Dxers Unlimited
Dxers Unlimited's weekend edition for 3-4 MAY 2008
By Arnie Coro
radio amateur CO2KK
Hi amigos radioaficionados ! Welcome to the weekend edition of Dxers Unlimited,
coming to you from Havana, via short wave and also via the world wide web audio
feed from http://rhc.cu <http://rhc.cu/> in English from 05 to 07 UTC. I am
Arnie Coro, radio amateur CO2KK, your friend here in the beautiful, sunny
capital city of Cuba where the temperature at noon Friday was about 28 degrees
Celsius. At the time that I was digitally recording the show, early morning
Saturday the temperature was at 24 degrees Celsius with the relative humidity at
60 percent… and yes , we were enjoying a beautifully blue sky due to the
presence of a high pressure ridge that may produce a nice tropospheric ducting
opening at any time now.As a matter of fact, this the ideal to go to the beach
and also to generate a good tropo duct opening !!! Now here is item one: My four
diode voltage quadrupler crystal set for AM medium wave broadcast band reception
generated a lot of interest among listeners to the last weekend program, who
asked for more information about this very interesting and super efficient
circuit.The SUPER VOLTAGEQUADRUPLER CRYSTAL SET can be built on top of your
kitchen table in just a few hours, you won´t need special tools and it does not,
I repeat this, it does not use any hard to find electronic components...I have
made two ot them using recycled components and yes it's a nice weekend project
amigos !!! . Stay here until the end of the program because as ALWAYS when I am
in Havana, at the end of the show, have your tape recorder ready for Arnie
Coro's Dxers Unlimited's HF plus 6 meters propagation update and forecast , a
practical guide for optimizing the enjoyment of your radio hobby , be it short
wave listening or amateur radio, or any other of the more than 83 ways we can
enjoy radio !!!
Now at the request of several listeners here is a re-run of the piece about the
very easy to implement modification to linear solid state power supplies....Amigos,
it just took me a few minutes to solder 4 small .01 microfarads or 10,000
picofarads, disk ceramic capacitors in parallel with each of the power solid
state power supply's diode rectifiers... and the hum that was making reception
so uncomfortable for my friend just vanished... As a matter of fact, that's
something I do to each and every linear type of power supply built at my
workshop... each rectifier diode is always wired in parallel with a disk ceramic
capacitor of between 5000 and 10000 picofarads, that is from.005 to .01
microfarads ..., its really a very simple modification for any power supply, and
the results are really amazing, reducing the so called hum modulation problems
to practically zero...I understand that some of the more modern encapsulated
bridge rectifiers have the diode bypass capacitors built in .
Now let´s make it clear the switched mode power supplies, that operate under a
totally different electronic circuits concept, do not usually give you AC hum
problems, but let me warn you all that they are capable of producing some rather
bad interference problems with radio reception, because if the switched mode
power supply is not properly designed and very well shielded, the harmonics, the
multiple frequencies of the switching frequency may leak into your receiver´s
front end, and even reach your outdoor antenna as I have seen in some
particularly bad cases. So, before buying a new power supply for your radio
receivers or amateur radio transceivers, run a very comprehensive check, so as
to be sure that they don´t radiate radio frequency interference that will block
your reception. A few weeks ago an engineer friend of mine was telling me that
conventional linear power supplies with their big, heavy and expensive
transformers are rapidly vanishing from the radio and electronics world, they
are no longer available from manufacturers ,and he added that properly designed,
for a very low radio frequency signature, switched mode power supplies are
unfortunately rather difficult to find among the many types offered by
manufacturers of radio and electronic equipment.
Here is now another edition of the also very popular ANTENNA TOPICS section of
Dxers Unlimited…Just a reminder about the very useful and also easy to homebrew
long ferrite rod antenna for AM medium wave broadcast band reception, easily
made by glueing together two or three ferrite rods so that the overall length of
the antenna is about thirty centimeters long. The extra long ferrite rod antenna
provides much sharper nulls when turned around, and for that reason helps a lot
to add new stations to your broadcast band DX logs. Any antenna that is capable
of providing very sharp nulls is of great help in helping to discriminate
between two or more stations that are operating on the same AM broadcast band
frequency. Just to give you a practical example, here in Havana I can pick up
two stations on 900 kiloHertz during the local evening hours. One is located in
Holguin province of eastern Cuba and carries the Radio Progreso national network
program and the other station is XEW from Mexico City. Using my loop antenna , I
can select one or the other at will, or place the position of the loop so as to
pick up both stations at the same time. The long ferrite rod antenna produces an
even sharper null than my standard 30 centimeters diameter loop, and that´s why
I use it so much when Dxing on the AM broadcast band, one of my favorite ways of
enjoying our hobby, especially now during solar cycle 23´s minimum.
