[BC] Directional Antenna Proofs - Ground systems.

[Rene Tetro]

Cowboy wrote:

"I'm not aware of any DA's currently, personally, either, but
I seem to recall that now WNTP and then WZZD was 4 tower elevated
radials at one point...."

That is correct.  WIBG/WZZD Tower 5 did have an elevated ground
screen.  According to the paperwork I have on hand this was done
for two reasons:  

1) The towers are located on a gently sloping hill and tower 5 was
much lower than the others.  It was believed by the engineers in
those days that the elevated ground screen would help increase
stability to the system, particularly the night array which was
very finicky.  Which brings us to....

2) In the night pattern, tower 5 was a negative tower.  Again, the
consultants believed that the elevated ground screen would in this
case increase stability.

It should be noted that the elevated ground screen was did not
stand alone as the ground side of that tower.  It did also have the
standard buried radials around the tower base.  As standard
practice requires, the buried ground screen consisted of 120
radials of 1/4 wavelength, except where they were limited by the
property boundaries.  And, of course, the radials between towers 5
and 4 were bonded to a ground strap where they met at the half-way
point between them.

When one of the towers was dropped in 1986 (the old tower 1,
furthest from the transmitter building) and the array was rebuilt
as a four-tower system, the elevated ground screen on tower 5
(thereafter, tower 4) was removed as it was felt it was unnecessary
in the new array.

Regarding the current system shared by WFIL and WNTP, there are
indeed six towers in place, only one of which is diplexed.  Three
of the four original towers are used exclusively by WNTP.  Two
additional towers that were installed in 1997 are used by WFIL.
The diplexed tower is the original WIBG tower 5, closest to the
transmitter building.  For WNTP it is inline tower #4.  For WFIL it
is a slightly dog-legged Tower 3.  The dog leg is almost
unnoticeable unless you are looking for it, as it is only about 1.5
degrees out of line from WFIL's towers 1 and 2.

By the way, at WNEW-AM (later WBBR) we also had elevated ground
screens around each of the station's four towers.  These, like
WIBG's tower five, were not isolated, but connected to the main
ground system of each tower at the tower bases.

Rene'

Rene' Tetro
Director of Engineering & IT
WNTP-WFIL
Philadelphia