Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited's mid week for 24-25 October 2006
By Arnie Coro
Radio amateur CO2KK
Hi amigos radioaficionados ! Welcome to the mid week edition of Dxers Unlimited, coming to you when our amigo SOL, 93 million miles away from us is going through a period of very low activity... As a matter of fact
the latest solar flux figures show near baseline levels, approaching the minimum detected solar flux of a bit less than 70 units. So, get ready for really very low ionospheric absorption and much better propagation conditions on frequencies from 500 kilohertz to 7 or 8 megaHertz during your local
evening hours , from local sunset to sunrise... More information about propagation conditions as always at the end of the show.... Item two: Amateur radio operators worldwide are becoming quite concerned about alarming lack of activity on the ham bands, especially during
weekdays... during the weekends and especially during the big contests as the one coming up this next weekend, you can certainly monitor much more activity on the favorite DX bands, but still, in my opinion way down from what used to be heard ten or fifteen years ago... Again, in my opinion, this lack of activity is to be traced back to the widespread presence of
computers and the availability of Internet services in developed nations and at the most important cities of less developed countries..., mainly national capitals. But, surprisingly, every time that there is one of the big contests in progress, the HF bands show a tremendous level of activity, with thousands and thousands of stations trying be among the winners of the contest.
So, the fact is that there are lots of amateur radio stations in perfect operating conditions ready to be used, but they ar actually getting less use, because their owners are spending more of
their spare time, the time previously used to be on the air, now used for operating the computers and surfing the world wide web.
Item three: The amazing four power sources radios are making illiteracy campaigns possible in remote rural areas, thanks to an training program created here in Cuba, YO SI PUEDO is the name of the illiteracy eradication program, that when translated into English reads YES I CAN... emphasizing the fact that people that don't know how to read and write can certainly learn even at a relatively advanced age in life... YO SI PUEDO, the Cuban training program to help people learn how to read and write using a combination of printed materials, coaches that help the trainees, and radio broadcasts is being used successfully in Haiti, Venezuela and New Zealand among other nations... Yet another fascinating use for radio broadcasting , that was
made available absolutely free of charge to UNESCO, so that its use may be extended around the world to help the more than 800 million inhabitants of Planet Earth that are illiterates. As
you have just heard, radio can play a vitally important role in helping the world’s illiterate persons learn how to read and write at much lower cost than any other way.
Item four: Antenna topics... A question... sent in by several listeners... they all want to know what exactly is meant by an antenna system often described in advertisements as " A NEST OF DIPOLES" or A DIPOLES NEST.... so stay tuned here for the answer to this question and
other features at today's mid week edition of Dxers Unlimited...
I am Arnie Coro in Havana, back with you in a few seconds amigos !!!
According to our correspondence department statistics, Dxers Unlimited is among the most popular programs of our station, and the antenna topics section is ranking always between the second and third place of the list of more mentioned sections of this show... Today's antenna
topics section combines with LA NUMERO UNO...the number one, YOU HAVE questions in this feature, aiming at clarifying the concept of " a nest of dipoles" or a "dipoles nest"...
Si amigos, yes my friends... several antenna manufacturers, especially those that offer VHF and UHF antennas are promoting an antenna system by the name of " DIPOLES NESTS", a name given to a certain number of half wave dipole antennas tuned to specific frequencies, and connected in parallel at their common feed point... The dipoles nests are not exactly a broadband antenna, because each of the elements has a definite resonant frequency, but in actual practice staggering the resonant frequencies of a certain number of half wave dipoles can prove to be a quite useful antenna system. Although, this is not properly a broadband antenna, like the fan , conical and biconical dipole elements that have been so well described
in the antenna engineering literature.
For example, amateur radio operators have for a long time now used a group of between two and four half wave wire dipoles connected in parallel and fed with a single coaxial cable, typically 50 ohm flexible coax.
One of the favorite combinations for this ham’s wire version of a dipole's nest is used for covering the 20, 15 and 10 meter bands, while another less common system covers 17, 12 and 10 meters. According to my practical experience , using more than three dipoles is
possible, but interaction between the antennas becomes more of a problem. Another popular antenna among amateurs is a dipole's nest for 40, 20 and 10 meters, where the 40 meter band antenna is also used as a 15 meters three half wave in phase element, effectively providing four band coverage...especially if you happen to have an antenna tuner connected between the feed line and your amateur radio transceiver. The tuner is required to match the almost 2 to 1 voltage standing wave ratio presented by the 40 meters antenna when operating on 15 meters, but for 40 , 20 and 10 meters the three wire antennas can be carefully trimmed and tuned on site to obtain a voltage standing wave ratio of less than 1.5 to one, which is considered to be perfectly acceptable by most modern solid state transceivers.
