VK6RBS Busselton - History Page

Note: Busselton VK6RBS is currently not operational.
Please Read - The Future: - at foot of this page.

VK6RBS Busselton began operation from a site at the Geographe Bay Yacht Club in 1984.

The main purpose is to investigate and provide a warning of the
development of the coastal duct which frequently forms along the
Western Australian coast north to Exmouth, about 1500 Km distant.

It was also arranged that there would be radiation generally to the East
to explore the possible extension of the Great Australian Bight path so commonly
open from the southern coastline of Western Australia towards South Australia.

The site is unusual in that the antennas are located on a 10 metre tower which
is virtually at sea level and only about 50 metres from the water's edge.
This has proved to be no handicap for propagation to the north into the duct,
parallel to the coast in the direction of Perth, Exmouth and Northwest Cape.
Transmitters and Antennas:
The primary source of RF is a transmitter on 144.022 Mhz with a power
output of 40 watts, with associated FSK morse ident and power supply.
This is housed in the Yacht Club storage loft adjacent to the tower.

The 40 watts on 144.022 Mhz is fed up the tower to a 3dB power divider,
with one feed of 20 watts split between a pair of 5 element yagis, one facing
north, the other east. The other 20 watts on 144.022 is fed to a varactor
diode multiplier to 432.066 Mhz, which produces about 10 watts. This in
turn feeds another 3dB power divider, one split feeding about 5 watts to
the 432 Mhz antenna and the other to yet another varactor diode multiplier
to 1296.198 Mhz, producing about 2 watts output. The power dividers
and multipliers are housed in a weathertight box adjacent to the antennas,
so feeder losses on 432 and 1296 Mhz are at a minimum.

The 432 Mhz antenna is a centre fed, three halfwavelength dipole with a
screen back reflector. This produces a three lobed pattern and is oriented
to provide one lobe to the north and one to the east, with the centre lobe
directed towards the city of Bunbury across Geographe Bay.

The 1296 Mhz antenna is a corner reflector directed to the north.

The northerly bearing from Busselton is approximately
at right angles to the local coastline.
Results:
The beacon has proved to be a useful indicator of the state of propagation
between Busselton and Perth. The 144 and 432 Mhz transmissions are
always audible over the 200 Km path, with the signal varying between
scatter levels to free space. The 1296 Mhz signal is not always audible,
but when enhancement occurs the signal level is comparable with the other
outlets. The transmissions have been received over a wide area along the
coast to the north and inland, but reports of extension to the east have not
eventuated. The latter could be attributed to the sea level location.

The beacon outlets have also provided useful propagation indicators to the
viability of the path for 2304 and 3456 Mhz contacts between Perth and Busselton.
Photographs

VK6RBS Transmitter

Antenna tower
The Future:
Despite its economies and efficiencies, an obvious disadvantage of
the multiplying system is the inflexibility of the frequencies resulting.
The present operating frequencies do not 
and cannot conform to the recommended Band Plan.
In addition, the use of FSK with the multiplying system results in
increasing shift in proportion to the multiplication used.

The WA VHF Group therefore propose 
at some time in the near future 
to rebuild the system around separate transmitters.

Initial plans are to close the 144 Mhz frequency, which would be
serviced by VK6RBU and to provide outlets on 432.560,
1296.560 and 2403.560 Mhz at Busselton.
Beacon index