Radio Havana Cuba

Dxers Unlimited's mid week edition 16-17 October 2007

By Arnie Coro

radio amateur CO2KK

Hi amigos radioaficionados around the world and orbiting the Earth,
because, yes, there are radio amateurs in space at this moment, and they
do communicate with hams using 2 meters band equipment aboard the
International Space Station... I am Arnie Coro , radio amateur CO2KK ,
host of this twice weekly program and someone that has had the unique
opportunity of talking to cosmonauts orbiting the Earth... a unique
experience amigos, and one of the more than 81 ways of enjoying our
wonderful radio hobby: space amateur radio communications.... Item two:
zero, zero, zero, one after the other is the result obtained by Solar
Observatories around the world that monitor the number and
characteristics of sunspots... Zero sunspots and a solar microwave flux
of below 70 mean that high frequency bands from 20 megaHertz up are
behaving like VHF bands as regards to ionospheric propagation. Simply
there are not enough free electrons available at the ionosphere to send
short wave signals back to Earth on frequencies above 20 megaHertz or so
for 95 percent of the days... An occasional 15 meters amateur band
opening does happen, and one can pick up an international broadcast
station operating on the adjacent 13 meters band, but those band
openings are very short lived.... We must be patient and wait until the
next solar cycle starts and the daily sunspot number and solar flux go
above no less than 20 for the sunspots and 80 to 90 for the solar flux ,
that are the required figures to bring back our much wanted higher
frequency bands amigos...

Stay tuned for more radio hobby related information, coming to you from
Havana , I'll be back with you in a few seconds , after a short break...

.....

This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and
yes amigos, we do QSL , we do verify reception reports with beautiful
QSL cards... send your reception reports to arnie@rhc.cu, or VIA AIR
MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba... and here is now
item three of the mid week edition of the program.

Our technical topics section, that is rapidly competing with ASK ARNIE
and the HF plus low band VHF Propagation update and forecast in
listener's popularity... The technical topics today is about the design
criteria for an optimized homebrew receiver, using the lowest parts
count that is still consistent with good overall performance. I have
been working on two such receivers during the past several weeks, as
they will be part of the radio amateurs academy training program now in
progress at my Plaza Radio Club here in Havana, where we have joined
efforts with the nearby Cerro Radio Club to provide training for the
newcomers to the radio amateur hobby that will soon be taking the ham
radio license test, required to own and operate an amateur radio station.

Receiver prototype one, is an all solid state design, using locally
available parts and components, and like in the case of receiver
prototype two, that is a hybrid vacuum tubes and transistors radio, no
attempt has been made to miniaturize the sets. A lot of nice open space
where to work with the soldering iron, parts well separated from each
other, and the printed circuit designs using wide strips of copper for
interconnecting the components. This design philosophy leads to very
easy to build by the newcomers radios... receivers that can be also
easily modified to add new features, and the most important thing of
all, these two prototypes provide very good reception within the
frequency range from 500 kiloHertz all the way up to the 50 megaHertz or
6 meters amateur band. But again, no attempt was made to provide
bandswitching using conventional multiposition switches to select the
tuned circuits, instead a much more up to date switching arrangement
using saturated transistors is used...

Prototype one, the all solid state receiver, follows a modular design
criteria, that starts with the power supply, the first item that the
newcomer assembles and tests under the supervision of the instructor.
This power supply is based on a locally plentiful power transformer, and
the voltage regulator used can provide up to 2.5 amperes at 13.8 volts,
so that it can also be used, in the future, to power a QRP or low power
amateur radio transmitter. Taking into consideration the locally
available components, this power supply can be considered as a basic

building block that the newcomer to the hobby can use both for operating
his receivers and transceivers, as well as for doing a lot of
experiments with different circuits. The power supply can be later
modified to provide variable output voltage, as well as several lower
voltages that may be required for other equipment like a CW keyer

or an external audio filter.

The building blocks concept has proven to be a very nice approach,
because during the radio and electronic lessons, we assemble one unit
and test it in front of the class. For example, the input signal
attenuator, bandpass tuneable filter and radio frequency amplifier
module has become the de facto standard to add as an outboard accesory
to portable solid state receivers, that lack adequate input selectivity.
A simple demonstration of the improvement to a Sony ICF7600 D receiver
to which the prototype RF input module was connected by means of a short
length of 50 ohms coaxial cable showed a great improvement in reception
, especially within the frequency range of 5 to 12 megaHertz, where at
this particular

phase of the solar cycle are the most used . The presence of super power
international broadcast stations is one of the problems that makes
reception difficult with those radio receivers that have a very poor
front end design. And, just to provide a bit more of information, the
use of the basic RF signal attenuator, bandpass tuneable filter and RF
amplifier module with a more sophisticated receiver, also proved to be
worthwhile, because the tendency by designers is to use fixed tuned
input filters that are switched when the bands are changed, in contrast
with my receiver prototype that offers the user the possibility of
having a sharply selective tuneable input filter .

