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

[JOE]

At 09:30 AM 1/4/2004 -0600, you wrote:
> >    c) What does the cellular industry use for clamping
> >runs of hard-line up towers?

I work for a wireless company.  Most hardline is first supported at the top 
with a cable grip.  These cable grips resemble one of those Chinese finger 
cuffs kids use to play with.  The cable grip fits around the cable at gets 
smaller when it is pulled on.  The cable below the grip is then held to the 
tower with cable clamps.  These fit around the hardline, and the newer ones 
snap into a hole.  Some of the older ones were screwed to a beam clamp and 
fastened to the tower.   Ground kits are usually installed at the top of 
the tower and at the point where it just leaves the tower on the 
bottom.  In a monopole installation, the cable grip holds the hardline at 
the top and the line just hangs inside the tower.

> >    d) What in your experience has proven to work well?
The above works well on large towers, but not on small towers.  Tie wraps 
are probably the easiest way to attach hardline to a small cross section 
tower.  BUT, you have to be very careful not to distort the hardline when 
you tighten the tie wrap.  Replacement may be necessary every 5-10 years, 
even if you use the black UV resistant tie wraps.  Even these can get 
brittle after 3-4 years.


> >2) What are the pro's and con's of greasing mating hard-line coax 
> connectors?
Never, never use grease to waterproof a hardline connection.  If the water 
is getting to the connectors, you are doing something wrong with the 
weather sealing of the joint.  You have to stop the water BEFORE it gets to 
the connector.  Good quality black tape and weather sealing should be used 
to make the connectors waterproof.  Try not to use an RG-8 jumper on 
hardline outdoors.  You may get the connector weather sealed perfectly, but 
water can get into the joint by running down the inside of the RG-8 cable 
from the other side.  I have seen RG-8 act as a hose, bringing water from a 
dipole into a ham shack on a 100 foot run of coax.  Water was dripping onto 
the floor from the coax.

> >    a) If one uses a grease, say Lithium or Permatrox,
> >what does this do to the DC resistivity of the mating
> >connectors?
Applied to just the threads of an N type connector, probably not much.  The 
electrical/RF connection is done inside the N connector, and the threaded 
part just makes the mechanical connection.

> >    b) Any thoughts about what this grease does at RF
> >mating junctions?)
Disaster!!  One wireless company experimented with a substance called 
STUF.  http://www.wavehunter.com/stuf.htm  This was a brainstorm of an 
engineer and created all kinds of issues.  Connections became very 
unreliable and noisy after time.  It all had to be taken out.

> >    c) Dissimilar metals used in connector mating
> >junctions, appears to be a problem in cellular industry.
Use good quality connectors, try to use similar metal junctions.  NO 
Ratshack connectors

If you use all good quality cable, a properly weather sealed connection 
will last for many years.  I have taken apart connections that are 10 years 
old and still look brand new.

Joe, K1ike