At 11:54 17/01/00 -0800, G3KEV wrote:
There is a big difference in the radiation pattern and angle of take off
between a high vertical antenna and a very low antenna given the same rf
power
to the antenna. 1 Watt erp from a dummy load or low horizontal wire is
hardly
the same as 1 Watt erp from a vertical antenna at 120 ft. There is also
the RX
consideration especially on long haul signals. At LF the delivery system ie
ANTENNA is the most important factor. Even with large towers, and high
elaborate antennas, which are still physically small relative to 137 khz
and a
limit of 1W erp, one has to realize the limitations, but at least there
might
be a chance.
Indeed the radiation angle is important. But on longwave we have a very
strong groundwave, so radiation at 0 degrees (or close to that) might be
'bound to the earth' and not participate in the skywave. I am not sure that
a vertical is better for long distance propagation than a long horizontal
wire. Recently DJ9IE is using a horizontal wire (200m long at 15m hight)
and despite the fact that he is at only 200km from me I can notice up to
10dB 'QSB' on his signal at night. Other stations in the 200km range, using
more conventional Marconi antennas do not have this QSB.
73, Rik ON7YD
| 