In an upcoming edition I will be describing the third module of the
solid state receiver prototype, the double balanced broadband mixer and
first local oscillator.

Now Dxers Unlimited's mid week edition will continue with another
popular section of the program; Antenna Topics, coming up in a few
seconds ...

..........

You are listening to Radio Havana Cuba's twice weekly radio hobby
program, and here is now our Antenna Topics section that today will be
devoted to feedback from listeners that are experimenting with the
double spiral loaded dipoles , following the design ideas of Petlowany
and Tektorian... Spiral end loading of antennas is nothing new at all,
and it has been used by low frequency stations that for obvious reasons
could not make use of the extremely high masts or towers required to
achieve resonance at the quarter wave of a wavelength.

By adding simple top capacitive loading , the so called UMBRELLA
antennas have made possible rather efficient radiators at frequencies

as low as the long wave AM broadcast band still used in Europe, Africa
and Asia, but that was never brought into use in the Americas.

The spiral top loading is a stept further, that adds both capacitive and
inductive loading to the antenna, but that does require a rather complex
mechanical arrangement... But until very recently that type of loading
was not experimented with dipole antennas. The latest version of these
spirals end loaded dipoles is the so called TAK ANTENNA, that according
to its designer is able to achieve a very

high radiation efficiency with a very short horizontal length .A 40
meters band TAK Antenna is claimed to have more than 80 percent of the
efficiency of a full size antenna, while requiring only about three
meters of horizontal space for its installation.

Reviews by top antenna experts are very favorable to both the Petlowany
and TAK spiral end loaded antennas, but there is just one objetion
about their use, and that is that they are narrow band systems, in other
words they provide a reasonable good match at a center operating
frequency, and then if you need to move up or down in frequency, the
standing wave ratio goes up very fast.

Nevertheless these spiral loaded antennas are an excellent option for
radio amateurs that are very short of space to install their antenna
systems, and are of particular interest at this phase of the solar cycle

when the higher frequency bands, where smaller antennas can be used, are
absolutely useless due to the extremely low solar activity.

The basic spiral loaded dipole uses two large diameter wire spirals that
have a bit more than a quarter wavelength of wire wound in about 7 to 10
turns with proper spacing between turns. The matching is done on site,
on an experimental basis, by moving a feed wire along the spirals to
find the lowest possible standing wave ratio...

Again these are narrowband antennas, but you can understand how useful
they are, when you realize that a 40 meters band TAK TENNA is less than
three meters long, as compared to the 20 meters length required by a
full size wire dipole !!!

.......

Now here is ASK ARNIE, la numero uno, the most popular section of Dxers
Unlimited according to your e-mail messages, letters , postcards and
phone calls amigos... Today I will be answering a question sent by
listener Claire from Indiana, USA. Claire wants to know why she can't
listen to an otherwise strong and in the clear

short wave signal when she is using her hair dryer.... and she even adds
that she has borrowed one from a neighbor and exactly the same

type of buzzing noise erase the short wave station she was listening to.
The answer amiga Claire, is that hair dryers, and blenders, as well as
fish tank pumps, and many other home appliances generate wide

band radio frequency noise that interferes with short wave reception.

The hair dryers, kitchen mixers and blenders are particularly noisy
because they use a type of electric motor that use carbon brushes to

feed electricity to the motor's rotor, and very small sparks jump across
causing the generation of radio frequency energy, exactly as it was done
by the first primitive radio telegraph transmitters, the so called

SPARK TRANSMITTERS, that had to be banned because they generated wide
band noise all over the radio frequency spectrum !!!

.....

And now amigos as always at the end of the program when I am here in
Havana, get ready to copy Arnie Coro's HF plus low band VHF propagation
update and forecast.. Solar activity continues at extremely low levels,
with the effective sunspot numer ESN at just four units Tuesday at 15
hours UTC. The geomagnetic field is also extremely quiet too, and the
maximum useable frequency curve is a very slow starter after local
sunrise, reaching only about 18 to 20 megaHertz at the best times of the
day... According to solar scientists we will have to wait at least one
more year to see a significant improvement on short wave propagation
conditions amigos !!!

Hope to have you all listening next Saturday and Sunday UTC days

to the weekend edition of Dxers Unlimited !!! Same time, same short wave
frequencies, same world wide web connection, same satellite feed you are
picking us up.