On 12/26/2011 3:02 PM, Cqtestk4xs@aol.com wrote:
> ...and some food for thought. For those of us who live in wooded areas
> where all the trees lose their leaves for the winter and go dormant, is this
> less of a problem in the winter than the summer? Less moisture in the tree
> when it's winter? Just asking, any biologists out there?
>
> Bill KH7XS/K4XS
>
I've had antennas of many configurations in and above the trees.
> 1) Some trees DO absorb RF, and the absorption (loss) increases with
> frequency.
Most green (Deciduous trees) follow this pattern and disappear in winter.
> 2) The absorption (loss) seems to be greatest for straight vertical
> trees (pines, firs, redwoods)
I can easily eliminate two of those here in Michigan. The firs don't
seem to bother from much more than a few wave lengths...or less.
I have a 80 meter sloper at 60 deg that runs through several of the
deciduous trees and ends about 6 ft off the ground and the same distance
from a pine.
A 40 meter sloper when installed in the same spot ends much farther from
the pine, but still has one side of the dipole running right through the
large tree with no apparent effect summer of winter.
>
> 3) The absorption (loss) seems to be greater for vertically polarized
> signals
Which makes sense as most of those trees are vertical unlike the
deciduous which run in all directions although the trunk is more or less
vertical, but usually on the short side...but not always. We have Ash
trees that are a very dense wood that when trimmed look like a very
large flag pole or ships mast and unbelievably heavy.
Unfortunately we have "the Emerald Ash Borer" which can kill on in a
matter of days. So there are a lot of those ships mast around here and
our wood is quarantined.
A 20 foot stump is likely to weight over a ton and be no more than a
foot across at the top...maybe 18 to 20 inches at the bottom. It's an
extremely dense wood. The larva work under the bark so the core that's
left after the bark falls off would make one whale of a antenna support.
It'd probably outlast the pulley and rope by several times.
>
> 4) The closer the antenna is to the tree(s) the greater the loss
>
> When I say "dense redwood forest," I'm talking about trees that are
> typically 3-6 ft in diameter at their base, 100 - 175 ft tall, and often
> within 10-15 ft of each other. it's quite common for a very old (tall)
> tree to be surrounded by three or four younger (shorter) trees only a
> few feet away. It took me four years to find a place I could turn a
> 3-el SteppIr.
Most of the trees around here are "trash" and very fast growing. The
woods behind and to the North of our yard will grow up and die within
about 10 years, resulting in a lot of dead falls. Were I younger (and in
a lot better shape) I'd be out there cleaning out the dead stuff for my
neighbor who burns wood.
Actually the first 100 feet was a cleared lot when we moved here. Now I
have to work to keep the woods from encroaching on my yard. Ah,
well...the healthy ones to the West make good supports for the ends of
the 75 meter sloper fan dipoles. I have an AV640 mounted at 24 feet, in
the NW corner of the yard about 30 feet from a maple to the East, 50
feet from a large Oak to the NNW and just lots of *stuff* to the West.
They do not seem to make any difference whether winter or summer. OTOH I
seem to have picked up many new resonances (apparently related to coax
length) for each band and adjusting the stubs is out and out confusing
compared to when it was mounted on a 32 foot tower at the end of the
shop. It worked better at 32 feet than at 40 and it worked much better
at 40 than it does out at the end of an additional 100 feet of coax.
I've run LMR 400 direct, LMR-400 to the remote antenna switch at the
tower and even LMR-600 with the results being roughly the same AND it's
been like this with two different AV640's. I finally gave up and
purchased a new one and it acts exactly like the older one which has
lived a rough life.
> After living here nearly six years, I have six wire antennas suspended
> by trees, all of them up about 110 ft. I also have a SteppIR at 120 ft,
> monobanders for 20M at 45 ft, 15M at 35 ft, and 10M at 20 ft. The
> horizontal antennas all work well.
