No guys here.
The commercial push up mast I use [sorry, I can't remember a brand name]
is made of an aluminum profile that is kind of octagonal in shape, with
spring clips that pop out to hold each section up when extended. Being
about 20' tall, and fairly large in OD, it is pretty rigid. There is an
opening at the top where I add a 6' section of light duty galvanized TV
mast to add a bit of height, and an extra antenna.
Before I found the commercial push up mast, I done the same thing you
are planning. I used EMT conduit to build my own push up mast.
There are a few obstacles you will run into. I don't want to sound
negative, you can do this, I just want to share some of the problems I
ran into.
The biggest thing is the weight. If you use large enough conduit to
stay pretty straight, it will become very heavy. Even with just 4
bands, it will be a real chore to raise and lower. Particularly if you
go a full 30' tall.
Another issue is you will have to come up with a way to pin them
together when lowered, or you will have to tie down the yagis to keep
them from turning while you drive.
And, if you go that tall, you will have to guy the mast to keep it
vertical. The space between each section of standard conduit is wide
enough to allow the tubes to move quite a bit. This will cause the mast
to lean one direction or another. So you will need to park in a nice
level spot each time, and will likely need to guy the mast. I think I
have some pics of my "leaning tower of yagis" somewhere, I'll send you
some if I can find them :-)
September VHF, 2004
http://s135.photobucket.com/albums/q148/Indiana_Dan/?action=view¤t=fest1.jpg
June VHF, 2003
http://s135.photobucket.com/albums/q148/Indiana_Dan/?action=view¤t=dsc_196.jpg
Another issue that can lead to disaster; If you lift the inner section
too high, it can come all the way out of the outer section and leave you
holding all of that weight by the bottom end of the mast!! You will
want to take steps to prevent this, trust me :-) What I did was paint
the bottom 2 feet of each section to give me a "warning track" when I
was approaching the bottom of the mast. This will keep you from doing
the "oh s**t dance" while holding your homebrew 4 element 6 meter yagi
over your head and desperately trying to get the end of the mast back in
the hole! =-O
Here is another tip I learned the hard way. To pin the mast sections
together when raised, don't just drill a hole through both sections of
mast and try to put a bolt through the hole. The trouble with this is
you have to hold the mast extended with one hand, while you are trying
to line up the holes with the other and stick the bolt through. This
can be a real pain in the a**. A better way is to drill a hole through
the inner pipe only, and cut a "V" notch across the top of the outer
pipe. This way you can extend the inner pipe a little higher than
needed [carefully!!], insert the bolt in the hole, then lower the pipe
until the bolt contacts the top of the outer pipe. After the weight is
on the bolt, you can then rotate the inner mast until the bolt drops
into the "V" notch to align the mast sections. I hope this makes
since. It's a simple concept, but difficult to explain...
Another thing to keep in mind is the overall "collapsed" height of the
mast when mounted on your truck. Most states require you to stay under
13', I believe. 11' gives me enough trouble with tree limbs, so I try
stay under 11 feet'ish. My homebrew mast used 7' of one inch conduit
for the inner section, then 6.5' of inch and a quarter conduit, 6' of
inch and a half, etc... My truck bed adds about another 3 feet to the
overall height, so you get the picture. Staggering the mast section
lengths gives you enough room at the top of each section to mount the
yagis. When raised, each yagi is separated from the next enough to stop
interaction. And when lowered, they stack one on top of the other for a
nice compact stack ready to move...
Before I found the commercial mast, I was planning a version 2 of my
homebrew mast. My plans were to buy some aluminum tubing from Texas
Towers, or somewhere similar. This should drop the weight appreciably,
and they also carry sizes that telescope much tighter. This should take
a lot of the lean out of the mast, plus make it easier to push up. I
didn't get a chance to try this, however.
Another idea I've been considering is the low cost, telescoping flag
poles I have seen advertised. I have seen them advertised at places
like Harbor Freight pretty cheap. I haven't tried it, but it seems to
me if they would support a decent size flag a few small yagis shouldn't
be any problem.
