Re: NEC-LIST: short towers near tall trees

Quoting GrantBingeman_at_cs.com, on Sat 19 Jul 2008 05:53:18 AM PDT:

> I was wondering if anybody knows of any studies of the absorption of RF by
> trees within the near-field of electrically short towers operating
> at the high
> end of the AM broadcast band, for example, a 75 foot tower on 1610 kHz less
> than 50 feet from a 100 foot tall tree-line. Would this impair
> signal intensity
> at 10 miles, say.
>
> A recent question I could not immediately answer, in a similar vein, is "Can
> a tree close to a short antenna act as a lossy parasitic element,
> thus causing
> a directional radiation pattern?" Does anybody have any experience or
> insight with this type of behavior? Thanks. g
>
> p.s: I am familiar with the Viet Nam studies of RF propagation in the jungle.
>
> Grant W. Bingeman, P.E.

There's a fair amount of work from researchers in Brazil, among other
places, on the RF properties of forest/jungle. However, it's all in
the nature of modeling the propagation on a larger scale (i.e. can you
model the forest as a dielectric slab), and a lot of it is at VHF and
higher. (Cavalcante is one author (82,83, 94, 98), Tamir is another,
1967 and 1977)

There might be some literature out there that talks about measuring
the EM properties of a single tree, for use in a model of many trees
for work like the above. I was hunting down something like this in
2004, but didn't find anything particularly useful (lots at mm wave
frequencies, not much at HF)

Jim Lux

-- 
The NEC-List mailing list
NEC-List_at_robomod.net
http://www.robomod.net/mailman/listinfo/nec-list