But there are better ones, as the MV
contains some principle deficiencies.
From the coax only the inner part is connected and the brain is left open.
This is wrong in principle, as the 50 Ohm coax "sees" no 50 Ohm termination
and consequently is searching one.
If a coax is not terminated with its proper load, one calls this a mismatch.
In order that a wave can leave an antenna, the radiating pole needs a counter
poise. As this one is explicitely not available in the MV, the outer part of
the coax begins to swing and searches a counter poise.
According to the setup, a way is found to the ground (capacitive) and a
ground current is flowing. Depending on the environment, this way has
more or less restistance in which power is burned.
This process also causes a heavy load on the coax, and consequently,
unnecessary power is lost in the coax.
2. Coax back current choke
In order to allow the coax to swing, after a length of coax a choke (current balun)
is inserted into the feeding coax.
The impedance at this point is very high, as a high voltage is required to
permit sufficient ground current to develop. The impedance is in the
order of kiloOhms.
The resulting high RF voltage causes high losses in the current choke.
Furthermore, the layout of the separated
coax is tricky, as it
has to compensate the mismatch in order to obtain an approximate
match to the transmitter.
Sources of loss
The three main sources of loss (besides the obvious copper losses) are:
- unnecessary ground current losses
- Coax losses due to unterminated coax end
- Losses in current choke
By constructing an antenna which prevents all the above mentioned losses
one arrives at a much more efficient construction.
The above deficiencies are one side of the explantion, why the new HB9ABX
antenna is radiating more efficiently.
The improvement in comparison to the "improved MV-500" is in the order of
a factor 10, that means, that the HB9ABX antenna produces in the average
a 9 to 10 dB stronger signal, as confirmed by field tests.
Felix Meyer, 22.Juli 2005