News Digest 1997-2000
Excerpts from VK1 News Broadcasts
Compiled by Waldis Jirgens, VK1WJ
Latest Update: December 5, 2012.
Antennas for The ACT
VHF Propagation Depending on WX
EWWA Countries List
Do you think to rotate a Satellite Antenna array in azimuth and
elevation costs and arm and a leg? Think again. To rotate two
crossed yagis in elevation a simple TV antenna rotator is strong
enough. In azimuth just add a horse-bridle like rope contraption
around a support at the mast, run it to the shack door, and Bob's
Mode A Receiving Loop
Jim, NU0C passed along a nice construction idea for a mode A RX
loop. He suggests to "check with your local CB crowd and see if you
can find anyone with a busted-up 'Moonraker 4' antenna." Jim says it
looks to be fairly rugged, and should work well flipped over on its
side as the framework for a RS-13 style 10-metre loop with a single
Rod VK2BQJ suggests: For yagis try Aluminium TIG rods. 5mm is a
standard size. Your friendly welding shop usually has these loose.
Not quite as stiff as 3/16" tube but quite satisfactory.
And while on the subject of things aluminium, try Techni-2000
aluminium brazing rods and make an all metal aluminium array.
Working temperature around 400 centigrade. An LPG gas torch is
satisfactory but an LPG-oxy torch is better. Oxy-acetylene is too
hot, unless a very big job and TIGing is probably more in order. No
flux is required, just a conventional brushing of the job with a
stainless steel wire brush. If you have tried all the rest, try this
material. Is total magic. Is a fraction the price of AluTin 51, and
while the latter can be quite successfully worked with a very very
hot iron, it must be coated with preferably a two pack polyurethane
to prevent erosion of the alloy. Not a problem with Techni-2000.
WIA SA Division
The Wireless Institute of Australia (SA Division) Equipment Supply
Committee catalogue is now back on-line. At the moment, only the
kits have been placed in the catalogue, but the components will
follow shortly. You can access the catalogue at:
The catalogue will be updated bi-monthly. It's well worth a look!
Currently most of the kits are VHF/UHF related.
Antennas for The ACT
In the ACT all structures (except TV antennas) which are more than 5
metres high have to be approved by the Canberra local government.
This also applies for wire antennas for Amateur Radio use. In our
view this is a ridiculous situation. We from the News Team will
present in the news a new section: "Antennas for The ACT", which
will show ways around this restriction.
New info: The mentioned
restriction applies only in areas with underground powerlines!
effective broadband antenna for VHF/UHF/SHF is the simplified horn
radiator. It consists of 2 sheets of metal, each forming an
equilateral triangle. The length of the sides should be at least
half a wavelength at the lowest frequency used. The 2 sheets are
mounted like 2 opposing sides of a pyramid, just not touching at
the apex, which is the feedpoint. Maximum radiation occurs towards
the base of the pyramid. The input impedance at the lowest
frequency is around 380 Ohms, slightly increasing with frequency.
This antenna can be used with increasing gain throughout the
VHF/UHF spectrum, without any resonance gaps. Thus it is the ideal
TV antenna and works also on the various VHF/UHF amateur bands.
Gains claimed are 7 DBD at the lowest frequency, rapidly
increasing. A prototype with 2.5 m side length, the sides made out
of chickenwire with 2cm gaps showed a gain of 16 DBD on 2 m. It
should be noted, that for UHF and SHF the wire-mesh is
unsatisfactory, and the antenna should be full metal. I myself use
a 40 cm side length version of this antenna for UHF TV reception
with excellent results. Being a TV antenna, this aerial does not
fall under the 5 m maximum height law!
A very low profile antenna is the DDRR.
Contrary to what the name suggests, it was NOT invented in the
former East-Germany, but stands for "Directional Discontinuity
Ring Radiator". It is a thick radiator, a bit less than a quarter
wavelength long, that forms a very short vertical portion topped
with a coil with 1 winding only. Thus it can be viewed as an
extreme form of the "Rubber Duck". The end of the radiator is
grounded. It is fed via a gamma match without the series
capacitor. Overall height above ground is, wait for it, 0.00875
lambda, that is 17.5 cm on 20 metres and only 1.4 metres on 160
metres. The thickness of the radiator varies. it is around 1/1000
of the wavelength, make it a bit thicker on VHF/UHF and a bit
thinner on the low hf bands. The feedpoint for the gamma match
must be determined experimentally, 0.002 lambda into the
horizontal portion is a rough guide. At the high voltage end of
the antenna a very high quality capacitor is used to resonate the
antenna at the desired frequency (that's why the radiator length
had to be shorter than a quarter wavelength). Values for the
capacitor range between 5 pF on 2 metres and 150 pF on 160 metres.
