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Author Topic: homebrew tower  (Read 1198 times)
KDUV7462
Member

Posts: 32




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« on: January 16, 2006, 11:37:33 PM »

hello. Hm, In your parlance here, I suppose I would say I do QRP on 11m. K3LTY is an old friend of mine since I was young, I think you guys would call him an "elmer". K3 always encouraged me to run low power and learn about tuning the antenna and antenna construction details. I would have to say i take a certain pride in using an UN-clipped and UN-peaked legal 11m transceiver on 4W, worrying more about fanatically tuning the mobile antenna for lowest SWR's than just getting porrly done "mods" and stomping a poor signal out.

I have detected the "pinched nasal" sound of people running HD450 cheap power amps, yet curiously enough it never strikes them to wonder how they hear ME at the equal distance (smile)

I have recently upgraded my cheapie 11m rig for a much better new one, and i must say i love sideband with my low power setup.

I now want to homebrew an antenna, and want to get the thing up into the air a bit, as you guys here might well imagine. Rather than set about mortgaging my house to build an antenna tower that rivals the commercial broadcast antennas and raise the ghost of Wardencliffe, and a huge zillion beam Yagi my first time out, I was thinking along the lines of a modest homebrewed tower and a dipole of J-pole for 11m.

If you've heard RUMORS of a lone CB guy in my state, being a courteous operator, running low power and refusing to go in for the mods that turn the sine into square tops, well, thats me (lol)

Going sideband recently, its refreshing to be able to discuss electronics theory with guys homebrewing equipment on 11m.

Question: searching all night for tower brewing, there seems to be a dearth of a "tweener" tower. Everything either requires oxygen tanks to climb it, or is just a ten foot pole pushed into the ground.

I was thinking more along the lines of bolting several 14' 2x12's together lengthwise, and forcibly spreading out the bottoms to make a rudiomentary "tower" that can be raised and lowered.

I SEEM to recall plans for this or somethign similar I saw before, now cant locate it. You guys know anything in this "middling" gound as far as homebrewing plane or ideas?

A pipe on a hinged setup raised by a winch is a distant second option, but I'm open to other ideas.

I havent ruled out a wire antenna yet, but like the idea of a straightforward dipole or j-pole.
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K4SAV
Member

Posts: 1850




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« Reply #1 on: January 17, 2006, 10:55:16 AM »

You will be much better off using something like a small push-up mast, or even a single large pipe, depending on how high you want to go. Wooden towers are very heavy.  A single 2x12 by 14 feet, weather treated, will probably weigh between 60 and 90 pounds. These also have a lot of wind loading and need to be heavily guyed.

If you want something that can be raised or lowered easily, consider a smaller version of this:
http://www.n6rk.com/falling_derrick_gme/falling_derrick_gme.html

A J pole for CB band will be 3/4 wave or 27 feet high. It will have to be built of substantial meterial and guyed if placed on the top of a tower. If I were doing a J pole like this I would place it on the ground.

Jerry, K4SAV
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WB6BYU
Member

Posts: 13479




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« Reply #2 on: January 17, 2006, 03:24:04 PM »

Certainly I'd recommend looking into a TV push-up mast if
you aren't going to be putting too much antenna load on
top.  These will want to be guyed, but you can mount it
against the edge of the roof, put the antenna on top,
and push the sections up to full height.  Also easy to
bring it back down when you want to try a different
antenna (or when the first one blows apart in the wind...)

The old ARRL handbooks showed a couple of wooden masts
for many years.  (They still might.)  One was an A-frame
using a pair of long 2 x 3's at the base, bolted to a
single 2 x 3 for the top section.  The two legs were
spread out at the bottom to give it sideways stability,
and with 16' boards it gave a heigth around 30'.  Another
design used a 2 x 3 for the bottom section, a pair of
1 x 3's in the middle (spaced on either side of the
bottom post, and with a spacer block in the middle), and
a 2 x 2 for the top section.  Both of these needed guys
to keep them up, and were realy designed for wire
antennas rather than rotary beams.

Many towers are designed in short sections, so, for
example, you can put up as many 10' sections as you
want.

For anything over about 20' with any sort of antenna on
top, the biggest problem is usually getting the whole
thing vertical.  Either it has to be strong enough to
tilt up with the antenna on top (which puts a LOT of
stress on the mast), or you have to be able to put the
antenna on the top after erecting the tower, which
usually means being able to climb it (or renting a crane
or a heliocopter.)  That is the main reason whey there
isn't much of a mid-range in antenna supports.  

But if you have a hgih point on your house to secure
it to, you can use a long pipe or wooden mast and tilt
it into place with a pulley at the peak of the roof.
In that case, two 21' lengths of galvanized pipe (of
different sizes so one slips inside the other in the
middle) probably could be used.  Square aluminum
"hollowbar" would be stronger, but more expensive.  At
least until you had to replace bent pipes very often.
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