How to attach hard-line coax to the tower and
how to protect hard-line coax connectors

The following discussion about how to attach hard-line coax to the tower and how to protect hard-line coax connectors took place in the Moon-Net reflector. I found the subject so interesting that I decided to put together all the messages in this page.

On 4-Jan-2004 WB9OWN wrote:
Pardon my the cross postings, I have 2 questions concerning using hard-line coax, (attached it up tower structures and the moisture preparation of the RF connector mating surfaces.)

1) How does one attached hard-line coax up a structure without causing problems due to it's weight? 

a) Plastic tyraps don't seem like a good idea to use in cold weather due to plastic becoming "brittle" (for the lack of good terms.)
b) Metal hose clamps seem like a more positive clamping solution, however one could puncture the plastic/rubber coating and cause problems, (intermod.) 
c) How about using a rubber gasketing around the hard-line (a short section garden hose slit lengthwise) for clamping to the tower? c) What does the cellular industry use for clamping runs of hard-line up towers? 
d) What in your experience has proven to work well?

2) What are the pro's and con's of greasing mating hard-line coax connectors? 

a) If one uses a grease, say Lithium or Permatrox, what does this do to the DC resistivity of the mating connectors? 
b) Any thoughts about what this grease does at RF mating junctions?) 
c) Dissimilar metals used in connector mating junctions, appears to be a problem in cellular industry. 
d) Ever hear of "tweak" (a conductive substance that some audiophiles use on phono or line output jacks? 
e) Black electrical tape doesn't like to stick to hard-line connectors if one is sloppy. ;-)

In advance, thank you for taking time in writing me a response to these questions. Regards.

On 4-Jan-2004 WA3BZT wrote:
I use 3/4 hard-line, Rohm 45 tower, 40 foot with a hazer no guyed lines.. My hard-line is secured to the inside of the tower with metal hose clamps the process I use is electrical tape under the clamp about 1/2 inch extended above and below the clamp surface. On the boom area I use electrical tape and UV tyraps covered with electrical tape. On covering the connectors I us heat shrink tubing than a couple of layers of electrical tape then cover the area with liquid electrical tape. The liquid tape has to be redone once a year to insure it stays bonded. I used Bishop tape (this is the tape that is like putty when you apply it covers great and will keep moisture out)once and that causes a BIG problem to remove when you need to get to the connector.And you know you will need to get to that connector. Murphy law. I also have 1 5/8 hard-line that I plan on using in another project that came from a cell phone site. They wrap the connector in bishop tape and cover with electrical tape Big mess to get the connector cleaned up. they also use a metal clamp to a # 10 wire to secure to the tower. The clamp is connected to the metal outer jacket (insulation cut off to allow this connection). As for resealing each year this is a good time to inspect the antenna and support system for loose hardware and other problems due to high winds and moisture.( I should know hit by lighting twice, high winds have mover my settings (no slippage marking just did not get around to it))

I also would be interested in what others have to say. In fact I think we had some discussing about this a couple of years ago.

On 4-Jan-2004 KD1VV wrote:
Andrew Corp sells tower clamps, which is what I believe the wireless pros use. See, for example, their catalog at http://www.andrew.com/catalog38/ Go to page 601.

On 4-Jan-2004 K1FO wrote:
An easy way to securely attach your hardline to the tower is to just use big nylon tie-wraps (1/2" - 12mm wide or wider). You have to use black color wraps because white nylon ones will deteriorate and snap in a couple of years from the ultraviolet light.

I have used both hose clamps and tie-wraps. The advantage of the hose clamps is that they are re-useable, but they are slow and a pain to install and as someone said you can have metal to metal contact problems.

Tie-wraps are quick and easy to install and you will not have any metal to metal contact problems, but they are not re-useable, although with some style wraps they may be re-useable. I have used tie-wraps on 1-5/8" LDF.

The professionals usually use special hanger clamps designed for the coax.

On 4-Jan-2004 GM4ISM wrote:
David, In the UK the the majority of comercial operators use Remclamps http://www.lpa-industries.co.uk/remstraps.htm They are fine in the Scottish mountains so I guess they are reasonable when cold.