Of course if you can tolerate narrow bandwidth (like 50 kHz on 40
metres), you can dispense with the capacitor and lengthen the
radiator slightly. Needless to say, that the antenna needs
excellent ground. A sheet of chickenwire extending well beyond the
ring is the minimum. Construction details can be found in the ARRL
Antenna Book (14th edition). This news is being radiated using 3
watts power and a DDRR antenna on 2 metres. If you like some maths
to calculate your own DDRR antenna, here is a formula for the
inductance of a single turn loop (which is the basic ingredient
for a DDRR): L = Mu0*R*(ln(8*R/r)-2) where R = loop radius in
metres, r = wire radius in metres, ln = natural logarithm, i.e.
the logarithm to base e, Mu0 = 4*pi*10**(-7) = 1.26 microH/m
Contributed by: Ruud, PA2RHB @ PI8WFL
This is a more conventional
antenna form, a dually loaded shortened quarter wave. It consists
of a vertical section, which is loaded by a coil, and an
umbrella-like top, that constitutes top loading via a capacitive
hat. Thus it resembles a Hills Hoist or a big mushroom.
The dimensions will depend on the following:
1. The inductance of the loading coil (the more L, the shorter the
2. The placement of the coil (the further down, the shorter the
3. The size and shape of the capacitive hat (the higher its
capacity towards ground, the shorter the aerial).
The ARRL Antenna book 14th edition shows a 40 m antenna being 1.80
m in height with a hat diameter of 2.10 m (8 spokes of 1.05 m
length each, connected by wire at the outside). The loading coil
is near the top. The vertical section is insulated against ground.
An L/C network is used for impedance matching. The system is
placed on a small ground mounted metal disk with 60 radials
attached to it. These run just above ground.
1. It is simpler to ground the antenna and couple the cable via a
gamma match (forget about the series capacitor - it is
2. Instead of the 60 radials a mat of chicken-wire could be used -
the bigger the better.
3. The loading coil could be brought closer to ground, decreasing
the number of turns required. Be however aware, that the coil must
be of very high quality wire. The closer to ground it is, the
higher the currents induced will be. The efficiency is claimed to
approach a full size vertical. The bandwidth is relatively narrow:
50 Khz on 40 m for an SWR of 1.5 or less. Again it must be
stressed, that the dimensions given are not binding, and can be
adapted to suit your local environment. To gain maximum bandwidth,
use as much height as possible. To gain maximum performance, use
the best ground (radial) system feasible.
Tonight we will focus on a quite conventional antenna: The loaded
vertical. As you will recall, the DDRR and the Mushroom antenna both
fall into this category. The DDRR can be viewed as a one-loop
loading coil on top of a very small vertical section, whereas the
Mushroom antenna was doubly loaded: inductively by a coil and
capacitively by a hat. If you take one of the loading elements away,
you have a simple loaded vertical. The coupling to the coax is best
achieved via a gamma match (as mentioned before, if the radiator is
shorter than a quarter wavelength, you can dispense with the series
capacitor in the gamma match).
As with all physically short radiators, an excellent earth is of
utmost importance. A short antenna using a good earth will beat a
full size antenna with a poor earth system hands down! And you even
can compete with hams, who are the proud owners of beams. To
illustrate the point, let's do a little calculation: A normal 3
element 3 band beam may claim 7 DBD gain on 20 metres. If you look
at it closely, you will notice, that the beam is a compromise. Its
radiator is too short for 20 metres, the director and reflector are
too close by, and the rf has to negotiate 12 traps! You can safely
subtract 3 dB from the claimed gain, leaving a real gain of 4 DBD. A
quarter wave vertical, full size over ideal ground, has a gain of 3
DBD. If you use a shortened (say 0.6 full size) loaded vertical, you
might lose 2 dB gain, still giving you 1 DBD. Thus your signal will
be 3 dB down when compared to the beam owner's. This is only just
- Top loading by a capacitive hat can be achieved by various
means: An umbrella like configuration like the one with the
Mushroom antenna. This can be made to slide up or down the
vertical portion, thus enabling to tune the resonance throughout
the band. This is particularly important for short verticals.
Another possibility is to run a horizontal portion of wire at
the top; that's for instance how you can use a 20 metre long
Windom antenna on 80: By using the feedline as a loaded
- Base loading is achieved by a coil at the bottom of the
antenna.As with the Mushroom antenna, this coil must be of very
high quality. My first QSO on 160 ended, when my loading coil
for a 7 metre vertical caught fire! And this with 100 Watts
output only! It is questionable, if putting the loading coil
higher up is of much help: You can get away with a lower quality
coil, however you will have to increase the number of turns
dramatically, the higher you go with the coil.
