jim at audiosystemsgroup.com
Fri Jan 1 12:39:55 EST 2016
I can confirm Jim's experience that the Spiderbeam poles are NOT very
robust, and are not sufficiently robust to be used in the manner
Spiderbeam describes. We bought a 40 ft Spiderbeam pole to use as part
of an 80M vertical for FD and county expeditions for the California QSO
Party. The antenna worked fine -- until the wind blew and broke the
Spiderbeam mast at the point of attachment to the rest of the antenna.
The poles are advertised as being reinforced by crossed fibers; our pole
was not, which is why it broke.
The mechanical engineer for our antenna, Glen, W6GJB, is an M.E. by
degree, and practices as an aeronautical engineer in the space program.
He's quite familiar with materials and the stresses in a given design.
He holds a dozen or so patents.
I can also confirm that the antenna is NOT easy to erect, and for the
same reason Jim cited -- the top wobbles around, generating lots of side
stresses as it goes up, making it more difficult to raise. We needed
five people, one on each guy, and two at the antenna base. Our antenna,
and our experience, is described here.
We're very pleased with its performance and every aspect of its design
other than the Spiderbeam pole. We tested the antenna over poor ground
at Glen's QTH, and our FD and CQP sites also have poor ground. Over good
ground, the advantage of this antenna over the reference inverted Vee
would increase by 3-6 dB.
73, Jim K9YC
On Fri,1/1/2016 9:13 AM, Jim Garland wrote:
> I have the 26m (85.3 ft) Spiderbeam fiberglass vertical, with sixty 30m
> radials on top of sandy desert soil. It uses four 7m top hat wires, and is
> tuned to 1.820 MHz, where the VSWR is 1.47:1. I feed it with about 300m of
> buried hardline. The assembly instructions are clear and the antenna tuned
> to frequency very easily. It's a good perfomer, although the radiatmg wire
> only extends up to about 24m .
> Structurally, the antenna is relatively light duty. It has four levels of
> guy lines (16 guys total), the top two levels being 1 mm Kevlar and very
> thin polypropylene fishing line attached to the top hat wires.. The top few
> sections of mast resemble fishing poles and are very flexible. The bottom
> section is roughly 6 inch OD and with the supplied rubber cap fits tightly
> into standard PVC plumbing tubing. I anchored a 1m length of the PVC into
> concrete and that made a dandy anchor point for the mast.
> The top hat is made of very thin wire with a low breaking strength. Rodents
> ate through the Kevlar guys last year and toppled the antenna, which broke
> into three pieces. I redid the guys, elevating the anchor points, so don't
> expect that problem to recur. Don't be deceived by the YouTube video showing
> the pole being raised by two people. When the wire is attached to the pole,
> including the top hat wires, erection for me has been a four hour job
> involving a minimum of six people; four at each guy anchor and two to hoist
> the mast. The slightest wind makes erection very difficult because slight
> flexing prevents the nested sections from sliding. Last time I did this I
> mounted a 12 foot long 4x4 post in concrete next to the pole with an
> inexpensive hand winch to raise the sections. That helped a lot. I can send
> photos to anyone interested.
> Jim W8ZR
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