Barrett wrote:
If I join some extra wire to the ends of the G5RV half size and bring them
down towards the bottom of the 300 Ohm slotted feeder to make a triangle
shape, kept vertical. Would this radiate ok or would it be a waist of time?

The 300 ohm line is a series-section transformer that
works with the G5RVjr antenna feedpoint impedances
encountered on 40m, 20m, 10m, and 6m. If you change
the antenna, you change the antenna feedpoint impedance.
It would be a virtually impossible coincidence if the
same series-matching transformer worked well on a
different antenna.

Is there a modelling program I could buy for HF antennas?

EZNEC is available from www.eznec.com. Before buying,
you can test drive the free demo version which has
a 20 segment limit. EZNEC is a very time efficient
way to learn about antennas.
--
73, Cecil http://www.w5dxp.com