Dear Rik,
thank You for your
contribution. Especially your last sentence is interesting for me
because this
may explain the success of MF-stations operating close to the
coast.
Another example for exceptionally high antennas on MF for
me is
DI2AM, located on a museum ship in the harbour of Rostock. I have been
informed
that the antenna has been put up between two masts of 30 meter in
height.
Other favourable conditions are the low ground loss onboard of a ship
and also
the vicinity of water, of course.
In general I do not
have
any objections to Finbar's setup; it shows that effective MF antennas
can be
built up on a rather small area.
But I am not yet
convinced
that height of MF antennas should not matter, and I will continue to
observe the
scenery.
OK?
73 Ha-Jo,
DJ1ZB
"Rik Strobbe" <[email protected]> schrieb:
Dear HaJo,
But in general I feel that
antenna height should not be disregarded. Even with equal ERP sky waves
may develop better from higher aerials.
HW?
I guess that the only cause that 2 antennas fed with the same ERP
produce
different signals is a difference in the (vertical) radiation pattern,
ie. the takeoff angle.
I simulated a 30m, 10m and 3m vertical (at 502kHz) with mmana_gal and
found only very small differences: from 18.2 degrees for the 30m
vertical
to 18.6 degrees for the 3m vertical. This for a uniform ground with a
conductivity of 10mS/m.
Making the ground poor (1mS/m) results in a takeoff angle of about 26
degrees (+/- a few tenths depending on the height).
Increasing the conductivity to 100mS/m reduces the takeoff angle to
12-13
degrees.
73, Rik ON7YD - OR7T
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