- Continuous loading can be achieved by using a "rubber duck" on
the hf bands. I have seen a 2 metre long 160 metre antenna. The
bandwidth however will suffer greatly with such a contraption.
So far we have covered the Horn antenna, the DDRR, and various
shortened verticals. These all serve to comply with the ACT rule,
that every non-TV antenna higher than 5 metres needs approval from
the local government. To conclude this series, here now some more
- Horizontal antennas can be hung below 5 metres. On wavelengths
higher than 10 metres this will direct maximum radiation towards
the zenith. This need not be a bad thing; for satellite
communications it's actually useful, also on the 80 and 160
metre bands for local traffic.
- Sometimes a "Raingutter Antenna" works quite well: A wire
attached to your guttering and tuned with an ATU. Contrary to
what some antenna-books suggest, you need not insulate the
downpipes. I used such an antenna for years at my old QTH in
Sydney. The downside is, that it picks up any electrical noise
generated in the house, such as computer-hash, very well. Thus a
small additional vertical for receiving purposes might be
- Various antenna books describe methods of concealing antennas,
like using thin, coloured wire. Well, if such an antenna is
higher than 5 metres, you will still legally require a permit,
though it might take longer to catch you, if you haven't got
one. Thus we cannot recommend this procedure.
- I tried an indoor antenna whilst staying at a Motel in Morwell
in VK3 and worked stations from VK2, VK4 and VK5 on 80m in SSB
without really trying too hard. Amongst the QSOs was a rag-chew
of over an hour's duration! The trick is to run a wire from the
antenna end of the ATU as high up as possible, say to a curtain
track and drop the end of the wire (possibly rolled up) into a
far corner of the room. As counterweight take a similar length
wire and clamp the far end to something resembling earth, say a
metal window frame. With suitable coupling plugs both wires can
be made out of regular coaxial cable. If you find it impossible
to couple the antenna to the radio, lengthen it, until you can.
Of course this will only work if the motel room does not have a
metal roof. If it has, 80m is out, and you must use higher
bands. Of course it's all the better if you can install such an
antenna at home under the roof!
- If all else fails, there is always portable operation. Get out
in the bush, install temporary antennas, and have more fun than
at home! If you ever have participated in the John Moyle
fieldday, you'll love it. For best results on HF look for a site
with high groundwater level, say next to a river or lake. For
best VHF/UHF results look for mountaintops with little or no
VHF Propagation Depending on WX
Bob, ZL3NE writes:
Gentlemen. For the last four years I have carried out an extensive study
on VHF propagation, here are the results. Now before anyone rushes into
print let me ask them to, " try it out for say twelve months", I am sure
they will be surprised.
I kept a record of every opening, the time of day and the weather
pattern applicable when the opening took place. From an area such as
Auckland, propagation can only cover 180 degrees, and during an average
year, openings should occur on 6 meters, 50 days per year. I set out to
do three years, but after 28 months my permit had been cancelled which
slowed things down a bit, still I had recorded enough openings to make a
51-day average per year, without the last eight months. For the 28
months of the study, the following propagation took place as follows,
6 meters Auckland to VK2 VK3 VK4 ZL4
Along frontal zones ----------40 -----------6 -------57 ------- --
Across frontal zones --------- 3 -----------3 --------4 --------12
Across anticyclones 1024+ ----36 ----------15 -------42 ---------7
Total number days open--------79-----------24-------103 --------19
It was noted that propagation only took place, when one of the following
weather patterns was active in the propagation path.
These produced propagation when the pressure exceeds 1024 hPcls in
summer and 1040 hPcls in winter. Signals can vary from very weak to
quite strong, and depending on the air pressure and air temperature
combination, propagation can reach 1296 MHz. The higher the pressure,
and the hotter the average temperature, the higher the frequency of
Warm and Cold fronts /Ducts.
These are found where the isobars are very close together, such as in
the warm winds preceding warm or cold fronts. They quite often coincide
with jet stream winds, and often contain CB (or thunder). They are
prominent on weather maps shown in the daily papers, TV maps, and in
weather fax maps, even ducts have been displayed there. From these
weather maps, you will be able to pick out the paths of propagation and
see the principles I have shown. Signals can be extremely strong with
2-watt stations being able to contact on 2 meters to 2250 km. As with
the previous mode the higher the temperature, the higher the MUF goes.
