>Another repeater in the area had a DB224 mounted about 2'
off the side of a smaller tower about 400 ft up with the dipoles
>arranged omni with reasonable coverage. They went out to about 4'
off the side and pointed the dipoles in towards the tower >inline.
Performance dropped drastically, didn't take long for them to go back to the
other arrangement.
I am
tending more to keep the dipoles set up for omni and go at that. We can
only go up the tower once a year when there is tower maintenance, so we have
to live with the setup a year!
Roger
W5RD
----- Original Message -----
Sent: Sunday, February 12, 2006 12:08
AM
Subject: RE: [Repeater-Builder] dB224 4
bay 220 MHz Antenna on VERY LARGE TOWER face
I
can't speak to 220 Mhz but can provide info on the history of our club 2 meter
repeater at 1200 ft on a triangle TV station tower.
single DB224 on one leg about 2-3' out. mounted straight out form
the point of the leg. Worked great 60-70 miles out where you could
see the antenna but on the opposite side in the shadow of the tower maybe 20
miles range at best. Not a significant different between omni arrangment in
line mounting of dipoles pointed away from the tower.
Three DB224 one on each tower leg dipoles in line pointed away
from the legs antennas close mounted about 4" off the tower leg. You
could hear the repeater well in certain areas on all sides of the tower but
lots of nulls in the pattern. One of which went right across the major
population center. antennas fed in phase with a 3X divider. Bad
news setup.
DB228 close mounted on one leg of the tower about 2" dipoles in line
punted straight out from the point of the triangle. Faces the major
population area. DB224 close mounted on one of the other
tower legs dipoles in line perpendicular to the tower face and pointed
opposite the DB228.
Both antennas fed in phase with a 2X power divider. 70 mile radius
coverage for mobiles no nulls found in pattern. Everyone is happy with the
performance.
As a
side note to another thread it takes 250- 300W Tx power to balance the
repeater Rx coverage for mobiles stations.
Another repeater in the area had a DB224 mounted about 2' off the
side of a smaller tower about 400 ft up with the dipoles arranged omni
with reasonable coverage. They went out to about 4' off the side
and pointed the dipoles in towards the tower inline. Performance
dropped drasticaly, didn't take long for them to go back to the other
arrangement.
John Lock KF0M
Wichita KS
kf0m at arrl dot
net
Monday, I am having this antenna put up on a
triangular tower, whose face is greater than 20 ft. across where the antenna
is going on one leg. I know from years of operation on this tower (or
any tower that is this large), the antenna pattern will have
many nulls around the tower. Does anyone have any experience on
mounting an antenna on a large tower to minimize the nulls? The antenna
will be mounted on a leg (not in the center of the face which may be more
preferably). I have the choice of placing the dipoles equally around the
antenna mast, all facing the tower or all facing away from the tower. Any
suggestions (or does it really matter on a tower of this size)?
Roger W5RD