Mating surfaces using disimular metals are oftet coated with a thin layer of corrosion inhibitor 'Unial' or with Biccon X1 paste.(I can find our UK supplier if reqd) I have used both on surfaces carrying high power UHF and VHF services for broadcast for many years. I have never used any form of grease on normal mating connectors (eg N of 7/16)

Non sticking tapes! bane of my (former) life Waterproofing of connectors .. there are several methods in use, Good self amagamating tape (that sticks to itself so well you cannot seperate it if it touches) is used as an undercoat and an all weather PVC tape is used on top for UV protecttion. this sticks to most things but to itself best HI Alternativly any self amalg tape + a layer of Denso tape ( a ghastly brown 'grease' soaked cloth tape) is applied on top and smoothed down. This stuff is really good if applied correctly and has the advantage of being able to be formed round awkward shapes or close spaced connectors....but it messy to apply. There is a new alternative, a tubular sleeve of rubber filled with a silicon grease, this rolls up over the connector to be protected and grips and seals due to the pressure of the grease within the 2 walls of the tubing. Have not tried this myself but is being adopted by some parts of the telecoms industry for waterproofing connectors to Mast head SHF units.. quick change!

Usual disclaimer.. I have no interests in any of the suppliers of these products

On 4-Jan-2004 Nanko wrote:
Stainless steel braid works also very well,Or a plastic equivalent,used to keep seperate wires together. Make a hole in the braid and slip the coax through it. About 20 cm is sufficient to keep this sleeve in place. Attach the rest of the braid to the structure. The heavier the cable,the tighter the braid fits around the cable.

On 4-Jan-2004 AL7EB wrote:
You are getting a good sample of advice. I work in the telecom world so have much experience.

Up here in Alaska, we find even the best Thomas&Betts 1/2-inch tywraps get brittle in very cold weather, so either commercial tower cable trays or rubber cushioned clamps are used (spendy for hams). Or on smaller towers (like Rohn) we use insulated soft solid copper wire to make wire ties. They make secure connections fast by twisting with pliers and do not cause metal-to-metal issues. No prep of hardlines necessary. Wrap the wire around the cable and tower leg several times before twisting to distribute the forces on the coax.

For sealing hardlines connectors I shy away from greases (esp. if you are running QRO power levels). We have used a compound called as Contax sold by Union Carbide for mobile and ship-mounted antennas running 50w at VHF with no SWR problems...very nice to exclude moisture and anti-seize). I wrap my connectors with self-bonding or annealing tape (made by Scotch...type 30 or 33..not sure of the number...but too costly for ham use at $30/roll), with a covering of electrical tape (again scotch-88). That holds well over years of use. I have also used heat shrink covered by electrical tape. Be careful of the economy tapes, they do not stretch well...that is the secret for water-tight seals. For vertical lines double wrap the electric tape beginning at the lowest point and wrap up with overlaps, then wrap back down to your start point. This will have the tape seams on the last layer covered from water running down the cable. Scotch-Kote or Coax Seal works too but very messy to remove...not convenient for EME stuff that requires 3/4 of your time for repairing an 1/4 for operating...LOL!

A final help is using cable like the Times LMR line which is bonded with foil and uses foam center insulation...helps prevent moisture incursion. Air-insulated lines like Belden-9913 are very prone to moisture invasion. I have used it, but not where cable movement is likely.

Try to do your installations on sunny dry days...too :-) A real shame to seal in moisture on a rainy day! I use a can of dry-air to blow out and dry the connectors if I must work in rain.

I use a Hazer system for the 2m-EME array of 4xM2-xpol-20s. My 7/8-Andrew Tx-line is attached to 1/2-inch conduit that is run up inside the tower. This minimizes the attachments to the tower that might hang-up the Hazer cage when raising or lowering. It does still require climbing to disconnect the LMR-400 jumper, though. I run a separate Rx line.

On 5-Jan-2004 WB9UWA wrote:
I guess, I agree with Ed on his choice of using insulated copper wire to hang hard line. I use either #14 or #12 solid copper house wire to hold both 7/8" and 1/2" hardline to my 90 foot Rohn 25 tower. In the case of 1/2" hardline, it is lighter and only gets a single turn around the line and horizontal tower rung. All lines cover the S/W face of the tower and I leave room at the ends for fingers, when climbing. I space the wires about every 5 feet. This works well for RG8 runs as well. A few twist of wire using fingers only seems sufficient to hold the cable run. The ends end up inside the tower. I stay away from cable ties. Even the black ones can become brittle in the sun unless they are specifically UV rated. They are one time use anyway, so I like the low cost wire holders.

