Radio Habana Cuba
Dxers Unlimited
Dxers Unlimited's mid week for 27-28 Sept 2005
By Arnie Coro
radio amateur CO2KK
Hi amigos radioaficionados ! Welcome to the mid week edition of Dxers
Unlimited, that is on the air under excellent autumn equinoctial propagation
conditions... DX is plentiful and everyone seems to be enjoying listening to
distant stations on the AM broadcast band, the three tropical now thinly
populated Tropical Broadcast Bands, and the HF bands up to around 25
megaHertz... And you may ask why I am setting a top limit of 25 megaHertz
for the HF band openings, and the reason is no other that there is simply
not enough ionization to support good openings on the ten meters amateur
band...
I am sure that many of you will ask another question, a very logical one
indeed... and that is until when these excellent propagation conditions are
going to last... Well, here goes my answer: Expect enjoying them for no less
than ten weeks or so... But, the real equinoctial propagation conditions
will give way to the wintertime conditions in a swift transition that should
start by the end of October or even a bit earlier.
Item two: Many Cuban amateurs are now developing their digital
communications capabilities, using the proverbial Cuban ingenuity... At a
recent visit to a friend's QTH, I found an old 486 computer happily running
a PSK31 digital keyboard to keyboard mode program... I asked my friend how
he had done it, as the programmers of the software specified that it
required a much faster machine and more RAM memory...
Arnie, he told me, it was a matter of tweaking the software to reduce the
way it loaded the computer... and after several trials, I was able to make
the machine run the digital communications program without freezing up... OH
! I forgot to say that mi amigo, my friend, runs his 486 with a LINUX
distribution for which there are a lot of amateur radio software programs
available. The LINUX is not very user friendly so to speak, but , it is
really a star performer when the resources of the machine are limited, like
in this case...Digital communications systems offer radio amateurs with
hearing disabilities with a unique option to continue enjoying the hobby !!!
Dxers Unlimited's mid week edition will continue in a few seconds, but
before taking the short break, let me ask you to look around for paper and
pen or pencil to write my e-mail and postal address, so that you can send
your comments about this program, to help me make better and better amigos !
Send your e-mail messages to arnie@rhc.cu, or VIA AIR MAIL, send a postcard
to Arnie Coro, Radio Havana Cuba, Havana, Cuba... Now, standby for a short
musical interval.
......
You are listening to Radio Havana Cuba, the name of the show is Dxers
Unlimited, and here is another radio hobby related topic for your enjoyment.
.Funny things happen on the radio from time to time, and among the many
radio frequency incompatibility problems that I have learned about, was one
related to a misterious garage door that opened up and attempted to close
down at a certain rate... The owner of the house called the company that
sold him the garage door opening and closing device, and they sent their
service technician the next day... The technician stopped in front of the
house, and in just a few seconds was almost sure of what was happening...
Just across the street and two houses away he had spotted an amateur radio
antenna system... When he knocked at the door of the client with a smile in
his face, he said that the problem was almost surely caused by the nearby
radio amateur station... In about half an hour, the service technician
placed several radio frequency chokes made from ferrite material, and then
asked the owner of the house to please call the radio amateur neighbor to
run a test. Fortunately the ham operator was at home, and kindly acceded to
start testing on different bands... The automatic garage door device did not
opened and closed as it was doing before, despite the fact that the highly
directional antennas of the ham operator were aiming at the house where the
system was installed... This is a very good example of what is known among
engineers as an electromagnetic compatibility problem. In this case it was
caused by radio frequency energy from the amateur transmitter been picked up
by the receiver that actuates the opening and closing mechanism when a
signal from the transmitter in the car is sent . The misterious door
equipped with the ferrite ring RF chokes no longer started to act strangely,
thanks to the fact that the service techinician that went to try to solve
the problem, was also an amateur radio operator himself !!!
......
Antenna topics... a very popular section of Dxers Unlimited is back here
today... In today's program I will share with you information that came from
amateur radio operators that were providing emergency communications during
the Hurricane Katrina event. They found out that professional communications
systems using broadband TTFD antennas, the well known Tilted Terminated
Folded Dipole antennas, were not as effective as the single band antennas
for the 80 and 40 meters bands, where most of the traffic was routed, due to
the fact that the great majority of 2 meters and 70 centimeters band
repeaters were out of service for one reason or the other... and those
reason ranging from lack of AC powerline availability to the downing of the
towers where they were installed... The fact is that a typical TTFD may be
anywhere between 3 and 6 dB down from a standard half wave folded dipole,
and during poor propagation conditions , those 6 dB did make a great
difference !!
