Agreed. I think the type of tree and the time of year must have at some
effect on how lossy it might be. I had to cut down a large, live branch
(full set of green leaves) of an Arizona White Oak here a couple of
weeks ago, and when I cut it up into chunks I was amazed at how dry it
was. Granted it is a hardwood variety, but I was able to burn it in my
wood stove with no more smoke than with dry kindling. On the other
hand, I've cut pieces of Ponderosa Pine that had been laying on the
ground for at least a year that had so much sap (almost a kind of
turnpentine) left in them that they burned like old tires. I guess if
we knew (or measured) the conductivity and dielectric constant of
various types of wood the effects on nearby antennas could be modeled,
but most people (me included) probably don't want to be taking core
samples of their trees to find out.
I don't believe the attenuation from a quad due to its surroundings is
any less than for a yagi ... that just doesn't make physical sense. I
also don't believe that a quad at the same height as a yagi has any
lower takeoff angle ... simple modeling proves that to be an old wives
tale. If anything, as I understand it, a quad is a higher impedance and
higher Q antenna compared with a yagi and therefore would seem more
likely to be detuned by nearby structures (either conductive or
dielectric). I suspect someone out there could tell us whether or not a
quad showed a different change in SWR when rotated toward a nearby
structure (tree or building) compared with a yagi.
Just so nobody gets upset, I think quads are neat antennas and they do
have their advantages, but some of the folklore surrounding them should
have been put behind us long ago. Hopefully not to be replaced by new
folklore like "a SteppIR will work well at any height".
73,
Dave AB7E
Roger (K8RI) wrote:
> Trees, particularly in the warmer weather should show up as a *lossy*
> rise in the the landscape/terrain close in (near field). How much of a
> rise and how lossy is a real wild card but it could, in some cases
> have a substantial effect and very little in others. That variability
> would make it extremely difficult to model accurately.
>
> Although I hear it said often, I see no real reason for a quad treating
> the trees much differently than a Yagi.
>
> Roger (K8RI)
> David Gilbert wrote:
>
>> How, pray tell, does using a quad versus a yagi have any effect on the
>> attenuation of the signal after it leaves the antenna?
>>
>> Dave AB7E
>>
>>
>> Edward Sylvester wrote:
>>
>>
>>> My opinion is that, at treetop level, you will be ok with a Steppir, as the
>>> take off angles will be high enough to miss the trees....But if you are
>>> well below (50' tower below 70' trees), you will signal will suffer some
>>> attenuation. A quad won't suffer as much due to its closed circuit design.
>>>
>>> I have a Steppir, too but it's in the clear. Best of luck.
>>>
>>> Ed NI6S
>>>
>>> Joe <joe@wd0m.com> wrote:
>>> My 4L SteppIR is at treetop level - on a 55 foot tower. I've worked 307
>>> entities in about 4 years - SWR is flat across the bands, including 40,
>>> and 30M is about 1.5 or so to 1. A SteppIR will work wonders, and the
>>> tower height should of little impact.
>>>
>>> Good luck!
>>>
>>>
>>>
>>>
>> _______________________________________________
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>>
>
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