I have tried many methods of weatherproofing cables and have settled on a non-adhesive, low cost rubber electrical tape (Menards). I top it with a low cost vinal tape because the rubber tape falls apart in the sun light. The rubber tape aneals together, so it forms a really good seal. It is a good idea to replace the weatherproofing every 3 years or so. You can inspect for water damage when this is done. In the end, really, nothing can keep water out of a connection 100%. Start thinking in terms of keeping air in a tire and you will see what I mean. When the air pressure changes, moisture in the air can be sucked right in to your connection. Use connections that have little or no air spaces. This is one reason I don't like air power dividers. They must be designed like a drain pipe to let water out.

If I greese a connector, it is only the threads. I rarely bother unless it is steel to aluminum.

On 5-Jan-2004 W8WN wrote:
Attaching hard line to tower - for about 25 years I have used a couple of stainless-steel hose clamps (aluminum line to galvanized tower, then aluminum line to aluminum tower). Still seems OK.

I also use a coax connector that has an air input. This has always been fed with dry air thru a long windshield washer hose. It is dried by passing it thru a glass canning jar that is filled with desiccant silica gel (available sometimes at flower shops, hobby shops, etc, for drying flowers; and little packages regularly come in bottles of vitamins, with electronic equipment, etc). Two small (3/16" or so) pieces of brass hobby tubing are soldered to a metal canning top for hose attachments - the output-air tubing goes to the bottom of the jar, the input tubing extends only inside the lid. Thin cloth patches are attached to the ends of each of the fittings to keep the silica gel out. A 1/2" copper plumbing fitting is also soldered to the top, and a large, heavy "punch ball" kid's balloon is clamped over this to provide a reservoir for the air and to provide a constant pressure. Air is provided by a little aquarium pump(!) The whole thing (jar & balloon) are inside a cardboard cylinder. A microswitch is attached to the side of the cylinder, with a cardboard flap over it. When the balloon deflates too much, the pump starts and expands it slightly.

Very simple, but provides a small positive pressure to the air-insulated coax. The silica gel has to be poured into a flat pan and dried in the oven every winter. Balloons have to be changed every 2-3 months, and the rubber gasket on the jar's top fell apart and had to be replaced. It has worked well for about 25 years. Originally saw a similar set-up in QST way back then. Several others have used similar but slightly different set-ups.

For waterproofing connectors - plastic tape, with silicon rubber over it. Not the best, quite a bit of work to remove, but generally works.

On 6-Jan-2004 WA6PY wrote:
Please be careful with blowing air through the cable. I have bad experience from the past. While living in Sweden (cold and lot of rain) I've got heliax cable with air dielectric and spiral plastic support for the center conductor. I install this cable as a TX feed line on 13 cm. After the while of operation I could not hear my echoes any more, although return power was OK - no visible deterioration of VSWR. I checked cold sky to ground, it was normal. Finally I attached directional coupler and power detector at the input port of the feed and figure out that very little power is coming to the feed. Then I tried to blow really hot air through the cable to drive out moisture, but without much of the improvements. I asked around and the only advise I've got was to blow nitrogen instead of air. I purchased small cylinder of nitrogen and blow through the cable and then I kept cable under small pressure. Nitrogen was very inexpensive in Sweden.

On 6-Jan-2004 9H1PA wrote:
Blowing dry air is also used alot in waveguides, it is a primary source to keep the waveguides dry and also to indicate when there is a leakage in the waveguide run. Dehydrators are connected to the lines like Shelby has just described. Have had no problems with these waveguide runs for more than 17 years at my QRL Important an alarm on pressure switch and regular changing of Silica Gel. The way I water proof connectors over here is by first appling electical tape to the connector,then amalgamated tape and last coating of electrical tape.The first coating is so that the amalgamated tape comes of easy when inspecting the connector and the last coating due to the UV protection for the Amalgamated tape. If you wish to test something for UV protection bring it to Malta. UV factor in summer up to 11-12. Best electrical tape is the Scotch 33 but very hard to find it over here.

On 6-Jan-2004 SM5BSZ wrote:
Hot air is not hot after passing only a small fraction of the cable, it just moves the water a short distance along the cable.

Use cold air! Just blow the air through a tube that you place in the refrigerator at -18 degrees centigrade. The humidity will become ice on the walls of the tube inside the refrigerator. When the air is subsequently warmed up it will become dry and useful for drying up your cable. It works(of course) only when the cable is much warmer than the refrigerator.....


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