Dipoles nests are sometimes seen at VHF monitoring stations, and those professional systems may have up to six or even seven dipoles made of aluminum or copper tubing, connected to a very solidly built center insulator. But don't try to buy one of those, as they are pretty
expensive, and according to experts it is a much better option to invest your money in home brewing a broadband conical or cage dipole that will provide much better performance than the typical very much publicized " DIPOLES NEST" or NEST OF DIPOLES, whichever way the manufacturers advertise these antenna systems, that again, are nothing more than a certain number of half wave dipoles connected in parallel amigos !!! .....
You are listening to the mid week edition of Dxers Unlimited amigos, a radio program devoted to the promotion and development of this wonderful hobby that you and I enjoy so much...
Your radio hobby questions are most welcome ... send them to arnie@rhc.cu, again arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana , Cuba...
Here is now our next item of today's program... One of the more fascinating ways of enjoying this hobby is by using the most simple equipment ... an upcoming contest calls for the use of a
single active device receiver, be it a vacuum tube, a bipolar transistor or a field effect transistor... In an upcoming edition of Dxers Unlimited I will try be broadcasting the rules for this one active device receiver contest, but in the meantime let me tell you that my
single vacuum tube receiver using a battery operated 3S4 with a pair of high impedance headphones provides amazingly good reception . The little radio is powered by a big single 1.3 volts size D rechargeable cell, and two series connected 9 volts batteries, although adding a third one does improve the output volume. This little set is a regenerative receiver, and I have built coils for tuning from the low end of the AM broadcast band up to the 16 meters or 17.5 to 18.0 megaHertz international short wave broadcast band...The little radio is quite sensitive, and selectivity is also quite good when the regeneration control is carefully tweaked to put the
detector just at the point that it will start oscillating...
As you have just heard, this new short wave listening contest is quite a challenge, and the results, when published will show once again, that this is a hobby that can bring many nice rewards to both home brewers and those that enjoy participating in contests...
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This is Radio Havana Cuba, the name of the show is Dxers Unlimited, my e-mail address is arnie@rhc.cu, and the postal mailing address is Arnie Coro, Radio Havana Cuba, Havana, Cuba... surfing the web for new amateur radio software a few days ago I came across OLIVIA, yes OLIVIA is the name of yet another digital communications mode using the Multiple
Frequency Shift Keying system or MFSK, that makes possible two way contacts while using very low power. OLIVIA MFSK was first written for the LINUX operating system, but later ported to WINDOWS. There are already a few ham radio operators testing the OLIVIA mode on 14.108 kHz, but let me warn you that OLIVIA MFSK can not be decoded with any other software program than the one specifically created for operating it. OLIVIA is yet another variant of the keyboard to keyboard modes that use computer hardware and software connected to an HF transceiver, of which at this moment PSK31 continues to be the
most popular one of them all... PSK31 was created by British amateur Peter Martinez, and has become today's de-facto standard for keyboard to keyboard communications between amateur radio stations around the world, because it can be installed in almost any computer and interfacing with the transceiver is quite easy to implement...
Digital amateur radio communications , one of the more than 80 ways you and I may have a nice time playing with our radios and now with our computers too !!!
....
A quick answer to a listener in South Africa… amigo Roland from Cape town, yes, during the southern hemisphere’s solstice, around the 21’s of December, during the peak of the summer , you will be experiencing the peak of the sporadic E propagation season, and according to forecasts, due to the very low solar activity expected , this may be a nice sporadic E skip season in your part of the world….
And now amigos , as always at the end of the show here is LA NUMERO DOS, the second most popular section of Dxers Unlimited... Arnie Coro's Dxers Unlimited HF plus low band VHF propagation update and forecast...Solar flux now hovering around 75 units typical levels y seen during solar minimum years... providing low frequency bands enthusiasts with what I
expect to be excellent propagation for AM medium wave and the Tropical bands during the next three to five days...The sunspot number moved up to 50, five zero, and it may continue to move up during the next several days... see you at the weekend edition of the show amigos, and don't forget to send me your opinions about the program and any radio hobby related question that you may have , send mail to arnie@rhc.cu, and VIA POST send an AIRMAIL postcard to
Arnie Coro, Radio Havana Cuba Havana, Cuba