Dxers Unlimited
Dxers Unlimited weekend edition for 17-18 December 2005
By Arnie Coro
Radio Amateur CO2KK

Hi amigos radioaficionados around the world, and today
with a special
hello to a group of students in Canada that listen to
shortwave
and are participating in our station philately program
contest...So hello
Almonte, Ontario , Canada... This today is a good
start of this show that I am dedicating to the 6th grade
students of teacher's Neil Carleton's class, so that they
can get ready for next year's
Dxers Unlimited contests celebrating the 45th anniversary
of Radio
Havana Cuba, that started broadcasting back in 1961...
More about young people learning about the world in which
they
leave by listening to short wave later in today's
program. Item two:
Only two active sunspot regions that are easy to observe
visually
but let me add that both of them are rather small and
have no
significant magnetic development. Also the heliosysmic
technniques
show no relevant sunspots on the farside of the Sun...
So, if no
new and really big sunspot active region develops during
the next
two weeks, we are going to see a period of very low solar
active
that will come together with very low ionospheric
absorption...
in other words, propagation conditions will be very good
to
excellent for the frequency range between 100 kiloHertz
and 5
megaHertz... Item three: More letters coming in from
people that
have changed their computer monitors to solid state flat
screen
units ... they all agree with me that the reduction in
radio frequency
noise reaching their radios is really worthwhile the
extra money
spent in buying the flat screen solid state monitors...It
will take
many years for all cathode ray tube TV type computer
monitors
to come to the end of their useful life... but eventually
some day
in the future that source of RF noise will come to an
end...
Meanwhile, and also talking about RF noise, the so called
BPL
or Broadband over the Power Lines continues to generate a
lot
of controversy among engineers, and not only the
telecommunications
engineers are involved in the discussions... now I see
that power
company engineers are objecting the installation of such
systems
because, by their very own nature they add equipment that
may
break down and reduce the power distribution systems
reliability.
More radio hobby related information coming up in a few
seconds
as Dxers Unlimited's weekend edition continues....
......
Si amigos, this is Radio Havana Cuba, the name of the
show is
Dxers Unlimited, I am Arnie Coro,radio amateur CO2KK your
host
here at this twice weekly show now sending Seasons
Greetings
to our worldwide audience and expecting that all of you
will
have a very nice year 2006... Now today's program item
four:
Selecting the semiconductor diode that will be used in a
crystal radio can make a lot of difference on the
performance
of the set. Not all diodes have the same characteristics,
and
variations on a batch of the same type can prove to be
really outstanding.
My favorite diodes for high performance crystal radios
are , as
expected germanium types, that to the best of my
knowledge are
no longer in production . High quality germanium signal
diodes
do exist, but they may prove hard to find if you have not
kept them
in your parts bins for many years. Sometimes they can be
found at
hamfests at rock bottom prices, because few homebrewers
use
germanium diodes for the projects nowadays. Searching for
the most
sensitive diodes is a time consuming but certainly
rewarding process...
Finding a really sensitive diode can make a lot of
difference on any
crystal radio design, but it is not important at all when
you are using
the diode for AM detection after one or two stages of
radio frequency
amplification, as used in the so called tuned radio
frequency sets.
A digital multimeter is a very useful tool for running a
first screening
of a batch of germanium diodes. You will separate from
the group
those that show the lower forward voltage drop...again,
what you
want to have at hand is a many germanium diodes as
possible with the
lowest forward voltage drop... Then phase two of the test
for the
ones that will make your crystal radio more sensitive
starts...
You can do the test in a very simple way, just by tuning
in to
weak station during the daytime, in order to rule out
propagation
changes on the AM broadcast band ...Tune in to a really
weak
signal and start changing the diodes one by one...
writing down
the difference in audio recovery that you appreciate on
the high
impedance headphones... It is amazing how a well trained
listener
can discriminate between diodes of different
sensitivities...
I mark the diodes with a number and run the test using my
standard HIGH Q crystal radio connected to a rather short
wire
antenna and to ground. In a more objective test, I
measure the
sensitivity of the germanium crystal diodes using a
rather different
method... it requires the use of a high precision high
impedance
voltmeter, and connecting the crystal radio receiver to a
long
wire or T antenna of a large size. This method is very
accurate
as it measures the voltage of the rectified carrier wave
of the station
that the radio is receiving. The higher the voltage
reading, the more
sensitive the crystal diode proves to be.
Another different type of diodes may also be used for
crystal
sets... they are known as hot carrier diodes, but I must
tell you
that I have never experimented with them...
Experimenting with homebrew crystal sets is one of the
more
than 77 ways you and I enjoy this wonderful hobby: Radio
!!!
......

