Thanks to all who offered advice.
Executive summary:
Pulling the two 1/2" runs of hardline/heliax through 265' of 4" conduit was
much easier than expected. In fact, it was so easy and went so fast that my
helper had his hands full guiding the cables into the conduit and was unable
to put any lube on them! He had squirted a few ounces on the first three
feet or so of the cables, but that was all we ended up using. I returned
five unused liter bottles of the stuff to Home Depot the next day.
The Details:
The biggest challenges were putting Ring Flare connectors on the LDF4-50 and
dealing with near-100 degree temp and near 100% humidity last Wednesday.
On advice from TowerTalk members, I decided not to use the air dielectric
1/2" heliax. It's too delicate, kinks too easily, and I was concerned by
stories of long-term failure in conduits with sweeps. Instead, I used 300'
of RG-331/U given to me by my helper. I think it's mil-spec because it has a
solid copper center conductor instead of copper-clad aluminum. The loss is a
bit higher than the heliax -- about .477 dB per 100' at 30 MHz versus about
.357 dB for LDF4-50 and the air heliax. The RG-331/U is really rugged, but
almost as flexible as the LDF4-50 and has a nice slick jacket. I was able to
score some Cablewave RG-331/U connectors for a great price on ebay.
We decided to temporarily install connectors on the cables and test them
prior to the pull. This took a lot longer than anticipated. The RG-331/U
connectors were easy to put on because the solid aluminum outer conductor
requires virtually no prep. But I found that the 1/2" LDF4-50 heliax is much
harder to prep than the larger sizes I've used. We needed a vice and a
sharp, fine hacksaw blade. The heat and humidity didn't make the job any
easier. It took a long time to put on the connectors and test the cables
with a transceiver, a dummy load and a Bird wattmeter (we took a lot of
hydration breaks.). Both runs tested very close to specs as far as loss was
concerned.
It took additional time to unroll the cables (they weren't on spools) and
get ready for the pull. The old LM400-UF pulled out of the conduit easily,
but when I had pulled about 65 feet of it out, dirt started appearing on the
cables. About five feet later, moisture began to appear on the cables. 65-70
feet is the distance between the end where I was pulling and the turn in the
conduit I described in my earlier post. It was clear that water has
accumulated at the turn, which happens to be the low point of the conduit.
My guess is that there's a leak at one or more of the conduit joints, though
it's conceivable that the water is the result of accumulated condensation
over a 14 year period. The utility boxes are sealed, but one end of the
conduit is exposed to air from inside my house. Perhaps that's where the
moisture came from.
I would guess that the dirt on the cable came from a break, too, but not
necessarily. It could easily have come from dirt that got into the conduit
when it was originally installed. It isn't easy to keep dirt out of
conduits, especially large ones, when you're wrestling them around in the
bottom of a trench.
With the conduit buried 4-feet down under very hard and rocky soil, there
isn't much I can or want to do about the water. I don't believe it poses any
problem for the hardline and heliax, as they're both outdoor rated.
The next step was to prep the new cables for pulling. I found a 1/2" hauling
grip in my parts box that fit the LDF4-50 perfectly. That item was very good
to have for this job. I think it's something I got at the local electrical
supply shop years ago. I used tape to secure the nylon pull rope, which was
already in the conduit (I had pulled that rope 14 years ago and it didn't
come out when I pulled the old coax out.) Also used tape to bind the RG-331
to the LDF4-50 and the rope. The rope felt very secure -- it wasn't going to
pull off.
I probably didn't mention it in my earlier post, but it wasn't feasible to
remove the utility boxes into which the conduit connects. Way too much stuff
to disconnect. That made it a little trickier. It was clear that pulling the
rope straight up at the pull end was going to be very difficult, so I rigged
a pulley above the hole so I could pull the rope horizontally. I slipped a
nylon strap through the slats in the wooden panel to which the utility box
is mounted and attached the pulley to that. The strap length positioned the
pulley perfectly against the top leading edge of the box. Without this
setup, there's no way I could have pulled the cables alone.
When we first started pulling, the cables wouldn't go past the first sweep
at the other end. My helper removed the cables and slightly bent the leading
edge and it went right through. As I pulled, there was definite resistance,
but no more than I would expect from the friction of the cables against the
conduit and the drag provided by two 300' runs of hardline laying on the
ground (about 100 lbs.) I could feel that that the cables were moving
steadily and smoothly through the conduit. The pulley setup was such that I
could pull only about 5-6 feet before I had to shorten up and pull closer to
the pulley. Even so, I was doing this so fast that my helper didn't have
time to lube the cable. We had radios, but he didn't have time grab his and
tell me to stop. Besides, he could feel that the cables were sliding through
nicely and figured the lube really wasn't necessary.
I ended up with 50 feet of LDF4-50 and 40 feet of RG-331/U left over. It
took several more hours of work to roll up the old coax and the leftover
heliax/hardline, put connectors on both ends of the heliax/hardline and make
up four short coax jumpers between the cables and switch boxes / lightning
suppressors. Thank goodness for crimp connectors!
Initial testing wasn't so good -- high SWR, antennas appearing not to be
connected, etc., but that turned out to be due to several unrelated issues
with my relay switching system, at least one of which appeared to be due to
the extreme heat. Anyway, I got all that sorted out and the new cable runs
are working just fine.
Today I was finally able to test losses in the cables. They're exactly the
same as we measured in the shack before pulling the cables. Whew! A
long-put-off job finally completed.
Thanks again for the advice. I was glad I had all that lube on hand, even
though I didn't use it!
73, Dick WC1M
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