So, here is my advice, if you ever have to deal with an actual
communications emergency, requiring the use of the Near Vertical Incidence
Skywave propagation mode, don't use TTFD antennas, install a standard half
wave dipole for the each band you are going to use, and place them close to
the ground, so as to obtain the adequate vertical radiation pattern...
Now, another antenna related topic: Although most amateur radio antennas for
the VHF and UHF bands are made of aluminium tubing or rod, you can certainly
make them using copper tubing... As a matter of fact, the typical Super J
pole 6 dB gain antenna is ideally suited for making it using copper tubing
that is welded with silver solder... Such antenna will last a lifetime, and
it will need very little maintenance, because copper won't corrode the way
aluminium does.
Like the antenna topics section... sure, then let me add yet another antenna
related tip right now... When homebrewing the classic 300 ohm twin lead J
pole antenna , so popular among 2 meter band users, be sure to find the
highest possible quality of TV twinlead...as the EL CHEAPO, low cost
twinlead may work, but not as efficiently as the higher quality type... It
will surely cost you a bit more, but the extra cost is worth every single
cent, as your TV twinlead J pole may be the antenna required to come into
service during a communications emergency !
.......
Now Dxers Unlimited's mid week edition continues with ASK ARNIE, la numero
uno, THE most popular section of this radio hobby program... Today's
question came from listener Greg in Ottawa , Canada. Amigo Greg wants to
know more about so called NADENENKO dipoles, that he read about in a Russian
antenna handbook. Well amigo Greg, the NADENENKO dipoles are nothing more
than yet another form of braodband antenna that is based upon the large
diameter antenna elements. A typical NADENENKO dipole designed by my good
friend Senior RHC transmitter engineer Hector Esperon, provides a very low
standing wave ratio from nine to eighteen megaHertz, making it an excellent
standby antenna for the 31, 25, 22, 19 and 16 meter bands... By connecting
four of these dipoles in front of a wire screen, an excellent broadband
curtain antenna array is obtained. The typical NADENENKO dipole antenna is
very heavy due to the use of copper tubing rings that form the cage to which
the wires are attached, so you amigo Greg, won't see them used by amateur
radio operators for obvious reasons...
......
Si amigos, yes my friends , oui mes amis, there are more than 78 ways that
you and I may enjoy the radio hobby, from the unique earth-moon-earth
communications to homebrewing super sensitive crystal radio sets, from
spending a few weekend assembling a nice transceiver kit, to going out to a
beach or camping with your ham radio equipment and working Dx while enjoying
the extremely low noise levels that are typical of remote areas... And
talking about noise, man made noise continues to increase according to
recent research done by several radio science related organizations... long
term measurements of radio noise at several of the world's most populated
cities continue to provide scientists with data that show that as more and
more electronic devices become part of our daily lives, electromagnetic
radiation on the frequency range between 5 kiloHertz and five thousand
megaHertz continues to increase, making the use of certain communications
equipment more and more difficult or even impossible.
And now as always at the end of the show, when I am here in Havana, here is Arnie Coro's exclusive and not copyrighted HF propagation update, low band VHF data and the short term forecast for the next several days... Solar flux continues to be hovering around 80 units, just 10 units above the figure that scientists consider to be the Sun's baseline activity, and although it is rather low, it's enough to pump enough energy to the ionosphere to provide nice communications during the equinox... The A index went up to 16 units, due to a high speed solar wind gust, but it will move back down again after Tuesday UTC day ends...The optical sunspot number count is around 25, and although it is not of any significance for HF radio wave propagation, let me comment that solar scientists are watching very carefully a solar prominence of hot hydrogen gas that is holding itself above the Sun's surface due to the action of magnetic fields... This solar prominence is the largest seen in many years, and it may or may not be an advance of more things to happen 93 million miles away from Earth. Hope to see you all at the weekend edition of the program amigos, and don't forget to send you e-mail reports and comments to arnie@rhc.cu, and your postal mailings to Arnie Coro, Radio Havana Cuba , Havana, Cuba