VK3MO KYNETON CALLING
Visiting Ian (VK3MO) at his home in
Kyneton Victoria and witnessing the completion of his new 60metre
tower.
Published in the WANSAC (Western
& Northern Suburbs Amateur Radio Club) monthly club magazine
Vol 38 Issue July 2007
http://www.wansarc.org.au/
VK3MO Kyneton Calling by Peter Miles
Twice in the last month I have had the pleasure
of meeting Ian Williams VK3MO and his family whom as it turns out is
a cousin of my wife. Small world! As many in the amateur radio
community know, Ian is major player in the 20 metre band DX seen and
operated one of the worlds leading antenna systems in Kyneton.
Unfortunately the antenna systems including the famous rotatable
mast and its four stacked cubical quad antennas were destroyed by an
uncharacteristic serve storm.
My first visit in late May 2007 coincided with
installation of the second of the four, five
element 20metre band mono-band yagi antennas on the newly replaced
60metre (200') rotatable mast. This is the most impressive amateur
radio antenna system I have ever seen and that includes the
internet!
The first of the below photos is Ian preparing
to climb the mast to attach the yagi. The
antenna is being hauled into position by a rope with pulleys at the
top and bottom of the mast which is attached to a truck in the next
paddock being operated by John VK3VN. The second of the photos is
yours truly (That would be the red pixel just below the second yagi)
at the 150 foot level. At this time my wife,
Colleen
yelled up that it was time to go! I responded just give me fifteen
minutes to climb down.
Oddly enough with the ladder on the inside of
the tower I did not feel overly height exposed and it only took a
short while to feel comfortable and move around and well enjoy the
view!
Ian works fast and by my second visit two weeks
later all the antennae were installed and he was well into
installing the cabling.
The below group of photos show the complete
installation with a house for scale. The guy cables are Kevlar as steel wire even with sectionalising insulators would distort
the ideal radiation pattern of the yagi antennas. The guys are
secured to sections of railway track concreted 3 metres into the
ground.
The
antenna switching system results in any one of the Yagi antennas
being operated as a single antenna or they can be operated as a
phased array.
The effect of the ground on the various yagi
antennas results in a slightly differing take off angle for each
antenna and this may at times manifest its self as multi-path
distortion for the receiving station. But when using a single yagi
there is the opportunity to select the antenna with the optimum take
off angle of radiation to target a particular station or location in
the world.
Facts
and Figures
Antenna
mast height: 60mtr (200ft)
All
the tower sections have an 80mm face, but the leg diameters reduce.
The lower sections use 50mm solid bar and reduce gradually to 37mm
diameter on the upper sections) Total weight of the tower is 6000kg.
Each of the guy ring assemblies weights 200kg
The
mast is designed to be self supporting. This means that the mast
could have been assembled on the ground and then lifted into
position. For economic reasons the first half of the mast was lifted
into position by local crane operator and the final half of the mast
was lifted into position by a large 200' crane brought in from
Melbourne
.
Antennas:
4 five element 20metre band mono-band yagi antennas 44ft booms
Antenna
switching: Each antenna can be switched in separately or all four
can be feed in phase.
Rotator
motor: 240VAC, single phase 3/4 Horse with a double worm gear box.
Antenna
mast can rotate 360 degrees in about a minute.
Mast
guys are 14mm diameter Kevlar with a polyester jacket to provide UV
protection. Breaking load is 8000kg with low stretch.
Feed
line and phasing harness are 1/2" heliax
Yagi
antennas were designed for optimum performance using EZNEC Pro
Software.
Total
Array gain is 20dBi @ 6.1 degrees. The vertical beam width is
7 degrees with -3dB points of 3degrees and 10 degrees.
Antenna
switched with vacuum relays

As I say, Ian works
fast and the last report I got was that as of Monday (11/06/2007) it
is all connected and seems to performing well with good VSWR for all
antenna combinations.
I found this comment
on a
UK
amateur radio newsgroup: uk.radio.amateur
Anyone
who's every heard Ian, VK3MO on 14MHz ssb, using 1 watt to his
stacked
beams knows that output power is not everything.
....
he's usually S9 on whatever power he's using... the answer lies in
the antenna., as we all know.
Peter,
G3PHO
Ian's antenna
system is a truly impressive engineering achievement.
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