I like your RBN testing - nice idea. I wonder if the process could be
automated to some extent by using WSPR. By proper programing you could
alternate antennas. Might be an interesting to try. This way you could let
it run over a period of time, and collected. Data is gathered in SNR and 6
digit grid. Data can then be analyzed and presented in a suitable format.
I would try it but no antennas are up now nor will be for the foreseeable
future.
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Jim Brown
Sent: Friday, January 01, 2016 12:40 PM
To: topband@contesting.com
Subject: Re: Topband: Anybody?
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.
http://k9yc.com/80M-FDVertical.pdf
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.
> 73,
> Jim W8ZR
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