm from the back edge of the connector proper.
The back side of the insulator is just over 10mm forward from that same
The back edge of the center pin is flush with the back edge of the center
The crimp sleeve is about 13 mm long.
The rear of the connector that fits over the coax center insulator is about
Note this means the crimp sleeve is 5 mm longer than the portion of the
connector over which it crimps
This means the sleeve will extend 15 mm beyond the end of the center
insulator after it is trimmed back for the center connector.
So...Given these numbers:
I slide the crimp sleeve over the coax jacket and push back out of the way.
Using a box cutter or similar sharp trimmer I cut 6 mm off the outside of
the coax all the way to the center insulator. This means the rear of the pin
will be flush with the LMR-400 foam dielectric.
I remove about 20 mm of the jacket which should provide enough room for the
crimp sleeve to extend over the braid with a bit of room.
I push the braid back enough to give me room to trim the foil off the
dielectric at the end.
I trim the foil shield back a couple mm from the end and make sure no pieces
are left on the end.
I solder the center pin in place.
I insert the coax into the connector from the rear, pushing hard enough to
seat the center connector.
>From the front the tip of the center pin should come out flush with the
grounding flanges at the center of the connector.
The crimp sleeve is slid forward over the braid leaving about a 2 mm space
between it and the rear of the connector. There should be no lose ends of
braid sticking out to the sides of the crip sleeve.
The sleeve is then crimped in place. This may take a surprising amount of
pressure and strength to complete. The LMR-400 connectors actually take more
force than crimping the ones for LMR-600.
These connectors should come with a piece of heat shrink tubing to seal them
from the elements. (Not all will have the heat shrink. I believe most
Amphenol connectors will have it.)
I prefer to use the flooded heat shrink made by 3-M. The size is 0800 IMCSN
.08"/.22" 20/5.6 mm. It's about $9 or $10 per length. This stuff is rugged.
This stuff looks large and will slide right over the connector, but it will
shrink down tight on the LMR-400. The hot glue (flooding material) will do a
very good job of sealing the connector.
OTOH if you seal up the system after, (or as) you install it there may be no
need for the individual sealing. I seal them when I put them together and
then I seal them when the connections are made outside. At this point hams
can use what ever is their favorite connection/splice sealing method for
outdoor use. I prefer to seal all connectors when I assemble them as it
protects the braid for those used indoors.
Hope this is of use.
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
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