1. Reference Story
rotating extreme antennas
Some 40 kilometres east of the City of Oulu in Northern Fin- magnitude requires soft acceleration at start, soft decelera-
land lies the small village of Arkala. Visitors suddenly come tion at stop and smooth control of the speed while running,
across an unbelievable sight: a forest of high – extremely high and it is difficult to achieve this with a softstarter. Since he
– towers. Welcome to Radio Arcala! has a technical background, Mr Kontas installed and com-
missioned the Vacon AC drive himself. He set the maximum
Radio Arcala started as a hobby and technological research output frequency of the drive to 25 Hz, which means that it
project for the owners, Veijo Kontas (OH6KN) and Juha Hulk- takes about 5 minutes to turn the 40 tonne tower a full 360
ko (OH8NC). The two men are keen amateur radio enthusiasts degrees.
and technology advocates who like things extreme. Today,
their project has reached global dimensions, and Vacon ro- Another extremely important factor is proper earthing of the
tates their biggest antenna. tower and the devices running, for two reasons. Firstly, in
combination with effective LC filters it minimizes the noise
Currently, there are seven extremely high towers ranging generated by the AC drive at low frequencies around 1.8 MHz.
from 42 metres (125 ft) to 105 metres (350 ft) at Radio Arcala. Secondly, when thunderstorms occur - and that is unavoid-
But the real pride is the newest member of the antenna farm, able in the summer - the lightning strikes the 100-metre
a 100-metre high tower that weighs approximately 40,000 kg tower more often than not. However, the Vacon AC drive has
(80,000 lbs). This is the largest rotating tower of its kind in the survived these attacks during its two years of operation with-
world, hosting a 3-element directional antenna for 1.8 MHz, out a scratch. And there have been no interruptions to its op-
a 5-element directional antenna for 3.5 MHz and a stacked erations at all.
4-element directional antenna for 7 MHz. The tower is rotated
by an 11-kW AC motor equipped with an 18 kilowatt high-per- Mr Kontas and Mr Hulkko erected their first radio tower at
formance Vacon NXP AC drive. Arkala in 2003. In 2007, Radio Arcala obtained new members
and became a Finnish high-tech consortium with a 100% fo-
“Choosing the Vacon NXP AC drive for the task was easy, and cus on amateur radio contesting. Activities include coaching
I did not even consider other brands or alternatives. There young talents and enthusiasts, advancing different aspects
were two reasons; firstly, I had previous experience of a of amateur radio technology such as remote operation of ra-
smaller Vacon AC drive running my electrical winch system, dio stations from different parts of the world via the Internet,
and secondly – the unrivalled performance of the Vacon NXP,” studying radio-signal propagation on shortwave frequencies
says Mr Kontas. via the ionosphere, and optimizing the take-off angle perfor-
mance of the antennas, using simulations and real-life ob-
Initially, Mr Kontas considered using a softstarter instead of servations.
an AC drive, but this had drawbacks. A rotating tower of this

2. Amateur radio is the licensed and private use of designated
radio frequency bands, for purposes of private recreation,
non-commercial exchange of messages, experimentation,
self-training, and emergency communication. Amateur radio
stations are issued with a designated call sign to allow iden-
tification of stations. Broadcasting to or communication with
the public with amateur radio equipment is prohibited.
The ionosphere is a shell of electrons and electrically charged
atoms and molecules that surrounds the Earth, stretching
from a height of about 50 km to more than 1000 km. On short-
wave frequencies, the ionosphere is the only means of deliv-
ering radio signals (“bouncing” from the ionosphere down to
ground) to all parts of the globe, at the speed of light.
The 105-metre tower with a weight of approximately
40,000 kg at Radio Arcala, is the largest rotating tower of
its kind in the world. Photo courtesy of Radio Arcala.
Mr Kontas at Radio Arcala. Photo by Jari Perkiömäki.
Vacon Group
Runsorintie 7
65380 Vaasa, Finland
RS000148A
Tel. +358 (0)201 2121
Fax. +358 (0)201 212 205
E-mail vacon@vacon.com
www.vacon.com