The point here is not whether some Mosley antennas will hold up for 27
years. The point is that there is no way on earth that Mosley has the
statistically valid data to support their claim that the average life
without maintenance of their antennas is 27 years ... to one year
resolution, no less. It's an irresponsible claim, and their eagerness
to make it should make potential customers a bit skeptical about their
other claims, such as those for gain.
But in case that doesn't register with you, here is a more direct
comparison that might.
I own an Optibeam OB16-3 tribander. It has four full size elements on
20m, four full size elements on 15m, and eight full size elements on 10m
... all on a 31 foot long boom. All sixteen elements are separate and
they are more or less optimally spaced within the constraints of the
boom length. On 10m the element spacings sacrifice a small amount of
gain in order to be able to cover a wider bandwidth, so I consider it to
be approximately the equivalent of a six element yagi instead of eight.
I assembled the antenna myself and I can say with great certainty that
there are minimal resistive losses anywhere in the antenna itself,
although there could be some small losses in the balun. Here is a link
to a closeup picture of the feed system so that you can understand why I
say that. As a scale factor for viewing the picture, the square boom is
three inches on a side.
(the picture can be found at the top of this page ...
http://www.ab7e.com/AB7E_Antenna_Page_4.html)
The published gain figures for the OB16-3 are 7.1/7.5/8.5 dBd
(20m/15m/10m). I took all of the dimensions of the OB16-3 (element
diameters, stagger, element lengths, element spacings, etc) and loaded
them into the EZNEC 5+ antenna modeling program and got almost exactly
the same calculated profiles for gain and SWR as the published plots
from Optibeam. With the help of a ham friend who lives about 40 miles
from me I carefully plotted the azimuth gain profiles of my OB16-3 on
all three bands and got almost the exact same pattern profiles as the
published plots from Optibeam. My measured SWR plots match the Optibeam
plots almost exactly. Taking all of that into account I tend to believe
that the published data from Optibeam is reasonably accurate for gain.
My antenna height (73 feet) is even virtually the same as used for the
Optibeam specs.
By comparison, the Mosley TA-34 with a claimed gain of 8.2/9.1/9.5 dBd
has traps on all elements. The TA-34 has only four elements on a much
shorter boom (21 feet) and the elements are not a full wavelength on 15m
and 20m. The element spacings are a compromise for the three bands and
are not optimized for gain or bandwidth on any single band.
There is simply no way I can think of that the TA-34 could have more
gain than the OB16-3 when mounted at the same height above ground, and
in fact the physical comparisons make me strongly suspect that the
actual results would be the other way around by a considerable margin.
To clarify, I am not suggesting that the TA-34 or any other Mosley
antenna is not a decent antenna, or that any other antenna would be a
better choice in any particular situation. Compared with the OB16-3,
for example, the TA-34 is less expensive, weighs less, and has a shorter
turning radius ... all valid reasons why someone might choose it.
However, this message thread started with someone being inclined to
choose the TA-34 over the products from other manufacturers based
primarily upon Mosley's published gain specs, and in my opinion that
would be a highly flawed rationale.
73,
Dave AB7E
On 8/23/2012 6:49 PM, Mike Krzystyniak wrote:
> I agree with John. I have had several Mosley Pro 57 and Pro 67 series
> antenna here in north Texas. All we bought used and they all disassembled on
> site easily due to the initial application of penetrox anti-ox. And after
> applying a fresh coat of the gray goup they went right back together. Some
> were up for a few years, one old Mosley I bought was up for 20 years (and it
> came from the Texas coast line). No issue on element or bracket disassembly.
>
> For many days of the year MY Mosley beams are steadily pressed by our
> prevailing southern winds. We also get high winds from fast moving t-storms
> or straight line winds from microbursts or collapsing cells. The Mosley
> beams came through it all. The real test a couple years ago when an ice
> storm delivered 1 inch ice followed by winds. Many locals lost or had damge
> to most every type of beam you can think of. The Pro-67C3's I have held up
> and stayed up. And after the ice dropped off the beams came right back to
> original form.
>
> Regarding 27 years without maintenance, with proper assembly and
> application of a few other sound assembly techniques I would not be surprised
> they are close to that. As always YMMV.
>
> 73 Mike K9MK/5
>
>
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