Wimpie wrote:

snip

My results (IE3D, now Mentor Graphics Hyperlynx):
Quarter wave radiator over 4 quarter wave radials, no sloping:
impedance at resonance 23 Ohms, Gain at zero elevation: 1.52 dBi

0.625 wave radiator over 4 quarter wave radials, no sloping:
Gain at zero elevation: 1.52 dBi, 2.29 dBi at 20 degr elevation.

And an impedance in the hundreds of Ohms.

0.5 wave radiator over 4 quarter wave radials, no sloping:
Gain at zero elevation: 2.05 dBi.

And an impedance of about 1,000 Ohms.

Quarter wave radiator over 4 quarter wave radials, 45 degrees sloping:
Impedance at resonance 54 Ohms, gain at zero elevation: 1.97 dBi

Quarter wave radiator over 4 quarter wave radials, 85 degrees sloping:
Impedance at resonance 74 Ohms, gain at zero elevation: 2.14 dBi

All in free space, without a mast.

Again, in free space the maximum is ALWAYS at zero elevation.

Adding a mast, especially for the sloping case can give large
deviation depending on the CM impedance as seen from the floating
ground. I did simulations and current measurements for my own mast,
but the results cannot be applied to other configurations.

As I stated before, the difference between the configurations is
hardly measurable. Nice to see that the over-rated 5/8 lambda antenna
doens't perform better then the quarter wave antenna (at low elevation
angle).

I wouldn't call an impedance range of 20 Ohms to 1000 Ohms "hardly
measurable". In real life you have to feed the thing.

Though the design is more demanding, I prefer the half wave option as
you can use less, sloping, shorter radials without running into common
mode mast current problems.

And requires some sort of feed arrangement to transform 1,000 Ohms into
50 Ohms.

In my opinion, dealing with the added complexity of impedance matching,
which is almost always narrow banded, is not worth a dB or two of gain.

I think I will stick with 5% longer radials at 45 deg and some ferrite at
the feed point.



--
Jim Pennino