[TowerTalk] Connector Sealing

[Howard Hoyt]

Hi all,

I read:

>   I have never used "Stuff", I imagine that it would be  hard to clean...
I have been reading the submissions on this subject with interest, but having been a broadcast engineer since the late 1970's, I can honestly say that the connector weatherproofing problem has been solved for many years in the broadcast industry.  Other than just raw curiosity into alternatives, I see little need for investigations into an improved technique, as the established technique is pretty bulletproof.  If this procedure has been previously printed or has already been laid out, I apologize for wasting your time, I am a relatively new list member.

There are small modifications on the basic technique, but the basic procedure is:

1) Cut the cable so that the unsupported length from the last cable bracket to the connector can form a drip loop.  Keeping water away from the connector is important.  Supporting the cable on or near the drip loop is critical to reducing cable whip and flexing at the connector, which can cause weatherproofing failure.

2) Thoroughly clean the connector body/cable/antenna connector body where the weatherproofing will be applied.  Adhesion is greatly degraded by dust or grease.

3) Put down a flat, non-wrinkled single layer of 3/4" Scotch electrical tape extending several inches out on the cable jacket(s) and/or antenna connector, and covering the mated connector bodies.  This is to provide a clean surface for the butyl to fuse onto, as well as protect the connectors from the butyl adhesion.  If not for the need to service the connector in the future, this first layer would be unnecessary.

4) On top of this a layer of self-fusing butyl is adhered, stopping an inch inboard of the initial tape wrap layer.  This is the main waterproofing layer, so it is important to keep the butyl warm and thoroughly massage it into a homogenous mass around the the connector assembly.  In the winter, keep the rolls of tape and butyl inside your jacket or your arm pit until use.  It is also important to press it into grooves and attempt to mold the outside surface of the butyl into as smooth a cylinder as possible.  If this is not done, the top layer of tape will not lay flat and allow moisture ingress, as well as allow the butyl to be exposed and weather.  Make the transition from the cylindrical mass of butyl to the cable as gentle and as smooth a taper as possible.

5) On top of this several layers of 2" wide electrical tape are wrapped, extending out past the bottom layer of tape on both ends of the connector assembly.  The bulk of the tape should be applied using low tension to ensure that that is wrinkle-free and flat against the butyl and cable/antenna body.  This is why it is so critical to mold the butyl into a regular smooth cylindrical mass.  Do NOT wrap the tape tightly; when the assembly heats up in the sun the tension exerted by the tape will begin to extrude the butyl between the tape wrapped layers.  The final 6" of outer tape should be applied with very little tension so as not to put the adhesive on the unsupported end of the tape in shear.  The end of the tape must be cut, not torn, so there is no distortion or residual stress in the tape.  Wrap the final turns carefully, do NOT get dust, dirt, finger or other greases on the adhesive, and make sure the end of the tape lands flat and with zero tension.  If it pulls up for any reason,, the flag it forms will catch wind and eventually compromise the assembly.

When sealed correctly in this manner the weatherproofing will last for years and weather just about any condition, and when cut open for service show the mated pair to be dry and shiny.  Some people talk about flipping the initial layer upside-down over the connector to keep adhesive residue off of the connector bodies, but in my experience, with quality tape this is a non-issue.  I have on occasion used adhesive-less vinyl harness tape over the connectors to achieve this same result, but the problems keeping it in place while wrapping the critical first layer completely flat and wrinkle-free make it a pain and not worth the effort, IMHO.  I have stopped cobbling together parts for weatherproofing as well; the quality seems to vary greatly depending on the supplier, and a lot of tape these days seems to be low-quality from off-shore, so forget about Harbor Freight and other similar crap.  I have settled on using Andrew #221213 weatherproofing kits, which cost less than $20 each, include quality Scotch tape and can weatherproof one 3" Heliax, two 1-5/8" Heliax, four 7/8" Heliax or at least six or more 1/2" UHF/N connectors with each kit (they claim 12).  Considering how well they work, they are damn cheap, and I have never seen a moisture-ingress connector failure when using their kits, even after years at 1000 feet+ and after hurricanes.  I have had other tower riggers say that the Wireless Solutions WK-U kit also works well.  Either kit contains materials which pass theMIL-STD-1344A, Method 1002  test for weather resistance.

I have occasionally seen "aneurysms" develop in the weatherproofing, trapped air bubbles due to pressure release from the inside of the cable when using UHF connectors which are not pressure tight.  This pressure is caused by thermal cycling and air expansion.  According to Andrew techs, placing gel weatherproofing compound in connectors is also not recommended, as it can soften the gaskets in connector bodies, as well as be forced under expansion through the tape and contribute to degradation of the weatherproofing.

This is the broadcast industry standard, others may have different methods that work well for them, so the usual caveats apply...YMMV.  Also, there is more than one way to skin a cat, some people just like to be different, and others will spend hours to save pennies.  Since ham radio is a hobby, there is less financial pressure to make installations bulletproof.  In broadcasting if a connector fails at 1000 feet in the winter, you can bet your a$$ while you are freezing it off on the tower you will rue the day you used Harbor Freight tape.

Howie


-- 

*Howard Hoyt - WA4PSC
CE - WXYC-FM 89.3
UNC Chapel Hill
www.wxyc.org
1st on the internet*