For the antenna design you need two located near to each other heater
pipes. The pipes make a substitute open two ‘wire’ line. The line
is radiated by itself however if you are lucky and the substitute
open two ‘wire’ line is terminated on something that can be an
antenna (such case is not rare at all) the WHAS will work very
Use an ATU with symmetrical output for the design. Other versa, if you
have an ATU with unbalance output, find from experiments to which
tube need to connect the ATU ground. For better work the WHAS
install ferrite rings (5- 20 ring with any permeability) at two
ends of the coaxial cable going from TX to ATU.
Direct Feed WHAS
Direct feed WHAS has efficiency less the two above described WHAS but
this one is very easy to design.
Use direct feed WHAS if you can not use the two above described WHAS.
Fig. 3 shows the design of direct feed WHAS. Design
of the direct feed WHAS is simple. A clamp, which should provide
good electric connection, put on a pipe at any place. An ATU output
is connected to the clamp. A counterpoise of 5- 10 meters in length
is connected to the ‘Ground’ of the ATU through known device ‘Artificial