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FACTS ABOUT GAIN Gain is an
important specification with many variables to take into consideration.
Any qualified RF engineer (and the FCC) will tell you the standard for
this measurement is referenced against the gain of a half wave dipole.
Here is where it gets complicated with FM broadcast and typical multi bay
antenna installations. The dipole exhibits it's best gain when mounted in
an environment that is unobstructed by it's means of support. Such as the
horizontal dipole supported by it's ends with insulators and fed through
the correct matching network for impedance and matching to unbalanced
coaxial cable. Under these circumstances, this is the standard for what is
considered "unity gain" or 0 dbd. Here is what none of the big
manufacturers want to tell you. Lets say you take a four bay vertical
dipole array for FM broadcast use at an LPFM station with a 100 foot
tower. The manufacturer has told you the system has a gain of 6 dbd. In
the real world there are many things affecting this ideal gain because of
how the array must be spaced and side mounted on the tower, driven with RF
through power dividers, and tuned to equal resonance in all bays.
With
the metal tower directly in line with the bays, this distorts the
radiation pattern and effects gain. Some people know this and make the
best of the situation by placing the bays on the side of the tower where
the most coverage is desired. The tower effects the RF in at least three
major ways. First it blocks some RF in the direction where the tower
blocks the view of the antenna. Second, it reflects some (but not all) of
this energy back in the opposite direction of the tower. Third is that the
tower absorbs some RF energy because it is a non resonant, metallic object
that is grounded. This is where the tower differs from a resonant,
parasitic element that would be an efficient reflector. Then there is the VHF
power divider. Three power dividers are used to drive four bays and they
claim to have absolutely no loss with all of those connectors in the feed
line, or at least nothing is mentioned of any. Don't forget your bottom
bay is going to be 45 feet lower then the top of your tower. This is
critical at the LPFM installation since that bottom bay is only able to
make use of little more then half of your tower height. Lowering the
entire center of radiation and signal penetration.
When
compared to the half wave dipole standard, the Dominator has a true gain
of 3 dbd or 5.15 dbi. This is a power gain of two times the applied RF. So
if you have a 100 watt ERP you need to feed the antenna with 50 watts (not
calculating coax loss). When compared to the four bays side mounted on the
tower with a claimed gain of 6 dbd, a single Dominator at the top of the
tower provides the same coverage area as the four bays with a
true omni directional radiation pattern. This is unheard of in all other
Commercial FM broadcast antennas due to their required side mounting. The
Dominators unusually long .82 wavelength design emits an intense narrow
beam of low angle radiation on the horizon. Combined with it's single
radiation point being located at the top of the tower, gives it unmatched
performance by any other antenna and is why we claim it performs as effective
as the 6 dbd four bay system.
Having conducted business through the web for over five years I've personally seen some manufacturers make ridiculous claims and at times had people tell me the same without ever testing our product. It's not too hard to type something that sounds good to make a sale. It's an entirely different matter to develop an antenna that performs up to the standards required to carry the Norwalk Electronics guarantee. We put our money where our mouth is and stand behind the Dominator antenna 100%. Within 30 days of receiving your Dominator antenna, if for any reason you find it was not as advertised or did not live up to the claims we make here, simply send it back for a refund of your purchase price! Whether you're an LPFM operator needing a simple and powerful antenna, or running a 50 KW class B planning ahead for the time an effective backup antenna will save the day, the Dominator will exceed most expectations.
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