[BC] RF absorption by foliage

[DHultsman5@aol.com]

In a message dated 10/30/2005 11:54:48 PM Central Standard Time,  
ET at Munn-Reese.com writes:

Dave:

That's a good guess.  I've seen carrier nulling on  many arrays with tight 
nulls.  But this is different.  This  happens with dead carrier.  When your 
in the area where this happens  it makes no difference what station you tune 
in.  You can dial up any  Detroit, Toledo, Monroe station and watch the 
meter bounce up and hold  then bounce down and hold.  WJR is Non-directional 
and I seen it  happen on their signal.  It will do it for hours and then it 
just  quits and may not come back for hour or days.

ET


This  problem usually occurrs when the null is very deep.  As   modulation
>occurrs the power in the sidebands is not nulled as is the  
>carrier  power.  This
>will cause the FIM readings to  appear to jump.




************************************
 
Since it is not occurring with modulation  that quenches my  idea.  As you 
mentioned other stations that do this,  is this all over  or just in the area of 
the stations your are measuring?.
 
Since it also does it on other stations I would suspect a two-way radio  
transmission line on a water tower or building within 3-4 miles of the  array.  It 
is probably moving in the wind or may be getting a good ground  only when 
keyed up.  If it accurate to time to the second, (On-Off),   any type electrical 
bill board or sign in the 50 kW field.  
 
Can you use your field set an re-orient when the change occurrs to  determine 
where it may be coming from.
 
Sounds like broadband re-radiation of some type.
 
The incident I mentioned was the 12 tower array in Dallas.  We really  
concentrating on the power in major lobe as well as our three major nulls.   We were 
also looking for any additional losses and the jumping of the field set  in 
such a random jumps in field readings concerned us that someothing was loose  
in the system or on the radiators.  We in-lined everything with the OIB  trying 
to find a like jump in current and nothing,  We checked every  mechanical 
connection in the system by several persons including myself several  times.
 
Finally Ted Giles was looking at the array and explained the jumping in the  
major null.
 
It was that way for the first few years.  You are correct the audio  
distortion was terrible even with 7 mV/m.
 
Dave
 
from Scranton, PA 
on the way to SBE/PAB in Hershey