Howie,
Thanks for sharing. Its great to know how the pros do it !
Bob
K6UJ
On 5/15/16 12:44 PM, Chuck Dietz wrote:
Great post, Howie. Lots of good info there.
Chuck W5PR
On Sun, May 15, 2016 at 12:39 PM, Howard Hoyt <hhoyt@mebtel.net> wrote:
On 5/15/2016 12:00 PM, towertalk-request@contesting.com wrote:
From: <john@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
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