By Mike, G3JVL
The G3JVL 6M ground plane vertical is a compact antenna that
is ideal for portable operations. It packs away into a small bag
only 1.3 metres long which is an ideal size for hand-baggage on
aircraft.
Although a little engineering work is required, it well within
the abilities of the home workshop and all you newly licensed
amateurs!
The vertical itself is constructed out of four overlapping
sections of aluminium tube whose sizes are given in the diagram
opposite. The four tubes are meant to telescope so wall thickness
should be chosen to achieve this. In practice, 16swg or 1.6mm
might be OK but 18swg or 1.2mm will easily fit. The lengths are
held in place by three stainless steel self-tapping screws.
The vertical is bottom-loaded with a coil wound on an insulated
former (nylon or similar material - it is not too critical at
50MHz). - the former is 130mm long with the top 20mm turned so it
can be inserted into the bottom section of the vertical. The
loading coil consists of ten turns of 16swg (1.6mm) diameter
copper wire with one end connected to the bottom section of the
vertical with a machine screw and the other end connected to the
ground plate. A tap at 5-turns is connected to the input PL-259
socket.
 |
The construction of the 6m vertical antenna |
The four ground plane elements are Constructed from 1250mm
long, 9.5mm (3/8") diameter aluminium tube. These are
mounted to the base plate by the use of eight stainless steel
machine screws. This arrangement allows easy disassembly.
The vertical itself is supported by a piece of 350mm by 50mm x
4mm aluminium plate bent into a 'U' shape. The bottom section of
the vertical is insulated by a turned piece of nylon or similar
tubing. If you do not have access to a lathe any other insulating
arrangement should suffice so long as it is robust.
The overall length of the vertical is 3950mm including the
loading coil. The top section should be trimmed to set the centre
frequency. If the VSWR at resonance is not close to 1:1 then
alter the position of the tap on the loading coil (remember,
changing this will alter the resonance of the antenna!).
Once completed give the whole assembly several coats of varnish
to keep out the weather.
