S: Soil resistivity, ohm-metres
Which item to input if antenna is on
a roof?
----------------------------------------------

If it's corrugated iron then enter 0, Sea water or Very good.
If it's timber then enter 500 or Very Poor.

---------------------------------------------

H: Height of ends, metres ......
Is it the height from feedpoint
and the roof or from feedpoint
and ground?

------------------------------------------

Nothing to do with feedpoint.

The 'ends of the wire' are the ends of the wire.

Height of the ends above ground level is the height of the ends above the
roof - which so far as the antenna is concerned IS the ground.

Raise the height of the ends by 1 metre and the whole triangular shape,
including the apex, increases in height by 1 metre. That way you have
nothing to worry about. The length of the dipole and the apex angle remain
unchanged.

To vary the apex angle, vary the straight-line distance between the dipole
ends and the dipole length will remain unchanged.

Input variables can be swept by up/down keyboard keys between their extreme
values. All can be done in a second or two.

Set the apex angle to 180 degrees and you have the performance of an
ordinary 1/2-wave resonant dipole with its feedline, either coax, ladderline
or open wire.
---
Reg