[Microwave] Clamping hardline to towers & water proofing (greasing) RF connectors

[Christopher Boone]

David Garnier wrote:

> Hello,
> 
> 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?

Two ways its usually done in commercial installs
1) tie wires made of #12 or larger SOLID wire with insulation usually.
Wraps around the coax below a tower member (crossbeam etc) then both 
ends comes UP and back over and are tied on the outside of the coax 
AGAIN.....bend the wire into a U with long sides....push wire around 
coax and into tower...now bend ends UP and over tower horiz member..back 
out and now twist together on outside of feedline.

2) metal tower "hangers" designed to clamp the coax inside two metal 
brackets curved to fit the size of the cable. A bolt thru the top of the 
hanger secures it and it held to the tower by a unistrut style clamp OR 
a nut/bolt that is inserted thru a predrilled hole on the tower flat 
angle member OR a support place installed for such use.

HOWEVER in amateur use, if the cable is 1/2 in or smaller, regular BLACK 
vinyl tie wraps can be used in such an installation. DO not use white as 
they are NOT UV protected and do become brittle over a SHORT time (BLACK 
ones are toughened against the UV rays and will last 10-15 years if 
installed right.

> 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?

NO!! DO NOT USE A GREASE ON THE INSIDE OF ANY RF CONNECTOR! PERIOD!

>     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.

Use of metals that have LOW dissimilar properties (stainless or BRASS is 
used as a connection between two major dissimilar) reduces such problems
and cellular/Land Mobile RARELY have such problems...using COPPER to 
ALUMINUM is hardly done and is asking for trouble.

>     d) Ever hear of "tweak" (a conductive substance
> that some audiophiles use on phono or line output
> jacks?

Sounds like CB crap.......RF connectors are usually silver or gold 
plated...do NOT use anything else on them....AUDIO TWEAK IS TRASH AND A 
RIP OFF! At freqs to 15000Hz, use of anything above normal nickel 
plating in a decent environment is a waste of money...gold/silver 
plating reduces noise problems...but does not IMPROVE the audio response 
one bit!

>     d) Black electrical tape doesn't like to stick to
> hard-line connectors if one is sloppy. ;-)

Use the GREY "rubber" tape.....apply one-two layers to the connection 
1st then use Scotch 88 or 33 over that...then apply DUX or COAX SEAL 
liberally and then tape over than with a layer of RUBBER tape then one 
last layer or so of BLACK tape. Your goal is to keep WATER out...thats 
all...the connection will stay clean IF you do it right.......and its 
easy to get back into IF you need to do so...a cut LENGTHWISE along such 
sealant allows you to PEEL the tape, etc open like a potato....with a 
CLEAN and EASY to remove connection still in place...(also do NOT 
overtighten RF connections...hand tight is fine)

Chris
WB5ITT
Sr Telecom Egr Tech for Entergy Gulf States Utilities 1984-1996
Asst Radio Chief Egr, LBI Media, Houston
ARRL Technical Specialist for S Texas
Land mobile/broadcast tech for almost 30 years.
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