Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited's mid week for 24-25 October 2006
By Arnie Coro
Radio amateur CO2KK

Hi amigos radioaficionados ! Welcome to the mid week edition of Dxers
Unlimited, coming to you when our amigo SOL, 93 million miles away from
us is going through a period of very low activity... As a matter of fact
the latest solar flux figures show near baseline levels, approaching the
minimum detected solar flux of a bit less than 70 units. So, get ready
for really very low ionospheric absorption and much better propagation
conditions
on frequencies from 500 kilohertz to 7 or 8 megaHertz during your local
evening hours , from local sunset to sunrise... More information about
propagation conditions as always at the end of the show.... Item two:
Amateur radio operators worldwide are becoming quite concerned about
alarming lack of activity on the ham bands, especially during
weekdays... during the weekends and especially during the big contests
as the one coming up this next weekend, you can certainly monitor much
more activity
on the favorite DX bands, but still, in my opinion way down from what
used to be heard ten or fifteen years ago... Again, in my opinion, this
lack of activity is to be traced back to the widespread presence of
computers and the availability of Internet services in developed nations
and at the most important cities of less developed countries..., mainly
national capitals. But, surprisingly, every time that there is one of
the big contests
in progress, the HF bands show a tremendous level of activity,
with thousands and thousands of stations trying be among the
winners of the contest.


So, the fact is that there are lots of amateur radio stations in perfect
operating conditions ready to be used, but they are
actually getting less use, because their owners are spending more of
their spare time, the time previously used to be on the air, now used
for operating the computers and surfing the world wide web.
Item three: The amazing four power sources radios are making illiteracy
campaigns possible in remote rural areas, thanks to an training program
created here in Cuba, YO SI PUEDO is the name of the illiteracy
eradication program, that when translated
into English reads YES I CAN... emphasizing the fact that people that
don't know how to read and write can certainly learn even at a
relatively advanced age in life... YO SI PUEDO, the Cuban
training program to help people learn how to read and write using a
combination of printed materials, coaches that help the trainees, and
radio broadcasts is being used successfully
in Haiti, Venezuela and New Zealand among other nations...
Yet another fascinating use for radio broadcasting , that was
made available absolutely free of charge to UNESCO, so that its use may
be extended around the world to help the more
than 800 million inhabitants of Planet Earth that are illiterates. As
you have just heard, radio can play a vitally important role in helping
the world’s illiterate persons learn how to read and write at much lower
cost than any other way.
Item four: Antenna topics... A question... sent in by several
listeners... they all want to know what exactly is meant by an antenna
system often described in advertisements as " A NEST OF DIPOLES" or A
DIPOLES NEST.... so stay tuned here for the answer to this question and
other features at today's mid week edition of Dxers Unlimited...
I am Arnie Coro in Havana, back with you in a few seconds amigos !!!
......


