Antenna Swings In Wind - How Much Is Too Much
 

Hi,

I have a 4 el., 5 band quad on a Yeasu rotator on a Heights Aluminum tower.
The antenna is swinging, in a fairly stiff breeze today, a total of about 20
degrees of arc. Of course that's not a problem with the width of the beam of a
4 el quad, but the 24 el 2 meter antenna I plan to add might have an issue with
that much swing. I forget which model Yeasu rotator it is, but it is supposed
to be big enough for the 4 el. quad (30 ft boom). G450? I think?

Anyway, is 20 degrees in a stiff wind too much? Can I expect the rotator to
fail soon over this? The tower does not appear to be twisting. The rotor base
plate doesn't seem to be moving. I don't think there's that much play in the
bolts of the masting, and the tower appears tight to the mast. I think the
play is in the rotator.

Is it common for a rotator to have that much play?

Dave Head

I have been looking at my beam also thinking it is moving too much in
the wind. It is a Yaesu rotor and a Moseley 4 element beam. Almost looks
like the 2" mast (about 5 ft.) is flexing, but I am pretty sure that
can't be. It is up 45 feet on a Universal Aluminum unguyed tower very
firmly mounted in concrete.

Dave Head wrote:
Hi,

I have a 4 el., 5 band quad on a Yeasu rotator on a Heights Aluminum tower.
The antenna is swinging, in a fairly stiff breeze today, a total of about 20
degrees of arc. Of course that's not a problem with the width of the beam of a
4 el quad, but the 24 el 2 meter antenna I plan to add might have an issue with
that much swing. I forget which model Yeasu rotator it is, but it is supposed
to be big enough for the 4 el. quad (30 ft boom). G450? I think?

Anyway, is 20 degrees in a stiff wind too much? Can I expect the rotator to
fail soon over this? The tower does not appear to be twisting. The rotor base
plate doesn't seem to be moving. I don't think there's that much play in the
bolts of the masting, and the tower appears tight to the mast. I think the
play is in the rotator.

Is it common for a rotator to have that much play?

Dave Head

Dave:

Some of the huge commercial/government system rotators have built in torsion
relief in the form of some sort of springing, but I don't think the smaller
Yaesu have such. I would really be concerned with that much slack, as the
larger the swing is, the more inertia the assembly builds up to pound the
rotator internals into dust. Plus, if that model rotator has a positive
'brake' like the HAM series, then you are in a heap of trouble, as the brake
has definitely failed. Best get it repaired before the spring winds.

--
Crazy George
Remove N O and S P A M imbedded in return address
"Dave Head" wrote in message
...
Hi,

I have a 4 el., 5 band quad on a Yeasu rotator on a Heights Aluminum
tower.
The antenna is swinging, in a fairly stiff breeze today, a total of about
20
degrees of arc. Of course that's not a problem with the width of the beam
of a
4 el quad, but the 24 el 2 meter antenna I plan to add might have an issue
with
that much swing. I forget which model Yeasu rotator it is, but it is
supposed
to be big enough for the 4 el. quad (30 ft boom). G450? I think?

Anyway, is 20 degrees in a stiff wind too much? Can I expect the rotator
to
fail soon over this? The tower does not appear to be twisting. The rotor
base
plate doesn't seem to be moving. I don't think there's that much play in
the
bolts of the masting, and the tower appears tight to the mast. I think
the
play is in the rotator.

Is it common for a rotator to have that much play?

Dave Head

That is almost as much play as I had in my system, with a 2 el 40 m beam and a
tribander, but I had a 40 ft torque tube down the tower to absorb the forces.

73s,

Evan

Maybe its a Yeasu characteristic, but I doubt it. My biggest suspicion is
loose mounting bolts. Will have to crank it over soon and take a look.

Thanks for the info.

Dave Head

On Sat, 21 Feb 2004 16:38:40 -0500, Bill J wrote:

I have been looking at my beam also thinking it is moving too much in
the wind. It is a Yaesu rotor and a Moseley 4 element beam. Almost looks
like the 2" mast (about 5 ft.) is flexing, but I am pretty sure that
can't be. It is up 45 feet on a Universal Aluminum unguyed tower very
firmly mounted in concrete.

Dave Head wrote:
Hi,

I have a 4 el., 5 band quad on a Yeasu rotator on a Heights Aluminum tower.
The antenna is swinging, in a fairly stiff breeze today, a total of about 20
degrees of arc. Of course that's not a problem with the width of the beam of a
4 el quad, but the 24 el 2 meter antenna I plan to add might have an issue with
that much swing. I forget which model Yeasu rotator it is, but it is supposed
to be big enough for the 4 el. quad (30 ft boom). G450? I think?

Anyway, is 20 degrees in a stiff wind too much? Can I expect the rotator to
fail soon over this? The tower does not appear to be twisting. The rotor base
plate doesn't seem to be moving. I don't think there's that much play in the
bolts of the masting, and the tower appears tight to the mast. I think the
play is in the rotator.

Is it common for a rotator to have that much play?

