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Foliage Attenuation Study

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UPMan

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It comes up every year about this time...

"Everything sounded good yesterday, but suddenly I'm not getting signals on systems that used to be strong."

It doen't explain all causes, but if Spring is here, foliage attenuation can be a significant factor...especially for higher frequencies and / or marginal signals.

Found this study by the military with some attempts to quantify the affects:

http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=ADA055391&Location=U2&doc=GetTRDoc.pdf
 
Last edited:

af5rn

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Joined
Apr 4, 2008
Messages
1,059
Location
N. Tex / S. Fla
Wow, are you reading my mind? Have you got my house bugged? I was just discussing this with my wife last night after coming to the conclusion that we are losing a lot more cell calls at home these days than usual. I came to the conclusion that it must be the foilage, as the side of the house that faces the cell is bordered by a thickly wooded area a good thirty metres wide. Obviously, according to this report, the 1850mhz PCS signals tend to simply bounce right off of that. It's cool to see some validation in print!

Thanks!
 

KR4BD

Member
Joined
Jul 6, 2001
Messages
561
Location
Lexington, KY
Foliage Attenuation is a well-established fact. I notice it particularly on Frequencies above 150 mHz every year. As a ham, I use a lot of frequencies in the 222-225 and 442-450 mHz range and must use more power and/or higher gain attennas to punch through the trees in the area during the spring and summer months.
 

SCPD

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Joined
Feb 24, 2001
Messages
65,126
Location
Virginia
It is now fall and as the leaves descend from the trees one rather distance fire dept dispatch channel is once again starting to come in loud and clear here in Toronto.....very interesting and I bet that's what it is.

It comes up every year about this time...

"Everything sounded good yesterday, but suddenly I'm not getting signals on systems that used to be strong."

It doen't explain all causes, but if Spring is here, foliage attenuation can be a significant factor...especially for higher frequencies and / or marginal signals.

Found this study by the military with some attempts to quantify the affects:

http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=ADA055391&Location=U2&doc=GetTRDoc.pdf
 

Viper43

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Jul 23, 2005
Messages
3,301
A tornado hit my place last May, strange but I didn't loose signals like I normally do in the Spring and summer, maybe it's because 40 of 42 tress hit the ground....... I guess I won't have shade any more but then I won't loose signals either.....

V

It is now fall and as the leaves descend from the trees one rather distance fire dept dispatch channel is once again starting to come in loud and clear here in Toronto.....very interesting and I bet that's what it is.
 

N9JIG

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Far NW Valley
Sort of related...

I once heard that UHF signals don't work well in areas with a lot of pine trees as the needles tend to attenuate the signals. Apparently the needles are a 1/4 wavelength at UHF. Supposedly this was an issue with the Arizona DPS system in the Flagstaff area.

Any truth to this or is it just a myth?
 

jim202

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Messages
2,550
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New Orleans region
Having worked in the cellular field doing design engineering for cell coverage, you bet your
butt that the pine needles effect the coverage. The long needle pines just North of New
Orleans caused the cell sites to be built about every 2.5 to 3 miles apart at a max.

The trees were killing the coverage of the 800 MHz cellular system. The people were
in the NIMBY mode. (not in my back yard) They wanted their cell phones to work, but
didn't want the towers and mono poles to support the cell antennas. Can't have it both
ways. You either get your cell phone to work or you get no towers and no cell service.

The report from Lincoln lab / Hanscome AFB has alot of formulas that most people
couldn't understand even if they had to. When I was doing the computer plots of
the cell site coverage, we use to put in a number for ground clutter. This number
was used by the computer program to figure in the looses due to the trees and leaves.
That number was in the order of 20 db. Actual drive testing was used to refine this
number to make the plots come out.

Jim



Sort of related...

I once heard that UHF signals don't work well in areas with a lot of pine trees as the needles tend to attenuate the signals. Apparently the needles are a 1/4 wavelength at UHF. Supposedly this was an issue with the Arizona DPS system in the Flagstaff area.

Any truth to this or is it just a myth?
 

zz0468

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Joined
Feb 6, 2007
Messages
5,957
Location
175 DME, HEC 358° Radial
Having worked in the cellular field doing design engineering for cell coverage, you bet your
butt that the pine needles effect the coverage. The long needle pines just North of New
Orleans caused the cell sites to be built about every 2.5 to 3 miles apart at a max.

The trees were killing the coverage of the 800 MHz cellular system. The people were
in the NIMBY mode. (not in my back yard) They wanted their cell phones to work, but
didn't want the towers and mono poles to support the cell antennas. Can't have it both
ways. You either get your cell phone to work or you get no towers and no cell service.