………………
Dxers Unlimited is coming to you from Havana, and yes we do QSL here one hundred
percent... Send your QSL requests to inforhc at enet dot cu <mailto:arnie@rhc.cu>
via E-mail, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba...
And now at the request of several listeners that want to learn more about
broadcast stations using the Tropical Bands that can be picked up in Europe, and
also in North America here is a short list of several stations that were picked
up in Europe during the course of this week…
5035.05khz R.Aparecida ,Aparecida Brazil heard on May 2/ at 2319utc
4955khz R.Cultura Amauta, Huanta Peru also heard on May 2 at 2343utc
4845.20khz R. Cultura. O.T. Manaus Brazil May 3 at 0017utc
4805khz R. Dif do Amazonas ,Manaus Brazil 3/5 0029utc
4790.07khz R. Vision ,Chiclayo Peru 3/5 0043utc
4781.48khz R. Tacana,Tumupasa Bolivia 3/5 0054utc
3250.03khz R. Luz y Vida ,San Luis Honduras 3/5 0110utc
4799.79khz R.Buenas Nuevas,San S. Guatemala 3/5 0233utc
All of them were picked up using a Ten Tech Perseus digital receiver operated by
Belgian Dxer Maurits Van Driessche. Maurits is a very dedicated European
Tropical Band Dxers and he has also picked up some very nice AM broadcast band
DX from Latin America and the Caribbean.
Now here is our next item of this weekend edition of Dxers Unlimited, your
favorite radio hobby program… It´s the technical topics section , that today
will be devoted to providing additional information about masthead UHF TV band
amplifiers that are going to become very important in the near future , when
digital terrestrial TV broadcasts will be replacing the current analog TV
transmissions. For your information, digital UHF and also the VHF band signals
are much more sensitive to low signal levels, in other words, the digital TV
reception suffers from a complete blackout of the screen when the received
signal level goes below a certain value,and that´s why I am forecasting a
renewed interest in the installation of external TV antennas equipped with low
noise masthead pre-amplifiers, as well as the use of low loss high quality
coaxial cable downleads. In contrast with terrestrial analog TV signals that
slowly fade in and out generating a noisy picture, with the typical snow on the
screen, the digital terrestrial TV signals just vanish, they simply disappear
and that is really very annoying for the TV viewer… And more bad news about
digital terrestrial TV … the range of the station´s coverage for providing a
high quality TV service is much smaller than what is presently achieved by the
standard analog TV broadcasts that will be phased out in many countries in favor
of the digital terrestrial TV transmissions. So that´s also bad news for TV
Dxers that are already writing e-mail message telling me about their results
with the already on the air digital terrestrial transmissions. One of them
explained that in order to pick up a reliable signal from one of his favorite TV
stations that is now broadcasting a digital signal, he had to raise the height
of the antenna mast, install a new higher gain antenna and add a low noise high
gain masthead preamplifier as well as changing the coaxial cable downlead for a
much more expensive and lower loss cable.
And now amigos, as always at the end of the program when I am here in Havana,
this is Arnie Coro´s Dxers Unlimited´s HF plus low band VHF propagation update
and forecast. Solar activity is once again at extremely low level, with the
solar flux at 2800 megaHertz registering an ultra low figure of 66 units, that
is the lowest level registered in a long time. We are now enjoying more and more
of the typical late spring and early summer sporadic E layer openings that are
the delight of TV Dxers, FM broadcast band Dxers and of course radio amateurs
that operate on the 12, 10 and 6 meter bands… Hope to have you listening to our
mid week program next Tuesday and Wednesday UTC days amigos, and do remember
that Dxers Unlimited is a labor of love for all radio hobby enthusiasts
worldwide, so if you have any radio related questions just e-mail it to me and
you can be sure that I´ll do my best to answer it as soon as possible… Enjoy the
Sporadic E skip amigos !!! It is one of the most fascinating modes of long
distance radio communications !!!
