Dxers Unlimited's mid week edition for 28-29 July 2009

By Arnie Coro
radio amateur CO2KK

Hi amigos radioaficionados around the world and orbiting Planet Earth!
Welcome to the mid week edition of Dxers Unlimited.
I am Arnie Coro, your host here in sunny Havana, where fortunately the
Atlantic , Caribbean and Gulf of Mexico hurricane season has so far
been a very quiet one...It started on the first day of June, and after
almost sixty days, no significant tropical cyclone event has taken place.
Nevertheless amateur radio operators in the area where the hurricanes may
strike, are keeping their emergency communications nets in alert...
One of the main reasons why amateur radio is so highly regarded by
people living in this part of the world, is because hams are able to
provide instant , highly reliable, energy source independent
communications links when almost all other systems go out of service
due to the extremely high winds, heavy rains, floods and lightnning
strikes of the big thunderstorms that always accompany the tropical
cyclones.

Item two: Sunspot number ZERO, as updated 28 July at 12 hours UTC...
The number of consecutive days without a single sunspot showing up
will be reaching 18 today...But chances are that a new sunspot active
region will be on sight real soon. By the way, just to confirm your
observations about how poor the short wave propagation conditions
are, let me add that during this year 2009, seventy six percent of
the days we have not seen sunspots.
If we go back to the year 2004, when solar cycle 23 began its
downward phase, we have seen no less than 670 days without a single
sunspot in sight.... something that is in contrast with the fact that
according to well documented scientific data, the typical solar minimum
has 485 days without sunspots.
When will the Sun activate solar cycle 24 ? Well amigos that is an
excellent question, that in my opinion no one can come out with an
answer right now...
More radio hobby information coming up in a few seconds when Dxers
Unlimited's mid week edition will continue afer a short break for
station ID.
I am Arnie Coro radio amateur CO2KK in Havana
................................................
You are listening to Radio Havana Cuba, the name of the show is
Dxers Unlimited and here is our next radio hobby related item in
our antenna topics section. It is titled , if you have space for
a single HF antenna, what would be the best possible choice....
Again let me repeat the question that gave title to the antenna
topics section today... If you have space for a single short wave
antenna, what would be your best choice ?
ANSWER: After you do a well documented search you will end up with
quite interesting results ... and all of the really good ones will
take you directly to the need of having a well designed antenna tuner
for the frequency range you want to use, plus the need to use the
lowest possible losses transmission line to connect the antenna to
the tuner.
The fact is that the best possible transmission line , the one with
the lowest losses is the old faithful open wire balanced line....
That provides optimum performance when it is properly made so that
its impedance is between 300 and 500 ohms, with the optimum value
centering around 350 ohms, or to make it more precise, 377 ohms.
A PI network antenna tuner will always outperfom the L type of
tuner and the more common commercially made T type tuners. It is
interesting to notice that the PI network tuners are usually NOT,
and I repeat, NOT available from commercial sources, although they
make use of the same number of components as the typical common T
type tuner sold by many manufacturers of amateur radio equipment.
They are just a coil -inductance- and two identical variable
capacitors -capacitance-, configured to form a PI network.
So , you have now a clear idea of the type of tuner required, as
well as the optimum impedance low loss line .

Now its time to discuss the antennas.
Your options are three ... an inverted L antenna system , simple
to install , but not very efficient, and above all requiring an
extensive and expensive ground system to perform properly ...
In other words, this will be your last option if for some reasons
you are not able to install any of the two following options.
Let's review option TWO, the popular well know Tilted Terminated
Folded Dipole of TTFD broadband antenna.
























The TTFD is somewhat complicated because it does need a type of
terminating resistor with no or almost no inductance , in order
to perform properly.
The so called NON INDUCTIVE resistors are hard to find , but you
can make a nice substitute by connecting a number of common 2 Watt
carbon resistors, in a parallel – series combination in order to
obtain the value of between 800 and 900 ohms, at a dissipation of
between 20 and 30 Watts if your radio is going to operte with
transmitter or transceiver with an OUTPUT power of around 100 Watts.
The TTFD will also need several insulated spreaders to keep the wires
at the correct distance specified by the antenna design.
And, if you can't feed it with balanced line, then it will also
require a balanced to unbalanced radio frequency transformer, so
that it can be few with 75 ohms coaxial line, as recommended by
several antenna experts that have attempted to optimize the TTFD .
Your third option is the FAN DIPOLE....that when properly built is
an excellent broadband antenna system that will last for a long time,
providing coverage of a frequency range between 7 megaHertz and 29
megaHertz. Again when you feed the antenna with low loss air spaced
transmission line, there will still be the need for an antenna tuner,
just as with the other two previous types of antennas reviewed, the L
antenna and the TTFD.
For the typical short wave listener that is also a radio amateur , a
FAN dipole made of 5 wires on each side , that have an overall length
of 7 meters or 23 feet on each side of the dipole, will provide good
performance between seven and twenty nice megaHertz.
This broadband fan dipole design is somewhat complex from a mechanical
point of view, but it is worth every minute spent building and
installing it.
The 350 ohms balanced transmission line is connected to the center of
the dipole, making sure that there is an extremely good and reliable
connection between the five wires on each side of the dipole.
You will also need a specially built assembly that will act as the
center insulator, and each of the 10 wires that form the fan dipole
is finished at its end with a string of 2 high quality Teflon or
glazed ceramica strain type antenna insulators.

