Thanks for all the replies. Some good stuff in there.
Just to clarify, the 4-inch conduit is buried 4-feet down, and has been for
almost 14 years (the ground around here is very rocky and gets very hard
after a few winters.) I'm not about to dig up the conduit, remove the
sweeps, etc. This is my secondary antenna farm, used mostly for S&P on the
second radio in SO2R contesting, so there's a limit to how far I'll go to
reduce signal loss. After all, I've lived with coax for 14 years. Yeah, the
run loses about 1/3 of the transmit power on 10m and I'd like to improve
that. But dig up the conduit? Nah. My primary tower is fed with two 200'
runs of 1-5/8" heliax and 7/8" up the tower. If I need to be louder, I can
always use that antenna farm.
I'm doing this because the 1/2" heliax was free. If it turns out I can't
pull it, I'll put coax back in the conduit. And to answer one question, I
used LMR400UF because it's what I had on hand -- I was using it for the coax
going up a crankup tower, thinking it was the most flexible low-loss coax I
could use (Wrong. It's not all that flexible. Buryflex is much more
flexible.)
As for the turn in the "middle", now that I think back it probably wasn't
done with a 90-degree sweep. While the two ends are 90 degrees apart, I
don't really know how the turn was accomplished -- I don't recall the exact
path of the trench and I wasn't looking when that part of the conduit was
installed. The original invoice for conduit materials shows only two 4"
sweeps, which are the two at each end. That leads me to believe the turn is
more gentle than 90-degrees. After all, there was plenty of room to make it
gentle, and the guy who dug the trench and installed the conduit was an
expert. He knew cables would be pulled through it. Anyway, I guess we'll
find out how gentle that turn is.
Also, the turn isn't really in the middle. It's about 200 feet from one end
and about 65 feet from the other end. While it does make some sense to start
from the end closer to the turn so that some gentle pushing from the feed
end can help get past the turn, the run happens to go down a steep hill and
the end that's closer to the turn is at the bottom. I think it's a lot more
important to pull downhill -- 500+ feet of heliax is pretty heavy and I'm
not about to try pulling it uphill. So I'll be starting at the end farther
from the turn.
I just loaded up on 1.75 gallons of lube (all Home Depot had.) Hope that
will be enough.
FWIW, my plan back in 1997, when I installed the conduits and the antenna
farm in question, was to put two runs of 7/8" heliax in the conduit. The
tower rigger who advised me had said that I should size the conduit 2x the
cable diameter. So I figured 4" would be plenty. But when I mentioned to the
rigger that I needed to find some 7/8" heliax, he got very skeptical about
pulling it through the conduit. He said, "I thought you were talking about
1/2" heliax!" So much for the 7/8"! Now that I've worked with 7/8" heliax
more, I can see that it would indeed be a challenge to pull two runs of it
through the 4" conduit, even without the sweeps at the ends.
73, Dick WC1M
-----Original Message-----
From: Eugene Jensen [mailto:eugenejensen@nyc.rr.com]
Sent: Tuesday, July 19, 2011 10:24 PM
To: TowerTalk@contesting.com
Cc: 'Dick Green WC1M'
Subject: RE: [TowerTalk] pull lubricant
First of all, you have already violated the cardinal rule of 90 degree
sweeps. So do yourself a big favor, and dig up one of them and cut the pipe
there. And only pull thru two, or you will have to put a horrible amount of
strain on those coaxial cables regardless of how much lube you throw on
them. I am an electrician by trade, and you are not pulling electrical wire
with a donkey and pulleys. As for making a connection in the ground, if you
waterproof it correctly, I would guess I would go along with it, but I would
not personally do it. But that is just a matter of me personally. You
might be better off putting a pull box in the center where it makes the 90
sweep. You can purchase one down at your lawn center and they are used for
sprinkler boxes. I wish you the best of good luck with your project. 73's
Gene K2QWD Happilly Retired!
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Dick Green WC1M
Sent: Tuesday, July 19, 2011 7:48 PM
To: Tower
Subject: [TowerTalk] pull lubricant
Tomorrow I'll be doing a project I've been putting off for about 14 years:
replacing two runs of LMR400UF in a 4-inch 265-foot conduit between the
house and one of my tower locations.
I'll be pulling two runs of 1/2" heliax: one run will be Andrew LDF4-50 foam
dielectric heliax, and the other will be Andrew HL4RP-50A air dielectric
heliax. I have enough of the foam dielectric for a continuous run, but I'm
about 15' short on the air dielectric. The plan is that when we get close to
the end of the pull, put a connector on the end of the air dielectric heliax
and attach a 15' link of Buryflex to make up the difference. I don't think
there's ever been any water in the conduit, but the joint will be well
waterproofed just in case.
The question is whether I'll need to use pull-lube for this job. The
conduit-to-cable diameter ratio is a healthy 4:1, and there will be no other
cables in the conduit. I had no problems pulling the two runs of LMR400UF
through it. But there are three 90-degree sweeps in the conduit: one at each
end and one in the middle, and I plan to pull both runs together. Would the
experts out there recommend using pull lube?
(Another question: I have some concern about pulling the air dielectric
through the conduit. I've already seen how intolerant it is of any kinking
(long story, but that's why I only have 250'.) Can air dielectric heliax
make it through three 90-degree sweeps without damage? I have enough
RG-331/U to do the job if the consensus is that I shouldn't try to pull the
air dielectric stuff.)
73, Dick WC1M
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