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Author Topic: Building aluminum mast for portable use  (Read 7816 times)
WS4T
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Posts: 182




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« on: June 10, 2010, 05:19:43 AM »

This summer I am planning a bit of portable operation. I want to build an aluminum mast that I can transport with me and use to mount a single, small yagi (either 10 elements for 70cm or 5 elements for 2m with a boom length of about 2m). I plan to use one set of guys if necessary.

I found this product: http://www.radioworld.co.uk/~radio/catalog/atm65-11section-portable-aluminium-mast-198m-65ft-long-p-5382.html

I am thinking of buying some aluminum to try and build something similar but with max. mast height of 10 m.

Questions:
1. Is this a difficult project, assuming I can find the right aluminum?
2. Instead of building a telescoping mast, could I use 2m sections of identical diameter aluminum and join them? Maybe cut a short piece of overlapping aluminum tube and join sections with that?
3. What diameter and wall thickness of aluminum would suffice?
4. Would a 10m mast with a single VHF or UHF yagi be too heavy to lift on my own (in case no one is around to help)?
5. Would this sort of clamp work? http://www.dxengineering.com/Parts.asp?ID=2279&PLID=62&SecID=138&DeptID=43&PartNo=DXE-ECLS-150

Thanks in advance for any help! I going to buy some aluminum and try it out, but I'm hoping to spare a little bit of wasted effort by solicting ideas first.

Gary, ES1WST
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WX7G
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« Reply #1 on: June 10, 2010, 06:23:40 AM »

DX Engineering stocks the aluminum tubing you require by the piece and in kits with 3' and 6' lengths. Note that the pieces of tubing are slotted at one end only. If you want to build the 'tower' with identical diameter sections with an internal or external overlapping joing you will have to slot the tubing yourself.
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WB6BYU
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« Reply #2 on: June 10, 2010, 08:49:06 AM »

Quote from: WS4T

I am thinking of buying some aluminum to try and build something similar but with max. mast height of 10 m.

Questions:
1. Is this a difficult project, assuming I can find the right aluminum?

No.  It requires some assessment of the potential wind loading and required strength of the aluminum
tubing, and some adjustments to make it more practical, but what can be difficult about nesting
tubing sections and putting a clamp on one end of each piece?

Quote
2. Instead of building a telescoping mast, could I use 2m sections of identical diameter aluminum and join them? Maybe cut a short piece of overlapping aluminum tube and join sections with that?

Yes.  I have some of the military mast sections that are built this way, and I find them to be very
convenient.  Strength is maintained all the way to the top of the mast, which may be an advantage
for heavy loads.  I think my sections are about 1.75" ( 4cm ) in diameter and we have put up a
4-element 15m yagi at 28' ( 8.5m ) on it with one set of guys.  These use an insert that slips
inside the main tubing at each end.

Part of the decision may be whether you are buying the aluminum tubing in Europe or the US.
There are different standards, with the Metric tubing typically having thicker ( 2mm ) walls.
The US tubing tends to telescope better than the metric sizes, however.

I also found some old aluminum tent poles that stack nicely.  They are about 2cm diameter.
I only have enough to go up 6m right now, but I think if I can extend it to 10m it will still hold
a small yagi.

Telescoping sections take less space.

Quote
4. Would a 10m mast with a single VHF or UHF yagi be too heavy to lift on my own (in case no one is around to help)?

It depends how you try to lift it.  If you extend a 10m mast and try to tilt it up into place you will
find it quite difficult.  I've seen a number of the US steel push-up masts break when used this way
due to the weight of the load and the upper mast.  Tilting up a mast puts more stress on it than
anything else.

But I've put up my mast sections to 40' ( 12m ) by myself, and it isn't difficult if you know how.

First, the mast sections have to be SHORT enough.  Mine are 4' ( 122cm ) which is about right, and
I'm fairly tall.  It would be more difficult with lengths more than 1.5m without having a ladder, and
1m lengths would be even easier (though it would require more of them, of course.)  The choice will
depend on the lengths available to you.