The other dimension that must be dealt with when installing a
FAN DIPOLE is the separation of the wires at the end opposite
to the center insulator.
The “classic” FAN DIPOLE uses a three to one ratio... in other
words the wires are evenly spread at their ends with a separation
of a bit more than 2 meters, to be precise 2.30 meters, so the
wires are separated from each other by roughly 60 centimeters,
and let me add that this is not critical at all.
For optimum performance the antenna should be installed between
two masts of towers at a height of no less than 10 meters above
the roof or garden ....
If there is not enough space for a full horizontal installation,
you can still put up the FAN DIPOLE by raising one end at no less
than 15 meters and putting the other end at a height of between 5
and 10 meters, so the antenna will be sloping at an angle.
The center of the antenna must always be at no less than 8 meters
above the ground level for best performance.
After hearing this antenna topics section, or reading it while
cybersurfing, you have surely realized that if there is not enough
space for a full size horizontal dipole antenna resonant on the
80 meters band and configured with two wires on each side, the
antenna that is considered to be almost ideal for both short wave
listening and amateur radio operation on the frequency range between
3 and 22 megaHertz... the second best option is , without any doubts
the 14 meters overall length fan dipole fed with balanced 350 ohms
impedance transmission line.
OH YES... for sure, HF propagation conditions will take a turn for
the better and they will begin to improve by the end of the year....
a very good reason to start thinking about installing a good external
antenna system in order to be able to enjoy the peak of solar cycle 24 !!!
...........
QSL on the air, si amigos, QSL on the air , to listeners in the
South Pacific that are reporting our 6010 kiloHertz English language
broadcast from 05 to 07 hours UTC....
The curtain antenna is beaming to the center of the West Coast of
North America, and obviously our signals doesn't just stop there
providing excellent quality of service to listeners from Northern
Mexico to British Columbia in Canada ... it keeps going and gives
listeners in Australia, New Zealand and Japan, plus many Pacific
Ocean Islands , the opportunity to pick up Radio Havana Cuba all
along the southern hemisphere's winter season !!!
Now our next news item here at Dxers Unlimited's mid week edition.
Yes, it is absolutely true, but not much publicized ... talks are
in progress between amateur radio groups and communications
satellite operators....
The object of the talks is obviously related to the possibility
of an amateur radio satellite, taking a free ride aboard a big
communications satellite to be launched in the near future....
Negotiations so that dream may become true are rather complicated ,
but some of the participants on both sides are optimistic, even
though at this moment this are very informal contacts, not official
talks with a fully documented agenda .
There are not only many technical issues to be analyzed, reviewed
very carefully and implemented, but, as expected the legal and
liability issues are going to require a lot of expertise on the
side of amateur radio.
Anyway , this is not going to happen tomorrow, or even within a
period of two or three years, but in the long run it may become
a wonderful reality. Imagine one or more geostationary amateur
radio satellites in orbit, each covering a huge footprint,
providing access to it from even the most remote locations while
using not too large antennas and low power.
After all, when the first amateur radio satellite went into orbit,
just to reming you about amateur radio satellites, let me add that
thefirst amateur satellite simply named OSCAR-1, Orbiting Satellite
Carrying Amateur Radio, was launched on December 12, 1961, barely
four years after the launch of world's first satellite, Sputnik.
Also it is interesting to learn that OSCAR-1 was the very first s
atellite to be ejected as a secondary payload and subsequently enter
a separate orbit.
And now amigos, as always at the of the show here is Arnie Coro's
Dxers Unlimited's HF plus low band VHF propagation update and forecast.
Yes, you hear it right at the beginning of the program, solar activity
is going through an extended period of NO SUNSPOTS, but, my optical
observation Tuesday morning here, show something quite interesting
on the solar disk that may soon grow into an active sunspot region.
Solar flux at the below 70 unist level, and the daytime maximum useable
frequency curve barely reaching 20 megaHertz on the best paths...
Not very encouraging for amateur radio DX enthusiasts, who must be
monitoring for short skip signals indicating Sporadic E layer openings ...
Hope to have you all listening to the weekend edition od Dxers Unlimited
amigos, and I also ask you all to send your comments about todays program,
radio hobby related questions and signal reports to inforhc at enet dot cu,
or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.

Source: Tilted Terminated Folded Dipole antenna graphic taken from (for more visit the John Conover website) http://www.johncon.com/john/T2fd/