With a temperature change of say 10+ degrees. That is, from the warm
side of a front, to the cold side. The angle to cross these fronts is
above 70 degrees, But if the front contains a very active thunderstorm,
then from any angle. Under these conditions, back-scatter is very
prominent with skewed propagation as well.
This year I have been studying, weather types, during which NO
propagation has ever been recorded here. They are: -
1. Anticyclones with air pressures below 1024 hpcls. (Christchurch has
enhancements, which give propagation to 1020 hpcls).
2. Occluded fronts.
Now let us compare this season, Nov, Dec, and January 92 days?
In Auckland, occluded fronts were recorded on 29 days. Openings recorded
Weak anticyclones 1024 hPcls and below, were recorded on 44 days,
Intense anticyclones over 1024 hPcls, recorded on 7 days. Propagation on
all 7 days!
Fronts and tropical cyclones were recorded on 12 days; propagation took
place on all 12. If you wondered why Auckland signals were scarce you
now know why.
Propagation seasons are altered by the sun changing, the air temperature
to air pressure, and the relationship / quantity, of frontal activity.
As an example, an anticyclone in summer of 1025 hPcls with an air
temperature of 30c will produce propagation from VK to ZL, in winter
with an air temperatures of 15 c we need an anticyclone of 1040 hpcls!
See the relationship.
Propagation is always evident here on ten meters before showing up on 50
MHz. Therefore 10-meters can be used as an indicator of when the
propagation is going to open to 50 MHz. and higher. The first indicator
to look for in Northern New Zealand, is the VK2RSY beacon on 28.261 MHz,
it is always in first, and when it reaches S7 on my S meter the
six-meter band is open. From VK2, 3, 5, 7 use the ZL3 beacon on 28.228.
From VK2, 4 use ZL6B on 28.200. Another interesting beacon for me is the
JA5 on 28.264 MHz. When this reaches S7+, six is open to Japan. In all
my findings I have always had 10 meters open first, then 6 meters. When
6 meter signals are S9+, I find 2 meters opens, when 2 meters reaches S7
or above, 70 cm opens.
Could I suggest that an approach be made to your local TV channel with a
request that any major CB activity within 1500 km of your area, or in
any propagation path be shown or announced in their weather maps /
reports. I have done that here, they were surprised anyone was
interested, but were willing to co-operate. Repeatedly I am advised of
CB coming before it provides propagation. May I say, always look ahead,
and try to improve your percentage of opening strikes. This is what
Amateur VHF DX is about.
Gentlemen this is a brief run down on the subject. Take the next year,
and see how you go with it. See if you can increase your number of
contacts, good luck. Bob ZL3NE.
EWWA Countries list
||ZK2 NIUE ISL
||ZK3 TOKELAU ISL.
||ZL NEW ZEALAND
||ZL7 CHATAM ISL.
UNITED ARAB EMIRATES
||ZS SOUTH AFRICA
||ZS8 PRINCE EDWARD & MARION ISL
||3B6 AGALEGA ISL.
PAPUA NEW GUINEA
||3B7 ST BRANDON ISL
||3B8 MAURITIUS ISL
||3B9 RODRIGUEZ ISL.
||3C EQUATORIAL GUINEA
||3C0 PAGALU/ANNOBON ISL.
SAN FELIX & AMBROSIO
TRINIDAD & MARTIN VAZ ISL.
FRANZ JOSEF LAND
||4S SRI LANKA
||4U1ITU UNO GENEVA
||4U1UN UNO NEW YORK
||4W TIMOR EAST
BELAU (WEST CAROLINES)
||5W WESTERN SAMOA
||7O SOCOTRA ISL
COUNCIL OF EUROPE
||9L SIERRA LEONE
||9M2 WEST MALAYSIA
||9M6 EAST MALAYSIA
ST PIERRE & MIQUELON
ST KITTS & NEVIS
AMSTERDAM & ST PAUL Is
WALLIS & FUTUNA
||9Y TRINIDAD & TOBAGO
||AT /VU ANTARCTICA
ISLE OF MAN
COCOS KEELING ISL.
LORD HOWE ISL.
TURK & CAICOS ISL.
SOUTH SANDWICH ISL
ST. ANDRES ISL.
GRENADA & DEPENDENCIES
ST VINCENT & DEPENDENCIES
||YS EL SALVADOR
US VIRGIN/PUERTO RICO
||ZD7 ST HELENA ISL
||ZD8 ASCENCION ISL
||ZD9 TRISTAN DACUNHA & COUGH
||ZF CAYMAN ISL
||ZK1 NORTH COOK
||ZK1 SOUTH COOK
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