The key is to erect the mast vertical when it is retracted (or has few sections), then extend it in
place.  I typically mount the antenna on two sections of mast ( 2.5m ), tie off the guy ropes to at
least two of the anchors, set the mast upright, then walk it to where the two guy ropes are snug
enough.  I should be able to lean it gently against the two ropes and have it stay upright.

Then I get the next section handy, lift up the mast with one hand (while keeping it leaning against
the two ropes), slip the new section underneath, and set it back down.  The secret is that you have
to keep moving the base of the mast closer to the guy anchors as you do this.  Just keep repeating
this process until you reach the desired height, then tie off the third guy rope.  (You may want to
adjust the guys if you want the base of the mast in a particular location, as it is difficult to get the
guy rope lengths and anchor points exactly right initially.  It takes some practice, but is simple once
you get the feel for it.

To take it down, reverse the process. 

If you are putting up a large antenna it probably is best to set up just the mast by itself first, get it
positioned where you want it and the guy ropes properly adjusted, then lower it, put the antenna on,
and put it back up in the air.

When we did the big 15m yagi we had three people lifting the mast and one keeping tension on the
third guy rope.  Unfortunately he didn't understand the process and keep pulling the rope tight,
making us have to work harder to lift the antenna.

I'd use the same approach with a telescoping mast - put the antenna on, tilt the mast to vertical,
then extend it one section at a time.  This requires that you be able to reach far enough above the
clamp to push the sections up, so 2m sections will require something to stand on.  Also, paint or
otherwise mark the lower part of each section to warn you to stop pulling, otherwise you may
pull the whole section out of the mast.  At that point it may be difficult to control.
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K0OD
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« Reply #3 on: June 10, 2010, 08:53:18 AM »

I removed the thin top 15 or so feet of my DX Engineering "43' vertical" and have been using the lower portion to hold up a 2-element 6 meter yagi at about about 25' without any guys. I walk the mast/yagi up using the supplied DXE base. Bottom section is about 2 1/8" double walled and the topmost one is about 1 1/2" diameter. This is a temporary setup for the June E season. But with one set of guys I would imagine it would survive high winds and could perhaps could be extended to 30' to 35' or used with a slightly bigger antenna.

I rotate the yagi easily by loosening a lower hose clamp and twisting.  

I've been eying DXE's new larger vertical (the 40/80 meter one) which uses 3" thick-walled tubing at the base and a heftier tilt up base which can be used with their optional hand cranked winch.

For some odd reason DXE doesn't separately sell the tilt up base of their larger vertical.   They do sell the 3" thick-walled tubing which I believe is specially made for them. I'm not a fan of the tilt up plate that comes with the MBVE-1 (their 43 footer)

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WS4T
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Posts: 182




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« Reply #4 on: June 16, 2010, 04:30:48 AM »

Hi Everyone --

Thanks for all the ideas! I am going to rent a car next week and try to purchase some aluminum. Unfortunately I'm stuck buying from local sources in Estonia. This project would be a lot easier back home in California. Have DX Engineering drop-ship it and done...

I'm also thinking that 10 m is too optimistic. Maybe I'll try for 6 m or so and then go higher if it feels comfortable. Last summer I used a fiberglass mast and nearly dumped my Elk log-periodic on my head a couple of times. I have grown wary.

As far as telescoping sections inside of one another, I have another question: I've found a local source of "45 x 2.0 mm" and "40 x 2.0 mm" round tubes (here's a link if you want to look: http://www.proplastik.ee/standard-profiilid). Would those dimensions work for telescoping, i.e. build the mast from the 45mm tubes and use short sections of 40mm tube with tube clamps to connect sections? (inner dimension of outer tube = 45 - 2 - 2 = 41 mm)

I'm hoping to make it to one of the Estonian islands and operate from a rare grid square (KO08) during the annual field day/VHF contest in August.

