Higher is NOT always better....N4KG
More comments inserted below.
On Tue, 16 Oct 2001 <email@example.com> writes:
> If you have flat terrain you would sure see an big improvement.
> Compare the vertical radiation diagramm for both heights (see the
> chapter "The effects of Ground" in the ARRL Antenna Handbook) and
> you will see the difference.
> For 20 Meters this means:
> 50 ft high (0,75 lambda): a main lobe just right up at 90 degrees -
> this is only usefull for short distances and a waste of power for
> DX. The second lobe is at about 20 degrees, still rather high for DX.
The ground reflection pattern includes a lobe straight up.
The free space pattern of the antenna is focused forward.
The radiated pattern is the vector product of the free space
antenna pattern and the ground reflection pattern.
An MUF of 30 MHz will support takeoff angles up to 24
degrees on 20M. An MUF of 45 MHz (typical midday MUF
at high sunspot levels) will support takeoff angles up to 40
degrees on 20M. N4KG
> 100 ft.high (1,5 lambda): The highest lobe is at 57 degrees, much
> less power at 90 degrees. Your lower lobe is at 10 degrees. That
> sure makes a difference on DX !
> 73s Juergen - OE5CWL
The lobe at 57 degrees will not be supported by the
ionosphere. It is also wasted energy. N4KG
My TH7 at 40 ft has always been stronger to Africa
than my Telrex 3L20 at 75 ft by 6 to 20 dB, even
during Low Sunspot Activity. It is OFTEN stronger
to Europe during the afternoon.
ANY horizontally polarized antenna more than 3/4 WL
above ground will have 2 or more lobes in the vertical
plane with NULLS between those lobes. The way to
fill in those nulls is with a lower antenna whose main
lobe coincides with the NULL in the pattern of the
Bottom Line: It takes HIGH and LOW antennas to
cover ALL the angles supported by the ionosphere.
People with only ONE antenna never seem to "get the picture".
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