After finding the commercial push up mast I gave up on building version
2 of my homebrew mast. However, for the past year or so I've been
playing with ideas on how to homebrew my own crank up mast for the Rover
:-) I've come to the conclusion that actual construction may have
to wait until I can teach myself to weld ;-)
Good luck with your project!
http://s135.photobucket.com/albums/q148/Indiana_Dan/?action=view¤t=6-28-2007011Small-1.jpg
73
Dan
--
K9ZF /R no budget Rover ***QRP-l #1269
Check out the Rover Resource Page at: <http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!
k4gun@comcast.net wrote:
> I like that a lot. That's pretty much what I'm going for. You don't
> have the upper portions guyed do you?
>
> This is actually giving me other ideas about perhaps changing to rigid
> conduit, going taller with 4 sections and keeping all 4 on a single
> mast. I'll see what I can figure out.
>
> Thanks.
>
> Steve
>
>
> -------------- Original message --------------
> From: Dan Evans <dan.evans@insightbb.com>
>
> > Hi Steve,
> >
> > Sounds like you will be getting very close to the setup I run.
> >
> > I have a commercial made push up mast I found at Dayton a few years
> > ago. It's 20', or 4 five foot sections. Plus I usually add a 6'
> > extension at the top. It's a bit difficult to explain, but
> basically I
> > mount an antenna at the top of each section of the push up mast.
> The
> > top antenna is usually the Par Moxon for 6, at 26'. Next is
> generally
> > the 432 yagi at 20'. And then the 2m yagi at 15'. No 222 until I
> can
> > swing another transverter, but it would go under the 2m yagi, at
> 10'
> > above the truck. Sometimes I switch the order of the yagis, but
> this is
> > the basic layout. When lowered, the yagis all stack one on top
> of the
> > other as I nest the push up mast. Nested height is about 11
> feet, watch
> > those tree limbs! I can't really use them while moving, but I am a
> > solo Rover so I don't generally operate on the move anyway. [If
> I do, I
> > run a recorder to do the logging]
> >
> > The last time out I braced the mast with a cross bar across the
> bed of
> > my F150. And the bottom of the mast goes in my AR40 rotator
> which is
> > bolted to the bed of the truck. I plan to add a set of ladder
> racks to
> > the truck soon to make for a better cross brace for the mast.
> >
> > So I currently run 3 bands on one mast. Setup consists of me
> getting
> > out of the truck, climb in the back, spend 2 or 3 minutes
> raising the
> > mast, get down and call CQ. When I'm ready to roll, I turn the
> mast to
> > face front, lower the mast, and hit the road.
> >
> > Here are links to a couple of pics from last September:
> >
> &g t;
> http://s135.photobucket.com/albums/q148/Indiana_Dan/?action=view¤t=6-28-20
>
> > 07007.jpg
> >
> http://s135.photobucket.com/albums/q148/Indiana_Dan/?action=view¤t=07sepvh
>
> > fqsoparty009-1.jpg
> >
> http://s135.photobucket.com/albums/q148/Indiana_Dan/?action=view¤t=07sepvh
>
> > fqsoparty004-1.jpg
> >
> http://s135.photobucket.com/albums/q148/Indiana_Dan/?action=view¤t=07sepvh
>
> > fqsoparty018.jpg
> >
> http://s135.photobucket.com/albums/q148/Indiana_Dan/?action=view¤t=6-28-20
>
> > 07012.jpg
> >
> > 73
> > Dan
> > --
> > K9ZF /R no budget Rover ***QRP-l #1269
> > Check out the Rover Resource Page at:
> > List Administrator for: InHam+grid-loc+ham-books
> > Ask me how to join the Indiana Ham Mailing list!
> >
> >
> >
> > k4gun@comcast.net wrote:
> > > I'm already plotting improvements to my rover rig for June.
> After the January
> > contest, I learned a lot of lessons. I need better antennas.
> > >
>
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