On 11/17/2014 10:56 AM, Gary J - N5BAA wrote:
Caution: N-Type connectors may not be your answer.
I crimp nearly all coax connectors here as well, but went back to UHF
connectors on all vertical runs on the tower as well as sloping dipole
feeds.. N-type connectors have a problem and it can be a big one on
vertical runs. On most N type connectors the center pin is not captive.
The weight of the coax center conductor can cause it to migrate down,
taking the center pin with it, either creating a poor electrical
connection, or none. The same problem exists in center feeding half
wave, sloping dipoles. When the temperature is well below freezing, or
even below zero is not the time to find out you have this problem.
The problem can be reduced with a 360 degree loop in the coax
immediately after the connector, but not so close as to induce leverage
into the connector. I have also resorted to using a strong 2-part epoxy
to pot the coax in the connector "with good success".Leave a space
between the back end of the center pin and the dielectric. Completely
fill this area with epoxy. Use a good, high quality epoxy that has a
high resistance when cured. It likely will have a much higher dielectric
constant than the coax, but such a small area will not be noticed at HF
and VHF. It also needs to have a high breakdown voltage. Don't use a
low viscosity (thin, or runny) epoxy and do not get any on the mating
surfaces of the connector. It works, but can take time to install
properly (needs to thoroughly cure before coax installation) and is easy
to make mistakes. I've done a lot of epoxy work so I'm comfortable with
it, but it might be a bit much for the inexperienced.
With a 100' 45G this became a major issue which raised other issues. I
went from LMR400 to LMR600 on the vertical runs. (not the sloping
dipoles). Sticker shock is quite descriptive of the price for UHF
connectors that fit LMR600. I prefer DIN 7-16 connectors, but they cost
more than the UHF for LMR-600.
As LMR600 is larger and heavier, the center conductor migration on
vertical runs is worse than on LMR400. Some inexpensive LMR 600 UHF
connectors may easily break off with very little applied leverage. That
360 degree loop needs to be far enough away from the connector that the
cable can be held to make the loop with out applying leverage to the
connector. Also make the loop large enough that there is no side force
applied to the connector when the loop is taped to the tower.
Here in the North country (Michigan) with our major temperature swings
from highs in summer to lows in winter the expansion and contraction
makes this problem even worse.
I had nearly all vertical runs fail at the top N-Type connector on the
45G the first winter they were up.
I also had the connectors fail from nearby lightening strike. So far,
I've never had a UHF connector fail from that.
I had a double female connector in a splice to a 40M sloping dipole
fail. Looks goos. Shows good with an ohm meter, but is shorted at 100W
of RF.
73
Roger (K8RI)
I crimp all my coax connectors now too, and horrors upon horrors made
the jump from UHF Pl-259's to Crimp N connectors at the same time. I
made the change to N connectors because I was buying new crimp
connectors anyway and it made sense to change to the much better
connector at the same time. The next time I am inside my Elecraft K3
and P3 I will change out the SO-239's for female N connectors, and
until then I just use adaptors. I must admit I am probably not a
"Real Ham Operator" since I am not a good solderer. I can manage to
solder the N pins though. I say all the above with trepidation
though, as recently on our club reflector I started a UHF vs N and
solder vs crimp war that has resulted in one of our club members
resigning his membership. Being a 3 year ham, I had no idea that the
opinions on connectors ran so deep.
Is there a source for just the crimping dies for Power Poles that
might fit in my crimpers?? My crimpers came from below - they are the
same as 90% of the crimpers out there and buying here gets you two
crimper pliers vs one crimper and two sets of dies.
http://www.amazon.com/gp/product/B00KNC6E4G/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
Gary J
N5BAA
-----Original Message----- From: Bill Turner
Sent: Sunday, November 16, 2014 8:55 PM
To: Towertalk
Subject: [TowerTalk] Some advice about crimp ;type coax connectors
I haven't seen this discussed before so I thought I'd throw in my 2
cents. Might help someone.
I love crimp type coax connectors. Done right, they are faster and
more reliable than solder type. I will never go back.
First, there are two types of crimp connectors. They both are designed
to have the braid crimped, but some of them are designed to have the
center pin soldered. Do not mix up the two kinds. The solder type has
a small cutout for the solder like PL-259's have had forever. The
crimp type has a round pin with no cutout. DO NOT try to crimp the
solder type and do not try to solder the crimp type. It won't hold.
Don't ask how I know. :-)
Always crimp or solder the pin first and then give it a good pull
before you crimp the braid. It should not pull out, obviously. How
much pull? I don't know exactly, but i think it should withstand at
least ten pounds or so. More is better.
In order to get a god crimp on the braid of the coax, all the braid
wires must all be intact. In other words, if you nick a few strands
and remove them, the crimp will not be as tight as it should be.
Do it over.
In order to get a really tight crimp, I like to put a single wrap of
electrical tape over the braid first. The ferrule is not part of the
electrical connection, so don't worry about that. it's only purpose it
to press the braid tightly to the connector. The tape just enlarges
the diameter and increases the pressure applied by the ferrule. You
could instead use heat shrink tubing of the appropriate size.
I highly recommend using a coax cutting tool, the kind that makes two
cuts at once - one down to the center conductor and one down to the
braid. It is well worth your time to get the depth of cur just right.
These cutters are adjustable so practice on a piece of coax and figure
wasting a foot or two until you have the cut perfect. You will be well
rewarded in the long run.
I learned all this the hard way. Hope this saves someone some grief.
Comments welcome.
73, Bill W6WRT
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73
Roger (K8RI)
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