[TowerTalk] MA-850 tilt over base (long)
Dick Green WC1M
wc1m73 at gmail.com
Sun Jan 26 15:07:07 EST 2014
I don't see any replies, so I'll take a swing at this. I have the MDP-720
One issue you may have is that the base doesn't fold over. It's the mast
that folds over. So yes, the 23.5' portion will lay flat a small distance
above the ground. But the base that supports the mast is fixed. The vertical
member of my base is about 6'-7 high. I don't know if the MA-850 base is
taller, but it stands to reason that it might be because it weighs 85 lbs
more than the base for the MA-720. Your neighbors might not like seeing a
tall steel pier sticking up in your yard, so camouflage will probably be
I know you plan to use camo paint, but depending on the surrounding flora,
you might want to consider camo netting for both the base vertical member
and mast when retracted and folded over. Google "camo netting" and you'll
find many options. This could be a more effective way of hiding the
Another problem is that the MAF raising fixture stands several feet above
the top of the vertical member. I think it's at least 4', maybe more. So I
believe that the total height would be 10'-12' -- maybe more. If your HOA
won't go for that height on a permanent basis, you would have to install the
raising fixture only when the mast needs to be raised and lowered, then
remove it . This will require you to provide sturdy supports for the mast
when it's folded over (you need to do this anyway -- see below.) The down
side is that it's a pain to install and remove the raising fixture. The
version for the MA-850 weighs 80 lbs and has to be lifted at least six feet
off the ground to mate with the base, possibly higher. I used to be able to
lift my 75 lb raising fixture up that high but I'm not sure I can do it now.
Definitely plan for it being a job for at least two people.
Now to your question: The mast pivot point on my tower is roughly 24" above
the concrete base. I say roughly because I can't run out and measure it at
the moment -- the tower is 265' away with a lot of snow on the ground.
Besides, the pivot point height for the 72' and 85' versions might be
slightly different. I've seen one 85' version and my recollection is that
the pivot point is in about the same position as it is on my tower.
Unfortunately, I can't recall what the base vertical member height was. The
base was *way* beefier than mine, and I'm almost certain it was somewhat
You can probably get the exact measurement from US Tower, but it might take
a bunch of emails and phone calls (and patience.)
In the meantime, you could tell the HOA that the mast will be no more than
4' off the ground. That'll give you plenty of slack.
You should provide at least one support under the mast when it's folded over
and maybe two. Although the steel cable of the tilt-over fixture is massive,
it's not wise to have that be the only support for long periods of time, and
since the mast can swing to-and-fro slightly when suspended from the cable,
sideways torque could deform the pivot bolts. A couple of stacks of concrete
blocks would solve that problem nicely, and they would be covered by the
camo netting too. A minor benefit of supporting the mast is that you can
disconnect the cable from the raising fixture and stow it out of sight
(assuming they don't make you remove the raising fixture.)
Installation/removal of a C3S won't be too hard because the boom is only 12'
long and the antenna weighs only 26 lbs. But you'll need a fairly tall step
ladder to do it -- I would estimate an 8-footer minimum. Definitely easier
for two people to do the job -- one to steady and help lift the antenna, and
the other to tighten the nuts and bolts. What do you plan to do with the C3S
when it's off the mast? It's not terribly hard to take the elements off, but
it'll be time consuming.
Personally, I would push the HOA to accept the largest antenna for which the
MA-850 is rated, even if you're just planning to put a C3S on it. The max
wind load is on the order of 10 sq ft, so the dimensions of a TH-7 or 4-el
SteppIR will do. Sounds like you're a contester, like me, and inevitably
you're going to want a bigger antenna. That would bring with it more
difficulty of installation/removal/disassembly/reassembly, but it's best to
leave your options as open as you can.
One last piece of advice: try to get the HOA to accept the MA-85, but
consider getting the MA-720 instead. There's a big difference in cost and
overall visual impact of the two. The question is whether 14' or so in extra
height will make any material difference. Bear in mind that 72' is high
enough to get excellent performance on 20m and up. If you haven't already, I
would get a copy of HFTA and spend some time learning how to use it. Then
check the gain and patterns for each of the contest bands. It's quite
possible that there's no advantage to the extra height. I ran some very
quick analyses that assume your antenna would be above flat ground. They
showed that there's no more than about .1dB additional gain from the extra
height. The pattern of the higher antenna give you about .5-.7 dB better
"figure of merit" on 20m, but provides no better figure of merit on 15m and
Note that if your terrain isn't essentially flat out to about 5 miles,
you'll have to verify this with your actual terrain: if it's hilly, then the
additional height could help -- or it could make things worse!
If it were me, I'd seriously consider buying the MA-720 and a 3el SteppIR.
The SteppIR will give you a better match on all the bands, and the third
element will give you more gain than the extra height. It operates on 6m as
well. You would also have the option of a 40m dipole if you get that version
of the 3el SteppIR (though it could be tough to push that "trombone" element
past the HOA). The 3-el SteppIR is quite a bit heavier (50-60 lbs) and the
boom is longer (16'). You'll need an even taller stepladder to
install/remove it, and definitely a helper. Since you will install/remove
frequently, you'll want to obtain one of the quick-disconnect options for
the control cable. The straight elements (empty fiberglass tubes) are easy
to install/remove. Installtion/removal of the trombone element tubes of the
40m option is a bit more involved.
Yet another option would be the 2-el SteppIR. That'll give you the same
frequency coverage as the 3-el, on a 4.75' boom. The performance should be
comparable to the C3S because the element lengths are adjusted on the fly to
give you complete coverage of any band. The boom is so short that you might
be able to install/remove the antenna with no stepladder or assistance.
I know that the published gain figures seem to indicate the C3S is
substantially superior to the 3-el SteppIR, but I don't see how a 2-el on a
16' boom could outperform a 3-el on a 16' boom, especially when the element
lengths of the 3-el can be optimized for any frequency. In other words,
never trust the published gain figures. You're better off modeling the
antennas yourself in EZ-NEC (I'm sure other hams have put together models
for all the antennas you would consider, and would be happy to email you
Between the two SteppIRs, you would lose about 2dB gain on each band and
quite a bit of F/B. But the low-profile 2-el could be worth the sacrifice if
your HOA doesn't like the C3S or 3-el SteppIR.
73, Dick WC1M
> -----Original Message-----
> From: ko7ss at yahoo.com [mailto:ko7ss at yahoo.com]
> Sent: Saturday, January 25, 2014 12:45 AM
> To: towertalk at contesting.com
> Subject: [TowerTalk] MA-850 tilt over base
> More HOA "details" need to be worked out. How high above ground is the
> point for the MA-850 MARB fold over base? 18-24" ? It may come down to me
> having to retract the tower, remove the antenna (a C3-S), and lay the
> over flat, except for the 6 contesting weekends I have designated.
> So, it would look like a 23.5' long, 10" diameter camouflage painted log
> above ground?
> It will be worth it if I can get this through the HOA !!!
> Bill KO7AA in Tucson, AZ
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