With a tribander at 40 feet or 100 feet the trees seem to make no
difference.
They do affect both 144 and 440 noticeably and the difference between
summer and winter is like night and day.
I've never tried the 7L 6-mter Yagi below the tops of the trees which
are generally between 70 and 80 feet.
>
> The only vertical that works well is an 86 ft Tee vertical for 160M with
> about 70 radials that vary in length from 70 ft to about 120 ft. I've
> tried resonant quarter-wave verticals on 80 and 40 over the same set of
> radials, and they don't work well. The 160 vertical is near the middle
> of my clearing (roughly an acre), and it seems to work OK. My tower is
> not in that clearing, surrounded by the dense forest, and I've tried
> loading wires hanging on it on 160M. NEC says it should have a few dB of
> gain relative to the Tee vertical, but the Tee Vertical outperforms it
> on transmit, and by more than a few dB. I have a 40M end-fed vertical
> dipole hanging in a redwood from a pulley at the 110 ft level, perhaps
> 10 ft away from the tree at the low end of the antenna. It works, sort
> of, but it's close to being a dummy load compared to the two horizontal
> dipoles at 110 ft.
I have a Diamond, duoband (repeater?) antenna mounted at 16 feet on the
North side of the shop and very close to the trees along with a row of
pines which seems to work fine, but I only use it for the repeater and
short haul simplex. I have another of the same make and model side
mounted at the 50 foot level on the 45G It seems to hear well and I
occasionally use it on simplex. There is a low ridge about a 1/4 mile
to the West of me, but it seems to hear well right through the trees at
that distance.
I did have stacked 11's on 440 and 12's on 144 for DFing and passing
info to the NWS. They can not hear either vertical.
>
> I have a loaded vertical for 2M and 440 sitting on a 20 ft mast just
> outside my shack, also near the center of my clearing, that I use to
> work repeaters. It's got about 3dBi on 2M and 6dBi on 440. I can't work
> much on 440, due to a lot of absorption from the trees. I can work a
> little more on 2M. The local DX club has a repeater that's about 17 air
> miles from me that I can bring up with 150W, but my signal strength is
> far too low to talk it. So I bought a 22ft long Yagi for 2M about 15
> dBi, mounted it vertically on the side of my short tower that is also
> surrounded by close-in trees, and pointed it to that repeater. It can't
> even bring up that repeater. Next I stuck a short 5-el Yagi designed
> for vertical mounting (about 9dBi) on a 20 ft mast near the shack, in
> the clearing. It can work the repeater, and while I'm still noisy into
> it, I can talk it.
>
> Virtually NO cell phones work up here in the forest.
There are probably close to a dozen cell towers within 10 miles, maybe
more. I counted recently but have already forgotten the number.
So getting cell phone service is no problem except for one carrier
(forget which but it's not the one I use). My cell phone gets full
signal inside my shop which is lined with bonded barn metal. HT doesn't
even do much on the local repeater which is just over 5 miles.
> Several years ago,
> I read anecdotal reports from a tech who was responsible for installing
> cell systems in the pine forests of the American southeast, and he also
> reported very strong absorption (high loss) for his systems. My
> neighbor WA6NMF, an engineer who has considerable experience with UHF
> and microwave systems, says "Jim, at cell phone frequencies, think -3dB
> per tree."
We had the small satellite dish on a 20' mast at the South end of the
house. Worked great for some years and then poor signal. The neighbor
to the South has some of those ornamental firs that get about 30 feet
tall and only a few feet across. One had grown up in front of the dish,
so I moved the dish to the 20 foot level on the 45G at the NW corner of
the garage. worked great for some years. THEN the big willow tree in the
the neighbor's yard to the West of the first neighbor grew high enough
to partially block the signal. Looks like I'm going to need to raise
that dish another 10 or 20 feet. Most of the time it's good, but rain
or snow on the willow turns it into a brick wall for satellite signals.
73
Roger (K8RI)
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