My conduits terminate in metal utility boxes. One is mounted on a panel
supported by 4x4s next to a tower. Coax runs from all antennas enter the box
via Polyphaser bulkhead feed-through lightning suppressors. Rotor and
control cables enter through feedthrough bushings you can get from any
electrical supply house. Polyphaser rotor suppressors are mounted on a
grounded panel inside the box. The box is connected to an extensive ground
system at the tower (12 ground rods with heavy wire radials connecting them,
all joints Cadwelded.)
All the cable runs then go into a pair of conduits, one 4" for coax and one
2.5" for rotor/control. The conduits enter the box through large holes cut
with a hole saw. Note that I used PVC electrical conduit, not the standard
Schedule 40 plumbing PVC. Electrical conduit is grey, not white, and
numerous special fixtures are available for it. Where the conduits enter the
box, there are threaded ends glued on which have steel nuts screwed on to
fix the ends to the box. Each run then goes into an expansion joint. This is
a pre-fabricated set of nested pieces of conduit with lubricant between them
so they can slide easily without moisture entering. It prevents damage to
the box by absorbing any ground shifting due to frost (needed here in NH.) A
vertical piece then connects to a 90-degree sweep which ends at 4' deep (the
frost line in NH.
The conduit then runs 260 feet to the house, where there is a second box
mounted. The sweeps, expansion joints and conduit entrance into this box are
identical to the tower box. A second set of Polyphaser suppressors is
mounted inside the box (panel mount coax suppressors instead of bulkhead
feedthoughs.) Two large holes are cut at the bottom of the rear wall of the
box (had to cut a notch out of the grounding panel so the holes would be
accessible.) The cables pass through the holes to the shack. Each hole is
fitted with the same threaded ends used to attach the conduits (the ones
with the large metal nuts), only without any conduit attached. These protect
the cables from the sharp metal edges of the holes. The box is grounded to a
single point ground rod. All shack equipment is grounded to a large copper
bar, which is in turn grounded to the box.
Another approach for the tower end is to use special cable exit fixtures
available for electrical conduit. If a termination box is not used, these
could be attached to a vertical section of conduit at the end of the run.
The fixture is sort of a large oval thing that bends over like the head of
bird at the end of a long neck. Reminds me of a flamingo or a crane. The
fixture has holes in the bottom for the cables to exit. This allows moisture
to drip down off the cables, keeping it out of the conduit. You might see
terminations like this next to light poles or other utility fixtures. Where
a termination box is used, the fixture can be used on the cable runs that
enter the box -- this would be used for the cable entrance instead of the
bulkhead feedthroughs I used.
Hope this helps.
73, Dick WC1M
> -----Original Message-----
> From: Paul Ash [mailto:email@example.com]
> Sent: Monday, November 01, 2004 8:11 PM
> To: firstname.lastname@example.org
> Subject: [TowerTalk] Conduit ends?
> Hello All,
> I have been considering running my coax, antenna
> selector control cable and rotor control cable through a
> 3"-4" inch conduit. I would like to get some opinions on the
> best way to handle the ends that are projecting out of the
> ground. I did read a former thread that talked about two 90
> deg bends (sounds good for water/rain.) what about
> bugs/rodents/varmints etc... Anyone have a good idea how to
> seal the ends that would still provide
> passage of the cables and could be removed with a minimum of
> effort whenever it comes time to replace or add to the cables?
> Paul W4QG
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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