[BC] Conductivity vs Skywave

[DANA PUOPOLO]

Plus you must consider we're talking electrical length here. Physical length
is usually less then electrical due to the area of the tower. An example is
WEEI in Boston. They use 180 degree towers. Unfortunately, they also have 10
foot faces. This makes their electrical length more then the physical one.
It's also why you hear a lot of seclective fading at night on this station
about 30-50 miles from the transmitter. The towers (due to their area) are
more like 5/8 wave electrically. The high angle skywave produced bounces right
back to earth and cancells out the groundwave. We calculated that if they
removed about 50 feet from the tower, this problem would likely disappear. Of
course, the daytime signal would suffer due to the drop in tower gain (1/2 vs
5/8 wave).

-D



------ Original Message ------
Received: Sun, 15 May 2005 12:23:14 PM PDT
From: "Richard Fry" <rfry at adams.net>
To: "Broadcast List" <broadcast at radiolists.net>
Subject: [BC] Conductivity vs Skywave

Peter Haas:
>195 degrees, the average over all U.S. ND-U Class As, gives
> about 400 mV/m/kW at 1 km.  A Franklin gives about
> 510 mV/m/kW at 1 km.

By your numbers (and mine), a Franklin produces 2.1 dB more field strength 
in the horizontal plane than a 195? radiator.  As I posted earlier, this may

not be enough difference in groundwave field at the receiver/listener level 
to justify the costs needed to install and maintain a Franklin.

BTW, from data I checked the average radiator height for all U.S. ND-U Class 
As is about 188.8?.

>As the horizontal field increases with height, the vertical field
>decreases. Then the vertical field begins to increase again at 180
>degrees.

This depends on the radiator height and elevation angle being considered. 
For example, radiators with heights between 180? and 225? have less 
elevation (vertical) field than a 180? radiator at elevation angles ranging 
from about 15? to 50? (all over a perfect earth).

RF 



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