Quote:
Why are looking at a flat panel directional antenna when you want a
omnidirectional antenna?
Mikek
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First sorry that i forgot to attach the picture of my tower, it's attached now in this RAR File :
http://www.mediafire.com/?cse8yiyn5d4jtd9 .
I'm Forced to use panel antenna cause the person i'm buying the antenna from told me that my tower specs can handle nothing but a panel antenna to get the desired coverage cause if i use another system of antenna the tower will make a shadow to the transmitted signal and that's an information i don't trust, the panel antennas are so expensive and heavy for shipping so i'm asking for a replacement for those antenna that will work with my tower and gets me an omni-directional coverage.
can you verify this information?
Quote:
You might be able to use a simple sleeve dipole, ground plane, or suchlike
at the top of the mast if that's vacant and you can get an antenna that's
happy to work as the lightning finial, but the antenna gain will be low to
the intended service area; possibly less than 0 dBd, particularly in the
case of a ground-plane antenna (upward-tilted VRP: radiation pattern in
the vertical plane). For police communication at similar frequencies in
the UK, four two-element yagis around a pole were used at the top of the
structure, the pole actining as the finial. Usually, two such arrays were
stacked vertically. The small radius of such an array gives a good omni
HRP (radiation pattern in the horizontal plane).
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Unfortunately i'm renting a place in the tower which is 80 m high and the parameters of the tower at 96 m high is 2.5m x 2.5m so it's not gonna be small in radius for the antenna system.
Quote:
A service area of 60 km^2 would have a radius of 4.4 km if it were
circular - is yours? The required ERP depends on the required minimum
field strength at the limit of service. For simple spherical spreading,
taking no account of antenna VRPs and reflections/multipath,
E=(7/r)sqrt(ERP) ... which can be found in ITU texts and is easy to derive
from first principles ... so if you were to use, for example, a minimum
field strength of 5 mV/m (stereo, in a large city with lots of sources of
interference, using low-gain receiving antennas) at r=4.4 km, then
ERP=9.9W. If your service area isn't circular, say it extends out to 10
km in one direction, then to achieve 5 mV/m at 10 km would require ERP =
51.0 watts. A 600 watt transmitter into an antenna system with a net gain
of, say -3 dBd (accounting for VRP, HRP ripples, and
combiner/feeder/power-splitter loss), would provide an ERP of 300 watts
so, in the latter case, a margin of 7.7 dB. This would provide some
resilience to multipath fading (although P-P=0, no matter how large P
is!). In other words, you probably wouldn't need a higher-powered
transmitter in this case - but it does depend on the shape of the service
area, and on your definition of 'service'.
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Ok let us Stick to the 600w transmitter, i'm not an expert in waves calculations glad to have such help from you, you can see exactly the picture of the tower and the position of it in this RAR FILE
http://www.mediafire.com/?cse8yiyn5d4jtd9 , attached also a placemark from google earth for the tower location in the city, Benghazi's surface has a lot of area exposed to the sea at the north west, and there are hills at the south east, i only want to cover the residental area in between which is a cicule of 15 km of radius, getting a wrong pattern antenna will waste most of my signal into the sea, please recommend me an antenna system which works with the 600w transmitter and the tower specs i mentioned ( tower angle 4 leg (leg size = 10 x 10), parameter at 96 m height = 2.5m x 2.5m ) and also for the geographical charecteristics of the city and also want to get use of the gain of the antenna i will get to strength the signal ( my tower is the one at the left )
thanks in advance