K7LXC@aol.com wrote:
>
> In a message dated 99-07-22 18:38:30 EDT, k9zm@frontiernet.net writes:
>
> > Has anyone had any problem with the M2 6M7JHV antenna? This has a 30'8"
> > Boom which is only 1.5" dia. I am looking to get on 6m and want the most
> > value for the buck. This seems to be it. However, everything I have ever
> > read says to use a larger boom for this type of length. Just curious if it
> > is a bit too floppy in the air. Should I consider another antenna of
> > similar size/gain? I am planning on putting this at about 52' in the air
> on
> > a second tower with possibly a 5 el 10 meter antenna a few feet under it.
> > This would be my primary 6m antenna. Other suggestions would be
> > appreciated?
>
> M2 is NOT known for poor mechanical designs. They probably use Kurt's
> YagiStress software but I don't know for sure.
>
> 6M elements aren't real substantial so I'll bet you a nickel that it'll
> be just fine. The antenna is rated to 85 MPH so it's not a heavy duty 100 MPH
> version. Logan County is a 70 MPH windspeed zone so you really don't have
> much to worry about.
>
> M2 6M antennas work very FB so go for it!
>
> Cheers, Steve K7LXC
>
Sigh, I can't let all of this go by without comment, Drats!
Since, we eat the elephant one bite at a time:
A 30'8" Long x 1.5" dia x .065 wall boom, with EIA-RS222 C wind loads,
is safe with 85 Mph static wind loads, if the mast is mounted at the
center of the boom.
Don't know of the antenna being discussed is the same, but that is how I
got YS to say 85 mph.
M2 does not use my software to design antennas. I sent them a beta
version prior to the initial software release in 1992, because they
simply had to have it right away. When the software was done and
released, I was told that they did not need it. Haven't heard from them
since, and don't expect to.
Most amateur antennas are not designed or spec'd with the current EIA
222 F methods. There's some hair in the butter here! Current EIA antenna
loads are dependent on height. How many manufacturers know what height
you are going to install your antenna? Any antennas designed to 222 F
would have a long list of different antenna safe speeds at different
heights.
Most antennas are designed according to older, height insensitive
spec's.
So, it's hard to directly correlate antenna ratings with tower ratings.
The best we can do today is ask for the max projected antenna areas and
use them to evaluate the tower.
I'm pretty sure we can't even compare antennas from various vendors,
because we don't know how each one is determining the loads. At least,
it is not evident in the literature. There is certainly no industry
standard being used in the antenna field!
Before we pull the rest of our hair out, we should know that for heights
from 30'-80', there's not much difference between the spec's.
Generally speaking, anything good to 100 Mph according any of the spec's
is gonna be a pretty reliable antenna.
I'd personally not consider anything below 85 Mph, but it's windy here
and that's just my opinion.
Empirical evidence supports this. Some antennas known to be unreliable,
rate at or below 85 Mph using RS 222 C.
YMMV!
Someday, when I can get to it, I'll put something on my website about
this.
Till then, we can all be a little bit confused and frustrated, but the
subject can provide some entertaining discussion.
When in doubt, just ask your antenna designer what his number means!
This should provide some more entertaining discussion!
I was hoping we'd get meaningful antenna areas from everyone before we
got around to this one!
73, Kurt
K7NV "That's K7 "Nevada"
YagiStress - The Ultimate Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress/
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