[TowerTalk] COAX SEAL

[kq2m at kq2m.com]

There should be another part to this discussion that I have not yet seen 
mentioned.  Coefficient of Thermal Expansion.

If the connectors are water tight/air tight, then in theory no taping of 
connectors should be necessary if the connections are all 
electrically/mechanically sound and very tight and no large physical 
stress in placed on them.  Furthermore, if tape is used and water 
manages to get in, then it can potentially be sealed which over time 
could create problems.  But changes in heat/humidity can cause 
condensation INSIDE the wraps anyway.  So not using anything to wrap the 
coax/connectors would allow immediate exposure to the elements and 
simultaneously allow for moisture drainage away from the 
coax/connectors.

But none of that addresses HOW and WHEN those physically tight 
connections might become less tight.  Enter Coefficient of Thermal 
Expansion.

We all know that various metals get hot faster than the outer jacket of 
coax, in response to direct sunlight and hot ambient temperatures in the 
Summer. Conversely, we know that objects (like connectors) will shrink 
in size response to the cold more than coax will shrink because of 
differences in the Coefficient of Thermal Expansion (the reverse of how 
they all expand with an increase in temperature).

Because connectors will shrink more in response to colder temperature 
than coax will, a tight connection will begin to loosen and will allow 
for water to get in.  This is especially true in Winter in more Northern 
climates.
So that "waterproof" connection becomes non-waterproof.  And if water 
can get in, ice can form and expand the gap and damage the the coax or 
connectors or both.  By using tape and sealant we are already protecting 
against that.

But note that this is already happening anyway in microscale because the 
coax jacket and the connectors are neither perfectly smooth nor exactly 
the same shape, so there are already tiny ridges and depressions on the 
surfaces of the coax jacket and the connectors that are allowing air and 
moisture to get in even though you can't see it.  But these tiny gaps 
can easily be seen under an electron microscope even though is not 
visible to the naked eye.  Bottom line: Pro or not, you really should 
use some sort of quality tape/wrap anyway.

73

Bob, KQ2M


On 2024-03-10 11:15, Steve Maki wrote:
> You may have a different definition of "pro" that others do. Is it just 
> the broadcast industry that utilizes "pros"? That's another subject for 
> discussion.
> 
> It's true that modern connectors are theoretically weatherproof, and I 
> do not weatherproof the many 7/16 DIN connectors on my own ham station, 
> whether they are on Heliax or 3/8" RG8 stuff.
> 
> But in my (dare I say it?) professional work, our customers (AT&T, 
> Verizon, T-Mobile, etc) require it. Until recently it was always 
> tape-butyl-tape. Nowadays it's custom rubber boots...but still, it's 
> external weatherproofing.
> 
> -Steve K8LX
> 
> On 03/10/24 7:04 AM, Rob Atkinson wrote:
>>> I'm pretty certain that the pros use butyl mastic
>> The "pros" don't use anything because they don't use UHF connectors.
>> They are working with Heliax, waveguide, or ridgid line and the lines
>> are often pressurized.  Connectors made for those kinds of lines don't
>> require all these wild methods involving tar, and tape and do more
>> harm than good by sealing in moisture.stevek at jmr.com  is correct.
>> The ideal method is nothing.  If you have a feedline run laying on or
>> under the ground that's subject to flooding, then elevate the
>> connections.  I'd want to do that anyway to make it easier to
>> troubleshoot.  I tried all the tape, tar, grease, and so on a few
>> times early on and realized it was heading in the wrong direction.
>> 
>> 
>> 73
>> Rob
>> K5UJ