73,
Gary, ES1WST (WS4T)
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WB6BYU
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Posts: 13488




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« Reply #5 on: June 16, 2010, 08:42:39 AM »

The 4.5cm and 4cm material is pretty close to what my military mast sections are made of, and I'd
have no qualms about putting up an HF tribander on it at 10m.  (Though perhaps not something like a
TH6-DXX.)  How well the smaller material slips inside the larger one depends on the manufacturing
tolerances, and you can't know that until you actually try it.  My concern would be that it may be
a bit too loose.  If so, you can make the inserts longer to minimize the wiggle, add a piece of thin
tape or a coat of paint to shim it, or perhaps bother it a bit with a ball peen hammer to increase
the peak diameter.

Probably the simplest approach to building the sections is to insert the smaller piece inside one end
of the larger and pass a couple of screws through them.  That way you don't need any clamps,
and the upper section just rests on the lower one.  Makes it easy to assemble and take apart, too,
as there is nothing required except sticking the end of one inside the other.

I don't see any reason why you can't got the full 10m, unless the overall weight of the mast gets
too heavy for you to lift by yourself.  I was just teaching some folks the erection technique this
last weekend using 28' of the fiberglass mast sections, and everyone was able to put it up and take
it down by themselves - in spite of their expressions of surprise when I first told them what they were
going to do.  This is a very stable process, and once folks got the feel of it I didn't see any cases
where the mast would have been unstable or in danger of falling, even with an antenna on top.

For a relatively small VHF antenna you probably can get by with smaller tubing, perhaps 3cm, if that
is easier to get.  But the 4.5cm material will be plenty strong for any sort of DXpedition.  If it comes
in 2m lengths, cut it into 1m sections and plan on two sections of the smaller material (unless it makes
a very snug fit, in which case you might get by cutting 9 joiners out of a 2m piece.)  One nice thing
about this approach is that you can put up however many sections you want to use each time, or
even make 2 masts of 5m each instead.  (I've also used the mast sections as rollers for moving heavy
objects.)

Good luck!
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WS4T
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Posts: 182




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« Reply #6 on: June 20, 2010, 06:22:53 AM »

Hi WB6BYU,

Thanks again for so many details.

One last question: How to guy the mast so it can be hand-rotated? I can't think of an easy way to do that so the mast will turn inside of the guy mount.

I found this (search for "guy clamp") but it looks complex and it ain't exactly cheap: http://www.wimo.de/cgi-bin/verteiler.pl?url=mounting-hardware_e.html

Gary, ES1WST (WS4T)
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K2MK
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Posts: 403




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« Reply #7 on: June 20, 2010, 07:01:10 AM »

An idea for floating guy rings. Once you know the diameters of your individual tubing sections you can purchase bronze thrust bearings of the proper ID so they will stop at the junction where one tube slips into another. These are not expensive. In the US you could purchase them cheaply from McMaster Carr.
http://www.mcmaster.com/#catalog/116/1121/=7m4f1d

Then cut some flat metal discs to sit on top of the bushings. Perhaps aluminum.
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WB6BYU
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« Reply #8 on: June 20, 2010, 08:36:32 AM »

I'm getting ready to put up a triband HF yagi and a 6m beam on my mast sections for Field Day.
Rather than rotating the mast I just tie a piece of rope to one end of the yagi and pull it around
to point in the direction I want - a cheap and simple "Armstrong" rotator.  This simply requires
that the antenna be able to rotate on the mast.  Usually I can do this by clamping it loosely
to the protruding end (that would normally slip inside the next section.)  A better approach
might be to have a short piece of the larger tubing that the antenna mounts on which then
slips over the end - it needn't be any longer than the normal joint.  (Some grease inside might
be helpful.)

In fact one of my tasks for today is to figure out what size of pipe I need to do that with my
masts.  I may end up with a length of pipe that slips INSIDE the top section if the U-bolts on
the antenna mounting bracket are too small.

