This VHF antenna was originally constructed as part of the author’s research into the impedance of an elevated groundplane antenna, as set out in the June 1999 issue
of SILICON CHIP. In particular, the author wanted to establish that an impedance matching section (or "Q" section) could be constructed, to match the 52Ω impedance of the feed cable to the
18Ω antenna impedance.
In fact, the finished device has proved to be a completely
practical antenna. It is simple to construct, easy to mount and because it
provides the correct load, it allows the transmitter to generate maximum
This view shows all the pieces of the antenna just before the final assembly. The copper tube forms part of the matching section. The materials used are all readily available and you should be able to scrounge most of the parts for little cost.
This is important because not every transmitting device is
completely safe from mismatch damage. Typical commercial power amplifiers
("afterburners") frequently carry a warning that an SWR above a specified figure
will void the warranty, for example.
A feature of the unit is that the "Q" section is of solid
construction. It makes a substantial "handle" which can be lashed or clamped to
a mast or, if the mast is in tubular form, the "Q" section can sit inside the
mast, along with the coax cable.
Another feature of the unit is the use of screw-on radials
which can be easily detached for transport. In fact, this antenna has proved
extremely useful as a temporary base antenna during WICEN exercises.
Alternatively, as a permanent base station antenna, it would suit any situation
requiring an omnidirectional VHF antenna for 2-metres