Good day all.
Have run into a bit of a problem matching my G5RV's support mast as a
vertical on 20 metres.
The mast is 7.5 metres high and insulated from ground with 4 radials at
ground level but insulated from ground by installation along fence lines.
Obviously a typical 1/4 wave vertical would be ~5.1 metres high, but I
had hopes of base loading the 7.5 metre mast to act as a sort of "short
5/8 wave" vertical on 20. Feed is 50 Ohm coax buried up to the matching box.
After a lot of research both in books and on the web I have found very
little information on the design of an antenna like this.
Anyone had any experience of such an idea?
I have plenty of airspaced inductor stock and TX type capacitors for the
network, and as I usually only run about 150 watts here that shouldn't
be too critical.
Any ideas gratefully received!

73's Cliff Wright ZL1BDA ex G3NIA.