A flat steel or aluminum plate with a hole that just clears the smaller section of the mast would
allow the guys to be attached and still rotate the mast, but if you are going to rotate the mast
from the bottom you also have to make sure that all of the sections rotate in unison.  (Duct
tape might be sufficient.)   

For temporary installations I sometimes drive a fence post in the ground and slip the bottom mast
section over it.  If you did something like that, so the mast stood upright by itself and used the
guys only for safety, then you could have them a bit loose and just let them wrap around the mast
as you rotated it.  It wouldn't be more than half a turn (in theory).


But I just use the rope on the end of the antenna boom.  (Though, to be honest, for Field Day
from the West Coast, no rotation is necessary on HF.  We may rotate the 6m beam, though.)
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WB6BYU
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Posts: 13488




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« Reply #9 on: June 20, 2010, 11:02:15 AM »

Update:  I checked a couple of the U-bolts that I plan to use and they don't quite fit around thea
smaller end of the mast.  But regular 1" (nominal, actually somewhat larger) plastic pipe fits inside
the small end of the aluminum sections, so I'll use two short pieces of that with a coupler that will
ride on the top of the mast and act as a bushing.  So the antenna bolts to one short piece of
plastic pipe, which is glued into a  coupler with another piece sticking out the bottom that slips
inside the mast.  I do have some steel tubing of about the same size that I may use for the HF
tribander with some sort of bushing in the center.

Best to plan this in advance, of course, and pick up all the necessary sizes of aluminum tubing
when you are at the source, rather than having to wander through the barn and the tractor
shed to find something that fits.

But if you build the mast from a size of tubing that fits the mounting bolts on your antennas, you
can just use a short piece of that to mount the antennas on and slip it on the top of the mast
to make a rotation joint.
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VE3WMB
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« Reply #10 on: June 21, 2010, 06:32:07 AM »

Gary :

An alternative might be to use a fiberglass DK9SQ mast (10m long & about 3 lbs).

http://www.qsl.net/dk9sq/

Walter also sells a 4 Element dual band (2m/70cm) Log periodic that can be very easily mounted
on the mast (vertical or horizontal polarization) that yields about 9dBD on 70cm and 5 dBD on 2m.
BTW this is the same antenna made by DL4KCJ.

http://www.antenna-engineering.de/Doppelband_Richtantenne_mit_Teleskopstaeben.html

Another option for antennas would be to build Cheap Yagis and use something like PVC pipe for the boom to keep the weight down so it can be supported on the DK9SQ.

http://www.iw5edi.com/ham-radio/?cheap-yagi-antennas-for-vhf-uhf,93

The DK9SQ products are very well made and durable. I have two masts, one which is at least 10 years old
and it is still going strong.

Michael VE3WMB

This summer I am planning a bit of portable operation. I want to build an aluminum mast that I can transport with me and use to mount a single, small yagi (either 10 elements for 70cm or 5 elements for 2m with a boom length of about 2m). I plan to use one set of guys if necessary.

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WS4T
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« Reply #11 on: June 22, 2010, 12:19:48 AM »

Michael,

I have a couple of fiberglass masts (Spiderbeam 12m mast + DK1RP 10m mast), but I figured they wouldn't be strong enough to support a small yagi. Hence the interest in aluminum. Plus I am hoping to get something up on the roof before winter, maybe even an HF yagi of some sort if I can find an affordable rotater, so I wanted to try my hand now with some metal on a smaller scale.

Thanks for the link to the DL4KCJ website. I hadn't seen that before.

I've already ordered two yagi kits from DL1NUX and am just waiting for them to arrive. He sells parts to build yagis, mostly using the DK7ZB design. Here is one of the kits I am getting (which I think would be too big for a fiberglass mast): http://www.nuxcom.de/product_info.php?info=p53_Kit----5-ele-Yagi-144-MHz-28-Ohm---2-00m-Boom.html

I also ordered a 10-element kit for 432 MHz from DL1NUX.

I'm really excited because I have finally tracked down all the aluminum I need locally. Estonia is shut down this week because the solstice/St. John's day is a big celebration, but I have a car reserved for next week to get the material home and start building.