This is the weekend edition of Dxers Unlimited... with
more radio
hobby related information amigos... Our 5965 kiloHertz
frequency
tests continue during this weekend. We are testing a new
100 kW
transmitter that is working with a new omnidirectional
antenna
system. The test is on the air from 00 to 05 UTC, and
the program
that is on the air is in Spanish. If you don't know
Spanish, you
can wait until the top of the hour or the half hour and
pick up
the station's id... "Esta es Radio Habana Cuba ", to be
sure that
what you are listening to is really our test broadcast.
Send your
signal reports and comments directly to me: mail to:
arnie@rhc.cu
again, arnie@rhc.cu, and you can also send an Air Mail
letter or
postcard to Arnie Coro, Radio Havana Cuba, Havana ,
Cuba...
there is no need for PO BOX number or zip code, as my
good
friends at Correos de Cuba, the Cuban postal service,
will
automatically send all correspondence with the name Radio
Havana
Cuba on the envelope to our PO BOX number is Havana,
which
by the way is PO BOX 6240 and the zip code is 10600...
The VHF bands of frequencies allocated to the amateur
radio
service are six meters, four meters and two meters...
corresponding
to 50 megaHertz, 70 megaHertz and 144 megahertz... But
the three of them are not allocated on an equal basis
around the
world... For example, the 70 megaHertz or 4 meters band
is allocated
to amateurs in just a few European countries, 6 meters,
that is
the band that starts at exactly 50 megaHertz , is now
authorized
to the amateurs in many more countries today than five
years ago.
The opening of six meters to ham radio operators in
Europe
is closely linked with the shut down of VHF Television
channels
that are no longer used in the Old Continent , because
they were
replaced with UHF allocations and the increase of cable
TV
and satellite signal distribution systems. The old VHF TV
channels
that were used in Europe since the very early days of
television
in that continent started on frequencies as low as 41
megaHertz,
so the 6 meters amateur band was completely covered by
one
of the TV channels, thus making impossible for the
amateur radio
service to use the frequency range from 50 to 54
megaHertz.
According to what may be considered a worldwide opinion
among
amateur radio associations, the two meters band is the
most
used one of them all... In Europe the band spans from 144
to 146
megaHertz, while in other parts of the world the range of
frequencies
between 146 and 148 megaHertz is also assigned to
amateurs, so
those living in those areas have access to a full four
megaHertz wide
band.
Because of the intensive use of the nearby 140 to 144
megaHertz
and 148 to 174 megaHertz bands for commercial and
government
two way mobile and fixed radio communications systems,
the
cost of amateur two meter band equipment is much lower
when
compared with the cost of ham radios for other bands,and
that's
one of the reasons for the popularity of two meters
worldwide...
If you decide to enter into the wonderful world of
amateur radio
by taking the test required by the telecommunications
administrations
to issue a valid amateur radio license, keep in mind that
your best
option for a beginner's transceiver, is a two meters FM
handie
talkie, that will also prove to be a very useful piece of
equipment
whenever an emergency arrives...
.....
At the begining of today's program I spoke about Neil
Carleton
a Canadian sixth grade teacher and radio amateur that has
achieved excellent results with his students by making
them
learn about short wave listening. For example, no less
than
31 entries to the Radio Havana Cuba's philately contest
with the
topic of space related stamps, have reached here from the
Almonte,
Toronto, Canada, where Neil is teaching to students like
Tiffany Boniface, who is eleven years old.
By the way, Mr Carleton's Grade 6 Class is at Room 22 of
the
R.Tait McKenzie Public School in Almonte, Ontario,
Canada.
It would be an excellent idea if other grade's 5 and 6
teachers
as well as those who teach at junior and senior high
schools to
include an introduction to short wave listening and
amateur radio
into the extracurricular activities plans...following Mr
Carleton's
excellent results in motivating his students.
Geography, languages, Earth Sciences and the
characteristics
of different cultures are among the many topics that can
be
learned in a much better way thanks to our wonderful
hobby
amigos !!!
And now before going QRT here, get ready for tape or
computer audio recording, or just taking notes of our
exclusive
HF plus low band VHF propagation update and forecast...
Solar activity is very low to low, and will continue to
decline
during the next several days if no new sunspot active
regions
develop. Solar wind speed is now very low, at barely 320
kilometers per second and the proton content is also at a
very
low count of 1.5 per cubic centimeter, but this may
change
in a few days when the Earth enters into a high speed
solar
wind generated by a coronal hole now in view. Solar
sunspot
count is now around 45 and moving down. Expect maximum
useable frequencies during the peak daylight hours not
higher
than 25 megaHertz on the best propagation paths.I expect
excellent propagation conditions on the AM long wave and
medium wave bands during the next two days. Be on the
lookout
for possible VHF openings within the frequency range from
28 megaHertz all the way up to the FM broadcast band.
Hope to see have you all listening to the mid week
edition of
Dxers Unlimited next Tuesday and Wednesday UTC days
amigos !!!