Barry,
I have an MA-770MDP with MARB base in New Hampshire. Not exactly the same,
but close enough for me to comment. Do not compare the MA-550 with SM2CEW's
tower. If it can be guyed, I doubt it's similar enough for a valid
comparison.
I wouldn't recommend any of the U.S. Tower tubular tower for high wind
conditions unless the antenna is a whip or very small yagi (i.e. a couple of
square feet windload.) With any appreciable windload, the tower sways like
hell in winds over 15-20 MPH. It's a scary sight. Even though the MA-550 is
20 feet lower than mine, the sections are correspondingly smaller diameter
and the section overlap is the same. Both towers are supported only by wire
rope, which though strong can break under extreme loads. The tower is
probably safe up to its max windload rating (10 sq ft) at either 50 or 60
MPH (I think U.S. Tower increased the wind speed when antenna manufacturers
changed their windload calculation formula, but I'm not sure.) However, I
would not consider it for anything higher. Personally, I leave mine
retracted all the time except for contesting and rare DX, and always lower
it when the wind speed gets above 25 MPH. I've got about a 6 sq ft windload
on it (20m monobander with 30' boom, weighs about 50 lbs.)
Note that in my case, lowering the tower from 70' to 50' makes a big
difference in stability because there's a lot more section overlap. I'd
probably be comfortable at winds up to about 35 MPH with the tower at 50'.
Below that, it's rock solid. If you can make sure the tower is lowered
whenever there are high winds, then it might work out for you. That's one
reason I got the motorized winch. The manual winch is incredibly slow and
takes a little elbow grease. I expect anyone would get tired of it fast and
not lower the tower when the winds are predicted to kick up. BTW, I have an
anemometer in the shack and keep close tabs on the wind forecast.
Icy conditions are another problem. The president of U.S. Tower warned me
explicitly not to operate the tower in icy conditions. Ice adds considerably
to the windload, severely reducing the tower's rating. I discovered another
problem with the motorized winch version last year: if you leave the tower
fully retracted in icy conditions, the Down limit switch can freeze in the
full-down position. You can then raise the tower, but it can't be lowered!
Luckily I was able to knock the ice off the limit switch with a long bamboo
pole. The permanent solution is to raise the tower a few inches above
full-down when fully retracted. This leaves the limit switch in the active
position.
I have never had a problem with the MARB base in snow, ice or cold. It
always works well. As long as the base is installed correctly (there are
some tricks) it should rotate OK. However, I did have a Hy-Gain Tailtwister
that froze up in the colds. That's a known design problem that affects some
units and I was able to get another Tailtwister that doesn't have the
problem.
Finally, there's no safe way to guy the U.S. Tower tubular towers. Guys put
too much downward pressure on the wire rope that supports the tower
sections. The old Wilson tubular towers on which the U.S. Tower design was
based had section pins that could be activated from the ground. That would
take the load off the wire rope and allow guying from the top. Too bad U.S.
Tower dropped the idea, though I'll bet it was because the pins sometimes
got stuck (no way to lower the tower, then!)
As long as you're considering guys, I'd recommend good-old Rohn 25. Given
the cost of taking the MA-550 down and transporting it, maybe the extra cost
wouldn't be too bad. Another alternative would be an AB-577 portable
military surplus mast, if you can find one. Similar windload capacity and
much more stable.
73, Dick WC1M
> -----Original Message-----
> From: towertalk-admin@contesting.com
> [mailto:towertalk-admin@contesting.com]On Behalf Of Barry Bettman
> Sent: Friday, December 06, 2002 2:40 PM
> To: towertalk@contesting.com
> Subject: [Towertalk] ma550 with marb in snow & icy & high winds
>
>
> Does anyone have experience with a US Tower MA550 tubular tower and the
> MARB rotating base in snow and icy and high wind conditions?
>
> I own a ma550 / marb and am considering moving it to my new qth in the
> Sierra Nevada mountains where we get snow, ice and high winds. I want
> to speak to other hams that this exact experience so I can make an
> informed decision about using this tower system in these weather
> conditions.
>
> Has any one every tried guying the ma550 / marb rotating tower to add
> strength?
>
> Thanks,
>
> Barry K6ST
>
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