Gary, ES1WST
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WS4T
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« Reply #12 on: June 22, 2010, 02:48:27 AM »

Hi Dale (WB6BYU),

Thanks for the Armstrong rotator idea (rope on yagi). I bet I can make that work and it sounds real simple. The yagis I'm building have a 15 x 15 mm boom and here is the mast clamp I plan to use: http://www.nuxcom.de/product_info.php?info=p120_Mast-clamp-for-15-mm-square-boom.html

I'm very excited because it looks like all the aluminum I need is in stock locally! Hopefully the 40x2 and 45x2 sections can be made to work for the mast. The supplier even offered to cut it for me.

Another idea/question: Do you think the same aluminum mast could be extended up higher and used in a year-round situation? Possibly as high as 18 m?  I currently have an inverted-L in my backyard for 40/80 m. It's on a 12 m fiberglass mast. I want to extend it to say, 18 m, and add a second trap so I can have 160 m too. I did it in the winter for the CQ 160 SSB test and it worked even on my 12 m mast, but 12 m is obviously too low. Here's where I found this design: http://one.xthost.info/gm0onx/6_band_inverted_l_antenna.htm

I guess then I would have to find a way to build the traps into the mast, but maybe that's doable.

Thanks again for your ideas!
Gary, ES1WST

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WB6BYU
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« Reply #13 on: June 22, 2010, 09:07:11 AM »

Mast strength will depend on the grade of aluminum you can get, which might not be well-regulated
there.  You'll just have to try it and see.  When you get the 45mm sections up to 10m you'll have
a good idea whether you want to attempt to nearly double it!  (It will also depend on the slop in
fit between the inserts and the mast - too loose and the sections will wobble more.)  At that
point the weight of the mast becomes more important, too, and you may find that it is more
difficult for one person to lift the mast to add the next section.

But I've put the fiberglass sections up to 12.2m before by myself.  I stopped there because the
joints aren't very strong, and there is a lot of stress on them when the mast is leaning.  With the
aluminum that shouldn't be as much of an issue.  Regarding weight - I can carry a full bag of the
aluminum mast sections (25 x 4' = 30.5m)  in one hand, but it is a pretty heavy load.

One other solution would be to use thinner mast sections at the top.  For example, if you had
10m of the 45mm diameter mast with 40mm plugs, you could use some 35mm tubing to slip
in the end (with a short ring of 40mm tubing as a stopper) then step down to 30mm or smaller
if you are only needing to support a wire.  Again, I'd say 45mm is considerably larger than
you need for small VHF beams:  the 6m yagi we'll use for Field Day is 5 elements on a 3.6m
boom, and we've put up a full-sized 4-element 15m monobander on the same size mast.
But that should handle all of your DX-pedition needs, and you can experiment with other mast
sizes (possibly in combination) once you are comfortable with the technique.

For traps, see what sizes of plastic pipe and tubing are available that fit the mast.  I'm using
about 35mm OD pipe that slips inside the couplers, and you might be able to slip some
additional metal pipe or rod inside of it for strength while maintaining insulation.  If you are
just supporting a wire then the strength isn't as important.  If the plastic pipe isn't strong
enough you may have to have coupler turned on a lathe, perhaps from a strong wood like oak,
that provides strength across the joint and can support a coil or trap wound on plastic pipe
on the outside.

[edited to correct 3.5mm to 35mm - WB6BYU]
« Last Edit: June 22, 2010, 03:10:11 PM by Dale Hunt » Logged
AH6RR
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« Reply #14 on: June 22, 2010, 09:34:05 AM »

Why not get some rigid aluminum conduit say 2" and couplers that would only be 3 10' sections it is threaded on both ends. I have used it in the electrical trade and that stuff is strong let me tell you anything over 3/4" and you need a hydraulic bender. Guy it near the top and your set. Most rigid aluminum conduit is schedule 40 .250" wall thickness not cheap but will last a long time.

Roland AH6RR
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