[TowerTalk] PL259 Connectors

[Howard Hoyt]

On 5/15/2016 12:00 PM, towertalk-request at contesting.com wrote:

> From: <john at kk9a.com>
>
> ...I'm not sure why more hams don't do what the pros do.

I've been watching the discussion with some interest to see where it 
would go, and to see if anyone has come up with a better system than the 
3/4" tape over the connectors/butyl seal/2" tape overall system.  I've 
been a broadcast engineer for over 30 years and have used the 2" wide 
Andrew tape and butyl weatherproofing exclusively. It is also important 
to tighten with wrenches or pliers to inhibit loosening from vibration 
or wind movement.  To date I have not had a connection fail due to water 
intrusion using this system.  If you examine the tens of thousands of 
connections on broadcast towers across the world on Heliax and coax 
products, this is what broadcast engineers and tower riggers use.  Keep 
in mind this sealing system has to be in use 24/7 and at thousands of 
feet up in the weather and last for years.   The very worst I encounter 
when dis-assembling a connection protected in this manner is tape 
adhesive residue on the connectors, but never moisture or corrosion.

The 2" wide thick tape is an important part of the system; when used as 
the top seal it inhibits the butyl from extruding between the wraps of 
tape, which can be a problem with 3/4" wide tape.  It also allows a more 
generous overlap for better adhesion.  The high-quality tape Andrews 
specs (not always 3M...) will not lose adhesion even after years of UV 
and high winds.  Of course the last few wraps must be made at low 
tension and laid flat without wrinkles, AND making sure the surface of 
the tape it is adhering to has no dust, oils or greases to inhibit 
adhesion. (see below on using greases)

Packing the connectors with any sort of grease is problematic for a few 
reasons: Some greases have a fairly high film strength, and the wiping 
action of the mating parts may not fully displace it resulting in a poor 
connection, compatibility with dielectrics or seals (BNC/N) is not 
guaranteed, and unless the product is guaranteed to be free radical and 
moisture free (most are not), you are potentially adding a source of 
corrosion.  Also, it can bleed, it makes a mess and seems to get on your 
hands/gloves no matter what you do so you end up getting it on the 
connector and coax.  This film can then interfere with the adhesion of 
the primary seal you put on the outside of the connectors.  An example 
of this problem: when installing flanged hardline or Heliax connectors 
you must grease the o-rings, but then you must be be meticulous about 
cleaning your hands/new gloves before you install any grounding kits 
which include taping.  Basically, if you do the external sealing 
correctly you just plain do not need grease with non-flanged Heliax or 
coax connectors.

You must be very careful how you use dual-wall adhesive heatshrink for 
use on flexible cables, even the thick marine grade type.  It is 
important to clean the jacket with a degreaser such as isopropanol 
before installing to ensure a good bond.  Also, extend the heatshrink 
4-6" onto the coax to ensure the zone near the connector remains 
relatively rigid even if the bond at the end fails.  I have had 
factory-supplied FM antenna multi-bay phasing harnesses weatherproofed 
with short lengths of adhesive heatshrink tubing fail after being 
aggressively flexed by wind in cold weather when the hot-melt glue 
became very stiff and brittle.  The bond between the glue and coax 
jacket then failed and resulted in moisture intrusion.  I have since 
installed cables with much longer heatshrink and many coax supports to 
inhibit any movement.  I took a picture of this exact connection after 
rework on my website here (note broken phasing network cover due to 
falling ice):

https://proaudioeng.com/wp-content/uploads/2016/05/20140822_103713.jpg

For connections with hardware such as lugs under screws and nuts, as 
well as sealing exterior cabinet panels we use Scotchseal 800 which in 
my experience will give years of life and seals pretty well to metals 
and plastics even when exposed to UV and weather.

Remember: bonding occurs at the molecular level which means the 
molecules you wish to bond together must be able to interact.  Oils, 
moisture, and dust can all inhibit tape/adhesive bonding. Cleanliness is 
imperative.

Just my $0.02 worth,

Howie - WA4PSC
CE - WXYC-FM
UNC Chapel Hill, NC