Larry Banks wrote:
> Hi Jim,
>
> I am moving my station to Maine -- and asked the "QST Doctor" about trees
> and antennas back in January 2007. There is a response in the July 2007 QST
> "The Doctor Is In" column. I also received this correspondence from W3ZZ,
> Gene:
> ------------
> Hi Joel and Larry
>
> Everyone appears to have an opinion on this subject but definitive
> scientific works are more difficult to find -
I can only speak from experience at one location. We don't have a lot
of hardwoods, but we do have a *lot* of "soft wood" and the trees
definitely have a noticable effect on both the verticals and the
horizontal antennas. They are after all, quite conductive. the effect
is much more pronounced in VHF compared to HF and more at UHF than VHF.
>From the upper UHF range and on up they are pretty much opaque to RF
when the sap is flowing. IOW my C-band dish can see right through them
in the colder months, and not even find a signal once the sap starts
flowing in the spring even before the trees are fully leafed out.
> at least on the Internet. From
> a practical observational standpoint, I have found that low band verticals
> particularly 80 and 160 do not seem to be bothered by deciduous hardwood
> trees. However I used these during contests that occurred mainly in the
> colder months though I am reasonably sure that the sap has NOT drained by
> the end of October and I never noticed a difference between late October
> [leaves have turned but half of them are still ON the trees] and February
> [leaves gone and sap drained if it really does drain in MD].
>
>
If the leaves are turning it's likely the sap has stopped flowing as
they are no longer using it.
> ...snip...
>
73
Roger (K8RI)
> The best reference I can give is section 2.3 [on p. 18] in a 1978 paper by
> A.G.Longley at the U.S. Dept. of Commerce.
>
> http://72.14.205.104/search?q=cache:IEqG7929jj4J:www.its.bldrdoc.gov/pub/ot/ot-78-144/complete_report.pdf+radio+wave+attenuation+trees+HF&hl=en&gl=us&ct=clnk&cd=22
>
> That paper and others that I have found agree that avoid trees entirely is
> the best course. Anything at 100 MHz and more is unacceptably attenuated by
> trees with non-deciduous pine trees being somewhat worse than deciduous
> hardwoods. At HF the effect may be quite a bit less noticable. Verticals at
> HF may be more affected but again the difference is only a very few dB more.
> Pine trees at HF are worse for the reasons you have already noted.
>
> ...snip...
>
> Good luck.
>
> 73 Gene W3ZZ
> ------------------------
>
> 73 -- Larry -- W1DYJ
>
>
> ----- Original Message -----
> From: "Jim Brown" <jim@audiosystemsgroup.com>
> To: <towertalk@contesting.com>
> Sent: Sunday, April 05, 2009 8:09 PM
> Subject: Re: [TowerTalk] EZNEC- needs improvement
>
>
>
>> On Sun, 5 Apr 2009 16:00:50 EDT, RLVZ@aol.com wrote:
>>
>>
>>> Yes- do have poor performance with verticals, but you mentioned that you
>>> live in a heavily wooded area. Verticals work poorly in heavily wooded
>>> areas so I don't believe that's a fair environment to compare verticals
>>> to horizontals.
>>>
>> I've looked for published scientific work on this and all I've found
>> addresses VHF/UHF (either military, 2-way, or cellular applications). What
>> I've seen generally agrees that absorption that increases with frequency,
>> and that correlates with my experience. Can you point me to anything that
>> addresses MF or HF in forests and heavy vegetation?
>>
>> 73,
>>
>> Jim K9YC
>>
>>
>> _______________________________________________
>>
>>
>>
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>
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