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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