Hmm. Well, I stand corrected. I have a manual for the Wilson ST-77B, which I
believe was the predecessor of the US Tower MA-770, which is the model I have
(MA-770MDP with MARB base, to be exact.) The Wilson manual does say you can guy
the top section (only) to handle up to 20 sq ft of windload at 80 MPH, and says
they have an optional guy kit that includes a collar so the tower can still
rotate. It even has a little drawing of a guyed 77B. It doesn't say anything
about not overtightening the guys. It also doesn't appear to have any support
pins. I don't know where I got that idea. Maybe someone told me about a tubular
tower that had such a mechanism and I got it mixed up with the 77B. Sorry.
The manual makes a good suggestion. It says the tower is rated for 50 MPH
(without guys, presumably.) They say if the wind kicks up, lower the tower at
least 15 feet. This dramatically increases the windload capacity. When I used
my crankup tower more often than I do now, I used to keep it at 50 feet most of
the time, extending it to 72 feet only when needed. Having the motorized
remote-control version helps a lot in that regard. Nowadays, with 110' of Rohn
55 supporting the main station antennas, I only raise the crankup for contests
(it has a Force-12 4-el 20m monobander on it.) The crankup lives at 22 feet the
rest of the time.
I agree with LJ -- if you want a guyed tower, go with Rohn 25, 45 or 55. It'll
be cheaper and capable of handling much more windload.
73, Dick WC1M
> -----Original Message-----
> From: larryjspammenot@teleport.com [mailto:larryj@teleport.com]
> Sent: Wednesday, May 07, 2008 11:01 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Experience with MA550 tower
>
> I have a 3-section Wilson MT-61B crankup tubular tower, which is not
> installed - it's just lying on the ground as I don't have any
> particular plans for it right now. I just looked through the manual
> for it, and then went out and actually looked at it - it doesn't
> appear to have any kind of steel pins anywhere, just the single
> raising cable. I also had the 40-foot tall 2-section version of the
> same Wilson tubular tower about 16-17 years ago, same thing. I did
> have it braced against the house with a bracket, and it worked out
> well with a 2-element tribander quad on it. If I remember correctly,
> Wilson also made a 77-foot, 4-section version of this tubular tower.
>
>
> I also have the RB-61B Rotor Base/Raising Fixture manual for this MT-
> 61B Tower (but not the actual fixture), and the manual for the
> companion GK-61B Guy Kit. Looking through the TT archives and
> following the related discussions, it seems that the US Towers MA-550
> is the modern replacement for the Wilson MT-61B. The top section of
> the MA-550 is a square tube, while the Wilson top section was round,
> and maybe a few other design changes. I believe I saw info about
> people ordering the MA-550 series raising fixture, rotor base, etc.
> from UST to use with their older Wilson MT-61B.
>
> The GK-61B Guying Kit manual specifies four guy wires going to the top
> of the tubular tower. The pictorial on the front page shows the tower
> being used with the RB-61B Rotor Base/Raising fixture, out in the
> clear, away from any buildings.
>
> A couple of notes that make me hesitant to try to guy any of these
> tubular towers though - these notes are from the GK-61B guying kit
> manual (dated 06/01/80):
>
> "NOTE: With this Guy Kit properly installed the tower is capable of
> supporting a 20 sq. ft. antenna at 80 mph."
> "Do not over tighten guy cables. Leave enough slack so tower top can
> move about 1 ft. from vertical."
>
> It sounds to me like the single set of guys are just loosely attached,
> and will hopefully keep the tower from falling over if the wind blows
> TOO hard! It doesn't look like a very encouraging, stable way to
> support an antenna. This is one of those situations where I don't know
> if I'd really want to "Do what the manufacturer suggests", by guying a
> lightweight tower like these.
>
> If Wilson was still in the tower manufacturing business, I have doubts
> that they'd still be offering this guying kit. If I wanted a guyed
> tower, I think I'd find a way to go with Rohn 45, or similar.
>
> LJ
>
>
>
>
> -----Original Message-----
> >From: Dick Green WC1M <wc1m@msn.com>
> >Sent: May 7, 2008 10:20 PM
> >To: "'larryjspammenot@teleport.com'" <larryj@teleport.com>,
> towertalk@contesting.com
> >Subject: Re: [TowerTalk] Experience with MA550 tower
> >
> >The MA-550 cannot be guyed and there's no kit for it. Guy wires would
> exert substantial downward force on the tower, and all of this force
> would be borne solely by the wire rope cables that raise and lower the
> tower and provide all support for the structure when it's raised. The
> greater the wind, the greater the downward force. I don't know the
> specific numbers, but would imagine even a modest wind could exceed
> the breaking strength of the cables.
> >
> >Though I've never seen one, I have a manual for one of the Wilson
> tubular towers. They had steel pins to support the tubes independently
> of the cables. After raising the tower, the pins would click into
> place and you could slack off the cables. Then the guys could be
> tensioned, exerting their force on the pins, not the cables. For
> lowering, you would slack the guys, then operate a mechanism that
> would pull out the pins (I imagine you had to crank up the tower
> slightly to take the pressure off the pins.) Then you could lower the
> tower. Obviously, this design was intended for leaving the tower up
> most of the time, rather than raising and lowering it frequently. It
> certainly wouldn't be compatible with the US Tower motorized
> raising/lowering and remote control systems, and I suspect most of US
> Tower's tubular tower customers buy the product because they don't
> want a guyed tower.
> >
> >73, Dick WC1M
> >
> >> -----Original Message-----
> >> From: larryjspammenot@teleport.com [mailto:larryj@teleport.com]
> >> Sent: Wednesday, May 07, 2008 12:19 PM
> >> To: towertalk@contesting.com
> >> Subject: Re: [TowerTalk] Experience with MA550 tower
> >>
> >> I don't know just how exact the old discontinued Wilson MT-61 tower
> is
> >> compared to the UST MA-550. I've seen several articles that say
> >> they're basically the same tower, can use the same raising fixtures
> >> and other accessories.
> >>
> >> Someone sent me .pdf files of the installation manual about a year
> ago
> >> for the MT-61 and a separate manual for the optional guying system
> for
> >> it. Maybe there's some similar guying method available for the MA-
> 550?
> >>
> >> LJ
> >>
> >>
> >>
> >>
> >> -----Original Message-----
> >> >From: K7LXC@aol.com
> >> >Sent: May 7, 2008 9:02 AM
> >> >To: towertalk@contesting.com, gdslagel@yahoo.com
> >> >Subject: Re: [TowerTalk] Experience with MA550 tower
> >> >
> >> >
> >> >In a message dated 4/29/2008 8:37:00 A.M. Pacific Daylight Time,
> >> >towertalk-request@contesting.com writes:
> >> >
> >> >> Anyone have favorable/unfavorable comments about this tower?
> >> >
> >> > On the plus side, aesthetically they're pretty reasonable.
> This
> >> is a
> >> >light-duty tower with a limited amount of capacity. If you live
> in a
> >> windy area,
> >> >I'd be pretty careful.
> >> >
> >> >> I'm thinking of a used one and, looking at the 4 eham reviews,
> >> there's a
> >> >lot of talk about moving towers and needing to add guy wires.
> >> >
> >> > Huh?!? Where does the manufacturer specify guy-wires? More
> >> amateur
> >> >engineering. :-( My advice is to follow the LXC Prime Directive
> to
> >> "DO what the
> >> >manufacturer says." The reverse is also true.
> >> >
> >> >Cheers,
> >> >Steve K7LXC
> >> >TOWER TECH -
> >> >Professional tower services for hams
> >> >Cell: 206-890-4188
> >> >
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|