[NLRS] Is there published data on tree foliage ...

[Rolf Krogstad]

Thanks for the correction, Donn.

Another example of why the math teachers always insisted we show all of our
steps!

Rolf  NR0T



On Fri, Jul 11, 2014 at 12:02 PM, Donn, WA2VOI <wa2voi at mninter.net> wrote:

> I think you made error in reading/writting, Rolf.  You show "432^.03,"
> where it should be 432^0.3 !  Your math is correct for the value you used;
> with the "correct" value, the answer is ~1.1 meters, or about 42 inches.
>
> Does that look better ?
>
> As for what "foliage" means, the example that Bulletin 70 states is
> "...for a penetration of 10 meters (which is a single large tree, or two in
> tandem)..."
>
> Helps ?
>
> 73 Donn
> WA2VOI/0
>
>
> ----- Original Message ----- From: "Rolf Krogstad" <
> rolf.krogstad at gmail.com>
> To: "Jon Platt" <w0zq at aol.com>
> Cc: <nlrs at mailman.qth.net>
> Sent: Friday, July 11, 2014 4:11 PM
> Subject: Re: [NLRS] Is there published data on tree foliage ...
>
>
>
>>
>> This is interesting.  What is the mystery here to me is what is meant by
>> foliage, or the variable R.
>> If we assume, that Jon's numbers derive from Donn's formula, which may or
>> may not be valid, we can calculate for R.  Let's use 432 MHz in the
>> example:
>>
>> 432^.03 = approx. 1.2
>> so .2 * 1.2 * R^0.6 = .09 db (from Jon's table)
>> R^0.6 = .375
>> R = approx. .195 meters
>> .195 for us non-metric types is about 7.7 inches.
>>
>> This exercise has still left me confused.
>> Does that mean the total width of the foliage if stacked and compressed is
>> 7.7 inches?
>> How does one apply that to real life?
>>
>> 73
>> Rolf   NR0T
>> EN34it
>>
>>
>> ======================================================
>> Donn, WA2VOI wrote:
>>
>> Foliage loss
>> L(dB)= 0.2 * f^0.3 *R^0.6
>> where: f = MHz
>> R= depth of foliage (in meters)
>> Valid for 200 - 95,000 MHz
>> Depth of foliage R < 400m
>> ======================================================
>>
>> On Fri, Jul 11, 2014 at 8:00 AM, Jon Platt via NLRS <nlrs at mailman.qth.net
>> >
>> wrote:
>>
>>
>>>
>>>
>>> Another source of interest is ITU-R P.833-5 titled Attenuation In
>>> Vegetation.   The paper does include a table that shows "attenuation
>>> through woodlands" in dB/m vs frequency.   In their work they found a
>>> different attenuation rate for vertical vs horizontal polarization below
>>> 1
>>> GHz stating that this was perhaps due to trees trunk.
>>>
>>> Here are some eyeballed values off the table.
>>>
>>> Freq            -----  dB/m ------
>>>   50            0.01 (H)    0.03 (V)
>>> 144            0.03 (H)    0.06 (V)
>>> 432            0.09 (H)    0.15 (V)
>>> 1 GHz          0.2
>>> 10 GHz        2
>>> 24 GHz        5
>>>
>>> No comments on wet vs dry but they do say these are ball park numbers
>>> that
>>> vary significantly based on the type of trees and whether they are leafed
>>> out or bare.   Also they talk about increased attenuation when they are
>>> moving due to wind  ..... foliage movement increases attenuation.
>>>
>>> 73, Jon
>>> W0ZQ
>>>
>>>
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