[TowerTalk] Some advice about crimp ;type coax connectors

Mon Nov 17 21:00:02 EST 2014

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)