On 11/17/2014 9:00 PM, Roger (K8RI) on TT wrote:
On 11/17/2014 10:56 AM, Gary J - N5BAA wrote:
Caution: N-Type connectors may not be your answer.
I forgot to add, tape the cables together where they cross and tape the
coax coming out of the loop to a tower leg so the connector is not
supporting the entire weight of the vertical run I typically run the
coax down about a foot (give or take). make a gentle 90 to take the coax
to a tower leg, make the loop at the leg and continue down the leg with
the coax. I tape it to the leg about every two feet. I only use about
two wraps at each point. Make the loop as small as the "repeatable"
bend radius if possible. The smaller the better for preventing the
center conductor migration. NOTE: Nothing comes for free. The tighter
the loop and the longer the run the more likely you will get the center
migrating to the side instead of linerally.
2 or 3 larger loops, evenly spaced might work better with less tendency
for the center conductor to migrate off center. IOW use a loop with a 2
or 3 times the repeatable bend radius.loops
73
Roger (K8RI)
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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