[BC] RF absorption by foliage

[Ed Trombley]

>There was a station in Denver that the consultant swore was affected by a 
>line of trees less than a mile away. When the trees were in full bloom, 
>the pattern went "out" ... and when they dried up, the pattern "settled."


Back when the TVRO thing was a big deal we used to tell clients to plant 
jack pine trees around their dishes to block MCI and AT&T long line 
microwave interference.  There was this microwave tower located at Lacy, 
Michigan that cut a 5 mile wide interference path east and west half way 
between Jackson and Lansing.  Truck & tree spade would plant 6 trees in a 2 
row pattern that made for max pine between LNA and the microwave tower.  It 
worked very good in all seasons.  Building top sites were a different 
problem with a different solution.  Times have changed.  As I travel around 
the country I sometimes note that the dishes are gone but the trees are 
still there and 70 feet high.

Over the last 12 years I've trained a bunch of guys on the proper art of AM 
field measurements.  One of the things I've always told then is that 
measuring on the station side of a large tree will give you a higher 
reading and measuring on the side away will give you a lower reading.  Some 
measurement points require acts of desperation.  Digging a hole, then 
throwing the meter in or measuring under the truck or measuring under the 
road in a large drainage tube is considered by most consultants to be foul 
play.  The trainees always had that look like my wing nut was cross 
threaded.  But at some point in the measurement phase they discover by 
accident the tree thing works.  Its hard to beat a spring time Sugar Maple 
with a sap bucket hanging on it for RF bending qualities.  The dry season 
effect is much less.

Up here in certain parts of Michigan as well as some parts of northern Ohio 
and Indiana big conductivity swings are just a fact of life.  It usually 
happens when the ground is wet from fall rains and freezes for the 
winter.  After the ground is frozen and gets some snow on it the 
conductivities will come down some.  Then the reverse happens in the spring 
and conductivities spike when the frost melts and ground turns into 
mud.  Ask anybody that takes care of a directional array in Down River 
Detroit.  That area around Flat Rock, MI seem to be the worst.

Also around Flat Rock we have another strange anomaly.  I have seen 
locations in the middle of a clear square mile, can't blame it on wires, 
where the FIM read some number, say 1mV and a second later its 5 mV a 
second later its back to 1 mV.  The meter will bounce fast, not slow, but 
fast between two numbers on one second intervals and do it for hours.  On 
some radial heading it will do this for miles along the radial.  There is 
no click or snap in the audio.  It has something to do with the ground 
conductivities.  Sometimes when near a power line the effect goes 
away.  Its the strangest darn thing.  I figure that up in Detroit someplace 
there is a steel mill with an arc furnace that has a ground fault and its 
the AC making it way back to the Nuke plant at Monroe.

And for anybody that's interested.  We just got program test on WFDF, 
Detroit's newest 50 kw array.

Ed Trombley
The well traveled field guy
Munn-Reese, Inc.