According to our correspondence department statistics, Dxers Unlimited
is among the most popular programs of our station, and the antenna
topics section is ranking always between the second and third place of
the list of more mentioned sections of this show... Today's antenna
topics section combines with LA NUMERO UNO...the number one, YOU HAVE
questions in this feature, aiming at clarifying the concept of " a nest
of dipoles" or a "dipoles nest"...
Si amigos, yes my friends... several antenna manufacturers, especially
those that offer VHF and UHF antennas are promoting an antenna system by
the name of " DIPOLES NESTS", a name given to a certain number of half
wave dipole antennas tuned
to specific frequencies, and connected in parallel at their common feed
point...
The dipoles nests are not exactly a broadband antenna, because each of
the elements has a definite resonant frequency, but in actual practice
staggering the resonant frequencies of a certain
number of half wave dipoles can prove to be a quite useful antenna
system. Although, this is not properly a broadband antenna, like the fan
, conical and biconical dipole elements that have been so well described
in the antenna engineering literature.
For example, amateur radio operators have for a long time now used a
group of between two and four half wave wire dipoles connected in
parallel and fed with a single coaxial cable, typically 50 ohm flexible
coax.
One of the favorite combinations for this ham’s wire version of a
dipole's nest is used for covering the 20, 15 and 10 meter bands, while
another less common system covers 17, 12 and 10 meters.
According to my practical experience , using more than three dipoles is
possible, but interaction between the antennas becomes more of a problem.
Another popular antenna among amateurs is a dipole's nest for 40, 20 and
10 meters, where the 40 meter band antenna is also used as a 15 meters
three half wave in phase element, effectively providing four band
coverage...especially if you happen to have an antenna tuner connected
between the feed line and your amateur radio transceiver. The tuner is
required to match the almost 2 to 1 voltage standing wave ratio
presented by the 40 meters antenna when operating on 15 meters, but for
40 , 20 and 10 meters the three wire antennas can be carefully trimmed
and tuned on site to obtain a voltage standing wave ratio of less than
1.5 to one, which is considered to be perfectly acceptable by most
modern solid state transceivers.
Dipoles nests are sometimes seen at VHF monitoring stations, and those
professional systems may have up to six or even seven dipoles made of
aluminum or copper tubing, connected to a very solidly built center
insulator. But don't try to buy one of those, as they are pretty
expensive, and according to experts it is a much better option to invest
your money in home brewing a broadband conical or cage dipole that will
provide much better performance than the typical very much publicized
" DIPOLES NEST" or NEST OF DIPOLES, whichever way the manufacturers
advertise these antenna systems, that again, are nothing more than a
certain number of half wave dipoles connected in parallel amigos !!!
.....
You are listening to the mid week edition of Dxers Unlimited amigos, a
radio program devoted to the promotion and development of this wonderful
hobby that you and I enjoy so much...
Your radio hobby questions are most welcome ... send them to
arnie@rhc.cu, again arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro, Radio
Havana Cuba, Havana , Cuba...
Here is now our next item of today's program...
One of the more fascinating ways of enjoying this hobby is by using the
most simple equipment ... an upcoming contest calls for the use of a
single active device receiver, be it a vacuum tube, a bipolar transistor
or a field effect transistor... In an upcoming edition of Dxers
Unlimited I will try be broadcasting the rules for this one active
device receiver contest, but in the meantime let me tell you that my
single vacuum tube receiver using a battery
operated 3S4 with a pair of high impedance headphones provides amazingly
good reception . The little radio is powered by a big single 1.3 volts
size D rechargeable cell, and two series connected
9 volts batteries, although adding a third one does improve the output
volume. This little set is a regenerative receiver, and I have built
coils for tuning from the low end of the AM broadcast band up to the 16
meters or 17.5 to 18.0 megaHertz international short wave broadcast
band...The little radio is quite sensitive, and selectivity is also
quite good when the regeneration control is carefully tweaked to put the
detector just at the point that
it will start oscillating...
As you have just heard, this new short wave listening contest is quite a
challenge, and the results, when published will show once again, that
this is a hobby that can bring many nice rewards to both home brewers
and those that enjoy
participating in contests...
......
This is Radio Havana Cuba, the name of the show is Dxers Unlimited, my
e-mail address is arnie@rhc.cu, and the postal mailing address is Arnie
Coro, Radio Havana Cuba, Havana, Cuba... surfing the web for new amateur
radio software a few days ago I came across OLIVIA, yes OLIVIA is the
name of yet another digital communications mode using the Multiple
Frequency Shift Keying system or MFSK,
that makes possible two way contacts while using very low power. OLIVIA
MFSK was first written for the LINUX operating system, but later ported
to WINDOWS. There are already a few ham radio
operators testing the OLIVIA mode on 14.108 kHz, but let me warn you
that OLIVIA MFSK can not be decoded with any other software program than
the one specifically created for operating it.
OLIVIA is yet another variant of the keyboard to keyboard modes that use
computer hardware and software connected to an HF transceiver, of which
at this moment PSK31 continues to be the
most popular one of them all... PSK31 was created by British amateur
Peter Martinez, and has become today's de-facto standard for keyboard to
keyboard communications between amateur radio stations around the world,
because it can be installed in almost any computer and interfacing with
the transceiver is quite easy to implement...
Digital amateur radio communications , one of the more than 80 ways you
and I may have a nice time playing with our radios and now with our
computers too !!!.....
A quick answer to a listener in South Africa… amigo Roland from Cape
town, yes, during the southern hemisphere’s solstice, around the 21’s of
December, during the peak of the summer , you will be experiencing the
peak of the sporadic E propagation season, and according to forecasts,
due to the very low solar activity expected , this may be a nice
sporadic E skip season in your part of the world….
And now amigos , as always at the end of the show here is LA NUMERO DOS,
the second most popular section of Dxers Unlimited... Arnie Coro's Dxers
Unlimited HF plus low band VHF propagation update and forecast...Solar
flux now hovering around 75 units typical levels y seen during solar
minimum years... providing low frequency bands enthusiasts with what I
expect to be excellent propagation for AM medium wave and the Tropical
bands during the next three to five days...The sunspot number moved up
to 50, five zero, and it may continue to move up during the next several
days... see you at the weekend edition of the show amigos, and don't
forget to send me your opinions
about the program and any radio hobby related question that you may have
, send mail to arnie@rhc.cu, and VIA POST send an AIRMAIL postcard to
Arnie Coro, Radio Havana Cuba
Havana, Cuba