Gary
I had an A3 side mounted at the top of the 3rd section, fixed NE, on a
TX-472 (there was a C4S mounted just above the top section). At first I
simply used u-bolts through the boom-mast mounting plate and around the
tower leg. I had some problems with the antenna turning (I think due to the
mismatch in size between the tower leg (smaller than 2" diameter) and the
u-bolts (designed or 2" OD mast)), and was concerned about the damage this
was doing to the top of the tower leg. In addition, when raising/lowering
the u-bolts around the tower leg would rub against the inside tower section,
removing the galvanizing and wearing away the u-bolts slightly.
At that point I had a local metal shop fabricate something similar to the
mount for the ring rotor, however it only utilized two of the tower legs.
It had pegs (fairly long - 6-8") that slipped into the top of the tower legs
that were welded to a fairly thick plate of steel, and then had a 2"OD 12"
long mast offset a few inches from the tower and welded to the top of the
plate to mount the antenna on. The weight of the mount plus the weight of
the antenna held it all in place - no clamps etc. Never had any problems
(other than the antenna turning with the first setup) with either mounting
solution. Since the antenna mounted at the top of a section in both cases,
it did not interfere with raising/lowering. I had this made about 10 years
ago, and if I remember correctly, the whole thing was put together for under
$100 by the shop (including galvanizing - which BTW, you need to take into
account the thickness of the galvanizing when you pick your peg diameter).
I was never concerned about the wind loading or engineering situation. I'm
no engineer, however with the tower rated at 18 sq ft of antenna at 50MPH,
and having only about 10 sq ft on the tower, I felt fairly safe. Also, the
tower was lowered most of the time, and only raised up during weekends when
I participated in a contest. Otherwise the tower was lowered to about 35'
which made the two antennas about 10 feet apart. I felt that the top
antenna was still very usable (SWR curves did not change, f/b seemed intact)
with that close spacing (although I never did any modeling etc to verify
those assumptions other than sweeping with an antenna analyzer).
Good Luck.
73 de Al, KE1FO
On Jan 18, 2008 10:34 AM, Gary Slagel <gdslagel@yahoo.com> wrote:
> Does anyone have any idea if its possible to stack a
> couple yagis on a crank up tower? I'd really like to
> be able to put something at about 50' and 70' but I'd
> also really like to not have to climb a tower. Can't
> figure out how to do it and still be able to nest the
> tower when I crank it down.
>
> Thanks, Gary
>
> Gary Slagel/N0SXX
> Lakewood, CO
> http://marina.fortunecity.com/sanpedro/351
>
>
>
>
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