The report from Lincoln lab / Hanscome AFB has alot of formulas that most people
couldn't understand even if they had to. When I was doing the computer plots of
the cell site coverage, we use to put in a number for ground clutter. This number
was used by the computer program to figure in the looses due to the trees and leaves.
That number was in the order of 20 db. Actual drive testing was used to refine this
number to make the plots come out.

Jim
I do similar propagation studies, except for public safety and microwave systems. I've come to routinely add about 15-20 db of path loss on 800 MHz and 900 MHz plots to account for various losses. In suburban areas, it's buildings, in mountainous areas, it's trees. The problem with most such software, is it doesn't allow you to develop a figure such as db loss per mile, so we end up with plots that are overly pessimistic in clear areas, and right dead nuts on the money in an amongst the trees. Some programs have land use attenuation tables, but I find the land use data can be pretty out of date.

On a microwave path, one branch of pine needles can add 10 or 15 db of loss at 6 GHz.
 

SCPD

Member
Joined
Feb 24, 2001
Messages
65,126
Location
Virginia
The California Department of Parks and Recreation started the conversion of a low band radio system to a 800 MHz system in the early 80's. They left the northwest coast of the state to be the last in this conversion. A lot of testing found that these high frequencies did not provide the coverage they needed in that area, one with a lot of state park units (beaches, historical sites, redwood state parks, historical sites) and a lot of trees. The northwest coast of California is very similar to western Oregon. They found two repeater pairs in the VHF High band and installed them on just a few more existing sites than they had with use of VHF Low.

Caltrans is struggling with the same area and also left their District 1 as last in the conversion to 800 MHz from a low band system. A review of their FCC licenses really tells the story when you realize how many repeater sites they have.

Pine needles don't fall off in the winter unless you are dealing with Tamaracks and Larch trees, so they are more of a problem than in areas with a predominance of deciduous trees.
 

policefreak

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Location
Berlin, NJ
Just outta curiosity, what is more pernicious to UHF signals, trees (a mixture of oak and pine) or buildings (2 floor dwellings packed closely together)? Where I live I have a UHF digital TRS in the 500's that is about 15 miles from my house and receive marginal signal. It comes in remarkably clear for each frequency only getting between 0-1 bars of power. Yet in the spring I notice I lost the control channel while having it sit up on the windowsil. So now I have my 396 (which sucks at receiving control channels as good as the radio is) up on two big oatmeal containers in the kitchen in front of a cabinet, and I have to make sure I don't turn the TV on. But I'm curious because they just put in a development in back of my house about 3 years ago, clearing some of the trees to do so. Has it help signal, or hurt?
 

ka5lqj

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Joined
Dec 13, 2003
Messages
427
Location
Near Lakeview, LA (Caddo Parish)
Trees & "RF".....

Gentlemen:

Having been a "student" of electromagnetic signals, the art of receiving or transmitting a radio frequency signal, since 1958, when I was 12 years old, I can assure you that in all my research, trees and other foliage *do* make a difference. The only way to eliminate this is to (1) mount the antenna above the offending trees, which leaves you vulnerable to lightning strikes, despite precautions taken. (2) Cut all the trees down for 100 yards in each direction. LOL!

It certainly would be nice to have a home atop a high mountain or butte that afforded us lots of room for tall towers or at least tall, wooden, utility poles to put multitudes of antenna on. But, unfortunately, we are all not Warren Buffett or T.Boone Pickens to purchase land like this. :-( Maybe one day, in HEAVEN, huh?
So, at best we have to compromise and do the best we can.

I live in the city and within 2 blocks of the Trauma Center for this part of Louisiana. There are medical helicopters landing a lot of times. Now, I'm not griping. I know when these "birds" land at L.S.U. Medical Center, someone is in bad shape, and I pray for the patient and the helo crew's safety. The helicopters, a lot of times will fly directly over my home and "hell-bent-for-leather" and rightly so. Due to the low pattern, I'm at a disadvantage to put up a pole or tower much over 40', which is below the trees. Pin oak and Hackberry trees line the three sides, with only a South-facing side open for the street.

So, the best I can do is to erect quads, and "inverted V's" to hear or transmit on as a Ham radio operator. Oh, I forgot to mention the electrical high voltage lines run East/West in the "closed" alley on the back (North) of my property and the "drop" runs half-way up the East fence line, then crosses the property to the back of the house. NOT an ideal place for a longwire, LOL! But, as Dr. "Pill" (It's all about ME!) says, "It is what it is." Hi,Hi.

