Topband: Last Ditch

[Tom Rauch]

Hi All,

> Since time immemorial conventional wisdom has it that trees do not
> interfere with radio.  This is what the ARRL has been putting in the
> books for years, and this is the way it should be.

I really haven't seen much one way or another in except in 
microwave discussions. Lewallen (W7EL) and I have discussed 
this at length, and we both concluded there was no real data one 
way or another.  

> My family owns a Green Acres-style summer cabin under a thick stand of 150
> foot tall redwood trees in an area just north of Henry Cowell Redwood
> State Park -- along Hwy 9 out of Santa Cruz, CA.  I've occasionally
> operated from there -- climbing the trees to the 70 foot level to hang
> dipoles.  Redwoods are really easy to climb, if you know how to avoid the
> dead branches.  I've never actually heard the bands switch on and switch
> off while I was there.  But I've operated when the bands were on then
> returned to the rig later to discover the bands had switched off -- and so
> on. 

I have the same effect here, with no trees. The question would be 
how did the bands compare to an antenna in about the same 
location without any trees?

If you have no way to compare that, you have no way to tell what 
effect trees might have.

One valid test would be to install two small reference verticals with 
reasonable grounds (so they are stable with weather) on either side 
of a thick stand of trees that is about to be cleared, and observe 
the FS change when the trees are removed.

My bet is the trees, if close by and thick, mainly have an effect on 
the electric field and can cause some small additional 
attenuation...but will noticeably affect performance if you get the 
strong electric induction field of an antenna into an area of thick 
growth.

That's based on what I see when working with industrial RF heating 
equipment operating at HF where a very strong electric field is 
required to heat wet wood, and FS measurements at AM BCB 
frequencies where there is generally not a large change in 
attenuation rate while on the other side of thick woods while doing 
a proof.

WA4TT's Inverted L antenna was in thick woods and brush, and it 
didn't stop him from working DX with only 800 watts on 160m. He 
was only a little bit behind my 4-square (which is in the clear).
73, Tom W8JI
W8JI@contesting.com