Dave Head

On Sat, 21 Feb 2004 16:43:14 -0600, "Crazy George"
wrote:

Dave:

Some of the huge commercial/government system rotators have built in torsion
relief in the form of some sort of springing, but I don't think the smaller
Yaesu have such. I would really be concerned with that much slack, as the
larger the swing is, the more inertia the assembly builds up to pound the
rotator internals into dust. Plus, if that model rotator has a positive
'brake' like the HAM series, then you are in a heap of trouble, as the brake
has definitely failed. Best get it repaired before the spring winds.

I think its supposed to have a brake. It is a Yeasu 800 DXA. Suspect loose
mounting bolts - it hasn't been up so long for the rotator to simply fail, I
think. The antenna is a Cubex 4 el, 5 band quad that is 7 sq ft and has a 30
ft boom. I think that rotator ought to handle it, as did the guy at Ham Radio
Outlet. He actually talked me up to this one, when I was going to get a 450,
but he pointed out the "K" factor, and how I needed the heavier rotator for
that long boom. Something still isn't right, tho, I think.

It could be the masting, tho. I have a 3: diameter piece that goes into the
rotator and is "pinned" there by a bolt, as well as clamped, then it goes to a
"jackshaft" that is a smaller, about 4' length of 1 3/4" stainless steel with 1
or 2 1/4" bolts thru it. That goes thru the 1 3/4" top section collar, then a
3" heavy aluminum mast slips over the stainless jackshaft and is secured with 2
quarter-inch bolts. There's probably some play in the bolts, but I don't think
there's that much. Mounting bolts on the bottom of the rotator - I think those
may be loose.

Thanks for the info.

Dave Head

Dave

On 21 Feb 2004 23:33:49 GMT, (K9SQG) wrote:

That is almost as much play as I had in my system, with a 2 el 40 m beam and a
tribander, but I had a 40 ft torque tube down the tower to absorb the forces.

73s,

Evan

Makes mine sound excessive, alright. Fortunately, this is one of those heights
towers that cranks over. I'll likely have a look at it later this week.

Thanks,

Dave Head

On Sat, 21 Feb 2004 23:52:08 GMT, Dave Shrader
wrote:

Dave Head wrote:
Hi,

I have a 4 el., 5 band quad on a Yeasu rotator on a Heights Aluminum tower.
The antenna is swinging, in a fairly stiff breeze today, a total of about 20
degrees of arc.

SNIP

Is it common for a rotator to have that much play?

Dave Head

No!!

That's what I thought.

Possibly the support mast, quad to rotator, is not pinned [pin failure]
or the brake in the Rotator has failed.

I don't think the pin has failed, but will look later this week. If the pin
failed, I think it'd just turn all the way around.

But, more than likely the G-450 is too small for your antenna.

My mistake. Its an 800DXA.

The specifications for the G450 are for 'small yagi''. Also, page 7 of
the manual, which can be found at: [the link is complete. Just click it
and locate the manual]

Yeah, I misremembered the size. I went up to HRO _intending_ to get a 450.
Got an 800 when the fellow there talked me up to it, pointing out the size of
my quad, esp. the 30' boom length.

http://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=104&encP rodID=X35dwkkMbr0%3D&DivisionID=65&isArchived=0

indicates that two terms are required for evaluation of load. The first,
the cross section wind load; the second, a K factor as defined by Yaesu.

I really suspect the antenna is too large for the G450.

Hope you can solve your problem.

Will crank it over soon and have a look. I do remember significant "play" in
the system when it was tilted over before. Probably should have looked at that
a little more critically.

Thanks for the info.

Dave Head

Deacon Dave, W1MCE

Dave:

From that description, I suspect you are going to find all the bolt holes in
the tubing elongated from torque. We usually drill slightly oversize holes
for our fasteners, but in this high stress application, the holes should
start undersize so the fasteners have to be driven in and are tight from the
get-go. Also, it is necessary to select fasteners which do not have threads
where they pass through the walls of the tubes. This is often the most
difficult challenge.

--
Crazy George
Remove N O and S P A M imbedded in return address
"Dave Head" wrote in message
...

snip
It could be the masting, tho. I have a 3: diameter piece that goes into
the
rotator and is "pinned" there by a bolt, as well as clamped, then it goes
to a
"jackshaft" that is a smaller, about 4' length of 1 3/4" stainless steel
with 1
or 2 1/4" bolts thru it. That goes thru the 1 3/4" top section collar,
then a
3" heavy aluminum mast slips over the stainless jackshaft and is secured
with 2
quarter-inch bolts. There's probably some play in the bolts, but I don't
think
there's that much. Mounting bolts on the bottom of the rotator - I think
those
may be loose.

Thanks for the info.

Dave Head

Dave

On Sun, 22 Feb 2004 14:46:54 -0600, "Crazy George"
wrote:

Dave:

From that description, I suspect you are going to find all the bolt holes in
the tubing elongated from torque. We usually drill slightly oversize holes
for our fasteners, but in this high stress application, the holes should
start undersize so the fasteners have to be driven in and are tight from the
get-go. Also, it is necessary to select fasteners which do not have threads
where they pass through the walls of the tubes. This is often the most
difficult challenge.

That is certainly worth a suspicion or two. I had it tilted over a couple
months ago, after being up for a while, and inspected the bolts and found no
wear. The whole assembly was not "tight" at that time either, and I think it
was the rotor that had the play. But I'll tilt it over again and go through it
all.

Thanks,

Dave Head
K8DH