Even though I'm somewhat 'handi-capped' by my property, this does not discourage me nor deter me from building, erecting, or using various experimental antennas. ;-) I've been an 'experimenter' at heart since I was 12. I've still got some old, ARRL and Radio Engineer's manuals from the 50's, that have "tube" circuits in them that I want to build, someday. There's even circuits for a kW amp for 2 meters and one for 500 watts on 420 mHz, for ssb. Try buying an amp with that kind of power. LOL!

So, in conclusion, don't be discouraged if the signals aren't coming in during the Spring & Summer with the "antenna farm" you have. Try "rolling-your-own", to see if you can't improve your signal catching. You don't necessarily need a metal-working shop to drill, form, tap, etc. for antenna parts. You'd really be surprised at what you can do, if you put your mind to it. And, as always, DON'T put up antennas of any kind near ANY power lines, period. Wire antennas especially. By "transformer action", they will induce a voltage and current in the antenna and 'knock you on your butt', if not KILL you. :-(

Respectfully submitted,
73,

Don/KA5LQJ

P.S. - Sorry I got so "wordy", but that's just me. ;-)
 

LarryMax

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Joined
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Messages
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Could this be the Sequel to "The Happening" Instead of poisoning us, the trees now take away our cellphones...oh the horror!!
 

UPMan

Uniden Representative
Premium Subscriber
Joined
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Messages
13,287
Location
Arlington, TX
There is unrest in the forest
There is trouble with the trees
For the celllphones want more signals
And the Oaks ignore their pleas...
 

SCPD

Member
Joined
Feb 24, 2001
Messages
65,126
Location
Virginia
Gentlemen:

Having been a "student" of electromagnetic signals, the art of receiving or transmitting a radio frequency signal, since 1958, when I was 12 years old, I can assure you that in all my research, trees and other foliage *do* make a difference. The only way to eliminate this is to (1) mount the antenna above the offending trees, which leaves you vulnerable to lightning strikes, despite precautions taken. (2) Cut all the trees down for 100 yards in each direction. LOL!

It certainly would be nice to have a home atop a high mountain or butte that afforded us lots of room for tall towers or at least tall, wooden, utility poles to put multitudes of antenna on. But, unfortunately, we are all not Warren Buffett or T.Boone Pickens to purchase land like this. :-( Maybe one day, in HEAVEN, huh?
So, at best we have to compromise and do the best we can.

I live in the city and within 2 blocks of the Trauma Center for this part of Louisiana. There are medical helicopters landing a lot of times. Now, I'm not griping. I know when these "birds" land at L.S.U. Medical Center, someone is in bad shape, and I pray for the patient and the helo crew's safety. The helicopters, a lot of times will fly directly over my home and "hell-bent-for-leather" and rightly so. Due to the low pattern, I'm at a disadvantage to put up a pole or tower much over 40', which is below the trees. Pin oak and Hackberry trees line the three sides, with only a South-facing side open for the street.

So, the best I can do is to erect quads, and "inverted V's" to hear or transmit on as a Ham radio operator. Oh, I forgot to mention the electrical high voltage lines run East/West in the "closed" alley on the back (North) of my property and the "drop" runs half-way up the East fence line, then crosses the property to the back of the house. NOT an ideal place for a longwire, LOL! But, as Dr. "Pill" (It's all about ME!) says, "It is what it is." Hi,Hi.

Even though I'm somewhat 'handi-capped' by my property, this does not discourage me nor deter me from building, erecting, or using various experimental antennas. ;-) I've been an 'experimenter' at heart since I was 12. I've still got some old, ARRL and Radio Engineer's manuals from the 50's, that have "tube" circuits in them that I want to build, someday. There's even circuits for a kW amp for 2 meters and one for 500 watts on 420 mHz, for ssb. Try buying an amp with that kind of power. LOL!

So, in conclusion, don't be discouraged if the signals aren't coming in during the Spring & Summer with the "antenna farm" you have. Try "rolling-your-own", to see if you can't improve your signal catching. You don't necessarily need a metal-working shop to drill, form, tap, etc. for antenna parts. You'd really be surprised at what you can do, if you put your mind to it. And, as always, DON'T put up antennas of any kind near ANY power lines, period. Wire antennas especially. By "transformer action", they will induce a voltage and current in the antenna and 'knock you on your butt', if not KILL you. :-(

Respectfully submitted,
73,

Don/KA5LQJ

P.S. - Sorry I got so "wordy", but that's just me. ;-)
In the western U.S. the problem is not confined to just the spring and summer as we are dealing with evergreen conifers rather than broad leafed deciduous trees. The northwest coast of California, and almost halfway into the width of the state is heavily forested with conifers. On the western side of the coast ranges, the forest is quite dense. The 800 MHz systems up there have to have lots of sites and in the case of the State Parks they just gave up. VHF-Hi works quite well for them.
 
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