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[HCDX] RE; Dxers Unlimited´s weekend edition for 3-4 May 2008
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@xxxxxx> 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 !!!
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